James 5:1-6 “Now listen, you rich people, weep and wail because of the misery that is coming on you. Your wealth has rotted, and moths have eaten your clothes. Your gold and silver are corroded. Their corrosion will testify against you and eat your flesh like fire. You have hoarded wealth in the last days. Look! The wages you failed to pay the workers who mowed your fields are crying out against you. The cries of the harvesters have reached the ears of the Lord Almighty. You have lived on earth in luxury and self-indulgence. You have fattened yourselves in the day of slaughter. You have condemned and murdered the innocent one, who was not opposing you.”

Anyone who isn’t sleeping can see that there is an economic crash coming around the corner (all by design). After the dust settles from this, the U.S. will no longer be the world’s reserve currency. We will also get Universal Basic Income/Universal Basic Socialism, and we will become a cashless society. Oh, what fun, a Social Credit System, just like China! In the west, it’s already here in softer form: Banks shutting down the accounts of Christian ministries because their beliefs and opinions do not line up with the New World Order narrative. PayPal also likes to shut down people’s accounts. What about Social(ist) Media like Facistbook? Have you ever heard the terms “Cancel Culture” or “Deplatforming” or “Shadow Banning”? There are people banned off all major Social Media platforms. Google has banned some alterative news and natural health sites. This is no shock, since U.N. Agenda 21 has a thing called “Public-Private Partnerships”, in which governments and corporations and NGOs work together to implement the New World Order agenda piece by piece in ways that they couldn’t do alone, all the while giving the corporate fascists our resources/assets/infrastructure. Vaccine Passports anyone?…if you are good and take the vax every time you are supposed to, then you can freely travel about…Hello, Social Credit System! The ultimate Social Credit System will be the Mark of the Beast.

Authoritarianism, here we come! Digital slavery, oh what fun! Let’s microchip you; it’s for your own good, for your own enslavement! Bow down before the AI god, the Image of the Beast, or die! What a dream, what a utopia!

Proverb:
1. Literally, carpentry. One should always double check one’s measurements before cutting materials to minimize the chances of mistakes thus wasting materials, time, and money.

2. Figuratively, when describing oneself. Plan and prepare careful and thorough manner before taking action.

This amazing sewing and craft room is sponsored by ChiMia and Lagom!

Worktable: ChiMia – Workshop desk @ $50L Friday 4/30/21
Rugs: ChiMia – Flea Market Rugs @ $50L Friday 4/30/21
Computer: ChiMia – ChiDesktop Gift for VIP Group Gift @ Mainstore (FREE to join)

Polytron is one of the local electronic equipment brands that continues to innovate. You can also see the superior quality and technology in the speaker products. Not surprisingly, their products are in demand in the market, such as soundbar speakers, active speakers, and home theater speakers.

This article will discuss more about the complete Polytron speakers by selecting them. Sky Tower Home Theater Speaker, Muze Mini Bluetooth Speaker, and other good Polytron speakers are also discussed here. So, don’t miss the article, OK!

How to choose Polytron speakers

There are many Polytron speaker products that you can choose from. Each product has its own advantages. To make it easy for you to find speakers that suit your needs, here are tips for choosing them.

Choose according to the Polytron speaker category

Polytron releases several speaker categories that are tailored to your needs. Each category has its own features and specialties. Well, here is the review.

Active speaker, produce a loud sound

Polytron

Active speakers usually have an amplifier that will amplify the sound produced. This type of speaker is also equipped with a subwoofer that can maximize bass sound. Polytron speakers themselves are famous for their good bass sound quality such as the Polytron PAS 8C28.

In terms of size, on average, active speakers have a larger size. You can also see this on the Polytron PAS PRO 15F2 speaker. These specifications make this type of speaker very suitable for use in large rooms for the needs of events such as music concerts or parties.

Home theater speaker, bring the cinema at home

Polytron

This type of speaker generally consists of several sound system components so that it looks quite complex. As the name implies, home theater speakers are made to create cinema-style sound quality that you can enjoy at home. Therefore, this type of speaker is much sought after by film lovers.

This speaker consists of more than one speaker bar which aims to produce sound effects from various directions. Thus, the resulting sound will become more alive. So, for those of you who want to present a cinema at home, you can choose speakers such as the Sky Tower Home Theater PHT 728S.

Multimedia speaker, flexible for various activities

Polytron

If you are looking for speakers that are flexible in use, this is the type of speaker that is most appropriate. The sound quality of these speakers is usually suitable for indoor or outdoor activities. Not only that, these types of speakers generally have different types of inputs so they can be easily plugged into various devices.

You will also find various multimedia features, such as FM radio, MP3 player, or video player on this speaker. There are also speakers that have features that make it easier for you to karaoke, such as the Polytron Multimedia Audio PMA 9502 speaker.

Wireless speaker, easy to move and install anywhere

Polytron

Wireless speakers let you listen to music without the use of wires. So, you can place and move them anywhere more easily. This type of speaker is usually equipped with Bluetooth features such as the Muze Mini Bluetooth Speaker PSP B2.

In addition, there are also wireless speakers that have Wi-Fi features. Compared to Bluetooth, the Wi-Fi feature has a wider wireless range. In addition, the signal is also stronger so that the resulting sound quality is not intermittent. The Wi-Fi feature is also available on the Polytron Muze Multiroom Speaker PMS R1.

Speaker soundbar, the design is compact and takes up no space

Polytron

For those of you who have limited space, a speaker soundbar is the solution. The shape is very slim and not too big, making it take up less space. The appearance is also very simple so it won’t interfere with your minimalist room decor.

Even though the size is very slim, you don’t need to doubt the sound quality of this type of speaker. Many think, soundbar speakers have sound quality that is almost similar to home theater speakers. You can prove this assumption directly through the Polytron Soundbar PHT 225 / SB speaker.

Consider additional multimedia features to make them even more useful

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Polytron

When choosing speakers, also consider products that have additional multimedia features. Multimedia features will bring many benefits for your daily activities. You also won’t get bored easily because this multimedia feature is very entertaining.

To answer this need, Polytron adds many multimedia features to its products. For example, the Active Speaker PAS 8C28 has a video out feature that lets you play videos with this speaker.

There are also speakers with FM radio features such as the Muze Mini Bluetooth Speaker PSP C1 whose channels are free for you to choose. For you true music lovers, Polytron also facilitates music playback via the MP3 player feature. Not to forget, there is also a music recorder feature which is certainly useful for those of you who like to play music.

Also pay attention to the speaker connectivity

Polytron

Don’t forget to consider connectivity issues too, huh. The reason is, the connectivity feature will make it easier for you to connect speakers to various other devices. So, make sure the speaker you choose can be connected to the device you want.

For those of you who want to play music or videos from a flash drive or memory card, you can choose Polytron speakers with a USB input or micro SD slot. You can find this kind of connectivity on the Polytron PAS 8C28 and PAS PRO 15F2 speakers.

Meanwhile, Polytron speakers such as the Big Band Theater BB 5510 are equipped with aux input and microphone input connectivity . Thanks to this connectivity, you can connect the speaker to a musical instrument or microphone. You can also choose Polytron speakers such as the Muze Mini Bluetooth Speaker PSP C1 which can be connected to a smartphone.

Prioritize those that can be controlled remotely

Polytron

For those of you who don’t want to be bothered, choose speakers that have a remote control such as the Polytron Multimedia Audio PMA 9502. This remote control can help you control your speakers remotely. So, the use of speakers will be more practical and not waste energy.

Amazingly, now Polytron also has speaker control technology via smartphone like the one in the 5.1 Speaker System PHT 551. With this technology, you can control speakers with various types of smartphones that have the Polytron Audio Connect application.

10 Best Polytron Speaker Recommendations

The following are recommendations for the ten best Polytron speaker products that we have compiled based on price, type and specifications. Don’t forget to apply the points above when choosing, OK!

Polytron | Muze Mini Bluetooth Speaker PSP C1

Polytron

A multi – function speaker that can be used for making calls

It is easy to connect this speaker to your smartphone thanks to its high-speed Bluetooth feature. In addition, the Bluetooth range is also quite wide, up to 10 meters. Its slim and lightweight shape also makes it easy for you to carry it anywhere.

Interestingly, this speaker also has a small, supersensitive microphone. So, those of you who want to make direct telephone calls through the speaker can choose it. You can also listen to music from various sources thanks to the support of the USB slot, micro SD, and aux input on this speaker.

Polytron | Muze Multiroom Speaker PMS R1

Polytron

Channel sound throughout the room with its Multiroom mode

Not only Bluetooth, this speaker is also equipped with Wi-Fi features. This makes this speaker very easy to connect to similar speakers or other devices. Those of you who want to play music in multiple rooms at once will be pleased with this speaker.

You music lovers, of course, will also be spoiled by the S putrefy connect feature on this speaker. You can also select and play your favorite song from your Spotify list. In addition, through the UNDOK application, you can operate this speaker via a smartphone.

Polytron | Muze Mini Bluetooth Speaker PSP B2

Polytron

Waterproof, safe for outdoor activities

Those of you who like to do outdoor activities must have this speaker. This mini-size Bluetooth speaker is very practical to carry and store in a bag. Moreover, this speaker is also waterproof so it is safe to carry for outdoor activities such as sports, hiking or picnics.

In addition, this speaker will not get dirty easily because it is designed with dust-proof material. Amazingly, when the battery is full, these speakers can play music for up to six hours! The battery power is also more efficient because the speaker will automatically turn off if no device is connected.

Polytron | Active Speaker PAS 8C28

Polytron

With XBR Woofer technology, the bass sound is very jarring

Want to feel a powerful bass sensation? Active speaker PAS 8C28 is the answer! Designed with XBR Woofer technology with a 3 ways speaker system model, the bass quality of these speakers is excellent, clear, and detailed.

Not only that, this speaker is also supported with super bass technology, which keeps the bass steady even at a small volume. In addition, this speaker has a touch of prism cut and ambience light which makes it look very cool.

Polytron | 5.1 Speaker System PHT 551

Polytron

The surround effect is more pronounced thanks to 5 satellites

Speakers with 5.1 model consists of one main speaker and five satellite speakers. Thanks to the many satellite speakers, the automatic sound range is also wider. Well, for those of you who like sound effects from all over or surround, this speaker can be the right choice.

Equipped with the Polytron Audio Connect feature, you can control these speakers via a smartphone. This smart speaker is also equipped with various inputs that make it easy to connect to a computer, TV or DVD player.

Polytron | PHT 225 / SB Soundbar

Polytron

Simple speaker with clear sound quality

You certainly wouldn’t expect this minimalist speaker to have such great sound quality. This is because these speakers have been supported by a high quality subwoofer. The 2.1 channel model allows the sound produced by these speakers to span the entire room.

The ultra-slim design makes this speaker easy to place on a table or on a wall. For those of you who want to get a sound quality class like a home theater speaker in a limited space, this Polytron soundbar is the solution.

Polytron | Polytron Multimedia Audio PMA 9502

Polytron

Karaoke is even more fun with this speaker

Are you a karaoke fan? If so, this multimedia speaker from Polytron is the best choice. Has two microphone inputs, you can sing using the microphone. You can also adjust the echo sound on the microphone according to your taste.

This speaker is equipped with bass and treble control that will make your voice pleasant to hear when singing. With these speakers, it will feel like you are recording in a studio! In addition, this speaker is also equipped with a USB input so you can sing along to the music that you store on the flash.

Polytron | PAS PRO 15F2

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Polytron

A speaker with a wide sound range

For those of you who are looking for speakers with loud voices, choose these speakers. The PAS PRO 15F2 is equipped with a 15-inch woofer that will produce a very loud sound. For events like weddings or music concerts, these speakers are perfect.

This speaker also has a trolley that makes it easy to move around. In addition, this speaker is also equipped with a stand that can be adjusted in height so that the range is wider. Amazingly, this speaker is equipped with two power modes, namely battery and cable.

Polytron | Big Band Theater BB 5510

Polytron

Can be connected to various musical instruments, perfect for those of you who like music

This speaker is specially created for those of you who like to play musical instruments. How not, this speaker has a music instrument board interface that can be connected to a musical instrument such as a piano, electric guitar, or an electric drum.

No half-hearted, this speaker is also equipped with distortion and compressor effects that can reduce noise when you play a musical instrument. As a result, the sound produced is also clear. Apart from that, you can also record the sound of your music playing thanks to the single deck stereo cassette recorder feature on this speaker.

Polytron | Sky Tower Home Theater PHT 728S

Polytron

Watching a cinema-style movie at home? Sure, you can with this speaker!

Now you can make your own cinema at home with this speaker. This home theater speaker has four standfloor type speakers and one center speaker. Thanks to this composition, the speakers are able to provide clear sound quality like in a cinema.

This speaker is also equipped with XBR Subwoofer technology so that the bass quality is so superior. In addition, the PHT 782S speaker also supports video playback with high resolution up to 720p. What’s more, its simple and elegant design will perfectly match various room designs.

Closing

Finally, the discussion about Polytron speakers this time has been completed. All of the Polytron speakers we recommend are very attractive, right? We hope that this method of choosing will make it easier for you.

In addition, when buying speakers, pay attention to the power. We recommend that you adjust it to the maximum power capacity in the house so that there is no power drop when the speakers are used. In addition, so as not to take up space, also adjust the speaker size according to your room.

Price: (as of – Details)

USB CHARGE PORT WITH INBUILT CABLE – External USB port with built-in charging cable offers a convenient charging of your electronic device anywhere. This bag does not include a battery and you need a power bank to charge your mobile phone, tablet or speaker. There is a retro reflective tape on the front of the bag, which makes this backpack more conspicuous in the night. This is a safe backpack while walking, travelling or biking during the night.WATER REPELLENT OXFORD FABRIC – We use high quality 300D waterproof, cut-proof and dust-proof polyester and PVC fabric with nylon sponge, which protects your belongings during rain season. It has metal zippers, breathable mesh shoulder straps and 6-layers of breathable mesh back padding. It is durable, lightweight and comfortable.MULTI COMPARTMENT DAYPACK – 90° or 180° adjustable main compartment is equipped with large space for 15.6 Inch laptop and medium space for tablet computer or iPad. In addition there are multiple compartments that are suitable for keeping pens, mobile phone, calculator, mp3 player, wallet, passport, iPod, power bank, notebooks, keys, watch, headphones, clothes, umbrella, water bottle and many other items. 180° opening like a suitcase helps in organising stuff easily.ERGONOMIC DESIGN, PADDED STRAPS & CUSHIONING – Shoulder straps have an ergonomic design.

Western Veil Nebula (Caldwell 34), 06/25/2020

This object is part of a super nova remnant from a star that was 20 times more massive than the sun. When that star blew up some 10,000 to 20,000 years ago, it left behind ionized gas and dust that has expanded to cover an area of the sky roughly 6 times the diameter of the Moon. This picture is only one small part of that explosion.

This night was kind of a last-minute decision. I looked outside and saw clear skies so I quickly setup the gear. It was my first night using some new toys, a new light pollution filter and an Asiair Pro computer. The new equipment worked great but I did have a few issues. I had my gain set to 200 for some reason and the polar alignment was crap. But I think I salvaged the data and the image turned out pretty good.

Equipment:
RASA 8
CGEM-dx mount
ZWO ASI294MC-Pro
ZWO Asiair Pro
Optolong L-eHhance filter

Details:
Location – My back yard in Tacoma WA
Bortle Class 8
Gain 200
120 60-second Lights
60 Darks
60 Bias
60 Flats
Astro Pixel Processor
Lightroom
Photoshop

#astrophotography #astronomy #comos #nightphotography #space #telescope #deepsky #asi294mcpro #amateurastronomy #backyardastronomy #asiair #rasa #celestron #astropixelprocessor #optolong #telescope #astronomyphotography #deepskyobject #zwo #longexposurephotography #caldwell34 #veilnebula

Variant 1 with Hydrogen Alpha data, not sharpened.

M51 The Whirlpool Galaxy through moonlight and Saharan dust – my first (semi)complete astrophotography project

This is my first astrophotography project. After months of preparation, I’ve finally managed to acquire my own, complete set of data and process it.

ACQUISITION

· Over 5 nights- 21-25 February 2021, with nearly full moon and a lot of dust from Sahara over the sky in Poland. Poor seeing conditions that impacted acquisition and guiding, with very few stars visible to the naked eye.

· Location: backyard.

· L: 72 x 300 s

· RGB and Ha: 20x 300s each.

· 30 dark frames

· 30 dark flats and 30 flats per filter.

GEAR

· Telescope: Skywatcher Maksutov-Newtonian 190mm/1000mm.

· Camera: ZWO ASI 1600MM-PRO (cooled to -20, gain 139)

· Filters: ZWO L, R, G, B, Baader Halfa 7nm- 36mm

· Guiding: ZWO ASI 120MM Mini.

· ZWO EAF.

· Mount: Skywatcher NEQ6 with Rowan belt mod.

· Computer: ASIAir V1.

PROCESSING (done entirely in Pixinsight):

· Blink to reject the worst subs (about 15%).

· WeightedBatchPreprocessing: calibration, registration, stacking (Hydrogen alpha not calibrated with flats due to significant overcorrection).

· MureDenoise on all stacks.

· DynamicCrop

· DynamicBackgroundExtraction with custom settings and lots of it- 4-6 iterations. There were horrible gradients due to moonlight and dust and flats didn’t necessarily make the stacks better…

· LinearFit on all the stacks.

— Luminance:

o Deconvolution with custom masks and settings with the EZ Decon script,

o Denoise with EZ Denoise script with custom settings,

o MaskedStrech to non-linear with custom settings,

o LocalHistogramEqualization with custom settings.

— RGB:

o ChannelCombination

o PhotometricColorCalibration with BackgroundNeutralization (that worked very well indeed!)

o Further nuked visible color cast in the background with custom mask (range_mask+star_mask) and SCNR.

o Denoise with EZ Denoise script with custom settings,

o MaskedStrech to non-linear with custom settings,

o Mild deconvolution with custom masks and settings with the EZ Decon script,

— Hydrogen Alpha

o HistogramTransformation to non-linear with custom settings,

o Starnet to remove the stars with range mask to leave grainy structures in the galaxy’s arms in the picture.

o Curves, HistogramTransformation and masks to clip the background entirely and most of the diffuse Ha glow.

— RGB + Hydrogen Alfa

o ChannelExtraction: R, G and B from RGB stack.

o Pixelmath to combine R with Ha

o ChannelCombination to reintegrate R(with Ha), G and B.

o Slight ACDNR

— RGBHa + Luminance

o LRGBCombination with custom settings,

o EZ HDR with custom settings,

o Contrast slightly enhanced with Curves,

o Mild saturation enhancement with ColorSaturation,

o EZ Star Reduction (stars were bloated due to poor seeing and questionable guiding; still not happy at all with how they turned out),

o PNG to publish and gloat.

o Sleep!

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth’s surface.[1] Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.

The term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes).[2]

By definition, fog reduces visibility to less than 1 kilometre (0.62 mi), whereas mist causes lesser impairment of visibility.[3]

For aviation purposes in the UK, a visibility of less than 5 kilometres (3.1 mi) but greater than 999 metres (3,278 ft) which is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported.[4][full citation needed]

Formation
See also: Cloud physics

Minute droplets of water constitute this after-dark radiation fog, with an ambient temperature of −2 °C (28 °F). Their motion trails are captured as streaks.

A close-up view of water droplets forming fog. Those outside the camera lens’s depth of field appear as orbs.
Fog forms when the difference between air temperature and dew point is less than 2.5 °C (4.5 °F).[5]

Fog begins to form when water vapor condenses into tiny water droplets that are suspended in the air. Some examples of ways that water vapor is added to the air are by wind convergence into areas of upward motion;[6] precipitation or virga falling from above;[7] daytime heating evaporating water from the surface of oceans, water bodies, or wet land;[8] transpiration from plants;[9] cool or dry air moving over warmer water;[10] and lifting air over mountains.[11] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds.[12][13] Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.[14]

Fog normally occurs at a relative humidity near 100%.[15] This occurs from either added moisture in the air, or falling ambient air temperature.[15] However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.

Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets.[16] This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.

The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fog-bank it may contain, will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.

Types
Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred.

Radiation fog is formed by the cooling of land after sunset by infrared thermal radiation in calm conditions with a clear sky. The cooling ground then cools adjacent air by conduction, causing the air temperature to fall and reach the dew point, forming fog. In perfect calm, the fog layer can be less than a meter thick, but turbulence can promote a thicker layer. Radiation fog occurs at night, and usually does not last long after sunrise, but it can persist all day in the winter months, especially in areas bounded by high ground. Radiation fog is most common in autumn and early winter. Examples of this phenomenon include the Tule fog.[17]

Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds.[18] However, the term is usually a synonym for shallow radiation fog; in some cases the depth of the fog is on the order of tens of centimetres over certain kinds of terrain with the absence of wind.

Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background
Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled.[19] It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog). A strong enough temperature difference over water or bare ground can also cause advection fog.

Although strong winds often mix the air and can disperse, fragment, or prevent many kinds of fog, markedly warmer and humid air blowing over a snowpack can continue to generate advection fog at elevated velocities up to 80 km/h (50 mph) or more – this fog will be in a turbulent, rapidly moving, and comparatively shallow layer, observed as a few centimetres/inches in depth over flat farm fields, flat urban terrain and the like, and/or form more complex forms where the terrain is different such as rotating areas in the lee of hills or large buildings and so on.

Fog formed by advection along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coast-ward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline; a phenomenon known as a "southerly surge", typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain. Moderate turbulence will typically transform a fog bank, lifting it and breaking it up into shallow convective clouds called stratocumulus.

Evaporation fog or steam fog forms over bodies of water overlain by much colder air; this situation can also lead to the formation of steam devils, which look like dust counterparts. Lake effect fog is of this type, sometimes in combination with other causes like radiation fog. It tends to differ from most advective fog formed over land in that it is, like lake-effect snow, a convective phenomenon, resulting in fog that can be very dense and deep and looks fluffy from above.

Frontal fog forms in much the same way as stratus cloud near a front when raindrops, falling from relatively warm air above a frontal surface, evaporate into cooler air close to the Earth’s surface and cause it to become saturated. This type of fog can be the result of a very low frontal stratus cloud subsiding to surface level in the absence of any lifting agent after the front passes.

Ice fog forms in very low temperatures and can be the result of other mechanisms mentioned here, as well as the exhalation of moist warm air by herds of animals. It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions, which can cause many types of halos and other results of refraction of sunlight by the airborne crystals.

Freezing fog, which deposits rime, is composed of droplets of supercooled water that freeze to surfaces on contact.

Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms.

Hail fog sometimes occurs in the vicinity of significant hail accumulations due to decreased temperature and increased moisture leading to saturation in a very shallow layer near the surface. It most often occurs when there is a warm, humid layer atop the hail and when wind is light. This ground fog tends to be localized but can be extremely dense and abrupt. It may form shortly after the hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating.[20]

Upslope fog forms when moist air is going up the slope of a mountain or hill (orographic lifting) which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.

Freezing conditions
Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime.[21] This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is super-cooled, filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful".

File:Aerial View of freezing fog in the Okanagan Highlands.webm
Aerial Video of freezing fog in the Okanagan Highlands
In the western United States, freezing fog may be referred to as pogonip.[22] It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip is derived from the Shoshone word paγi̵nappi̵h, which means "cloud".[22][23] In The Old Farmer’s Almanac, in the calendar for December, the phrase "Beware the Pogonip" regularly appears. In his anthology Smoke Bellew, Jack London described a pogonip which surrounded the main characters, killing one of them.

The phenomenon is also extremely common in the inland areas of the Pacific Northwest, with temperatures in the 10 to 30 °F (−12 to −1 °C) range. The Columbia Plateau experiences this phenomenon most years due to temperature inversions, sometimes lasting for as long as three weeks. The fog typically begins forming around the area of the Columbia River and expands, sometimes covering the land to distances as far away as LaPine, Oregon, almost 150 miles (240 km) due south of the river and into south central Washington.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below −35 °C (−31 °F), making it common only in and near the Arctic and Antarctic regions.[24] It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Utqiagvik, Alaska. Ice fog often leads to the visual phenomenon of light pillars.

Morning freezing fog in Elko, Nevada

Pogonip fog in Virginia City, Nevada, from an early 20th-century postcard

Tree in field during extreme cold with frozen fog

Ice fog on Pyhäjärvi, Tampere during sunset.

Topographical influences

Fog over the Pedra do Sino (Bell Rock; left) and Dedo de Deus (God’s Finger; right) peaks in the Serra dos Órgãos National Park, Rio de Janeiro state, Brazil
Up-slope fog or hill fog forms when winds blow air up a slope (called orographic lift), adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.

Valley fog forms in mountain valleys, often during winter. It is essentially a radiation fog confined by local topography, and can last for several days in calm conditions. In California’s Central Valley, valley fog is often referred to as tule fog.

Sea and coastal fog
Sea fog (also known as haar or fret) is heavily influenced by the presence of sea spray and microscopic airborne salt crystals. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves. Except in areas of storminess, the most common areas of breaking waves are located near coastlines, hence the greatest densities of airborne salt particles are there.

Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. Another recently discovered source of condensation nuclei for coastal fog is kelp seaweed. Researchers have found that under stress (intense sunlight, strong evaporation, etc.), kelp releases particles of iodine which in turn become nuclei for condensation of water vapor, causing fog that diffuses direct sunlight.[25]

Sea smoke, also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land.[21] It often causes freezing fog, or sometimes hoar frost.

Arctic sea smoke is similar to sea smoke, but occurs when the air is very cold. Instead of condensing into water droplets, columns of freezing, rising, and condensing water vapor is formed. The water vapor produces the sea smoke fog, and is usually misty and smoke-like.[26]

Garúa fog near the coast of Chile and Peru,[27] occurs when typical fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a "transparent mist". Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers because of deposition of liquid water on hard surfaces.

Fog rolls into Seattle from the sea

Sea fog or "fret" encroaching on Brighton Pier

Sea fog in the Arctic Ocean near the island of Jan Mayen

Visibility effects

Heavy fog on a road near Baden, Austria

Light fog reduces visibility on a suburban street, rendering the cyclist very hazy at about 200 m (220 yd). The limit of visibility is about 400 m (440 yd), which is before the end of the street.
Depending on the concentration of the droplets, visibility in fog can range from the appearance of haze, to almost zero visibility. Many lives are lost each year worldwide from accidents involving fog conditions on the highways, including multiple-vehicle collisions.

The aviation travel industry is affected by the severity of fog conditions. Even though modern auto-landing computers can put an aircraft down without the aid of a pilot, personnel manning an airport control tower must be able to see if aircraft are sitting on the runway awaiting takeoff. Safe operations are difficult in thick fog, and civilian airports may forbid takeoffs and landings until conditions improve.

A solution for landing returning military aircraft developed in World War II was called Fog Investigation and Dispersal Operation (FIDO). It involved burning enormous amounts of fuel alongside runways to evaporate fog, allowing returning fighter and bomber pilots sufficient visual cues to safely land their aircraft. The high energy demands of this method discourage its use for routine operations.

Shadows

Sutro Tower casts a 3-dimensional fog shadow
Shadows are cast through fog in three dimensions. The fog is dense enough to be illuminated by light that passes through gaps in a structure or tree, but thin enough to let a large quantity of that light pass through to illuminate points further on. As a result, object shadows appear as "beams" oriented in a direction parallel to the light source. These voluminous shadows are created the same way as crepuscular rays, which are the shadows of clouds. In fog, it is solid objects that cast shadows.

Sound propagation and acoustic effects
See also: Acoustic location, Acoustic shadow, and Foghorn
Sound typically travels fastest and farthest through solids, then liquids, then gases such as the atmosphere. Sound is affected during fog conditions due to the small distances between water droplets, and air temperature differences.

Molecular effect: Though fog is essentially liquid water, the many droplets are separated by small air gaps. High-pitched sounds have a high frequency, which in turn means they have a short wavelength. To transmit a high frequency wave, air must move back and forth very quickly. Short-wavelength high-pitched sound waves are reflected and refracted by many separated water droplets, partially cancelling and dissipating their energy (a process called "damping"). In contrast, low pitched notes, with a low frequency and a long wavelength, move the air less rapidly and less often, and lose less energy to interactions with small water droplets. Low-pitched notes are less affected by fog and travel further, which is why foghorns use a low-pitched tone.[28]

Temperature effect: A fog can be caused by a temperature inversion where cold air is pooled at the surface which helped to create the fog, while warmer air sits above it. The inverted boundary between cold air and warm air reflects sound waves back toward the ground, allowing sound that would normally radiate out escaping into the upper atmosphere to instead bounce back and travel near the surface. A temperature inversion increases the distance that lower frequency sounds can travel, by reflecting the sound between the ground and the inversion layer.[29]

Record extremes
Particularly foggy places include[citation needed] Hamilton, New Zealand and Grand Banks off the coast of Newfoundland (the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south). Some very foggy land areas in the world include Argentia (Newfoundland) and Point Reyes (California), each with over 200 foggy days per year.[citation needed] Even in generally warmer southern Europe, thick fog and localized fog are often found in lowlands and valleys, such as the lower part of the Po Valley and the Arno and Tiber valleys in Italy; Ebro Valley in northeastern Spain; as well as on the Swiss plateau, especially in the Seeland area, in late autumn and winter.[citation needed] Other notably foggy areas include coastal Chile (in the south); coastal Namibia; Nord, Greenland; and the Severnaya Zemlya islands.

As a water source
Redwood forests in California receive approximately 30–40% of their moisture from coastal fog by way of fog drip. Change in climate patterns could result in relative drought in these areas.[30] Some animals, including insects, depend on wet fog as a principal source of water, particularly in otherwise desert climes, as along many African coastal areas. Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient. Fog can be of different type according to climatic conditions.

Artificial fog
Artificial fog is man-made fog that is usually created by vaporizing a water- and glycol-based or glycerine-based fluid. The fluid is injected into a heated metal block, and evaporates quickly. The resulting pressure forces the vapor out of a vent. Upon coming into contact with cool outside air, the vapor condenses in microscopic droplets and appears as fog.[31] Such fog machines are primarily used for entertainment applications.

Historical references
See also: Pea soup fog, Fog of war, and Theatrical smoke and fog
The presence of fog has often played a key role in historical events, such as strategic battles. One example is the Battle of Long Island (August 27, 1776), when American general George Washington and his command were able to evade imminent capture by the British Army, using fog to conceal their escape. Another example is D-Day (June 6, 1944) during World War II, when the Allies landed on the beaches of Normandy, France during fog conditions. Both positive and negative results were reported from both sides during that battle, due to impaired visibility.[32]

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth’s surface.[1] Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.

The term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes).[2]

By definition, fog reduces visibility to less than 1 kilometre (0.62 mi), whereas mist causes lesser impairment of visibility.[3]

For aviation purposes in the UK, a visibility of less than 5 kilometres (3.1 mi) but greater than 999 metres (3,278 ft) which is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported.[4][full citation needed]

Formation
See also: Cloud physics

Minute droplets of water constitute this after-dark radiation fog, with an ambient temperature of −2 °C (28 °F). Their motion trails are captured as streaks.

A close-up view of water droplets forming fog. Those outside the camera lens’s depth of field appear as orbs.
Fog forms when the difference between air temperature and dew point is less than 2.5 °C (4.5 °F).[5]

Fog begins to form when water vapor condenses into tiny water droplets that are suspended in the air. Some examples of ways that water vapor is added to the air are by wind convergence into areas of upward motion;[6] precipitation or virga falling from above;[7] daytime heating evaporating water from the surface of oceans, water bodies, or wet land;[8] transpiration from plants;[9] cool or dry air moving over warmer water;[10] and lifting air over mountains.[11] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds.[12][13] Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.[14]

Fog normally occurs at a relative humidity near 100%.[15] This occurs from either added moisture in the air, or falling ambient air temperature.[15] However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.

Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets.[16] This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.

The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fog-bank it may contain, will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.

Types
Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred.

Radiation fog is formed by the cooling of land after sunset by infrared thermal radiation in calm conditions with a clear sky. The cooling ground then cools adjacent air by conduction, causing the air temperature to fall and reach the dew point, forming fog. In perfect calm, the fog layer can be less than a meter thick, but turbulence can promote a thicker layer. Radiation fog occurs at night, and usually does not last long after sunrise, but it can persist all day in the winter months, especially in areas bounded by high ground. Radiation fog is most common in autumn and early winter. Examples of this phenomenon include the Tule fog.[17]

Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds.[18] However, the term is usually a synonym for shallow radiation fog; in some cases the depth of the fog is on the order of tens of centimetres over certain kinds of terrain with the absence of wind.

Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background
Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled.[19] It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog). A strong enough temperature difference over water or bare ground can also cause advection fog.

Although strong winds often mix the air and can disperse, fragment, or prevent many kinds of fog, markedly warmer and humid air blowing over a snowpack can continue to generate advection fog at elevated velocities up to 80 km/h (50 mph) or more – this fog will be in a turbulent, rapidly moving, and comparatively shallow layer, observed as a few centimetres/inches in depth over flat farm fields, flat urban terrain and the like, and/or form more complex forms where the terrain is different such as rotating areas in the lee of hills or large buildings and so on.

Fog formed by advection along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coast-ward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline; a phenomenon known as a "southerly surge", typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain. Moderate turbulence will typically transform a fog bank, lifting it and breaking it up into shallow convective clouds called stratocumulus.

Evaporation fog or steam fog forms over bodies of water overlain by much colder air; this situation can also lead to the formation of steam devils, which look like dust counterparts. Lake effect fog is of this type, sometimes in combination with other causes like radiation fog. It tends to differ from most advective fog formed over land in that it is, like lake-effect snow, a convective phenomenon, resulting in fog that can be very dense and deep and looks fluffy from above.

Frontal fog forms in much the same way as stratus cloud near a front when raindrops, falling from relatively warm air above a frontal surface, evaporate into cooler air close to the Earth’s surface and cause it to become saturated. This type of fog can be the result of a very low frontal stratus cloud subsiding to surface level in the absence of any lifting agent after the front passes.

Ice fog forms in very low temperatures and can be the result of other mechanisms mentioned here, as well as the exhalation of moist warm air by herds of animals. It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions, which can cause many types of halos and other results of refraction of sunlight by the airborne crystals.

Freezing fog, which deposits rime, is composed of droplets of supercooled water that freeze to surfaces on contact.

Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms.

Hail fog sometimes occurs in the vicinity of significant hail accumulations due to decreased temperature and increased moisture leading to saturation in a very shallow layer near the surface. It most often occurs when there is a warm, humid layer atop the hail and when wind is light. This ground fog tends to be localized but can be extremely dense and abrupt. It may form shortly after the hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating.[20]

Upslope fog forms when moist air is going up the slope of a mountain or hill (orographic lifting) which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.

Freezing conditions
Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime.[21] This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is super-cooled, filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful".

File:Aerial View of freezing fog in the Okanagan Highlands.webm
Aerial Video of freezing fog in the Okanagan Highlands
In the western United States, freezing fog may be referred to as pogonip.[22] It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip is derived from the Shoshone word paγi̵nappi̵h, which means "cloud".[22][23] In The Old Farmer’s Almanac, in the calendar for December, the phrase "Beware the Pogonip" regularly appears. In his anthology Smoke Bellew, Jack London described a pogonip which surrounded the main characters, killing one of them.

The phenomenon is also extremely common in the inland areas of the Pacific Northwest, with temperatures in the 10 to 30 °F (−12 to −1 °C) range. The Columbia Plateau experiences this phenomenon most years due to temperature inversions, sometimes lasting for as long as three weeks. The fog typically begins forming around the area of the Columbia River and expands, sometimes covering the land to distances as far away as LaPine, Oregon, almost 150 miles (240 km) due south of the river and into south central Washington.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below −35 °C (−31 °F), making it common only in and near the Arctic and Antarctic regions.[24] It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Utqiagvik, Alaska. Ice fog often leads to the visual phenomenon of light pillars.

Morning freezing fog in Elko, Nevada

Pogonip fog in Virginia City, Nevada, from an early 20th-century postcard

Tree in field during extreme cold with frozen fog

Ice fog on Pyhäjärvi, Tampere during sunset.

Topographical influences

Fog over the Pedra do Sino (Bell Rock; left) and Dedo de Deus (God’s Finger; right) peaks in the Serra dos Órgãos National Park, Rio de Janeiro state, Brazil
Up-slope fog or hill fog forms when winds blow air up a slope (called orographic lift), adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.

Valley fog forms in mountain valleys, often during winter. It is essentially a radiation fog confined by local topography, and can last for several days in calm conditions. In California’s Central Valley, valley fog is often referred to as tule fog.

Sea and coastal fog
Sea fog (also known as haar or fret) is heavily influenced by the presence of sea spray and microscopic airborne salt crystals. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves. Except in areas of storminess, the most common areas of breaking waves are located near coastlines, hence the greatest densities of airborne salt particles are there.

Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. Another recently discovered source of condensation nuclei for coastal fog is kelp seaweed. Researchers have found that under stress (intense sunlight, strong evaporation, etc.), kelp releases particles of iodine which in turn become nuclei for condensation of water vapor, causing fog that diffuses direct sunlight.[25]

Sea smoke, also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land.[21] It often causes freezing fog, or sometimes hoar frost.

Arctic sea smoke is similar to sea smoke, but occurs when the air is very cold. Instead of condensing into water droplets, columns of freezing, rising, and condensing water vapor is formed. The water vapor produces the sea smoke fog, and is usually misty and smoke-like.[26]

Garúa fog near the coast of Chile and Peru,[27] occurs when typical fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a "transparent mist". Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers because of deposition of liquid water on hard surfaces.

Fog rolls into Seattle from the sea

Sea fog or "fret" encroaching on Brighton Pier

Sea fog in the Arctic Ocean near the island of Jan Mayen

Visibility effects

Heavy fog on a road near Baden, Austria

Light fog reduces visibility on a suburban street, rendering the cyclist very hazy at about 200 m (220 yd). The limit of visibility is about 400 m (440 yd), which is before the end of the street.
Depending on the concentration of the droplets, visibility in fog can range from the appearance of haze, to almost zero visibility. Many lives are lost each year worldwide from accidents involving fog conditions on the highways, including multiple-vehicle collisions.

The aviation travel industry is affected by the severity of fog conditions. Even though modern auto-landing computers can put an aircraft down without the aid of a pilot, personnel manning an airport control tower must be able to see if aircraft are sitting on the runway awaiting takeoff. Safe operations are difficult in thick fog, and civilian airports may forbid takeoffs and landings until conditions improve.

A solution for landing returning military aircraft developed in World War II was called Fog Investigation and Dispersal Operation (FIDO). It involved burning enormous amounts of fuel alongside runways to evaporate fog, allowing returning fighter and bomber pilots sufficient visual cues to safely land their aircraft. The high energy demands of this method discourage its use for routine operations.

Shadows

Sutro Tower casts a 3-dimensional fog shadow
Shadows are cast through fog in three dimensions. The fog is dense enough to be illuminated by light that passes through gaps in a structure or tree, but thin enough to let a large quantity of that light pass through to illuminate points further on. As a result, object shadows appear as "beams" oriented in a direction parallel to the light source. These voluminous shadows are created the same way as crepuscular rays, which are the shadows of clouds. In fog, it is solid objects that cast shadows.

Sound propagation and acoustic effects
See also: Acoustic location, Acoustic shadow, and Foghorn
Sound typically travels fastest and farthest through solids, then liquids, then gases such as the atmosphere. Sound is affected during fog conditions due to the small distances between water droplets, and air temperature differences.

Molecular effect: Though fog is essentially liquid water, the many droplets are separated by small air gaps. High-pitched sounds have a high frequency, which in turn means they have a short wavelength. To transmit a high frequency wave, air must move back and forth very quickly. Short-wavelength high-pitched sound waves are reflected and refracted by many separated water droplets, partially cancelling and dissipating their energy (a process called "damping"). In contrast, low pitched notes, with a low frequency and a long wavelength, move the air less rapidly and less often, and lose less energy to interactions with small water droplets. Low-pitched notes are less affected by fog and travel further, which is why foghorns use a low-pitched tone.[28]

Temperature effect: A fog can be caused by a temperature inversion where cold air is pooled at the surface which helped to create the fog, while warmer air sits above it. The inverted boundary between cold air and warm air reflects sound waves back toward the ground, allowing sound that would normally radiate out escaping into the upper atmosphere to instead bounce back and travel near the surface. A temperature inversion increases the distance that lower frequency sounds can travel, by reflecting the sound between the ground and the inversion layer.[29]

Record extremes
Particularly foggy places include[citation needed] Hamilton, New Zealand and Grand Banks off the coast of Newfoundland (the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south). Some very foggy land areas in the world include Argentia (Newfoundland) and Point Reyes (California), each with over 200 foggy days per year.[citation needed] Even in generally warmer southern Europe, thick fog and localized fog are often found in lowlands and valleys, such as the lower part of the Po Valley and the Arno and Tiber valleys in Italy; Ebro Valley in northeastern Spain; as well as on the Swiss plateau, especially in the Seeland area, in late autumn and winter.[citation needed] Other notably foggy areas include coastal Chile (in the south); coastal Namibia; Nord, Greenland; and the Severnaya Zemlya islands.

As a water source
Redwood forests in California receive approximately 30–40% of their moisture from coastal fog by way of fog drip. Change in climate patterns could result in relative drought in these areas.[30] Some animals, including insects, depend on wet fog as a principal source of water, particularly in otherwise desert climes, as along many African coastal areas. Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient. Fog can be of different type according to climatic conditions.

Artificial fog
Artificial fog is man-made fog that is usually created by vaporizing a water- and glycol-based or glycerine-based fluid. The fluid is injected into a heated metal block, and evaporates quickly. The resulting pressure forces the vapor out of a vent. Upon coming into contact with cool outside air, the vapor condenses in microscopic droplets and appears as fog.[31] Such fog machines are primarily used for entertainment applications.

Historical references
See also: Pea soup fog, Fog of war, and Theatrical smoke and fog
The presence of fog has often played a key role in historical events, such as strategic battles. One example is the Battle of Long Island (August 27, 1776), when American general George Washington and his command were able to evade imminent capture by the British Army, using fog to conceal their escape. Another example is D-Day (June 6, 1944) during World War II, when the Allies landed on the beaches of Normandy, France during fog conditions. Both positive and negative results were reported from both sides during that battle, due to impaired visibility.[32]

During my sophomore year in high school, My mom bought us a trip to Spokane on the Greyhound Bus. Just her and me.

Primary objective was to buy the multi band radio I had been dreaming about in the Radio Shack catalog. No Radio Shack store in Pullman, back then.

While in the "city" she wanted me to see some sights.

The Crescent Department Store was all decked out in holiday trimmings. A must see; the animated window with moving Santa mannequin.

We walked around to the front of the block and entered through the main door where said window would be.

When we got there, my mom just kept walking while I stopped. I wondered why she suddenly lost interest. With some disgust in her voice she said, "It’s Christmas on the moon." Santa was in a space suit. No warm fire, snowy fields, or chestnuts roasting.

It was moon rocks and grey dust. Santa picking up rocks and placing them in specimen pouches.

Moving on, we did had a nice meal on the Crescent’s top floor cafe named The Tea Room. Then did a bit more window shopping in downtown Spokane before heading to pick up my prized radio.

I still have that radio, but due to dust in the band switches, it no longer works. It served me well from around 1971 till the late 1980s.

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth’s surface.[1] Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.

The term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes).[2]

By definition, fog reduces visibility to less than 1 kilometre (0.62 mi), whereas mist causes lesser impairment of visibility.[3]

For aviation purposes in the UK, a visibility of less than 5 kilometres (3.1 mi) but greater than 999 metres (3,278 ft) which is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported.[4][full citation needed]

Formation
See also: Cloud physics

Minute droplets of water constitute this after-dark radiation fog, with an ambient temperature of −2 °C (28 °F). Their motion trails are captured as streaks.

A close-up view of water droplets forming fog. Those outside the camera lens’s depth of field appear as orbs.
Fog forms when the difference between air temperature and dew point is less than 2.5 °C (4.5 °F).[5]

Fog begins to form when water vapor condenses into tiny water droplets that are suspended in the air. Some examples of ways that water vapor is added to the air are by wind convergence into areas of upward motion;[6] precipitation or virga falling from above;[7] daytime heating evaporating water from the surface of oceans, water bodies, or wet land;[8] transpiration from plants;[9] cool or dry air moving over warmer water;[10] and lifting air over mountains.[11] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds.[12][13] Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.[14]

Fog normally occurs at a relative humidity near 100%.[15] This occurs from either added moisture in the air, or falling ambient air temperature.[15] However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.

Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets.[16] This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.

The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fog-bank it may contain, will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.

Types
Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred.

Radiation fog is formed by the cooling of land after sunset by infrared thermal radiation in calm conditions with a clear sky. The cooling ground then cools adjacent air by conduction, causing the air temperature to fall and reach the dew point, forming fog. In perfect calm, the fog layer can be less than a meter thick, but turbulence can promote a thicker layer. Radiation fog occurs at night, and usually does not last long after sunrise, but it can persist all day in the winter months, especially in areas bounded by high ground. Radiation fog is most common in autumn and early winter. Examples of this phenomenon include the Tule fog.[17]

Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds.[18] However, the term is usually a synonym for shallow radiation fog; in some cases the depth of the fog is on the order of tens of centimetres over certain kinds of terrain with the absence of wind.

Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background
Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled.[19] It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog). A strong enough temperature difference over water or bare ground can also cause advection fog.

Although strong winds often mix the air and can disperse, fragment, or prevent many kinds of fog, markedly warmer and humid air blowing over a snowpack can continue to generate advection fog at elevated velocities up to 80 km/h (50 mph) or more – this fog will be in a turbulent, rapidly moving, and comparatively shallow layer, observed as a few centimetres/inches in depth over flat farm fields, flat urban terrain and the like, and/or form more complex forms where the terrain is different such as rotating areas in the lee of hills or large buildings and so on.

Fog formed by advection along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coast-ward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline; a phenomenon known as a "southerly surge", typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain. Moderate turbulence will typically transform a fog bank, lifting it and breaking it up into shallow convective clouds called stratocumulus.

Evaporation fog or steam fog forms over bodies of water overlain by much colder air; this situation can also lead to the formation of steam devils, which look like dust counterparts. Lake effect fog is of this type, sometimes in combination with other causes like radiation fog. It tends to differ from most advective fog formed over land in that it is, like lake-effect snow, a convective phenomenon, resulting in fog that can be very dense and deep and looks fluffy from above.

Frontal fog forms in much the same way as stratus cloud near a front when raindrops, falling from relatively warm air above a frontal surface, evaporate into cooler air close to the Earth’s surface and cause it to become saturated. This type of fog can be the result of a very low frontal stratus cloud subsiding to surface level in the absence of any lifting agent after the front passes.

Ice fog forms in very low temperatures and can be the result of other mechanisms mentioned here, as well as the exhalation of moist warm air by herds of animals. It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions, which can cause many types of halos and other results of refraction of sunlight by the airborne crystals.

Freezing fog, which deposits rime, is composed of droplets of supercooled water that freeze to surfaces on contact.

Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms.

Hail fog sometimes occurs in the vicinity of significant hail accumulations due to decreased temperature and increased moisture leading to saturation in a very shallow layer near the surface. It most often occurs when there is a warm, humid layer atop the hail and when wind is light. This ground fog tends to be localized but can be extremely dense and abrupt. It may form shortly after the hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating.[20]

Upslope fog forms when moist air is going up the slope of a mountain or hill (orographic lifting) which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.

Freezing conditions
Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime.[21] This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is super-cooled, filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful".

File:Aerial View of freezing fog in the Okanagan Highlands.webm
Aerial Video of freezing fog in the Okanagan Highlands
In the western United States, freezing fog may be referred to as pogonip.[22] It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip is derived from the Shoshone word paγi̵nappi̵h, which means "cloud".[22][23] In The Old Farmer’s Almanac, in the calendar for December, the phrase "Beware the Pogonip" regularly appears. In his anthology Smoke Bellew, Jack London described a pogonip which surrounded the main characters, killing one of them.

The phenomenon is also extremely common in the inland areas of the Pacific Northwest, with temperatures in the 10 to 30 °F (−12 to −1 °C) range. The Columbia Plateau experiences this phenomenon most years due to temperature inversions, sometimes lasting for as long as three weeks. The fog typically begins forming around the area of the Columbia River and expands, sometimes covering the land to distances as far away as LaPine, Oregon, almost 150 miles (240 km) due south of the river and into south central Washington.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below −35 °C (−31 °F), making it common only in and near the Arctic and Antarctic regions.[24] It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Utqiagvik, Alaska. Ice fog often leads to the visual phenomenon of light pillars.

Morning freezing fog in Elko, Nevada

Pogonip fog in Virginia City, Nevada, from an early 20th-century postcard

Tree in field during extreme cold with frozen fog

Ice fog on Pyhäjärvi, Tampere during sunset.

Topographical influences

Fog over the Pedra do Sino (Bell Rock; left) and Dedo de Deus (God’s Finger; right) peaks in the Serra dos Órgãos National Park, Rio de Janeiro state, Brazil
Up-slope fog or hill fog forms when winds blow air up a slope (called orographic lift), adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.

Valley fog forms in mountain valleys, often during winter. It is essentially a radiation fog confined by local topography, and can last for several days in calm conditions. In California’s Central Valley, valley fog is often referred to as tule fog.

Sea and coastal fog
Sea fog (also known as haar or fret) is heavily influenced by the presence of sea spray and microscopic airborne salt crystals. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves. Except in areas of storminess, the most common areas of breaking waves are located near coastlines, hence the greatest densities of airborne salt particles are there.

Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. Another recently discovered source of condensation nuclei for coastal fog is kelp seaweed. Researchers have found that under stress (intense sunlight, strong evaporation, etc.), kelp releases particles of iodine which in turn become nuclei for condensation of water vapor, causing fog that diffuses direct sunlight.[25]

Sea smoke, also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land.[21] It often causes freezing fog, or sometimes hoar frost.

Arctic sea smoke is similar to sea smoke, but occurs when the air is very cold. Instead of condensing into water droplets, columns of freezing, rising, and condensing water vapor is formed. The water vapor produces the sea smoke fog, and is usually misty and smoke-like.[26]

Garúa fog near the coast of Chile and Peru,[27] occurs when typical fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a "transparent mist". Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers because of deposition of liquid water on hard surfaces.

Fog rolls into Seattle from the sea

Sea fog or "fret" encroaching on Brighton Pier

Sea fog in the Arctic Ocean near the island of Jan Mayen

Visibility effects

Heavy fog on a road near Baden, Austria

Light fog reduces visibility on a suburban street, rendering the cyclist very hazy at about 200 m (220 yd). The limit of visibility is about 400 m (440 yd), which is before the end of the street.
Depending on the concentration of the droplets, visibility in fog can range from the appearance of haze, to almost zero visibility. Many lives are lost each year worldwide from accidents involving fog conditions on the highways, including multiple-vehicle collisions.

The aviation travel industry is affected by the severity of fog conditions. Even though modern auto-landing computers can put an aircraft down without the aid of a pilot, personnel manning an airport control tower must be able to see if aircraft are sitting on the runway awaiting takeoff. Safe operations are difficult in thick fog, and civilian airports may forbid takeoffs and landings until conditions improve.

A solution for landing returning military aircraft developed in World War II was called Fog Investigation and Dispersal Operation (FIDO). It involved burning enormous amounts of fuel alongside runways to evaporate fog, allowing returning fighter and bomber pilots sufficient visual cues to safely land their aircraft. The high energy demands of this method discourage its use for routine operations.

Shadows

Sutro Tower casts a 3-dimensional fog shadow
Shadows are cast through fog in three dimensions. The fog is dense enough to be illuminated by light that passes through gaps in a structure or tree, but thin enough to let a large quantity of that light pass through to illuminate points further on. As a result, object shadows appear as "beams" oriented in a direction parallel to the light source. These voluminous shadows are created the same way as crepuscular rays, which are the shadows of clouds. In fog, it is solid objects that cast shadows.

Sound propagation and acoustic effects
See also: Acoustic location, Acoustic shadow, and Foghorn
Sound typically travels fastest and farthest through solids, then liquids, then gases such as the atmosphere. Sound is affected during fog conditions due to the small distances between water droplets, and air temperature differences.

Molecular effect: Though fog is essentially liquid water, the many droplets are separated by small air gaps. High-pitched sounds have a high frequency, which in turn means they have a short wavelength. To transmit a high frequency wave, air must move back and forth very quickly. Short-wavelength high-pitched sound waves are reflected and refracted by many separated water droplets, partially cancelling and dissipating their energy (a process called "damping"). In contrast, low pitched notes, with a low frequency and a long wavelength, move the air less rapidly and less often, and lose less energy to interactions with small water droplets. Low-pitched notes are less affected by fog and travel further, which is why foghorns use a low-pitched tone.[28]

Temperature effect: A fog can be caused by a temperature inversion where cold air is pooled at the surface which helped to create the fog, while warmer air sits above it. The inverted boundary between cold air and warm air reflects sound waves back toward the ground, allowing sound that would normally radiate out escaping into the upper atmosphere to instead bounce back and travel near the surface. A temperature inversion increases the distance that lower frequency sounds can travel, by reflecting the sound between the ground and the inversion layer.[29]

Record extremes
Particularly foggy places include[citation needed] Hamilton, New Zealand and Grand Banks off the coast of Newfoundland (the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south). Some very foggy land areas in the world include Argentia (Newfoundland) and Point Reyes (California), each with over 200 foggy days per year.[citation needed] Even in generally warmer southern Europe, thick fog and localized fog are often found in lowlands and valleys, such as the lower part of the Po Valley and the Arno and Tiber valleys in Italy; Ebro Valley in northeastern Spain; as well as on the Swiss plateau, especially in the Seeland area, in late autumn and winter.[citation needed] Other notably foggy areas include coastal Chile (in the south); coastal Namibia; Nord, Greenland; and the Severnaya Zemlya islands.

As a water source
Redwood forests in California receive approximately 30–40% of their moisture from coastal fog by way of fog drip. Change in climate patterns could result in relative drought in these areas.[30] Some animals, including insects, depend on wet fog as a principal source of water, particularly in otherwise desert climes, as along many African coastal areas. Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient. Fog can be of different type according to climatic conditions.

Artificial fog
Artificial fog is man-made fog that is usually created by vaporizing a water- and glycol-based or glycerine-based fluid. The fluid is injected into a heated metal block, and evaporates quickly. The resulting pressure forces the vapor out of a vent. Upon coming into contact with cool outside air, the vapor condenses in microscopic droplets and appears as fog.[31] Such fog machines are primarily used for entertainment applications.

Historical references
See also: Pea soup fog, Fog of war, and Theatrical smoke and fog
The presence of fog has often played a key role in historical events, such as strategic battles. One example is the Battle of Long Island (August 27, 1776), when American general George Washington and his command were able to evade imminent capture by the British Army, using fog to conceal their escape. Another example is D-Day (June 6, 1944) during World War II, when the Allies landed on the beaches of Normandy, France during fog conditions. Both positive and negative results were reported from both sides during that battle, due to impaired visibility.[32]