Fall Asleep While Learning About Fog

In this episode of the I Can't Sleep Podcast, fall asleep while learning about fog. I grew up near a river and remember foggy days throughout the year, but never really understood how fog came to be. This episode goes into more detail about how fog is different from clouds and mist and will help you understand how it is formed. Oh, wait! You won't learn any of that because you'll be out like a light in 10 minutes. Never mind. Happy sleeping!

Transcript

Welcome to the I Can't Sleep Podcast,

Where I read random articles from across the web to bore you to sleep with my soothing voice.

I'm your host,

Benjamin Boster.

Today's episode is from a Wikipedia article titled,

Fog.

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface.

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 affects many human activities such as shipping,

Travel,

And warfare.

Fog appears when water vapor,

Water in its gaseous form,

Condenses.

During condensation,

Molecules of water vapor combine to make tiny water droplets that hang in the air.

Sea fog,

Which shows up near bodies of sailing water,

Is formed as water vapor condenses on bits of salt.

Fog is similar too,

But less transparent than mist.

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 ocean,

Or from nearby moist ground or marshes.

By definition,

Fog reduces visibility to less than 1 km,

Whereas mist causes lesser impairment to visibility.

For aviation purposes in the United Kingdom,

A visibility of less than 5 km but greater than 999 m is considered to be mist if the relative humidity is 95% or greater.

A low 95% haze is reported.

Fog forms when the difference between air temperature and dew point is less than 2.

5 degrees Celsius.

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 condensed include wind convergence into areas of upward motion,

Precipitation of virga falling from above,

Daytime heating evaporating water from the surface of oceans,

Water bodies,

Or wetland,

Transpiration from plants,

Cool or dry air moving over warmer water,

And lifting air over mountains.

Water vapor normally begins to condense on condensation nuclei,

Such as dust,

Ice,

And salt in order to form clouds.

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.

Fog normally occurs at a relative humidity near 100%.

This occurs from either added moisture in the air or falling ambient air temperature.

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 attains 100% and the minute cloud droplets begin to coalesce into larger droplets.

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.

Fog can form multiple ways depending on how the cooling occurred that caused the condensation.

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 winter months,

Especially in areas bounded by high ground.

Radiation fog is most common in autumn and early winter.

Examples of this phenomenon include tool fog.

Ground fog is fog that obscures less than 60% of the sky and does not extend the base of any overhead clouds.

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 centimeters over certain kinds of terrain,

With the absence of wind.

Advection fog occurs when moist air passes over a cool surface by advection,

Wind,

And is cooled.

It is common as a warm front passes over an area with significant snowpack.

It is most common at sea when moist air encounters cooler waters,

Including areas of cold water upwelling,

Such as along the California coast.

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 per hour or more.

This fog will be in a turbulent,

Rapidly moving,

And comparatively shallow layer,

Observed as a few centimeters 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 coastward,

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 a 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.

Frontal fog forms in much the same way as stratus cloud near a front when rain drops,

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.

The water vapor cools,

And at the dew point it condenses and fog forms.

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.

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.

Freezing fog occurs when liquid fog droplets freeze to surfaces,

Forming white soft or hard rime ice.

This is very common on mountaintops,

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 supercooled,

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.

In the western United States,

Freezing fog may be referred to as pogonip.

It occurs commonly during cold winter spells,

Usually in deep mountain valleys.

The word pogonip is derived from the Shoshone word ha-khenepi,

Which means cloud.

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 describes the pogonip which surrounded the main characters.

The phenomenon is common in the inland areas of the Pacific Northwest,

With temperatures in the 10 to 30 degrees Fahrenheit range.

The Columbia Plateau experiences this phenomenon most years during 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 distances as far away as Lapine,

Oregon,

Almost 150 miles 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 negative 35 degrees Celsius,

Making it common only in and near the Arctic and Antarctic regions.

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.

Frozen ice fog can become extremely dense and will persist day and night until the temperature rises.

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.

Ice fog often leads to the visual phenomenon of light pillars.

Upslope 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 Thule fog.

Thule fog 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's 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.

Sea smoke,

Also called steam fog or evaporation fog,

Is created by cold air passing over warmer water or moist land.

It may cause freezing fog or sometimes hoarfrost.

This situation can also lead to the formation of steam devils,

Which look like their 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.

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.

Parua fog,

Near the coast of Chile and Peru,

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.

Karua fog is nearly invisible,

Yet it still forces drivers to use windshield wipers because of condensation onto cooler hard surfaces.

Kamanchaca is a similar dense fog.

Depending on the concentration of the droplets,

Visibility in fog can range from the appearance of haze to almost zero visibility.

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 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.

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 canceling 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 the 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.

A fog can be caused by a temperature inversion where cold air is pooled at the surface,

Which helps 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.

Particularly foggy places include 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 Argentina,

Newfoundland and Point Reyes,

California,

Each with over 200 foggy days per year.

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 Sealand area in late autumn and winter.

Other notably foggy areas include coastal Chile in the south,

Coastal Namibia,

Nord Greenland and the Sevenaya-Zemlya Islands.

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.

Some animals,

Including insects,

Depend on wet fog as a principal source of water,

Particularly in otherwise desert climates,

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.

Artificial fog is man-made fog that is usually created by vaporizing a water and glycol or glycerin-based fluid.

The fluid is injected into a heated metal block,

Which evaporates quickly.

The resulting pressure forces the vapor out of a vent.

Upon coming into contact with the cool outside air,

The vapor condenses in microscopic droplets and appears as fog.

Such fog machines are primarily used for entertainment applications.

The presence of fog has often played a key role in historical events,

Such as strategic battles.

One example is the 1776 Battle of Long Island,

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.

Anti-fog agents,

Also known as anti-fogging agents and treatments,

Are chemicals that prevent the condensation of water in the form of small droplets on a surface which resemble fog.

They are one of many additives used in the production of plastics.

Anti-fog agents were developed by NASA during the Project Gemini for use on helmet visors.

During Gemini 9A in June 1966,

Astronaut Eugene A.

Cernan tested NASA's first space suit and discovered during the spacewalk that his helmet visor fogged,

Among other issues.

Cernan's suit was tested using the spacecraft 9 Life Support System after the flight,

When it was discovered that a small patch of the visor treated with an anti-fog solution remained clear of condensation.

Later Gemini flights all included the anti-fog solution for application prior to the spacewalk occurring.

Anti-fog agents are available as spray solutions,

Creams,

And gels,

And wet wipes,

While more resistant coatings are often applied during complex manufacturing processes.

Anti-fog additives can also be added to plastics,

Where they exude from the inside to the surface.

Most commercial anti-fog agents are surfactants that minimize the surface tension of the water.

Many other substances have been used as anti-fog agents,

Including home-based recipes containing detergents.

One method to prevent fogging is to apply a thin film of detergent.

This method is criticized because detergents are designed to be water-soluble and they cause smearing.

Divers often use saliva,

Which is a commonly known and effective anti-fogging agent.

A demister is a substance supplied to transparent surfaces to stop them from becoming fogged with mist deposit,

Often referred to as fog.

Scuba divers often spit into their masks and then wash the surface quickly with water to prevent mist buildup that can impair vision.

Several products are commercially available,

Such as C-drops,

That are generally more effective.

New mask lenses still have silicone on them from the manufacturing process,

So it is recommended to clean the lens with an appropriate mask scrub,

Then rinse the mask and then apply a demister solution.

Fog collection is the harvesting of water from fog using large pieces of vertical mesh netting to induce the fog droplets to flow down towards a trough below.

The setup is known as a fog fence,

Fog collector,

Or fog net.

Through condensation,

Atmospheric water vapor from the air condenses on cold surfaces into droplets of liquid water known as dew.

The phenomenon is most observable on thin,

Flat exposed objects,

Including plant leaves and blades of grass.

As the exposed surface cools by radiating its heat to the sky,

Atmospheric moisture condenses at a rate greater than that of which it can evaporate,

Resulting in the formation of water droplets.

Water condenses onto the array of parallel wires and collects at the bottom of the net.

This requires no external energy and is facilitated naturally through temperature fluctuation,

Making it attractive for deployment in less developed areas.

The term fog fence comes from its long rectangular shape resembling a fence,

But fog collectors are not confined just to this structural style.

The efficiency of the fog collector is based on the net material,

The size of the holes and filament,

And chemical coating.

Fog collectors can harvest from 2% up to 10% of the moisture in the air,

Depending on their efficiency.

An ideal location is a high-altitude arid area near cold offshore currents,

Where fog is common,

And therefore the fog collector can produce the highest yield.

The organized collection of dew or condensation through natural or assisted processes is an ancient practice,

From the small-scale drinking of pools of condensation collected in plant stems,

Still practiced today by survivalists,

To large-scale natural irrigation without rain falling,

Such as in the Atacama and Namib deserts.

The first man-made fog collectors stretch back as far as the Inca Empire,

Where buckets were placed under trees to take advantage of condensation.

Several man-made devices,

Such as antique stone piles in Ukraine,

Medieval dew ponds in southern England,

And volcanic stone covers in the fields of Lantarote have all been thought to be possible dew-catching devices.

One of the first recorded projects of fog collection was in 1969 in South Africa,

As a water source for an air force base.

The structure consisted of two fences,

Each 100 square meters.

Between the two,

11 liters of water was produced on average per day,

Over the 14-month study,

Which is 110 milliliters of water for every square meter.

The next large study was performed by the National Catholic University of Chile and the International Development Research Center in Canada in 1987.

One hundred 48-square-meter fog fences were assembled in northern Italy.

The project was able to yield on average 0.

5 liters of water for every square meter,

Or 33 liters for each of the 300 villagers each day.

Reviews

I didn’t know the difference between mist and fog, that’s interesting. Then it must have gotten really dull because I don’t remember anything else. 😂😂
Thank you! 🤗