050 04 00 00 CLOUDS AND FOG

Adiabatic cooling – as the air rises at the DALR, the temperature eventually reaches the dew point, beyond which condensation and cloud form, the air can continue to rise at the SALR until the tropopause or the ELR (where the atmosphere becomes stable) puts a stop to it.

Conduction – Direct contact, dew point and condensation again, this is radiation for or low level stratiform.

Advection – Warm air being cooled from below when moving to a cooler area, advection fog. Wind and temperature increase can lift the fog to stratus, can end up becoming nimbostratus with drizzle and rain.

Radiation – Over night, just after sun rise the land is at its coolest and cools the layer of air above to its dew point, then, again, fog. Can also lift. Common in a winter high pressure system with clear skies and light winds.

 

1 – Wind blowing over objects and thermal effects causing turbulence up to 3000′. the mixing can cause close formation at the top of the mixing layer, capped by the inevitable inversion. Stratocumulus – convective cloud capped by an inversion.

2 – Orographic uplift, forced up to its dew point. Unstable orographic uplift can cause thunder storms. Stable uplift can just cap the mountains causing dangerous mountain waves, rotor cloud and the Fohn effect discussed elsewhere.

Frontal uplift. Both warm and cold fronts can bring stratiform limbo or otherwise clouds, however, because of the nose of a cold front near the surface, warm air gets trapped under the advancing cold air which brings immediate unstable conditions, the warm air shoots up to embed CU in the stratus.

Stable are stratiform and unstable are cumuliform.

Increased warming – high pressure for example.

Descending from a mountain.

ELR change.

Low level < 6500′

Medium or alto 6500′ to 23000′

High or cirri 16500′ up to the tropopause.

Stratiform, flat, large horizontal size, limited depth

Cumuliform – Large vertical extent, limited horizontal.

Cirriform – Fibrous hight level in the troposphere.

Just did…

Cirrus	16000-45000′	Fiberous	Ice
Cirrostratus	16000-45000′	Halo phenomena , veil like	Ice
Cirrocumulus	16000-45000′	Mackerel sky	Ice
Altocumulus	6500 to 23000	High patches, shadows on the ground	Ice/Water
Altostratus	6500 to 23000	grey/blue sheet	Ice/Water
Nimbostratus	Ground to 15000′	Big, grey thick intimidating nastiness	Ice/Water
Stratocumulus	100 to 6500′	Dark bases, grey bubbly sheet	Both
Stratus	Ground to 6500′	Grey layered, low.	Both
Cumulus	1000 to 25000′	Isolated fluffy	Water drops, Ice crystals
Cumulonimbus	1000 to tropopause	Heavy and dense and massive.	Above but with hail

 

Castellanus – Alto clouds – castle like.

Lenticularis – Lens.

Congestus – Sprouting CU, great vertical extent. TCU.

Calvus – CU No fibrous bits.

Capillatus – Anvil bit of a CB.

Virga – Rain that doesn’t make the ground.

Basically covered above

In above table.

Stop the vertical movement

Clouds develop until they hit the inversion which basically flattens them out.

Just after sunrise the invention restricts vertical movement of air and if the ground is cooled enough by radiation it can cause radiation fog.

Due to the isothermal nature of the tropopause all vertical movement is capped, this is the reason for the anvil of a CB.

 

• Fog – <1000 m (small water droplets)
• Mist – 1000 m to 5000 m (Microscopic water droplets)
• Haze – < 5000m (Suspension of dust and general cack!

 

• Fog – Cloud on the surface – saturation.
• Mist – Same
• Haze – High pressure, pollution, inversions very visible.

 

Whenever the temperature and dew point are within 2 degrees C of each other.

High pressure and pollution.

Freezing fog – supercooled water droplets. Ice fog – tiny solid ice crystals that were previously tiny water droplets, can remain liquid to -40 degrees C

High humidity, light winds, clear skies and long nights, cooled by the ground just as the sun starts to wake up.

0 to 1500′, normal 500′. The fog itself helps cause an inversion and in turn stops any vertical movement.

Burns off and the sun kicks in, increase in temperature produces thermal turbulence. Increase in wind disperses by accelerated mixing with the above layers.

Warmer air advecting over cooler ground.

It is basically an air mass fog, so wherever is comes from it is the temperature difference with where it ends up that causes it.

Associated with warm stable air. Common over land in winter and cools sea areas in summer.

Lifting into stratus, air mass change, burning off or strong turbulence.

Cold stable air lies over relatively moist warm water. Evaporation fog. Same as the stream from a hot drink or kettle.

Inversion must be present.

Inversion can dissipate, general heating etc.

Warm rain from above saturates the lower air.

100s of miles long and 200miles deep.

Moves away with the front.

cools adiabatically when forced up a hill.

Capped cloud if the air is stable, on the windward side.

Same as the rest…heat, subsidence etc.