Chapter 5: Clouds And Stability

small volume of air

IF A PARCEL OF AIR EXPANDS AND COOLS, OR COMPRESSES AND WARMS, WITH NO INTERCHANGE OF HEAT WITH ITS SURROUNDINGS. as long as the air remains unsaturated (relative humidity is less than 100), the rate remains constant at 10 C per 1000 m

as long as the air remains unsaturated (relative humidity is less than 100), the rate remains constant at 10 C per 1000 m

is the rising air cools to dew point, it reaches 100 percent humidity. cloud forms and latent heat is released. 6C per 1000m.

rate at which the air temperature will be changing around us if we were to climb up in the atmosphere

when the rising air is colder and heavier than the air around it- when the environmental lapse rate is less than moist adiabatic rate (6C)

inversions that form as air slowly sinks over a large area

if the environmental lapse rate is exactly equal to the dry adiabatic rate, rising or sinking unsaturated air will cool or warm at the same rate as the air around it

when rising air is warmer and less dense; environmental lapse rate is greater than the dry adiabatic rate

when rising air is unsaturated, the atmosphere is stable because the parcel is colder than its surroundings; saturated air rising is saturated, the atmosphere is unstable because the parcel is warmer than its surroundings; occurs when environmental lapse rate is between the moist and dry rate

the elevation where the could first forms

lifting a stable layer with a dry top and moist surface, potential instability

mixing of cooling air into a rising cloud, increases the rate at which the rising cloud cool

forced lifting along a topographic layer

warmer air, leeward side of mountain, less precipitation

the addition/ subtraction of heat form air without external heating/ cooling

Dry adiabatic rate is roughly 10 C/km while the moist adiabatic rate is usually slower (around 6 C/Km) as condensation in the rising air adds latent heat

The environmental lapse rate is the actual decrease of temperature with altitude. This is often meaured by instrumented balloon. The dry adiabatic lapse rate is the rate at which air temperature would drop with altitude due to expansion.

Any process that creates a steeper lapse rate will cause the air to become less stable. This could be warming near the surface or cooling aloft or both.

Lake effect storms form when cold, stable air passes over a warm, moist surface. The heat added from below causes the lapse rate to increase (become less stable) while the mositure added from below becomes the source of the eventual precipitation.

Cumulonimbus clouds can grow to such a height that they encounter the bottom of the stratosphere, which is extremely stable with rising temperatures with altitude (inversion). The rising cumulonimbus cannot enter the stratosphere and hence spread out

46 F

convection

air motions caused by subsidence

decreases at a slower rate than the parcel temperature

cumulonimbus

thick, strong

stratus

mix the air in the layer, life the entire air layer, cool the upper part of the layer

stable, unstable

unstable

an inversion

stratus

cool the surface and warm the air aloft

stable

the fact that latent heat is released by a rising parcel of saturated air

temperature changes in a rising or descending parcel of unsaturated air

moist adiabatic lapse rate

environmental lapse rate

stable

15 C

always cools due to expansion

2500

air temperature 90°F, dew point temperature 60°F

conditional instability

clouds forming on the windward slope of a mountain

absolutely unstable

greater, less

11°C per 1000 m

latent heat is released by rising saturated air

warm the surface and cool the air aloft

10°C colder than at the surface