Online Quiz

Adiabatic Lapse Rates

Adiabatic process

dry adiabatic rate DAR = 10°C/Km
If parcel of unsaturated air expands & cools, or compresses & warms, with no interchange of heat withits surroundings

The Rate of adiabatic cooling or warming remains constant “only to unsaturated air”

Wet adiabatic rate WAR ≈ 6°C/Km
As the rising air cools, its RH increases, & at the Td, RH becomes 100%

Further lifting results in condensation, a cloud forms, & latent heat is released inside the rising air parcel

The air no longer cools at the DAR but at a lesser rate. Because the heat added offsets some of the cooling due to expanding

Lifted Condensation Level (LCL)

The height at which air that is cooling at the DAR becomes saturated & condensation begins

Processes that Lift Air

Orographic Lifting: forced over a mountain

Convergence forced to rise as it collides

Frontal Wedging: air is forced up due to difference in air T or ρ

Localized Convective Lifting differential  heating, Air is forced to rise to heating air & lowering its density

Air Parcels

Imaginary volume of air
– a few hundred m³

ASSUMPTION
1. no heat is transferred into, or out of it
2. Acts independently of the surrounding air
3. HIGHLY IDEALIZED

We use them to
1. Determines if the air will rise or sink by comparing parcel of air to its surrounding
2. predict if clouds will form

Adiabatic Lapse Rates ALR

WALR & DALR help us to
1. Understand if a parcel will rise or sink
1. Determines if a cloud will form
2. Determines type, & height of clouds

Environmental Lapse Rate (ELR)

Actual measureable T change with height

Atmospheric stability

Stable Air (Tair < Tsur.)

If a parcel cooler than the surrounding, it would be more dense, so sink back to it’s original position

Air resists vertical (up & down) motion

Air is in stable equilibrium when it tends to return to its original position

Unstable Air (Tair > Tsur.)

If a parcel warmer than the surrounding, it would be less dense, so rise to an altitude where it’s T equaled that of surrounding

Air that is in unstable equilibrium will move away from its original position

Stability & Daily Weather

If stable air is forced up, the associated clouds have little vertical thickness & precipitation is light

Clouds associated with unstable air are towering & accompanied by heavy rain

Thunderstorms produced by the unstable air that caused by the passing hurricanes

Changes in Stability

Stability is enhanced by the following
1. Radiation cooling of surface after sunset
2. The cooling of an air mass from below
3. General subsidence within an air column (sinking)
Stable atmosphere are cooling from below & warming aloft

Instability is enhanced by the following
1. Solar heating warming the lower atm
2. The heating of an air mass from below
3. Upward movement of air
4. Radiation cooling from cloud tops
Unstable atmosphere are heating from below & colling aloft

Vertical Air Movement

Subsidence downward motion of air

Stabilizes the air if the air above is warmed

Can result in the evaporation of clouds

The End