11.4 Static Stability and Vertical Soundings

There are two basic thermodynamic “processes” that meteorologists are concerned with for arising air parcel

dry adiabatic and moist (pseudo)adiabatic

The dry adiabatic process conserves…

potential temperature for a parcel that is unsaturated (gas phase)

Moist adiabatic ascent is applicable for…and conserves…

saturated air parcels in clouds; theta e (equivalent potential temp)

Since clouds normally form because of ascending air that originates near the surface, the LCL of a near surface parcel can be a good estimate of…

the cloud base

Equivalent potential temperature

Follow adiabat and pseudoadiabat to the top of the atmosphere, then descend adiabatically to 1000 hPa

Wetbulb temperature

Follow pseudoadiabat down from the LCL to the original temperature

Convective condensation level

Where the surface mixing ratio intersects the environmental temperature

Convective temperature

Follow the dry adiabat down from the CCL to the surface

Level of free convection

Follow the pseudoadiabat up from the LCL until it crosses the environmental temperature. It may not always exist.

Equilibrium level

Where a parcel rising above the LFC again crosses the environmental temperature. Normally this is near the tropopause.

The procedure for finding the LCL for a parcel on a Skew-T chart

When the mixing ratio line “intersects” with the parcel temperature line (adiabat), the parcel has reached 100% saturation. This is the LCL for that parcel