A cell of dry air is moved vertically from its original position under adiabatic conditions. Depending...

A cell of dry air is moved vertically from its original position under adiabatic conditions. Depending on the temperature profile of the surrounding atmosphere, this gas cell can keep on moving in the same direction, or it may come back to its original position. Explain why and when the atmosphere is considered to be convectively stable and convectively unstable.

Expert Solution

The value of the environmental lapse rate is one of the main factors that determines whether the atmosphere will be stable or unstable. Warming the air above the ground and/or cooling the air next to the ground will make the atmosphere more stable. The ground and the air above it cool during the night.

Lapse rate: The rate at which temperature changes in the vertical (slope of the temperature vertical profile)
Dry adiabatic lapse rate: the rate at which an unsaturated air parcel will cool if it rises or warm as it sinks (applies to an air parcel with a relative humidity of less than 100%). Dry adiabatic lapse rate = 10°C / km
Moist adiabatic lapse rate: the rate at which a saturated air parcel will cool if it rises or warm if it sinks (applies to an air parcel with a relative humidity of 100%). Moist adiabatic lapse rate = 6°C / km (on average in the troposphere)

To determine stability we need to compare the temperature of an air parcel to the temperature of its environment.

If an air parcel is warmer than its environment it will rise.
If an air parcel is colder than its environment it will sink.

genius_generous answered 2 years ago

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