|SUPERADIABATIC LAPSE RATE
METEOROLOGIST JEFF HABY
A super-adiabatic lapse rate occurs when the temperature decreases with height at a rate of greater than 10 degrees
Celsius per kilometer. A super-adiabatic lapse rate is usually caused by intense solar heating at the surface. Especially
when the winds are light and the soils are dry, heat from the sun will build at the surface. A super-adiabatic lapse
rate is common in the Southwest U.S. in the summer, but can occur in most regions of the U.S. in the
summer when the skies are
clear (maximum insolation), wind speeds are low (limited vertical mixing) and soils
are dry (no evaporational cooling).
A super-adiabatic lapse rate is labeled as
absolute instability. The super-adiabatic
layer is generally shallow and located near the earth's surface. Whether
a super-adiabatic lapse rate at the surface leads to precipitation is a function of the
moisture content of the
trigger mechanisms, and
upper level forcing mechanisms, etc. A
super-adiabatic lapse rate in the middle and upper troposphere is rare.
Another situation a super-adiabatic lapse rate can occur is over a warm lake. When a cold air mass moves over a
large lake (i.e. Great Lakes) the lake warms the air nearest to the lake surface. This can result in
and a large temperature decrease with height above the lake. In heavy
lake-effect snow situations there will
often be a super-adiabatic lapse rate above the lake.
A downsloping wind is another situation
it can occur. With a downsloping wind, air is warmed at the dry
adiabatic lapse rate as it sinks. This combined with surface
heating can produce a super-adiabatic lapse rate in the lower troposphere in the afternoon. If a dry adiabatic
temperature profile is heated on its lower end it will become super-adiabatic (lapse rate greater than 10 C/km).