2-14 shows an example of analyzed positive and the
negative energy areas as they would appear on a
Skew-T, Log P diagram.
Autoconvection
AUTOCONVECTION
is
a
condition
started
spontaneously by a layer of air when the lapse rate of
temperature is such that density increases with
elevation. For density to increase with altitude, the
lapse rate must be equal to or exceed 3.42°C per 100
meters. (This is the AUTOCONVECTIVE LAPSE
RATE.) An example of this condition is found to exist
near the surface of the earth in a road mirage or a dust
devil. These conditions occur over surfaces that are
easily heated, such as the desert, open fields, etc.; they
are usually found during periods of intense surface
heating.
Convection Stability and Instability
In the discussion so far of convection stability and
instability, PARCELS of air have been considered. Let
us now examine LAYERS of air. A layer of air that is
2-20
500
600
700
850
1000
ISOBARS mb
+
+
++
++++
++
++
++
UPPER
NEGATIVE
AREA
(BLUE SHADING)
EL
POSITIVE
AREA
(RED SHADING)
NEGATIVE
AREA
(BLUE
SHADING)
LFC
LCL
POINT A
T
T
T
T
d
d
AG5f0214
Figure 2-14.—Example of positive and negative energy areas (mechanical lifting).
