Ordinary-cell convective storms - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 108

Figure 3.13. Example of a ''CAPE robber''. Sounding at Amarillo, TX on June 15, 2010 at
12:00 utc (from Plymouth State College archives and graphics). While the convective tem-
perature is about 32 C and a substantial amount of heating is necessary to realize this
temperature, an elevated stable layer just below 500 hPa would ''rob'' the sounding of quite
a bit of potential CAPE, even if it were to be realized, as seen by the area under the yellow curve
(moist adiabatic at the LFC) and the red curve (temperature).
broken, convection may be initiated only locally and CAPE used up only locally.
It generally takes a relatively long time for CAPE to be built up via horizontal
advection on the synoptic scale (or mesoscale) of temperature and moisture, and
via temperature changes due to vertical motions on the synoptic scale (or
mesoscale).
On the other hand, where there is no or a weak capping inversion, convection
may be initiated over a broad region and CAPE used up over a broad region. In
the Southern Plains of the U. S. during the spring, synoptic and mesoscale vertical
motion and advection build up CAPE gradually, but the CAPE is depleted quickly
as convection is initiated. Soundings with high values of CAPE, but capping inver-
sions that suppress convective initiation are called ''loaded gun'' soundings ( Figure
3.1 ). When the rate at which CAPE is built up is approximately the rate at which
it is depleted, there is said to be a ''statistical equilibrium'' condition. Statistical
equilibrium occurs frequently in the tropics, where CAPE is not large and cold