Anatomy Of A Thunderstorm - Honeywell KMD-150 Pilot's Manual

Stormscope Operation
• Discharge rate indicator-displays estimated average discharge rate per
minute for current range and view
• Mic inhibit - inhibits thunderstorm processing when the communications
transmitter is keyed to prevent the processing of corrupted data (some
aircraft need to use this feature, others don't).

ANATOMY OF A THUNDERSTORM

The Stormscope model WX-500 is intended to help pilots avoid the dan-
gers associated with thunderstorms (convective wind shear, lightning,
icing, tornadoes, etc.). The WX-500 locates thunderstorms by detecting
the electrical discharges that thunderstorms always generate. Figure 13-
2 shows how thunderstorms create electrical discharges and radiate
electromagnetic signals.
Figure 13-2 - Electrical Discharges in Thunderstorms
a) The convective flow of air currents (warm air going up and cold air
going down) leads to friction between the opposing air currents and wind
shear in the space between the opposing air currents. The closer
together the opposing air currents are, the greater the shearing force of
the air currents.
b) The friction between the opposing air currents causes electrical
charges in the area to separate. As positive (+) and negative (-) electrical
charges are separated, they accumulate in masses of similar charges
(positive charges near the top of the cloud and negative charges near
the bottom).
c) Electrical discharges occur as the accumulated masses of separated
positive and negative charges attempt to rejoin. These discharges con-
tinue to occur repetitively as long as the convective wind shear persists.
A few of the discharges are visible as lightning, but most electrical dis-
charges occur within a cloud or between clouds and are hidden by those
clouds. Only a small percentage of discharges occur between the clouds
and the ground. Cloud to ground lightning occurs when the negatively
charged lower part of a cloud induces a positive charge on an object on
the ground. The immense charge separation finally breaks down the
insulating air and a discharge occurs dumping negative charge from the
cloud onto the object and the surrounding ground.
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Rev 1 Mar/2000 KMD 150 Pilot's Guide