PRIMUS
r
880
Digital
W
eather
Radar
System
A28-1146-102-00
RadarFacts
5-32
The following are some truths about weather and flying, as shown in
figure 5-26.
DTurbulence results when twoair masses at different temperatures
and/or pressures meet.
DThis meeting can form athunderstorm.
DThe thunderstorm produces rain.
DThe radar displays rain (thus revealing the turbulence).
DInthe thunderstorm’scumulus stage,echoesappearonthe display
andgrowprogressivelylargerandsharper.Theantenna can be tilted
up anddowninsmall incrementstomaximizetheecho pattern.
DIn the thunderstorm’smature stage, radar echoes are sharp and
clear; hail occurs most frequently early in this stage.
DInthe thunderstorm’sdissipating stage, the rain area is largest and
shows best with aslight downward antenna tilt.
Radar can be used to look inside the precipitation area to spot zones
ofpresent anddeveloping turbulence.Some knowledgeof meteorology
is required to identify these areas as being turbulent. The most
important fact is that the areas of maximum turbulence occur where
the most abrupt changes from light or no rainto heavy rain occur.The
term applied to this change in rate is rain gradient. The greater the
change in rainfall rate, the steeper the rain gradient. The steeper the
rain gradient, the greater the accompanying turbulence. More
important,however,is another fact: Storm cells are not static or stable,
but are in aconstant state of change. While asingle thunderstorm
seldomlasts more than an hour,asquall line, shown in figure 5-27 can
contain many such storm cells developing and decaying over amuch
longer period. Asinglecell can start as acumulus cloud only 1mile in
diameter,rise to 15,000 ft, grow within 10 minutes to 5miles in
diameter and tower to an altitude of 60,000 feet or more. Therefore,
weatherradar should not be used to take flash pictures of weather,but
to keep weather under continuous surveillance.