RADAR STORM OBSERVATION 
or other indicator operating in synchronism with the 
antenna azimuth control. This is also true for A- and 
R-scope azimuth readings. 
PRECIPITATION ECHOES 
30,000 RANGE MARKS AT 
10 MILE 
Di INTERVALS 
us 
q 
3 25,000 
x 
(o} 
[eg 
% AIRCRAFT 
< 20,000 ECHOES 
(i 
Ww 
WwW 
ow 
z 15,000 
ce 
Q 
& 
S 10,000 LOCATION 
° OF 
RADAR 
5,000 
RANGE (MILES) 
Fie. 5.—Diagram illustrating features of RHI scope of 
AN/TPS-10A radar (X-band). Photographic images (and this 
diagram) are reversed from normal presentation because of 
the design of camera used to obtain RHI-scope pictures which 
follow. Vertical distortion of scope about 10:1. Diagram il- 
lustrates appearance of mature thunderstorm at range of 40 
to 55 miles. 
Appearance of Scopes During Storms.? Precipitation 
may be divided into various types, using basic causes 
as the means of classification, as follows: 
A. Frontal precipitation. 
1. Cold front. 
2. Warm front. 
3. Occluded front. 
B. Orographic precipitation. 
C. Hurricanes or typhoons. 
D. Instability showers. 
1. Air mass. 
2. Thunderstorms. 
This breakdown is convenient for the purposes of 
this discussion because the horizontal and vertical dis- 
tribution of hydrometeors is indicative of the motivat- 
ing cause. This distribution in space can easily be ob- 
served with radar. 
A. Frontal Precipitation. 1. Cold front. Perhaps the 
most striking and easily understood of all radarscope 
displays is that of echo signals from the squalls asso- 
ciated with an active cold front. Photographs of PPI 
scopes similar to Fig. 6 have been widely published 
2. It should be noted that a single radar system cannot 
incorporate all the characteristics necessary for all types of 
radar weather observations. For example, the cloud-detection 
radar cannot be used for rain and snow observation because 
of severe attenuation of its energy when the size of the hydro- 
meteors becomes appreciable with respect to its wave length 
of operation. In fact, this radar cannot even be used for cloud 
detection when the precipitation becomes moderate or heavy. 
1271 
during the past few years and need little explanation, 
especially when accompanied by a synoptic map show- 
ing position and orientation of the surface front in the 
Fie. 6.—Photograph of PPI scope showing echo signals 
from showers accompanying cold front approaching Boston 
from the northwest. Isolated warm sector precipitation at azi- 
muth 0°, range 79 miles, and at azimuth 310°, range 20-40 
miles. (1730 EST, 3/27/48, S-band radar, range 120 miles, 
20-mile markers.) (V@.I.T. Weather Radar Research.) 
conventional manner. Over fairly smooth terrain a well- 
sited radar with sufficient power will detect the pre- 
cipitation accompanying an active cold front at dis- 
tances in excess of 200 miles, depending upon the 
heights of the squalls. 
Close examination of the precipitation pattern shown 
in Fig. 6 will reveal the distortion caused by finite beam 
width. This is a photograph of the PPI scope of an 
SCR 615B-type radar operating on a wave length of 
10 em and a beam width of 3° between half-power 
points. Notice that the individual cells have circum- 
ferential elongation [43]. This is not due to the meteor- 
ological situation, but is caused by the comparatively 
wide beam of this radar. Actually, the cells are usually 
almost as wide as they are long. This fact can be veri- 
fied by observation with a radar which has a much 
narrower beam. 
An important restriction on radar storm detection is 
the limited extent of the front which will pass within 
the range of this radar. As stated before, during favor- 
able conditions the maximum range of detection may 
be more than 200 miles, but large portions of the aver- 
age-sized cyclone will still escape detection by any 
single radar. This limitation is not due to the lack of 
power of radar systems, but rather to the curvature of 
the earth [49, pp. 58-55]. Under standard atmospheric 
conditions, the height h (in feet) of a horizontally 
directed beam above the surface of the earth at a range 
R (in miles) is approximately 
h = 4R?, (6) 
