Microstructure of Storms as Described 
by Quantitative Radar Data 
PauLINE M. Austin 
Weather Radar Research, Massachusetts Institute of Technology, 
Cambridge, Massachusetts 
Abstract—Instrumentation which has been developed recently presents radar echoes 
from precipitation in the form of range-corrected signal-intensity contours, thus making 
it possible to observe in a quantitative manner the smaller-scale features within the pre- 
cipitation areas which appear on the normal radar-scope presentation. This paper pre- 
sents some preliminary results of the analysis of such data for two types of storms: 
warm-front type rain in an unstable atmosphere, and showers associated with instability 
lines. Dimensions, durations and motions of areas of heavy rain and of individual 
shower cells are considered in an attempt to determine the scales of atmospheric cir- 
culations which are particularly significant in the production of precipitation. 
INTRODUCTION 
Studies of basie physical principles and _ per- 
formance of laboratory experiments have con- 
tributed greatly to our understanding of the 
physical processes involved in the development 
of precipitation particles, such as nucleation, con- 
densation, and coalescence, and have also shown 
the influence upon these processes of the imme- 
diate environment of the particle. However, the 
manner in which such processes occur in the at- 
mosphere and the influence of the larger scale 
environment in encouraging or inhibiting the 
growth of hydrometeors can be learned only 
through detailed observations of actual storms. 
Radar observations provide a description of the 
distribution of precipitation either aloft or as it 
reaches the ground, although until recently such 
information was largely qualitative. Instrumenta- 
tion described by Kodaira [1957] is now available 
which presents radar data in the form of range- 
corrected signal-intensity contours, thus making 
it possible to observe in a quantitative manner 
the smaller scale features within the precipitation 
areas which appear on the normal radar-scope 
presentation. It is the purpose of this paper to 
describe some of these small-scale features and 
their behavior for two types of storms: warm- 
front type rain in an unstable atmosphere, and 
squall lines. Dimensions, durations, and motions 
of rain areas are considered in an attempt to de- 
termine the scales of the atmospheric circulations 
which are particularly significant in the produc- 
tion of precipitation. 
The signal intensity contours are obtained with 
an SCR-615-B radar which employs 10-em radia- 
86 
tion. Therefore the measurements are not dis- 
torted by attenuation. However, the SCR-615-B 
radar is not sufficiently sensitive to detect light 
rain except at very close ranges. Therefore the 
data are supplemented by photographs of the 
PPI of the AN/CPS-9 radar maintained by the 
Air Force at Great Blue Hill and by hourly rain- 
fall records from the U. 8. Weather Bureau Co- 
operative Observer Network. 
Warm Frontat Rain 
General description of storms—Data are avail- 
able for four storms where the rain was of the 
warm-front type but was not associated with a 
coastal storm. Only two of these storms have been 
analyzed in detail: October 17-18, 1957, and 
November 8-9, 1957. In both cases a cold front 
oriented approximately north-south was ap- 
proaching from the west, a warm front lay to the 
south of the station, and the winds aloft were 
from the southwest. The lapse rate in the warm 
air ahead of the front was approximately moist 
adiabatic below 20,000 feet and slightly stable 
above that level. 
The rain patterns associated with these storms 
are very similar. The most striking feature is a 
broad loose band oriented in the north-south di- 
rection which was about 250 mi in length and 
40-50 mi across. The heaviest part of the pre- 
cipitation was in this band and it appeared to be 
about one hundred miles ahead of the surface cold 
front. On the PPI photographs the band had a 
pebbly structure, especially at long ranges, in- 
dicative of many small showers within the gen- 
eral rain area. RHI photographs also showed the 
