RADAR STORM OBSERVATION 
features in this type of precipitation except that, on 
occasion, it can be fairly uniform. Because of this factor, 
this type of precipitation might be useful for relating 
storm echo signals to precipitation intensity. 
C. Hurricanes and Typhoons. Radar detection of hur- 
ricanes and typhoons is even more dramatic than radar 
detection of cold-front squall lines [66]. The rain-distri- 
bution pattern as seen on a PPI scope is illustrated in 
Fig. 12. It is startling in its similarity to the symbol § 
Fig. 12.—Hurricane of 18-21 Sept., 1948. PPI-scope photo- 
graph made just prior to passage of the eye over the radar at 
Key West, Florida. (0900 EST, 9/21/48, range about 125 miles.) 
(Official U. S. Navy Photo.) 
which has been chosen to indicate the position of hur- 
ricane centers on weather maps. 
The spiral rain bands visible in Fig. 12 have been 
observed in all hurricanes and typhoons detected by 
radar. These bands move slowly around the center; 
the cells in the bands move along the bands and into 
the center in a counterclockwise direction (in the North- 
ern Hemisphere) [37]. As yet, no relationships between 
the band movement and winds aloft have been estab- 
lished, because of the difficulty of obtaining winds-aloft 
observations during storms of this type. It is possible 
that radar will also provide the solution to this problem. 
From Fig. 12, it will be noted that a very definite 
position can be found for the center of rotation as far 
as the rain is concerned. There is evidence that this 
center detected by radar does not always coincide with 
the center of low pressure. Also, a clear “eye” may or 
may not be present, depending upon the intensity of 
precipitation at this point. 
Radar hurricane detection is probably of greatest 
value in connection with aircraft hurricane reconnais- 
sance. Harly detection of the storm, while it is still far 
from land and out of range of land-based radars, is con- 
siderably facilitated by the use of air-borne radar equip- 
ment. It is not necessary for the aircraft to penetrate 
the storm in order to locate the position of the eye; 
this often eliminates the, necessity of flying under ex- 
tremely hazardous conditions [57]. 
1275 
By the time a hurricane is within range of land-based 
radars, its direction and speed are usually well known. 
However, these radars are useful for precise determina- 
tion of the storm’s position at any instant, and provide 
very valuable up-to-the-minute data on the storm [58]. 
It has been found by experience that the best wave 
length for use in hurricane detection is about 10 cm, 
at least from the standpoint of rain attenuation. Even- 
tually it may be possible to measure wind speed in 
different portions of hurricanes by means of radar, and 
to obtain other clues concerning the structure of these 
severe storms. The great decrease in loss of life from 
hurricanes in the southeastern United States is due to 
highly accurate data concerning movement and velocity 
of the storms and the early warning of their existence. 
The importance of the part radar plays in the joint Air 
Force, Navy, and Weather Bureau hurricane program 
cannot be minimized. 
The importance of radar as a research tool for study- 
ing the structure of hurricanes should not be overlooked. 
The possible use of this new presentation of the storm, 
in which the rain relative to the wind and pressure dis- 
tribution may be known, should greatly enhance our 
understanding of hurricanes. Much work is yet to be 
done; for example, few, if any, RHI-scope photographs 
of hurricanes have yet been taken. These would give in- 
formation concerning convective activity, and whether 
or not there are shearing forces present as indicated by 
sloping of the rain cells. It may well be that some of the 
spiral patterns shown in Fig. 12 are due to the shear 
and not entirely an indication of the shape of the con- 
vective cell. 
D. Instability Showers. 1. Air mass. Air-mass pre- 
cipitation, being largely convective in nature, generally 
shows somewhat finer detail in its echo signals on the 
PPI scope (Fig. 13) than does warm-frontal precipita- 
wo Oa ATE peel ANN 
Fic. 13.—Group of air mass precipitation cells moving 
north-northeast. Note showery appearance in contrast with 
Fig. 7. Precipitation was in the form of rain showers. Some 
tendency for band formation is evident. Passage of sharp cold 
front from west occurred about six hours after this photo- 
graph was taken. (1880 EST, 3/8/50, X-band radar, range 60 
miles, 10-mile markers.) (/.1.7. Weather Radar Research.) 
tion. There is an even greater lack of symmetrical ar- 
rangement of the convective cells; parallel bands (see 
Fig. 9) are rarely detected. Shear is rarely observed, 
