1288 
tals arriving at the ground at low temperatures and 
large snowflakes near the freezing point. The ideas of 
Ryde, and of Austin and Bemis, on the coalescence of 
crystals from the —4C level to below the bright band 
are corroborated; Ryde’s ratio of 40 to 1 between 
—4 and OC is not indicated by Browne’s observations. 
More observations similar to those by Browne for 
various cloud depths and precipitation intensities are 
desirable for a more detailed study of precipitation 
growth by diffusion and coalescence. 
Horizontal Structure of Precipitation 
On the PPI scope? of the radar, continuous precipita- 
tion appears as an extensive brightened area. Generally 
1350 EST 
! 1515 EST 
1415 EST 
1545 EST. 
RADIOMETEOROLOGY 
teras at 1230 EST and was moving eastward at about 
30 mph. At the 700-mb level a closed cyclonic center 
was located over southern Ohio, and south-southwest 
winds of about 20 mph prevailed over the New Jersey 
area. At 1350 EST showers appeared to be scattered 
almost at random out to a radius of 125 miles from the 
station. The remainder of the afternoon saw the virtual 
decay of the storms in the northern sector and a build- 
up of the storms to the south. At 1515 EST, what had 
previously been a loose coalescence of cells was a con- 
tinuous pattern about 30-50 miles wide but narrowing 
in its central portion to about 10 miles and trailing off to 
a thin line at its most distant point, 180 miles distant at 
160° azimuth. Farther south a strange pattern in the 
1445 EST 
G15 EST 
I SSE SERRE ES SE 
Fic. 4.—Precipitation patterns observed from Belmar, N. J., March 10, 1949. Circular range markers are at 25-mile inter- 
vals. (Courtesy Signal Corps Engineering Laboratories.) 
there are indications of definite edges to the storm, 
although in winter the precipitation may extend in all 
directions from the station out to the limit of the range 
of observation of the radar. An extensive area of warm- 
front precipitation is often seen to have an abrupt 
line of cessation. 
In showery activity the precipitation may appear as 
scattered cells, 3-6 miles in diameter, located at random 
in some sectors of the scope. Occasionally these cells 
develop to form an area of continuous precipitation and 
curious patterns often occur. Such a development char- 
acterizes the rain areas observed from Belmar, New 
Jersey, during the afternoon of March 10, 1949 (Fig. 4). 
A cyclonic storm was located just west of Cape Hat- 
5. PPI = Plan Position Indicator, a polar coordinate plot 
of azimuth versus range. 
form of a wavy line of individual cells of precipitation 
200 miles or more in length became visible at 1615 HST. 
A line squall that is observed to extend straight acress 
the PPI scope is rare. A more usual situation is a series 
of line squalls, each perhaps a hundred miles in length, 
in parallel bands. The edge of the squall in the direction 
of the high pressure often trails off into a group of cells. 
The parallel bands of precipitation are generally as- 
sociated with distinct wind shifts and pressure-gradient 
discontinuities. 
As a front passes over the radar, the range of detection 
of precipitation along the front diminishes considerably 
at 3-cm or shorter wave lengths, because of rain attenu- 
ation. By comparing the maximum range at a given gain 
setting before the front has reached the station with 
the maximum range when the front is directly over the 
station, it is possible with the aid of equation (4) to 
