BEHAVIOR PATTERNS OF NEW ENGLAND HAILSTORMS 
hail started falling four minutes after the heavy 
rain began, 
Hailstone shapes were reported only infre- 
quently, and are summarized in Table 5. Almost 
75% of the reported shapes are about evenly di- 
vided between spheres and oblate ellipsoids. 
Some of the observers reported the number of 
stones left on the ground per unit area, as well 
as size and duration of fall. Using Ludlam’s [1958] 
formula for fall speed and his estimates of drag 
coefficient, the number concentration of hail- 
stones was found. These are spotted on Figure 21 
as a function of diameter. Apparently the two pa- 
rameters are related only slightly. The median 
concentration decreases from 0.14 to 0.1 to 
0.07/m* in the 5-10, 10-15, and 15-20 mm diam- 
eter size groups. A few mass concentrations are 
included. It is interesting to note that the maxi- 
mum value, 6 g/m", agrees with Ludlam’s state- 
ment that the concentration of water in the form 
of hailstones has a maximum value of several 
g¢/m*. 
General conclusions—New England hailstorms 
exhibit a wide variety of characteristics. Some of 
these features have been presented here, derived 
from radar measurements and the observations 
of a network of cooperating observers. The most 
surprising result, and the least reliable one, is the 
derivation, from the intensity of the maximum 
radar echo, of extremely high water concentra- 
tions in the cores of many hailstorms at medium 
altitudes. Even if a possible calibration error of 
a factor of five is taken into account, however, 
this maximum concentration reaches a value of 
34 g/m* at a height of 23,000 ft in a tornado- 
producing hailstorm. 
Perhaps the most interesting result concerns 
the penetration of the tropopause by many storm 
echoes. The median rain-thunderstorm echo top 
40 
TIME HAIL BEGAN 
— TIME R+ BEGAN 
ow 
fo) 
n= 183 
OCCURRENCES 
n 
° 
-20 -10 ° 10 20 30 40 
TIME — minutes 
Fre, 20—Frequeney of occurrence of time be- 
tween start of hail and heavy rain 
367 
TaBLE 5—Shape of New England hail (from reports 
of Cooperative Observer Network during years 
1956-1958) 
avi Number of 
Characteristic shape reports 
Oblate 23 
Spherical | 22 
Irregular 10 
Conical 4 
Cylindrical 1 
Prolate 1 
Ratio of maximum/minimum dimen- | 
sions for oblate hailstones (six ob- 
servations): 1.25, 2, 2.1, 3, 3, 8 
Total | 61 
10 T T Trak i- a0 T 
© 05 9/m> 
© 08 g/m> 
1 a/m 
Tr 
. 
f © 30104 g/m? 
ie pee 
= eeereare Serie [ESSN 
15 20 
DIAMETER — mm 
Fie. 21—The relationship of the number con- 
centrations of hailstones to diameter 
falls short of the tropopause by 4000 ft and the 
median hailstorm with hail less than %4 inch in 
diameter has its echo top coincident with the 
tropopause. However, the median hailstorm hay- 
ing hail %4 inch or larger penetrates 5000 ft into 
the stratosphere, and 4 of these storms pene- 
trate 9000 ft or more. Extreme penetrations of 
10,000 to 15,000 ft occurred on five days; four 
of these were tornado days, with the tornado 
storms heavily involved. The increase of echo 
