202 RADIO WAVE PROPAGATION EXPERIMENTS 
Stability reduces the mixing to such an extent that 
the air is progressively modified during a long over- 
water trajectory. It is therefore necessary to introduce 
a fourth independent variable, length of over-water 
trajectory, to supplement I deficit, temperature ex- 
cess, and wind speed. 
Under ideal conditions there is reason to believe 
that the modification would pursue the course sketched 
in Figure 3. The final state would be an essentially 
homogeneous layer capped by a temperature inversion 
at the level already mentioned for the top of the fric- 
tionally produced turbulence in neutral equilibrium. 
The temperature of the layer would follow an adia- 
batic lapse rate from the water surface to the top. 
The water vapor would be saturated at the top of the 
layer, specific humidity being nearly constant through- 
out the layer except for a strong lapse at the surface. 
Intermediate stages in the formation of this final state 
are indicated qualitatively in Figure 3. 
It should be noted that the later stages have a 
transitional or S-shaped M curve and that qualitative 
theoretical considerations do not reveal which. The 
initial stage is, however, characterized by simple sur- 
face trapping, and it is this stage only for which data 
are presented below. 
The soundings have been studied to determine em- 
pirically how the ratio of height of M inversion to M 
deficit depends on temperature excess, wind speed, 
and length of trajectory. To eliminate complex M 
curves the analysis has been limited to cases con- 
forming closely to the following ideal conditions. 
1. Initially homogeneous air. 
2. Constant surface-water temperature along the 
air trajectory. 
3. Constant wind (wind not changing with time 
following a parcel). 
The ratio of height of M inversion to M deficit is 
found to increase with length of over-water trajec- 
tory quite markedly in the first 10 miles. From 10 
miles to 30 miles there is not much further increase. 
Beyond 30 miles the preliminary analysis reveals no 
general information. 
Figure 4 gives some tentative results based on 
various:sources of information. This includes the cases 
of neutral and unstable equilibrium in addition to 
stable equilibrium. Within the stated range of over- 
water trajectory this diagram gives the height of the 
AI inversion as a function of temperature excess, wind 
speed, and MM deficit. A complete analysis of the ob- 
servations will yield similar diagrams both more ac- 
curate and more detailed. These should prove of 
definite use in forecasting M curves. 
In conclusion, it should be made clear that the work 
summarized in this report is a group undertaking. 
A large number of persons, some of them members 
of Radiation Laboratory Group 42 and other mem- 
bers of the U. S. Army Air Forces, took part in the 
a 
3! 
° 
TEMPERATURE EXCESS IN DEGREES C 
a 
1 
a 
20 30 
WIND SPEED AT 1000 FT IN MPH 
Ficure 4. Ratio of height of M inversion to M deficit. 
For positive temperature excess the over-water trajec- 
tory is 10 to 30 miles. 
° 
Co) 
development and construction of the instruments and 
in the observing. 
METEOROLOGY OF THE SAN DIEGO 
TRANSMISSION EXPERIMENTS? 
During the summer of 1944 a rather intensive ex- 
perimental propagation program was carried on in 
San Diego area. The main purpose was to determine 
the distribution of radiated radio energy in the lower 
troposphere under the wide range of weather condi- 
tions prevailing during this season. A temperature 
inversion was present from around the first of June 
through October; the base of the inversion varying 
from the surface, on a few occasions, up to an alti- 
tude of some 4,000 ft. This inversion is characterized 
by dry superior air subsiding over moist maritime 
polar air. 
Methods of Observation 
The field strength data were taken in two ways. A 
fixed one-way link between San Pedro and San Diego 
gave continuous records on frequencies of 52, 100, 
and 547 megacycles, and vertical airplane sections 
taken at several different distances west of San Diego 
gave almost instantaneous records of the energy dis- 
tribution for the same range of frequencies. 
The meteorological data were obtained by the use 
of an airplane and wired sonde; the technique of the 
_ latter was described in detail in a previous report.® 
The captive balloon or wired sonde is a modified ver- 
sion of the Washington State College equipment.’ 
Daily soundings were taken at the Scripps Pier at 
La Jolla, 11 miles north of the laboratory. Two 1-week 
periods of continuous shipboard soundings were made 
from a YP ship operating in the middle of the San 
Pedro to San Diego link. 
The principal use of the airplane has been in tak- 
ing vertical field strength sections seaward from the 
*By Lt. A. P. Stokes, U.S. Navy Radioand Sound Laboratory 
