METEOROLOGICAL ASPECTS OF PROPAGATION PROBLEMS 
Some Special Meteorological Investigations 
For the phenomenon of advection of air from land 
to sea, a special attempt has been made to carry out a 
program of research such as that outlined above, bear- 
ing in mind the particular needs of radio propagation. 
The most satisfactory results at present available are 
contained in two papers by Craig [6, 7], although refer- 
ence may also be made to papers by Sheppard [15] and 
Booker [3]. The first of Craig’s papers describes meas- 
urements of temperature and humidity made at vari- 
ous heights and at various distances off the coast of 
Massachusetts in air that had drifted from the land 
over the sea, the measurements being carried out in 
such a way as to reveal the modification in the air mass 
due to advection over the sea. The second of Craig’s 
papers describes how these measurements were analyzed 
and fitted to a theory of the modification of the air mass 
by eddy diffusion. The center of interest in such a the- 
ory is the assumption to be made about the distribu- 
tion of eddy diffusivity with height. Taylor [19] had 
originally assumed a uniform distribution of eddy dif- 
fusivity, but this does not reproduce the logarithmic 
profiles of temperature, humidity, and wind speed usu- 
ally observed within the first few feet of the atmosphere 
[13]. Craig therefore used a model in which eddy diffu- 
sivity is proportional to height in the first few feet, but 
has a uniform value at greater heights. This is probably 
the most successful representation of the process of 
eddy diffusion near the earth’s surface for stable at- 
mospheric conditions that has so far been achieved. 
Other distributions of eddy diffusivity with height 
have however been employed. Following Sutton [18], 
Booker [8] has assumed that eddy diffusivity is propor- 
tional to a power of height above the earth’s surface. 
He shows that, for advection of a well-mixed air mass 
from land over a uniform sea, the heights at which the 
lapse rates of specific humidity and potential tempera- 
ture have the important values (2) and (8) reach maxi- 
mum values offshore which are proportional to humid- 
ity deficit and temperature excess, respectively, but 
which are independent of the absolute value of the 
eddy diffusivity. These maximum heights, which can 
be used in practice as radio duct-widths (see Fig. 2) 
over a wide range of distances offshore, do depend on 
the distribution of eddy diffusivity with height, even 
though they are independent of the absolute value at 
any particular level. The distances offshore at which the 
maximum heights occur, unlike the values of the maxi- 
mum heights themselves, are dependent on the value 
of the eddy diffusivity, but this is not too important 
for some practical applications to radiometeorology. 
Booker thus concludes that, when a radio duct is pro- 
duced over the sea by advection of air from the land, 
the radio duct-width is less dependent on the absolute 
value of the eddy diffusivity than might appear at 
first sight, and this result would probably also apply 
to the profile of eddy diffusivity used by Craig. The 
radiometeorological effect of changing the profile of 
eddy diffusivity is, however, quite important. 
1295 
Conclusion 
If all the meteorological phenomena involved in ra- 
diometeorology were subjected to as careful a treat- 
ment as that applied by Craig [6, 7] to the problem of 
advection of air from land to sea, it would be possible 
to feel that the basic meteorological factors underlying 
radiometeorology were understood as well as could be 
expected for some time to come. 
Reference may be made to the discussions of radia- 
tional cooling, fog, subsidence, advection, evaporation, 
sea breeze, etc., given elsewhere in this Compendium. 
Additional general references in connection with radio- 
meteorology are listed as [5], |11], and [14] in the 
references. 
REFERENCES 
1. Booxer, H. G., ‘‘Elements of Radio Meteorology: How 
Weather and Climate Cause Unorthodox Radar Vision 
Beyond the Geometrical Horizon.”’ J. Instn. elect. Engrs., 
93(1) : 460-462 (1946). 
2. —— “Radio Refraction in the Atmosphere.’’ Weather, 
3: 42-50 (1948). 
3. —— “Some Problems in Radio Meteorology. Quart. J. R. 
Meteor. Soc., 74:277-815 (1948). 
4. —— and Wa.xkinsuaw, W., ‘‘The Mode Theory of Tropo- 
spheric Refraction and Its Relation to Wave-Guides and 
Diffraction,” in Meteorological Factors in Radio Wave 
Propagation. London, The Physical Society, 1946. (See 
pp. 80-127) 
5. Burrows, C. R., (chairman) and Artwoop, S. &., (ed- 
itor), Radio Wave Propagation. New York, Academic 
Press, 1949. 
6. Craic, R. A., ‘Measurements of Temperature and Humid- 
ity in the Lowest 1000 Feet of the Atmosphere over 
Massachusetts Bay.’? Pap. phys. Ocean. Meteor. Mass. 
Inst. Tech. Woods Hole ocean. Insin., Vol. 10, No. 1, 47 
pp. (1946). 
7. —— “Vertical Eddy Transfer of Heat and Water Vapor in 
Stable Air.” J. Meteor., 6: 123-133 (1949). 
8. Enauunp, C. R., Crawrorp, A. B., and Mumrorp, W. W., 
“Further Results of a Study of Ultra-Short-Wave Trans- 
mission Phenomena.’’ Bell Syst. tech. J., 14: 369-887 
(1935). 
9. —— “Ultra-Short-Wave Radio Transmission through the 
Non-homogeneous Troposphere.”? Bull. Amer. meteor. 
Soc., 19: 356-360 (1938). 
10. Katzin, M., Baucuman, R. W., and Binnran, W., ‘‘3- and 
9-Centimeter Propagation in Low Ocean Ducets.’’ Proc. 
Inst. Radio Engrs., N. Y., 35: 891-905 (1947). 
11. Kerr, D. E., and others, Propagation of Short Radio Waves. 
Radiation Laboratory Series No. 18. New York, McGraw, 
1951. 
12. Mrcaw, Bl. C.58., ‘‘Experimental Studies of the Propaga- 
tion of Very Short Radio Waves.” J. Instn. elect. Engrs., 
93(1): 462-463 (1946). 
13. Monrcomery, R. B., ‘‘Observations of Vertical Humidity 
Distribution above the Ocean Surface and Their Rela- 
tion to Evaporation.’’ Pap. phys. Ocean. Meteor. Mass. 
Inst. Tech. Woods Hole ocean. Instn., Vol. 7, No. 4 (1940). 
14. Norton, K. A., Advances in Electronics, Vol. 1. New York, 
Academic Press, 1948. (See pp. 392-397) 
15. Sueprarp, P. A., ‘‘The Structure and Refractive Index of 
the Lower Atmosphere,” in Meteorological Factors in 
Radio Wave Propagation. London, The Physical Society, 
1946. (See pp. 37-79) 
