716 
duced by the receiving mechanisms are so blurred as to 
preclude the transmission of meteorological reports from 
each of the stations of our present-day observational 
network. Since such methods of communication as 
automatic writing and electronic scanning and trans- 
missions already exist and have been brought to a high 
level of efficiency and refinement in some of their appli- 
cations, it seems likely that meteorologists will in the 
near future have available some improved communica- 
tion system adaptable to detailed transmission work. 
Bellamy [3] has been working on this problem and his 
suggestions regarding it are discussed in an adjoining 
article.! The whole problem of the transmission and 
physical representation of meteorological data is 
pressing and should be an object of concentrated mete- 
orological research. 
Given an adequate method of transmission, with 
analysis centers located in strategic communication 
centers, even more specialized functions can be per- 
formed by the analysis centers. In addition to analyses, 
elaborate prognostic charts including information con- 
cerning precipitation and cloudiness along with isobars 
and isotherms could be sent out to the mdividual field 
stations to be reproduced there automatically. Local 
meteorologists at the field stations could apply objective 
techniques of forecasting to the various charts and data 
received, with the purpose of prognosticating the 
weather in detail for their respective limited areas. 
In the past, one of the difficulties which has arisen in 
connection with almost all analysis centers is a lack of 
confidence on the part of the men in the field in the 
analyses and prognostic charts sent out from the centers. 
The best way to correct this is, of course, to see that 
the central analysts are drawn from the ranks of the 
very ablest meteorologists, and that they work without 
the undue haste necessitated by meeting ill-advised 
transmission deadlines. Needless to say, these expert 
meteorologists would make use of all the latest refine- 
ments in the techniques of applied meteorology. 
We shall now consider some of these techniques more 
specifically. As has been pointed out, our present anal- 
ysis is based largely on the concept of fronts originated 
by the Norwegian meteorologists. There are, however, 
certain types of weather which seem to lie somewhat 
beyond the scope of the classical frontal models. The 
sort of phenomenon we have in mind is the prefrontal 
squall line (or instability line as it is now generally 
known). 
The Prefrontal Squall Line 
The prefrontal squall line is a line of showers or 
thunderstorms, which often appears in the warm sector 
of a cyclone, extending in a line roughly parallel to the 
cold front. It is usually not more than five hundred miles 
ahead of the front and is most often noticed between 
one hundred and three hundred miles ahead of the cold 
front. Meteorologists at first believed this squall line to 
be either the principal cold front which some previous 
1. ‘Models and Techniques of Synoptic Representations” 
by J. C. Bellamy, pp. 711-714. 
OBSERVATIONS AND ANALYSIS 
analyst had moved too slowly, or a weak cold front 
previously dropped, which, if it had been retained and 
moved along with the speed indicated by the baric field, 
would be at the present location of the squall line. 
During the past few years the independent reality of 
prefrontal squall lines has become generally accepted. 
Airline meteorologists [9] and others have brought this 
phenomenon to the attention of meteorologists as a 
whole and have ascertained rather conclusively that the 
prefrontal squall line does not represent a misplaced 
cold front, as had previously been thought. At most 
analysis centers an attempt has been made to include 
these squall limes in the analysis and to use for the 
detection of these lines the criterion of persistence in 
time and space of a line of showers. Such a standard for 
detection may be depriving the forecasters of most of the 
prognostic value of the concept of prefrontal squall lines 
in that it fails to provide a means for the recognition of 
the precursors of the squalls. Because of the lack of 
knowledge of the mechanics of the formation and struc- 
ture of these phenomena and the want of adequate 
observational techniques for their detection, there is 
much to be desired in the analyses. Recent investiga- 
tions, however, give promise of an imminent improve- 
ment in this part of the analysis program. 
These investigations have followed two avenues of 
approach. On the one hand, Fulks? and Williams [24] 
have constructed detailed descriptive models of the 
actually observed distributions of temperature, mois- 
ture, and atmospheric pressures associated with squall 
lines. On the other hand, a new theory of squall lines 
has been formulated, made possible by the introduction 
into meteorology by Freeman [8] of the concept of 
pressure jumps, the atmospheric analogy to the “hy- 
draulic jump.” Tepper [22], combining data of the types 
presented by Williams and the concept of pressure 
jumps in the atmosphere, has developed the theory that 
squall lines are caused by pressure jumps. He has 
demonstrated how squall lines and their concomitant 
weather can be initiated and propagated by pressure 
jumps and has further proposed that the intersection of 
two pressure-jump lines has properties which favor the 
formation of tornadoes. Currently, Tepper is testing 
this hypothesis by means of empirical data. The results 
of this work should make possible rapid improvement 
of our understanding of, and ability to forecast, squall 
lines and tornadoes. 
An article by Freeman? describing in detail the results 
of this type of inquiry into the nature of prefrontal 
squall lines is included elsewhere in this Compendium. 
Here we shall restrict our discussion to only a portion 
of the new results emerging from this research, that is, 
to those properties of the pressure jump which are 
pertinent to the problem of analytical procedure. 
Although still in a very early stage of development, 
2. Consult “The Instability Line” by J. R. Fulks, pp. 647— 
652 in this Compendium. 
3. Consult ‘‘The Solution of Nonlinear Meteorological 
Problems by the Method of Characteristics” by J. C. Free- 
man, pp. 421-433. 
