V 51.1 . Z ' INTRODUCTION 5 l
precision, and their amounts are variable and di?icult to relate to other
physical phenomena. V
The motions, temperatures, chemical composition, and cloud amount
of the atmosphere are closely interrelated by complex mechanisms.
Ideally all properties of the atmosphere should be predictable starting
n from aphysical model, imposing only the boundary condition of a given
n ?ux of solar radiation. Very little advance in this direction has yet been
made, although it is possible that electronic computers may yield some
results in the near future. Some simple model situations are treated in
this volume, but most investigations have attempted to isolate the 7
radiative aspects by concentrating attention on the radiative heating
as if it were a distinct and signi?cant atmospheric parameter.
. Two different classeslof study have resulted from these two ap-
proaches, one synthetic but limited in scope, the other descriptive but
aiming at completeness. The former, typi?ed by the early work of
Gold and Emden, approaches from the standpoint of local radiative
equilibrium in a cloudless atmosphere of known composition, and
inquires how far the structure of the real atmosphere can be explained
m this way. The other, of which Simpson’s Work forms the best-known '
example, accepts the observed atmospheric thermal structure, and
attempts to work out the resulting ?eld of radiation. The methods are
complementary; each throws some light on the nature of the hydro-
dynamic processes, the former by the ways in which the deduced
structure differs from that observed, the latter by the computed
departures from local radiative equilibrium.
,5 Most of this book is devoted to the methods of analysis of the radia-
l tion problem, comparatively little to the synthesis and still less to purely
empirical data. Since the analysis involves many different physical
ileas and mathematical methods our presentation is necessarily frag-
mentary and non-systematic, and moreover, for reasons which are not
strictly logical, it has been necessary to divide, the material into two 7
parts. It may therefore help the reader to indicate brie?y how the
i?erent chapters ?t into the scheme of ideas which has been outlined‘: ~
The remainder of Chapter 1 provides necessary background informa- V
?m to our problem in the form of a discussion of the thermal structure , ,
..-ad chemical composition of the atmosphere. Chapter 2 outlines the
lilmal mathematical theory required to handle problems of radiative
‘hansfer. Chapter 3 describes the physical processes of absorption, and
lllnpter 4 discusses methods which isolate from this mass of detail its
mntial statistical features. Chapter 5 then gives quantitative data