INTRODUCTION 7 



transported by winds to higher latitudes in order to counterbalance the 

 radiation deficit existing there. Simpson does not, however, examine 

 the manner in which the incoming radiation becomes available for heating 

 the atmosphere. He is therefore not concerned with the important part 

 played by condensation of water vapor in the atmosphere. Taking this 

 into account and considering also that part of the outgoing radiation 

 from the earth's surface escapes without influencing the heat budget of the 

 atmosphere, this heat budget becomes much more complicated, and 

 Simpson's numerical values for the heat transport by the atmosphere 

 across parallels of latitude lose much of their significance. 



The Oceans as Part of the Subsurface of the Atmosphere 

 Since the absorption of long-wave radiation from the earth's surface 

 and the condensation of water vapor that is supplied to the atmosphere 

 from the earth's surface are factors of dominant importance to the heat 

 budget of the atmosphere, it is evident that the thermal characteristics 

 of the surface must be examined when studying the atmospheric circula- 

 tion. Over the land areas, an interaction between the surface and the 

 circulation of the atmosphere evidently takes place. Thus, a covering 

 of snow greatly increases the reflection of incoming short-wave radiation, 

 dense clouds alter the radiation phenomena, heavy rainfalls that moisten 

 the ground change the possibilities for evaporation, and so on, and every 

 change must be reflected in a change in the pattern of atmospheric 

 circulation. 



The character of the ocean surface is very different from that of the 

 land, mainly because the ocean water can be set in motion. The heat 

 absorbed near the surface is distributed over a relatively deep water layer 

 through the stirring by waves and wind currents and it is transported 

 over long distances by ocean currents that are more or less directly pro- 

 duced by the prevailing winds. Heat which in one season is absorbed 

 in one part of the sea may therefore in another season be used for evapora- 

 tion in a different part of the sea, depending upon the types of currents 

 that the general circulation of the atmosphere induces. The oceans, as 

 far as their interaction with the atmosphere is concerned, are a flexible 

 medium that responds to changes in the circulation of the atmosphere. 

 Inasmuch as the greater part of the water vapor in the atmosphere is 

 supplied by evaporation from the oceans, the relation between the atmos- 

 phere and the circulation of the oceans becomes important, because this 

 relation will determine the seasons and the regions from which excessive 

 evaporation takes place. Thus the heat budget of the oceans and of the 

 ocean currents is of the greatest importance to the atmosphere. In order 

 to discuss this heat budget and the currents it is necessary first to deal 

 with some of the physical properties of sea water. 



