132 MALKUS [chap. 4 



system's operation and climatology, outlined descriptively in Section 2 of this 

 chapter (page 92). 



As can be seen from Fig. 13, four basic latitudinal zones exist in each hemi- 

 sphere, each with essentially different relationships of the heat-balance com- 

 ponents. In the equatorial zone, which extends north and south of the equator 

 up to 10° to 15° latitudes, the gain of heat from positive radiation balance is 

 supplemented by a comparably large net release of precipitation heating (water- 

 vapor flux convergence). These together assure the great export of heat by 

 atmospheric and oceanic advection, for which the relatively narrow region from 

 0° to 10° latitudes constitutes the primary energy source. Fig. 13 thus demon- 

 strates quantitatively that the equatorial trough plays its role as the atmos- 

 phere's firebox. This is not mainly due to excess radiation received but even 

 more largely because there the water-vapor fuel is combusted by precipitation 

 release, an energy source even more closely tied to circulation dynamics ; the 

 mechanisms by which it carries out this role are sought in Section 5-B, 

 page 164. 



Northward and southward from the equatorial zone are the tropical regions, 

 i.e., the locations of the atmosphere's famous easterly trade-winds which 

 prevail throughout the equatorward sides of the subtropical high pressure 

 cells, or "ridges". In these zones, with a positive (but diminishing with increase 

 in latitude) radiation balance, large expenditure of heat for net evaporation is 

 observed. In the major portion of the trade-wind regions, the loss of heat for 

 moisture exchange (from sea to air) approaches the value of the radiation 

 balance, and thus the input to sensible heat and potential energy advection 

 {Qvo and Qva) is small. The fact that the trade-winds act as the fuel accumulators 

 for the atmospheric heat engine is thus also shown quantitatively in Fig. 13. 

 Mechanistically how they do this, and how they serve also to pump the fuel 

 into the firebox, is examined in Sections 5 and 6 of this chapter. 



In the "subtropical ridge" region of 35°-40° latitudes a transitional zone is 

 found. In this area. Fig. 13 shows that the gain and expenditure of heat in all 

 the balance components is fairly evenly distributed and no component is 

 numerically large. The j^oleward energy transports themselves, however, are 

 maximum (Table I). In the high troposphere, this is the mean position of the 

 famous subtropical jet streams, whose wave -like meanders provide the channels 

 of poleward energy flow from the tropics. Thus the temperate atmosphere is fed 

 with the heat to balance its radiation loss, and to store in potential energy of 

 air-mass contrasts, a small fraction of which is released to maintain the charac- 

 teristic cyclonic storms and restless winds of the middle latitudes. 



Poleward of the subtropical ridge and jet stream, all higher latitudes are 

 regions of radiation deficit, increasing rapidly toward the poles. Energetically 

 this zone lives on imports : from excess precipitation over evaporation, atmos- 

 pheric advection and sea-current transports. Dynamically, it plays a very 

 important (some workers say the dominant) role in the operation of the global 

 circulations by concentrating and releasing the imported energy in complex 

 and wondrous ways, producing evanescent wind systems which themselves 



