SECT. 2] LARGE-SCALE INTERACTIONS 139 



motion bring these about and are themselves fuelled, braked and constrained 

 by them and by each other. The most regular and easily approachable geo- 

 physical time dependence is probably the seasonal cycle, since this is clearly 

 forced ultimately by the regular and predictable cycle in solar radiation input. 

 We next examine the system's response to this oscillating input in terms of the 

 heat-balance components, the mean annual configuration of which has just 

 been analyzed. 



D. The Seasonal March of Heat Balance and Exchange 



Time changes in energy sources are forced upon the air-sea system by 

 seasonal variations in incoming short-wave radiation. These variations in solar 

 input give rise to changes in circulation, often unstable, which in turn modify 

 the solar input and its seasonal progression. We take our first step toward 

 considering time changes in air-sea interaction by showing (in Figs. 16-21) the 

 seasonal variations in Qe, Qs and R in key oceanic regions. Interpreting these 

 in the light of Section 2 of this chapter on the overall operation of the system, 

 we are able to deepen our understanding of exchange dynamics, its role in the 

 major energy transactions, and in the maintenance of circulations and their 

 fiuctuations. 



Fig. 16 shows the annual march of Qe, Qs and ^ in a region typical of the 

 "firebox" : an equatorial oceanic climate (Pacific, 0° lat., 150°E long.). In this 

 area, the radiation balance changes only slightly during the year. However, 

 spring and autumn maxima are noticeable, shifted somewhat from the equi- 

 noctial months (spring maximum from February to March, and autumn 

 maximum from September to October). The heat expenditure for evaporation, 

 Qe, is close to the radiation balance value, ranging from 5-8 kg cal/cm^ month 

 or 160-255 cal/cm^ day (evaporation 0.3-0.4 cm/day). A turbulent heat flux, 

 small in its absolute value (~16 cal/cm^ day), is directed from ocean to the 

 atmosphere during the entire year. The difference R — {Qs + Qe) enables us to 

 obtain from (1) the sum Qvo + S. This quantity is the heat exchange between the 

 ocean surface and deeper water layers ; it is only identical with the transport 

 divergence Qvo on an annual average, since on a shorter term basis comparable 

 amounts of heat are commonly either being stored or removed from previous 

 storage in the ocean column. In these equatorial regions Qvo + S develops some 

 comparatively large positive values in autumn, when the heat gain from 

 radiation balance considerably exceeds the expenditures for evaporation and 

 turbulent heat emission. This surplus of heat, which is received by the water 

 masses during autumn, is clearly transported (see Table I) from the analyzed 

 region to higher latitudes by currents and macroturbulence, since there is found 

 no corresponding local deficit at other seasons. 



The annual march of the same heat-balance components in the oceanic 

 climates of equatorial monsoons is presented in Fig. 17 (the Arabian Sea 

 region). Briefly, the monsoons are the results of differential heating between 

 continents and oceans, and give rise to large-scale inflow onto the continents of 



