276 



SIMPLIFIED FEEDBACK BETWEEN THE SEA AND THE ATMOSPHERE 



The ocean/atmosphere feedback has been described in general terms in a 

 few publications in the past (e.g., Bjerknes, i960), but a complete descrip- 

 tion in terms of energy exchange is not available . In this chapter an attempt 

 is made to describe the synoptic feedback between the sea and the atmosphere, 

 based upon the results of previous chapters. 



An essentially diabatic simplified model is considered herewith, with 

 the conversion of energy in the atmosphere itself being largely neglected, 

 as it has been described by several authors earlier. Some existing numerical 

 meteorological models permit heat exchange input without extensive changes. 

 Tests with these models will clarify further the qiaantitative relations between 

 energy exchange and weather processes and will indicate the usefulness of the 

 inclusion of heat exchange parameters. 



The feedback system can easily be derived from Figures 8 to 11, a simpli- 

 fied description of which is given below. In this description it is assumed 

 that the sea surface isotherms are essentially latitudinal and equidistant at 

 the initial stage. Compass directions, rather than descriptive terms of the 

 sectors of cyclones and anticyclones, are used. 



Anticyclonic circulation ; 



Atmospheric circulation in relation to heat exchange . In the N part of 

 the anticyclone the eastward flow is approximately parallel to the sea surface 

 isotherms and would not result in appreciable sea-air exchange . In the NE 

 part of the anticyclone the air flow has a southerly component, which brings 

 colder air over warmer water. This factor can increase progressively in the 

 E and SE parts of the anticyclone. A slight pressure rise is usually observ- 

 able in the SE part of the anticyclone in the following days which gives an 

 apparent movement of the anticyclone to the SE, and an apparent location of 

 anticyclone center towards areas with negative sea-surface temperature 

 anomalies. 



The energy gain of the air in S and SW part of the anticyclone decreases, 

 and low or negative Q^ values are found in the NW sector due to the north- 

 ward component of the air across sea surface isotherms. In this area pres- 

 sure fall occurs. 



Changes in the ocean, caused by advection and heat exchange . If the heat 

 exchange and advectional effects in the sea and in the atmosphere were perfectly 

 balanced, few disturbances would result. However, due to local ineq^ualities 

 of heat exchange processes and to advectional changes sea surface temperature 

 anomalies are caused, which in turn may affect the heat exchange processes. 



In some cases advectional effects might accoimt for the greater part of 

 the anomalies in the oceans. In the W and NW part of the anticyclone, warmer 

 weather is advected towards W and NE. In the NE and E part colder water is 

 advected towards south. Further cooling of the ocean in the SE sector can 

 be effected by intensive sea-air exchange in this area. In the S and SW part 



