SECT. 2] LARt;E-S(ALE INTERACTIONS 253 



Not until dynamics, energy relations and thermodynamics are tied together in 

 some such framework will it be possible to gain further insight into the physics 

 behind exchange climatology, in which even the most exact and massive 

 descriptive approaches soon reach the stage of diminishing returns. Xor will it 

 be possible to bridge the gap between the real planetary fluids, dominated by 

 energv transfers, and driven and braked bv exchange, and the world of the 

 theoretician, who in meteorology and oceanography has been largeh' con- 

 cerned with purely dynamic problems. 



8. Exchange Fluctuations in Mid-Latitudes and Long-Period 

 Interaction Anomalies 



For the mid-latitude atmosphere, its contact with the sea surface is primarily 

 a braking mechanism by which the momentum of the winds is transferred to 

 the upper ocean layers, and their kinetic energy dissipated. An exception is 

 found at continental east coasts in winter. During polar air outbreaks, sensible 

 heat flux from sea to air reaches its all time high : arctic air-masses are modified 

 by the resulting convection and the birth of unstable cyclones is instigated or 

 materially aided by the resulting convergent mass flows. 



Actually, the most important exchange affecting mid-latitude atmospheric 

 circulations has already been discussed, namely evaporation from the tropical 

 oceans, which indirectly provides their maintenance. The dynamics of mid- 

 latitude flows have been more immediately concerned with the structure of 

 the westerly jet streams, the uneven importation of energy and momentum 

 across the subtropical ridge, and the release of the stored potential energy by 

 instability on the synoptic scale — the dominant feature of the motions. The 

 products of this dynamic instability, the travelling cyclones and anticyclones 

 and their arrangement, control the direction and speed of the air flow and, to a 

 large extent, the air-sea property difiBrences. Thus they bring about exchange 

 fluctuations which may even modify their own stability conditions and the 

 marine environment to be met by their successors. The climatology of middle- 

 latitude exchange cannot be interpreted without reference to the three- 

 dimensional structure of these disturbances : conversely, it is becoming ap- 

 parent that the modifying effects of even direct local exchange cannot remain 

 ignored in treating the dynamics of extra-tropical flows and their fluctuations, 

 from the synoptic up to the geological time scale. This whole frontier is a vast 

 jungle of nonlinear complexity, into the tangles of which only a few brave 

 souls have begun to beat paths. We shall confine ourselves here to several 

 explicit studies which have attempted to frame quantitatively pursuable 

 questions ; their shortcomings should not be judged too harshly in view of the 

 scope and difiiculty of the problems. 



A. Synoptic-Scale Exchange Variations off East Coasts in Wiyiter 



In re-examining the climatological patterns (see especially Figs. 7, 8, 11, 21, 

 39-43) we see that exchanges are maximal off continental east coasts in winter. 



