SECT. 2] 



LARGE-SCALE INTERACTIONS 



93 



affects solar radiation input) and the degrees of freedom or constraints limiting 

 these. For our planet, the ultimate energy source is the sun, and the major 

 constraints are the geometry and rotation of the earth, with an important 

 degree of freedom provided by the change in phase of water. 



The high ratio of the rotation rate relative to differential heat input [formu- 

 lated in terms of a "Rossby number" by those studying hierarchies of planetary 

 flow regimes in the dishpan (cf. Fultz, 1956; Riehl and Fultz, 1957)] constrains 



Fig. 1. Seasonal values of total evaporation, "LE in 10^ m^/day, as a function of latitude 

 for the North Atlantic and North Pacific Oceans combined. (After Jacobs, 1951a, 

 Fig. 10.) 



Computed by 10° -latitude belts from charts of evaporation per unit area of sea 

 surface for each ocean. Value for each 10°-belt entered at mid-point. Total oceanic 

 area included: 1.27 x 10^ km^. Mean annual evaporative loss to both oceans: 112.5 

 cm/year. 



the large-scale motions to be almost "geostrophic" or nearly at right angles to 

 the pressure gradient. Since fluid kinetic energy can only be thermally produced 

 by "ageostrophic" flows down the pressure gradient, this strait jacket of 

 rotation markedly complicates planetary circulations in comparison to those of 

 simpler non-rotating thermal fluid engines, and results in the storage of large 

 amounts of energy in "potential" form of sharp air- and water-mass density 

 contrasts, which can be released far in space and time from the input point. 



Solar energy, in short wave form, is received by our planet almost entirely 

 at the earth's surface, with less than 20% absorbed directly by the air and its 



