Theory of the Winds. 33 



heat the atmosphere, and, except over the unfrozen seas, 

 there will be a comparatively small amount of heat rising 

 by convection, and the troposphere will be thin. Balloon 

 ascents in the polar regions have shown that this is the 

 case. 



It must be remembered that the surface winds in middle 

 latitudes largely blow towards the polar regions, and that 

 the warm ocean-currents go with them. We thus have a 

 considerable amount of heat carried by convection from low 

 to higher latitudes. 



It is considered that the effect of the greater heating of 

 the upper atmosphere with increasing latitude does not 

 become marked until 30° N. and S. latitude have been 

 passed. The winds of the equatorial belt are, therefore, 

 produced by the surface temperature gradients. North 

 and south of 30° N. and S. latitude it is the superior 

 gradient of temperature in the stratosphere which controls 

 the winds. 



It must be admitted, as well, that the Thomson friction 

 effect is a valid one, and that the reduction in the velocity 

 of the surface winds by friction will assist to prevent cold 

 surface layers in high latitudes from flowing towards lower 

 latitudes. 



The action of the upper currents in the stratosphere moving 

 away from the polar areas is similar to that of a basin of 

 water which has a hole in the bottom, and in which the 

 water is rotating. The Antarctic area may be considered as 

 having the air abstracted from the upper portion of the 

 troposphere concentrically with the pole, and the circu- 

 lation is as shown in fig. 2. In the Arctic area, however, 

 the abstraction would appear to be from above the two 

 cyclonic areas, one over the N. Pacific and the other over 

 the N. Atlantic, as well as from the Asiatic plateau in the 

 summer. 



More information is required as to the temperature varia- 

 tions of the stratosphere with latitude. Until our knowledge 

 is more complete any theory based on temperature gradients 

 can only be a tentative one. If the theory here outlined in 

 some degree encourages further investigation into the tempe- 

 rature conditions of the stratosphere, it will not have been 

 given in vain. 



Phil. Mag. S. 6. Vol. 30. No. 175. July 1915. D 



