Notices of Memoirs — F. W. Harmer — Winds and Climate. 565 



31. — The Influence of the Winds upon Climate during Past 

 Epochs : a Meteorological Explanation of some Geological 

 Problems. By F, W. Harmer, F.G.S.' (Abstract.) 



THIS paper is a summary of a communication the author hopes 

 to make to the Geological Society of London during the present 

 winter, and is in continuation of one read at Dover in 1899, on 

 "The Meteorological Conditions of North-Western Europe during 

 the Pliocene and Glacial Periods." 



The irregular distribution of the isotherms in the northern 

 hemisphere is largely due to the direction of the prevalent winds. 

 In regions where these are constantly varying, as, for example, in 

 Great Britain, the climate varies diurnally, one day being often dry 

 or cold and the next rainy or warm. In others, where the wind 

 changes seasonally, one part of the year is rainless and another 

 pluvial. Permanent alterations in climate would equally result 

 were the course of the prevalent winds permanently changed. 



The direction of the winds, which must always be more or less 

 parallel to the isobars, depends on the relative position, and on the 

 form and alignment of areas of high and low barometric pressure. 

 The movements of the latter being largely interdependent, any 

 important meteorological disturbance, however caused, may make its 

 influence felt at a considerable distance from the focus of its origin. 



The winds blow round areas of high and low pressure ; outwards, 

 from the former, and to the north of the Equator, from left to 

 right ; and inwards, towards the latter, from right to left. Hence, 

 in the northern hemisphere, southerly winds prevail to the east of 

 a cyclonic centre, and northerly winds to the west of it, the contrast 

 between the temperature of the two areas being usually in proportion 

 to the distance the aerial currents may have travelled from the south 

 and the north respectively. Warm and cold winds must therefore 

 necessarily coexist, causing differences in climate in countries having 

 the same latitude. The winter temperature of Hudson's Bay is, for 

 example, 60° F. colder than that of Great Britain. Similar climatal 

 conditions must have also existed during the Pleistocene epoch. 



The continental regions of the northern hemisphere, being at 

 present warmer during summer than the ocean, are cyclonic ; in 

 winter they are colder, and consequently anticyclonic. Over the 

 great ice-sheets of the Glacial Period, however, high pressure must 

 have prevailed, more or less, at all seasons, and, generally, the 

 meteorological conditions, including the direction of the prevalent 

 winds, and local variations in climate must then have been widely 

 different from those of our own times. Oceanic winds, with copious 

 rainfall, may have prevailed in regions now arid, and mild winters 

 where they are now excessively severe. Such cases of anomalous 

 climate as those of the pluvial conditions of the Sahara, and of 

 Arabia and Persia, during the Pleistocene era, may be satisfactorily 

 explained by the changes iu the relative positions of cyclonic and 

 anticyclonic systems which were caused by the gradual growth and 



' Eead before the British Associatiou, Section C (Geology), Bradford, Sept., 1900. 



