The Recent Climatic Fluctuation in Lower Latitudes and the General Circulation of the Pleistocene

In order to compensate for the somewhat secondary interest commonly devoted to the problems related to general circulation anomalies of the Pleistocene in lower latitudes, the present writer (K. W. BUTZER 1957 b) has already discussed the meteorological significance of the pluvials in subtropical latitudes. In this essay it shall be attempted to analyze the character of the recent climatic fluctuation in the subtropics and tropics in order to assess its applicability to some further problems connected with the atmospheric circulation of the Quaternary, namely with interpluvial and interglacial epochs. A general warming up of the northern Atlantic region has been of great interest in the past decades, but the trends of precipitation in different geographical areas have not been given a deserving attention. These precipitation anomalies are of an equally striking nature and equal palaeoclimatological implication as the recent temperature changes. Consequently the emphasis here shall be upon the circulation changes related to precipitation in lower latitudes. The large number of well-qualified and important articles considering our present climatic fluctuation have also only paid passing attention to the mediterranean climatic province and the trade wind deserts of the Old World; and largescale maps of barometric pressure and precipitation anomalies have been based on too few stations in this area, with often misleading results. To help bridge this deficiency, pressure and rainfall changes in lower latitudes between 2zo0E and 750 W have been computed from the World Weather Records and presented in the form of three maps. Firstly January and July barometric pressure changes are summarized in Fig. I and 2. The differences are based on the records of 37 stations for the period before 192o and 1921-1940. This apparently inhomogeneous comparison is necessitated by the scarcity of stations, but largely eliminated by the fairly uniform trends between 1881 (earlier limit of records applied) and 192o. This procedure has already been employed by K. KRAMES (1951, 1952) for temperature fluctuations. Almost all of the stations used begin recording between 1881 and 1900oo. Based on 72 stations, Fig. 3 illustrates the rainfall anomalies for the 3o-year means before and after 191o for the greater