. Smithsonian miscellaneous collections. expansion of theair by heating as well as vertical expansion which is known to takeplace because of increased pressure on mountain summits. The next step in the inquiry concerns the relation between atmos-pheric pressure and the 11-year sunspot period. The short-termoscillations in pressure are relatively larger than short-term 20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 104 oscillations in sunspots, so that some process of smoothing is neces-sary to bring out the relations to longer pressure changes like the n-year sunspot period. In my earliest inve
. Smithsonian miscellaneous collections. expansion of theair by heating as well as vertical expansion which is known to takeplace because of increased pressure on mountain summits. The next step in the inquiry concerns the relation between atmos-pheric pressure and the 11-year sunspot period. The short-termoscillations in pressure are relatively larger than short-term 20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 104 oscillations in sunspots, so that some process of smoothing is neces-sary to bring out the relations to longer pressure changes like the n-year sunspot period. In my earliest investigations a latitude effectwas discovered in the difference of pressure between sunspotmaximum and sunspot minimum. In periods of marked solar activitythe pressure is lower than normal in the equatorial belt and higher NORTHERN HEMISPHERE EQUATOR SOUTHERN HEMISPHERE70* 60* 50* 40* 30* 20* 10* 0* 10* 20* 30* 40* 50* 60* ? 04 ^ ^ Fig. 14.—Mean difference of pressure at sunspot maximum from that atsunspot Fig. 15.—Correlation between sunspots and 3-year means of pressure. than normal in high latitudes, as will be seen in figure 14 taken fromWorld Weather, 1923. This figure shows the difference betweenthe mean pressure at each io° of latitude during periods of sunspotmaxima as compared with sunspot minima. In the mean the pressurefalls in the zone between about 350 N. and 350 S. and rises at higherlatitudes. However, the width of this belt varies at different longi-tudes under the influence of local conditions. Figure 15 shows the NO. 19 SUNSPOT CHANGES AND WEATHER CHANGES CLAYTON 21 correlation between 3-year means of atmospheric pressure and sun-spots. This figure includes observations down to It would besomewhat altered by the inclusion of later data, but these later datacontinue to show a high negative correlation of sunspots with thesmoothed values of pressure between Malaya and northern SouthAmerica. This region of high negative cor
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