The diurnal and semidiurnal barometric oscillations global distribution and annual variation

SummaryThe global distributions of the annual and seasonal means of the diurnal (S1) and semidiurnal (S2) surface pressure oscillations are investigated by spherical harmonic analysis. The main waves are,S11 (with wave number 1) forS1 andS22 forS2.S11 is much less predominant among the waves ofS1 thanS22 among those ofS2. As in the case of the lunar semidiurnal barometric tideL2 the pressure maxima occur earlier in the Southern than in the Northern Hemisphere. In the case ofS2 the standing waveS20 and the waveS23 are also of interest besidesS22. Although the present analysis extends only from 60°N to 60°S, whileS20 is largest at polar latitudes, its results show thatS20 should be smaller at high southerly than at high northerly latitudes, as has been observed. Thus this observed asymmetrical distribution ofS20 may be due to causes outside the polar regions rather than to their geographical differences. The best approximation to the observed distribution ofS20 is obtained by including a mode representing an oscillation independent of longitude and latitude indicating a small semidiurnal variation of the mean global surface presure, which is an unlikely result on physical grounds.The seasonal variation ofS11 expressed in percent of the annual mean is smaller than that ofS22, and both are less than the unexplained seasonal variation ofL22.The main wavesS11 andS22 are expressed not only by associated Legendre functions, but also by Hough functions.