, Volume 102, Issue 1, pp 193-222

The diurnal and semidiurnal barometric oscillations global distribution and annual variation

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Summary

The global distributions of the annual and seasonal means of the diurnal (S 1) and semidiurnal (S 2) surface pressure oscillations are investigated by spherical harmonic analysis. The main waves are,S 1 1 (with wave number 1) forS 1 andS 2 2 forS 2.S 1 1 is much less predominant among the waves ofS 1 thanS 2 2 among those ofS 2. As in the case of the lunar semidiurnal barometric tideL 2 the pressure maxima occur earlier in the Southern than in the Northern Hemisphere. In the case ofS 2 the standing waveS 2 0 and the waveS 2 3 are also of interest besidesS 2 2. Although the present analysis extends only from 60°N to 60°S, whileS 2 0 is largest at polar latitudes, its results show thatS 2 0 should be smaller at high southerly than at high northerly latitudes, as has been observed. Thus this observed asymmetrical distribution ofS 2 0 may be due to causes outside the polar regions rather than to their geographical differences. The best approximation to the observed distribution ofS 2 0 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 ofS 1 1 expressed in percent of the annual mean is smaller than that ofS 2 2, and both are less than the unexplained seasonal variation ofL 2 2.

The main wavesS 1 1 andS 2 2 are expressed not only by associated Legendre functions, but also by Hough functions.

National Center for Atmospheric Research, Boulder, Colorado, U.S.A., sponsored by the National Science Foundation.