Characteristics of Non-migrating Diurnal Tides in long-term CMAM30 Horizontal Winds

Abstract

Variability of non-migrating diurnal tides are investigated using Canadian Middle Atmosphere Model (CMAM30) in zonal and meridional wind data from 1979 to 2010. Diurnal stationary tide (DS0) is found to maximise during boreal summers in both hemispheres in the middle atmosphere while the diurnal westward propagating tide of wavenumber two (DW2) maximises during boreal winters in both hemispheres. Both tides show strong annual variations over sub-tropical regions centered over ±25° latitudes along with significant short term variability from 20 to 100 days. The investigations of short term variations of DW2 show significant correspondence with the variability of stationary planetary wave of wavenumber one (SPW1) in the high latitudes in both hemispheres as well as with DW2 amplitudes from lower atmosphere. It is thereby concluded in the current study that DW2 in the mesosphere is not only produced by non-linear interactions of SPW1 and the diurnal migrating tide (DW1) but also has contributions from sources in the lower atmosphere. On the other hand, variability of DS0 does not show any similarity with that of SPW1 and thereby indicate sources only from the lower atmosphere. In the high-latitude stratosphere, DS0 and DW2 amplitudes are negligible and thereby the contribution of non-linear interactions to their generation in this region is minimal.