Variability of diurnal tide in the MLT region over Tirunelveli (8.7°N), India: Consistency between groundand space-based observations

Abstract

Atmospheric tides propagating upward into the mesosphere-lower thermosphere region carry the variability from the lower atmosphere and influence the energy and momentum budgets of this region and above. A comprehensive understanding of these variabilities thus becomes important. In this work, we study the seasonal and interannual variabilities of the diurnal tides, in particular, the migrating DW1 (westward, wave number 1) tide and the nonmigrating DE3 (eastward, wave number 3) tide from two different platforms. Long-term observations from the MF radar at Tirunelveli (8.7°N, 77.8°E) constitute one data set. Temperature and wind data from Sounding of the Atmosphere using Broadband Emission Radiometry and TIMED Doppler Interferometer observations from the TIMED satellite mission constitute the other. Continuous radar observations yield long data records with high temporal resolution. Space-based observations, on the other hand, are relatively short but provide spatiotemporal information, the latter being useful in separating migrating and nonmigrating components. In this work, the consistency between the tidal signatures obtained from the ground- and space-based platforms is examined and subtle differences between the two data sets are brought out. One particular feature pertains to a possible solar cycle influence on the diurnal tide, a feature which is more prominently seen in radar observations, though restricted to a certain epoch of the solar cycle. A solar cycle dependence of the zonal mean densities observed in satellite data sets at similar altitudes appears to be a plausible source for the observed solar cycle signature in the diurnal tide, although the role of other agencies in modulating the diurnal tide activity in the solar cycle time periods cannot be ruled out.