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.
