Meteor radar observations of short‐term tidal variabilities in the low‐latitude mesosphere‐lower thermosphere: Evidence for nonlinear wave‐wave interactions

Abstract

Short‐term tidal variabilities in the mesosphere‐lower thermosphere (MLT) region using the meteor radar observations over Trivandrum (8.5°N, 77°E) during March 2006 to February 2007 are discussed. Spectral analysis of daily‐averaged zonal and meridional winds revealed the presence of planetary waves, with periods ranging from ∼2 to 30 days in the height region of 82–98 km. The hourly zonal and meridional wind measurements are then used to estimate day‐to‐day diurnal tide amplitudes in the MLT region for the first time over this latitude. Spectral analysis of zonal and meridional diurnal tide amplitudes revealed tidal modulations at periods ranging from ∼2 to 30 days. Further, during a strong episode of tidal modulation, which is identified from the wavelet spectra, a group of subsidiary spectral components around the diurnal tide is observed. The presence of subsidiary spectral components around the diurnal tide has provided evidence for nonlinear interaction between tides and planetary waves. To substantiate this result, bispectral analysis is carried out, which showed the nonlinear tide‐planetary wave interactions by revealing the presence of secondary waves exactly at the anticipated periods. As the present observational site is very near to dip equator, it is envisaged that the present results will have important implications in interpreting day‐to‐day variabilities in the equatorial ionosphere.