Troposphere-thermosphere tidal coupling as measured by the SABER instrument on TIMED during July–September 2002

摘要

Coupling between the troposphere and lower thermosphere due to upward propagating tides is investigated using temperatures measured from the SABER instrument on the TIMED satellite. The data analyzed here are confined to 20–120 km altitude and ±40° latitude during 20 July to 20 September 2002. Apart from the migrating (Sun-synchronous) tidal components, the predominant feature seen (from the satellite frame) during this period is a wave-4 structure in longitude with extrema of up to ±40–50 K at 110 km. Amplitudes and longitudes of maxima of this structure evolve as the satellite precesses in local time and as the wave(s) responsible for this structure vary with time. The primary wave responsible for the wave-4 pattern is the eastward propagating diurnal tide with zonal wave number s = 3 (DE3). Its average amplitude distribution over the interval is quasi-symmetric about the equator, similar to that of a Kelvin wave, with maximum of about 20 K at 5°S and 110 km. DE3 is primarily excited by latent heating due to deep tropical convection in the troposphere. It is demonstrated that existence of DE3 is intimately connected with the predominant wave-4 longitude distribution of topography and land-sea difference at low latitudes, and an analogy is drawn with the strong presence of DE1 in Mars atmosphere, the predominant wave-2 topography on Mars, and the wave-2 patterns that dominate density measurements from the Mars Global Surveyor (MGS) spacecraft near 130 km. Additional diurnal, semidiurnal, and terdiurnal nonmigrating tides are also revealed in the present study. These tidal components are most likely excited by nonlinear interactions between their migrating counterparts and the stationary planetary wave with s = 1 known to exist in the Southern Hemisphere during this period just prior to the austral midwinter stratospheric warming of 2002.