Seasonal-latitudinal variation of the eastward-propagating diurnal tide with zonal wavenumber 3 in the MLT: Influences of heating and background wind distribution

This study demonstrates how the mean zonal wind affects the propagation of tidal energy from the troposphere to the mesosphere-lower thermosphere (MLT) region (60–120 km). We diagnose the seasonal-latitudinal variation of the eastward-propagating diurnal tide with zonal wavenumber 3 (DE3), which is a prominent tidal component and agrees well between model and observation in recent studies. It is shown that during the course of a year the seasonal-latitudinal variation of mean zonal wind modulates and filters DE3 energy propagating upwards from tropospheric radiative and latent heating sources. Our results are based upon ISCCP and TRMM troposphere heating rates, SABER-derived zonal mean gradient wind, SABER tidal signatures and GSWM (the global-scale wave model) diagnoses. The tropospheric tidal heating rates are derived from ISCCP (International Satellite Cloud Climatology Project) radiative fluxes and TRMM (Tropical Rainfall Measuring Mission) latent heating profiles together with TRMM rainfall rates. The zonal mean winds are derived from measurements of geopotential height from the SABER (sounding of the atmosphere with broadband emission radiometry) instrument on the TIMED (thermosphere, ionosphere, mesosphere energetics and dynamics) spacecraft, and the tidal signatures are determined from SABER temperature measurements.

► Two of the determining factors in DE3's seasonal-latitudinal variation are examined by observation-based model and data.
► The two factors are troposphere total/net tidal heating and zonal mean zonal wind.
► Troposphere heating provides different tidal energy sources for different DE3 modes in different months.
► The horizontal zonal wind filters different tidal modes of DE3 in different ways at different altitudes through mode coupling.
► Different DE3 modes with different vertical wave lengths reach the MLT region with different magnitudes.