Long-Term Variability and Tendencies in Non-Migrating Diurnal Tide From WACCM6 Simulations During 1850–2014

This study reports the long-term variability and tendencies in important non-migrating (DE3, DW2, DW3) and stationary (DS0) diurnal tides using a three-member ensemble of historical simulations of National Center for Atmospheric Research Whole Atmospheric Community Climate Model latest version 6 for 1850–2014 (165 years). The climatological features of the tide in temperature (T), zonal wind (U) and meridional wind (V) are presented for equinoxes/solstices and winter/summer. The response due to solar cycle (SC), quasi biennial oscillation at 10 hPa and 30 hPa, El Niño-Southern Oscillation (ENSO), ozone depleting substances (ODS), carbon dioxide (CO₂), and stratospheric sulfate aerosol (volcanic eruptions) to change in tidal amplitudes with respect to 1850–1860 are analyzed using multiple linear regression. The annual mean amplitudes increase in the upper mesosphere and lowermost thermosphere (0.0001–0.01 hPa) in the three components predominantly due to increasing CO₂ and the ODSs play secondary role. However, the increasing trends are not pronounced until 1950 in the case of DE3 and DW3 amplitudes. The contribution due to ENSO shows decreasing trend in DE3, DW2, and DW3 while it causes increasing trends for DS0. Furthermore, the seasonal and latitude-pressure variations of the tidal responses to the above seven indices are presented in T and V. All the responses, except for the solar signal, are significant mostly in the upper mesosphere and lowermost thermosphere typically at equatorial/low latitudes.