Suppressed migrating diurnal tides in the mesosphere and lower thermosphere region during El Niño in northern winter and its possible mechanism

Abstract. As observed by the Sounding of Atmosphere using Broadband Emission Radiometry (SABER), migrating diurnal tide (DW1) in upper mesosphere and lower thermosphere (MLT) region decreased ? 10 % during El Niño Northern Hemisphere (NH) winter (December–January–February) from 2002 to 2020. According multiple linear regression (MLR) analysis, effects on tropical MLT DW1 are significantly negative both SABER observations SD-WACCM (the Specified-Dynamics version Whole Community Climate Model) simulations. The response NH is much stronger than its annual mean response. suggested simulation, Hough mode (1, 1) dominates tidal variation region. consistency between tropopause downward phase progression 15 100 km indicates direct upward propagation excitation source troposphere. suppressed heating rates troposphere (averaged over 0–16 35? S–35? N) contribute tide. To evaluate effect gravity waves (GWs) tide, GW forcing calculated as drag weighted relation wind. would suppress winter. This tide–GW interaction could be a dominant mechanism for Niño. During winter, increased ratio absolute planetary vorticity (R) suppresses waveguide thus amplitude subtropical mesosphere. However, might play secondary role due relatively weak