ENSO effects on MLT diurnal tides: A 21 year reanalysis data‐driven GAIA model simulation

Abstract

AbstractTidal responses to El Niño–Southern Oscillation (ENSO) in the mesosphere and lower thermosphere (MLT) are investigated for the first time using reanalysis data‐driven simulations covering 21 years. The simulation is carried out with the Ground‐to‐topside Atmosphere‐Ionosphere model for Aeronomy (GAIA) during 1996–2016, which covers nine ENSO events. ENSO impacts on diurnal tides at 100 km altitude are analyzed and cross‐compared among temperature (T), zonal wind (U), and meridional wind (V), which reveals the following salient features: (1) Tidal response can differ significantly among T, U, and V in terms of magnitude and latitudinal structure, making detection of ENSO effects sensitive to the parameter used and the location of a ground station; (2) the nonmigrating DE3 tide in T and U shows a prominent hemisphere asymmetric response to La Niña, with an increase between 0° and 30°N and a decrease between 30° and 0°S. In contrast, DE3 in V exhibits no significant response; (3) the migrating DW1 enhances during El Niño in equatorial regions for T and U but in off‐equatorial regions for V. As the first ENSO study based on reanalysis‐driven simulations, GAIA's full set of tidal responses in T, U, and V provides us with a necessary global context to better understand and cross‐compare observations during ENSO events. Comparisons with observations during the 1997–98 El Niño and 2010–11 La Niña reveal good agreement in both magnitude and timing. Comparisons with “free‐run” WACCM simulations (T) show consistent results in nonmigrating tides DE2 and DE3 but differences in the migrating DW1 tide.