Impacts of vertically propagating tides on the mean state of the ionosphere‐thermosphere system

Abstract

The National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) is utilized to understand the role that upward propagating tides play in determining the zonal mean state of the ionosphere‐thermosphere system. A sensitivity assessment of the TIE‐GCM shows that TIE‐GCM solutions greatly depend on the lower boundary conditions. We also establish the veracity of our TIE‐GCM solutions within and above the dynamo region. To isolate the mean effects of tidal dissipation, differences between TIE‐GCM simulations with and without lower boundary tidal forcing as specified by the Climatological Tidal Model of the Thermosphere are investigated. Dissipation of the DW1, (diurnal westward propagating tide with zonal wave number 1), diurnal eastward propagating tide with zonal wave number 3, and SW2 (semidiurnal tide with zonal wave number 2) explains most of ∼10–30 m s−1 seasonal and latitudinal variability in zonal winds within the dynamo region, with SW2 playing a greater role than ascribed in previous studies. Tidal dissipation at low latitudes causes a 9% decrease (30% increase) in [O] ([O2]) number densities near the F2 layer peak, leading to at least a 9% decrease in peak electron density (NmF2) throughout the year. F2 layer peak height (hmF2) differences of ‐4 to 2 km at low latitudes are explained by variations in the field‐aligned plasma motion driven by meridional wind differences induced by tidal dissipation. Compositional effects are mainly driven by DW1 and SW2, which differs from previous interpretations of tidal‐driven composition changes by DW1 “tidal mixing” exclusively. We suggest that tides may produce a net transport of constituents in the thermosphere similar to the way that, e.g., gravity waves can drive net transport of sodium in the mesosphere.