Climatology of upward propagating diurnal and semidiurnal tides in the thermosphere

A major challenge in delineating and understanding the "space weather" of the ionosphere-thermosphere system is the lack of global tidal observations in the 120-400 km "thermospheric gap" between satellite remote-sensing and in-situ tidal diagnostics. This paper aims to close this gap by presenting an observation-based Climatological Tidal Model of the Thermosphere (CTMT) of self-consistent upward propagating migrating and nonmigrating diurnal and semidiurnal tides from 80-400 km and pole-to-pole for moderate (F10.7 = 110 sfu) solar flux conditions. CTMT includes the 6 (8) most important diurnal (semidiurnal) tidal components for temperature, density, and zonal, meridional and vertical winds and is based on Hough Mode Extension fits to 2002-2008 mean TIMED satellite tidal diagnostics in the mesosphere/lower thermosphere (MLT). Validation with independent 2002-2008 CHAMP tidal diagnostics (F10.7 = 105 sfu) around 400 km proves that the approach captures nonmigrating tides well, indicating that these waves propagate directly upward without significant tidal forcing occurring in the thermosphere. Notable exceptions are the DW2 and D0 components that are most likely generated in-situ by nonlinear interaction forcing in the upper thermosphere. CTMT is suitable for driving upper atmosphere models that require self-consistent tidal fields in the MLT region as a lower boundary condition. It does not include migrating tides due to in-situ EUV absorption in the upper thermosphere but allows us to quantitatively assess thermospheric variability due to tides from the lower atmosphere. This is done by discussing longitude/latitude maps of reconstructed diurnal and semidiurnal tidal variations as function of altitude and local time.