Vertical coupling between the lower and middle thermosphere due to the eastward propagating diurnal tide with zonal wave number 3 (DE3) and the 3.5 day ultra‐fast Kelvin Wave (UFKW) is investigated using Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics‐Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED‐SABER) temperatures near 100 km and Gravity field and steady‐state Ocean Circulation Explorer (GOCE) neutral densities and zonal winds near 260 km. The analysis is performed between ±45∘ latitude during 2011, when reliable and continuous measurements are available. With geomagnetic and solar effects removed, DE3 and the UFKW are identified as dominant sources of day‐to‐day variability at both heights. Evidence is found for the vertical propagation of DE3 and the UFKW from the lower to middle thermosphere over a range of time scales. Over 60% of the variance due to DE3 and the UFKW at 260 km is traceable to variability occurring at 100 km. The not exact agreement is thought to be due to the influences of wave‐wave interactions, zonal mean winds, dissipation, and inherent transience that interfere with one‐to‐one mapping of structures between 100 and 260 km. Spectral and temporal analyses of the SABER and GOCE data also reveal the presence of sidebands due to the modulation of DE3 by the UFKW. These secondary waves are responsible for up to 10% to 20% of the longitudinal and day‐to‐day variability. Overall, vertical propagating waves together with sidebands from DE3‐UFKW nonlinear interactions are responsible for 60% to 80% of the total variability, while geomagnetic and solar effects correlated with ap and F10.7 account for less than 20% of the variance.
Recent observational and modeling evidence has demonstrated that planetary waves can modulate atmospheric tides, and secondary waves arising from their nonlinear interactions are an important source of both temporal and longitude variability in the thermosphere. While significant progress has been made on understanding how this form of vertical coupling occurs, uncertainty still exists on how the horizontal structures of primary and secondary waves evolve with height and the processes responsible for this evolution, in part due to lack of global observations between 120 km and 260 km. In this work we employ a Thermosphere Ionosphere Mesosphere Electrodynamics general circulation model simulation covering all of 2009 that is forced by Modern‐Era Retrospective Analysis for Research and Applications dynamical fields, to assess the relative contribution of zonal mean winds and molecular dissipation on the vertical coupling of the eastward propagating diurnal tide with zonal wave number 3 (DE3), the 3 day ultrafast Kelvin wave, and the secondary waves arising from their nonlinear interaction. By developing and applying a new analytic formulation describing the latitudinal structure of an equatorially trapped wave subject to dissipation and background winds, we show that dissipation is the primary contributor to the broadening of the latitudinal structures with height, while asymmetries in the background wind field are responsible for the distortion of the height‐latitude structures.
Over the past two decades mounting evidence demonstrated that terrestrial weather significantly influences the dynamics and mean state of the thermosphere. While important progress has been made in understanding how this coupling occurs on hourly to daily time scales, large uncertainty still exists on this effect around intraseasonal (∼30-90 days) time scales. In this work, analyses of Thermosphere Ionosphere Mesosphere Energetics Dynamics-Sounding of the Atmosphere using Broadband Emission Radiometry temperatures near 110 km and Gravity field and steady-state Ocean Circulation Explorer cross-track winds near 260 km reveal prominent intraseasonal oscillations in the equatorial (±15 • ) zonal mean lower and middle thermosphere. Similar intraseasonal oscillations are found in the amplitudes of the diurnal eastward propagating tide with Zonal Wavenumber 3 (DE3) and the quasi-3-day ultrafast Kelvin wave, two prominent ultrafast tropical waves (UFTWs) excited by deep tropical tropospheric convection. Numerical simulations from the Specified-Dynamics Whole Atmosphere Community Climate Model eXtended demonstrate a significant connection between these UFTW and the Madden-Julian Oscillation (MJO). Compared to the boreal winter mean state, thermospheric UFTW amplitudes are larger (+5 to +12%) during MJO Phases 2-3 and smaller (−3% to −12%) during MJO Phases 6-8. Significant variations are also found with respect to the phase of the mesospheric semiannual oscillation (MSAO) and stratospheric quasi-biannual oscillation (SQBO), with larger (±12-16%) thermospheric amplitudes during westward MSAO/SQBO phase and smaller (±3-6%) amplitudes during eastward MSAO/SQBO phase, in accordance with theoretical interpretations. This study suggests that UFTW may play a large role in coupling tropospheric intraseasonal variability to the thermosphere, raising important questions including implications for the whole atmosphere system.
We report on a new source of tidal variability in the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). Lower boundary forcing of the TIME-GCM for a simulation of November-December 2009 based on 3-hourly Modern-Era Retrospective Analysis for Research and Application (MERRA) reanalysis data includes day-to-day variations in both diurnal and semidiurnal tides of tropospheric origin. Comparison with TIME-GCM results from a heretofore standard simulation that includes climatological tropospheric tides from the global-scale wave model reveal evidence of the impacts of MERRA forcing throughout the model domain, including measurable tidal variability in the TIME-GCM upper thermosphere. Additional comparisons with measurements made by the Gravity field and steady-state Ocean Circulation Explorer satellite show improved TIME-GCM capability to capture day-to-day variations in thermospheric density for the November-December 2009 period with the new MERRA lower boundary forcing.
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