The Madden‐Julian Oscillation (MJO), an eastward‐moving disturbance near the equator (±30°) that typically recurs every ∼30–90 days in tropical winds and clouds, is the dominant mode of intraseasonal variability in tropical convection and circulation and has been extensively studied due to its importance for medium‐range weather forecasting. A previous statistical diagnostic of SABER/TIMED observations and the MJO index showed that the migrating diurnal (DW1) and the important nonmigrating diurnal (DE3) tide modulates on MJO‐timescale in the mesosphere/lower thermosphere (MLT) by about 20%–30%, depending on the MJO phase. In this study, we address the physics of the underlying coupling mechanisms using SABER, MERRA‐2 reanalysis, and SD‐WACCMX. Our emphasis was on the 2008–2010 time period when several strong MJO events occurred. SD‐WACCMX and SABER tides show characteristically similar MJO‐signal in the MLT region. The tides largely respond to the MJO in the tropospheric tidal forcing and less so to the MJO in tropospheric/stratospheric background winds. We further quantify the MJO response in the MLT region in the SD‐WACCMX zonal and meridional momentum forcing by separating the relative contributions of classical (Coriolis force and pressure gradient) and nonclassical forcing (advection and gravity wave drag [GWD]) which transport the MJO‐signal into the upper atmosphere. Interestingly, the tidal MJO‐response is larger in summer due to larger momentum forcing in the MLT region despite the MJO being most active in winter. We find that tidal advection and GWD forcing in MLT can work together or against each other depending on their phase relationship to the MJO‐phases.
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.
more » « less- NSF-PAR ID:
- 10374624
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 125
- Issue:
- 5
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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