Dynamical Response of the Middle and Upper Atmosphere to the February 2018 Sudden Stratospheric Warming Revealed by MERRA‐2 and SABER.

The middle and upper atmosphere plays a critical role in linking the lower atmosphere forcing with ionospheric variability, especially during strong atmospheric activities. This study examines the dynamical response in the altitude range from ∼20 to 80 km to a major Sudden Stratospheric Warming (SSW) event peaking on 11 February 2018. We compare the reanalysis product of the Modern‐Era Retrospective Analysis for Research and Applications Version 2 (MERRA‐2) from the Goddard Earth Observing System (GEOS) to the satellite observations by Thermosphere Ionosphere and Mesosphere Electric Dynamics (TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) TIMED/SABER that are not assimilated in MERRA‐2. Our study shows that the zonal mean wind and temperature and planetary wave 1 and 2 variations are generally consistent between the reanalysis and observations. We also identify a strong ∼6 day wave propagating both westward and eastward with zonal wavenumber‐1 with the westward propagating component likely generated by baroclinic/barotropic instability. However, important disagreements arise specifically above ∼60 km, where the wind and temperature are not well represented in MERRA‐2, causing differences in the day‐to‐day development of 6 day wave. This study highlights the need for additional assimilation of mesospheric data and development of high‐altitude vertically extended GEOS model. Plain Language Summary: The MERRA‐2 is a meteorological reanalysis product based on the Goddard Earth Observing System (GEOS) model, incorporating various observations from the surface up to ∼75 km altitude. At upper levels particularly between ∼60 and 80 km, fewer observations are used and thus the MERRA‐2 system is less constrained. This region is also near the mesopause, where dynamical processes such as Sudden Stratospheric Warming (SSW) have significant impacts. Although SSW is primarily a stratospheric phenomenon, its effects extend into the mesosphere and thermosphere/ionosphere. This study analyzes the MERRA‐2 reanalysis product and examines the SSW impacts on zonal mean states and planetary‐scale wave activities across altitudes from ∼20 to 80 km during the major SSW event in February 2018. Additionally, the MERRA‐2 results are evaluated through comparisons with the observations from TIMED/SABER mission/instrument. This finding highlights the importance of adding more observations and further developments in MERRA‐2. Key Points: Reanalysis results are compared with independent satellite observations at ∼20–80 km altitude during January and February 2018Both reanalysis and observation reveal zonal mean and planetary wave variations but differ in development of ∼6 day wave above ∼60 kmAdditional observations are needed in reanalysis to improve representations of day‐to‐day variations at higher altitudes [ABSTRACT FROM AUTHOR]