Thermospheric Composition O/N Response to an Altered Meridional Mean Circulation During Sudden Stratospheric Warmings Observed by GOLD

Abstract Observations from the recently launched Global‐Scale Observations of the Limb and Disk (GOLD) instrument on the geostationary SES‐14 communications satellite reveal a substantial response of the mean state of the thermosphere to the Sudden Stratospheric Warming (SSW) event in early January 2019. The observed O/N column density depletion of more than 10% starts at the onset of the SSW, maximizes at the time of the stratospheric wind reversal, and recovers toward the end of the SSW. A connection between SSW and thermospheric composition was previously predicted by model simulations but could not be observed before. The GOLD measurements support the scenario that enhanced global‐scale wave activity during SSWs causes an enhanced wave driving of the lower thermosphere zonal mean circulation that leads to a reduction in lower thermosphere atomic oxygen, which then propagates through molecular diffusion into the upper thermosphere.