Thermospheric Composition O/N ₂ Response to an Altered Meridional Mean Circulation During Sudden Stratospheric Warmings Observed by GOLD

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/N₂ 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.