A new look at the stratospheric sudden warming of 1979 using a modern data assimilation system

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Wednesday, 7 January 2015: 8:30 AM
212A West Building (Phoenix Convention Center - West and North Buildings)
Steven Pawson, NASA/GSFC, Greenbelt, MD; and L. Coy, K. Wargan, and E. Remsberg

The Arctic winter of 1978-1979 contains classic examples of a “wave-1” disturbance in January 1979 and a “wave-2” vortex split in February. These dynamical structures coincided with the availability of new satellite observations: the operational nadir radiance measurements from the Stratospheric Sounding Unit (SSU) and the research limb-profiles from the Limb Infrared Monitor of the Stratosphere (LIMS). As a consequence, this winter has been the subject of many classic research papers on the evolution and forcing of stratospheric sudden warming (SSW) events. This paper will present new insight into the 1978-1979 winter using an assimilation of LIMS Version 6 temperature and ozone observations into a modern data assimilation system (DAS), the GEOS-5 (Goddard Earth Observing System, Version 5). Potential vorticity maps (and their animations) show a rich dynamical spectrum of motions, revealing many previously undiscovered features at small scales, while confirming the broad interpretation of the large-scale Rossby-wave dynamics in early studies when analyses were performed at resolutions of several hundred kilometers, in contrast to the resolutions of a few tens of kilometers used in GEOS-5. The LIMS temperature profiles extend the vertical range of the DAS into the lower mesosphere that, along with conventional observations and nadir radiances from the Stratospheric Sounder Unit (SSU), which allows for a complete analysis of the SSW between the ground and the middle mesosphere. The wave and mean flow evolution and EP fluxes before, during, and after, the major SSW event as seen in the LIMS-based DAS are compared with earlier studies, and while results are mostly in agreement with past studies, there are some differences in the details of the EP flux polar focusing and low latitude wind evolution.