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SUMMARY:The Mechanism of Interhemispheric Coupling Revealed by a Gravity-W
 ave-Permitting General Circulation Model - Dr. Haruka Okui\, University of
  Bath
DTSTART:20241004T100000Z
DTEND:20241004T110000Z
UID:TALK221896@talks.cam.ac.uk
CONTACT:Siddharth Gumber
DESCRIPTION:Interhemispheric coupling (IHC) is a positive correlation betw
 een temperatures in the polar winter stratosphere and polar summer upper m
 esosphere and lower thermosphere. Over the two decades since its discovery
  through observations of polar mesospheric clouds\, several plausible mech
 anisms of the IHC have been proposed. However\, a consensus on the IHC mec
 hanism has yet to be fully reached. One of the most uncertain aspects of t
 he mechanism is the role of gravity waves (GWs). Since most GWs were param
 eterized in models used in the previous studies\, their contribution to th
 e IHC was not necessarily realistic when assumptions used in the parameter
 izations did not hold. We perform hindcast simulations of the whole neutra
 l atmosphere over seven boreal winters using a GW-permitting general circu
 lation model. The model is initialized through spectral nudging to state-o
 f-the-art reanalysis covering the whole neutral atmosphere. The IHC is ana
 lysed as a sequential development of anomalies from the climatology includ
 ing GW forcing. As a result\, it is revealed that consequential interplay 
 of GWs and quasi-two-day waves in the summer mesosphere is the key driver 
 of the IHC. The mechanism applies to multiple cases associated with sudden
  stratospheric warming and vortex intensification. In addition\, we will d
 iscuss the model representation of GWs in the summer polar mesosphere\, wh
 ich play a crucial role in the IHC\, by comparing resolved waves from the 
 high-resolution hindcasts with GW parameterizations and assimilation incre
 ments in the reanalysis. The outputs from hindcasts are highly useful in e
 lucidating global and climatological behaviour of GWs in the whole neutral
  atmosphere.
LOCATION:BAS Seminar Room 1 and Zoom
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