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SUMMARY:Atmospheric Responses to Solar Wind Dynamic Pressure - Dr Hua Lu (
 British Antarctic Survey)
DTSTART:20110309T140000Z
DTEND:20110309T150000Z
UID:TALK28979@talks.cam.ac.uk
CONTACT:Dr Scott Hosking
DESCRIPTION:Statistically significant responses of the Northern Annular Mo
 de (NAM) and the equatorial stratospheric Quasi-biennial Oscillation (QBO)
  to solar wind dynamic pressure are detected.\n\nThe stratospheric QBO res
 ponse to solar wind dynamic pressure is characterized by a vertical three-
 cell anomaly pattern with westerly anomalies both in the troposphere and t
 he upper stratosphere and easterly anomalies in the lower stratosphere. Th
 e QBO in the lower stratosphere is found to be preferably more easterly du
 ring July to October when the solar wind dynamic pressure is high. These l
 ower stratospheric easterly anomalies are primarily linked to the high fre
 quency component of solar wind dynamic pressure with periods shorter than 
 3-years. This anomalous behavior in tropical winds is accompanied by a dow
 nward propagation of positive temperature anomalies from the upper stratos
 phere to the lower stratosphere over a period of a year.\n\nIn terms of th
 e NAM\, it is found that when December to January solar wind dynamic press
 ure is high\, the Northern Hemispheric (NH) circulation response is marked
  by a stronger polar vortex and weaker sub-tropical jet in the upper to mi
 ddle stratosphere. As the winter progresses\, the Arctic becomes colder an
 d the jet anomalies shift poleward and downward. In spring\, the polar str
 atosphere becomes anomalously warmer. At solar maxima\, significant positi
 ve correlations are found between December to January solar wind dynamic p
 ressure and the mid- to late winter NAM all the way from the surface to 20
  hPa\, implying a strengthened polar vortex\, reduced Brewer-Dobson circul
 ation and enhanced stratosphere-troposphere coupling. At solar minima\, th
 ere is no signal in the NH winter but negative responses were found in the
  stratospheric NAM during spring.\n\nThese results suggest that the solar 
 wind dynamic pressure exerts a seasonal change of the tropical upwelling w
 hich results in a systemic modulation of the annual cycle in the lower str
 atospheric temperature\, which in turn affects the QBO and the NAM. Howeve
 r\, the route by which the effects of solar wind forcing might propagate t
 o the lower atmosphere is yet to be understood.
LOCATION:British Antarctic Survey\, Room 307
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