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SUMMARY:Tropical rainfall\, Rossby waves and initialised climate predictio
 ns - Adame Scaife (Met Office Hadley Centre)
DTSTART:20160118T130000Z
DTEND:20160118T140000Z
UID:TALK63804@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:Skilful climate predictions of the winter North Atlantic Oscil
 lation and Arctic Oscillation out to a few months ahead have recently been
  demonstrated but the source of this predictability remains largely unknow
 n. Here we investigate the role of the tropics in this predictability.  We
  show high levels of skill in tropical rainfall predictions\, particularly
  over the Pacific but also the Indian and Atlantic Ocean basins.  Rainfall
  fluctuations in these regions drive clear signatures in tropical and extr
 atropical atmospheric circulation that are approximately symmetric about t
 he equator in boreal winter. We show how these patterns can be explained a
 s steady poleward propagating linear Rossby waves emanating from just a fe
 w key source regions.  The sources of these waves are more or less active 
 as tropical rainfall varies from winter to winter but they do not change p
 osition because the wave sources are anchored to regions of strong vortici
 ty gradient associated with the extratropical jets.  Finally\, we show tha
 t predicted tropical rainfall explains a sizeable fraction of the predicte
 d year to year variance of the winter North Atlantic Oscillation.
LOCATION:MR4\, Centre for Mathematical Sciences
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