DATE2018-05-11 12:20:20
IDABSTRACT20180511122020-0162
CONTACTislas@ucar.edu
PRESENTATIONORAL
INVITED0
IDSESSION3
TITLETHE INFLUENCE OF UNCERTAINTY IN THE NORTHERN HEMISPHERE STRATOSPHERIC POLAR VORTEX RESPONSE TO CLIMATE CHANGE ON FUTURE PROJECTIONS OF MEDITERRANEAN HYDROCLIMATE.
AUTHORSIR Simpson (1), P Hitchcock (2), R Seager (3), Y Wu (3), P Callaghan (1)
AFFILIATIONS
  1. National Center for Atmospheric Research, Boulder, USA
  2. Laboratoire de Meteorologie Dynamique, Palaiseau, France
  3. Lamont-Doherty Earth Observatory, New York, USA
ABSTRACTGeneral circulation models display a wide range of future predicted changes in the Northern Hemisphere winter stratospheric polar vortex. Here analysis of the Coupled Model Intercomparison Project phase 5 (CMIP5) models will be combined with idealized experiments with the Community Earth System Model (CESM) to investigate the impact of this uncertainty in the stratospheric polar vortex response on future projected Mediterranean climate change. A regression analysis across the CMIP5 models reveals that with a relative weakening of the stratospheric polar vortex comes a relative drying over Northern Europe and wetting over the Mediterranean. Idealized CESM experiments in which stratospheric polar vortex responses on opposite ends of the CMIP5 range are artificially imposed through a nudging methodology confirm that the stratospheric influence inferred from the CMIP5 regression does indeed represent a true downward influence of the stratosphere on the troposphere below. While the stratospheric polar vortex influence represents a relatively small contribution to intermodel spread in future wintertime Mediterranean precipitation changes, the difference between models on opposite ends of the CMIP5 range in polar vortex responses can be substantial. The difference in wintertime Mediterranean precipitation changes between models with an extreme strengthening and those with an extreme weakening of the stratospheric vortex is of the order 0.25mm/day which is around 10% of the present day precipitation climatology in that region. Therefore, an improved understanding and narrowing of the uncertainty in the future of the stratospheric polar vortex may considerably improve projections of future wintertime hydroclimate in the Mediterranean.
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