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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-50
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-50
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Oct 2020

12 Oct 2020

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This preprint is currently under review for the journal WCD.

SST fronts along the Gulf Stream and Kuroshio affect the winter climatology primarily in the absence of cyclones

Leonidas Tsopouridis, Thomas Spengler, and Clemens Spensberger Leonidas Tsopouridis et al.
  • Geophysical Institute, University of Bergen, and Bjerknes Centre for Climate Research, Bergen, Norway

Abstract. The Gulf Stream and Kuroshio regions feature strong sea surface temperature (SST) gradients that influence cyclone development and the storm track. Smoothing the SSTs in either the North Atlantic or North Pacific has been shown to yield a reduction in cyclone activity, surface heat fluxes, and precipitation, as well as a southward shift of the storm track and the upper-level jet. To what extent these changes are attributable to changes in individual cyclone behaviour, however, remains unclear. Comparing simulations with realistic and smoothed SSTs in the atmospheric general circulation model AFES, we find that the intensification of individual cyclones in the Gulf Stream or Kuroshio region is only marginally affected by reducing the SST gradient. In contrast, we observe considerable changes in the climatological mean state, with a reduced cyclone activity in the North Atlantic and North Pacific storm tracks that are also shifted equator-ward in both basins. The upper-level jet in the Atlantic also shifts equator-ward, while the jet in the Pacific strengthens in its climatological position and extends further east. Surface heat fluxes, specific humidity, and precipitation also respond strongly to the smoothing of the SST, with a considerable decrease of their mean values on the warm side of the SST front. This decrease is more pronounced in the Gulf Stream than in the Kuroshio region, due to the amplified decrease in SST along the Gulf Stream SST front. Subdividing the winter climatology into dates with/without cyclones present in the Gulf Stream and Kuroshio regions, we find that cyclones play only a secondary role in explaining the mean states differences between the smoothed and realistic SST experiments.

Leonidas Tsopouridis et al.

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Leonidas Tsopouridis et al.

Data sets

The ERA‐Interim reanalysis: configuration and performance of the data assimilation system D. P. Dee, S. M. Uppala, A. J. Simmons, P. Berrisford, P. Poli, S. Kobayashi, U. Andrae,M. A. Balmaseda, G. Balsamo, P. Bauer, P. Bechtold, A. C. M. Beljaars, L. van de Berg, J. Bidlot, N. Bormann, C. Delsol, R. Dragani, M. Fuentes, A. J. Geer, L. Haimberger, S. B. Healy, H. Hersbach, E. V. Hólm, L. Isaksen, P. Kållberg, M. Köhler, M. Matricardi, A. P. McNally, B. M. Monge‐Sanz, J.‐J. Morcrette, B.‐K. Park, C. Peubey, P. de Rosnay, C. Tavolato, J.‐N. Thépaut, and F. Vitart https://doi.org/10.1002/qj.828

Storm-Track Response to SST Fronts in the Northwestern Pacific Region in an AGCM Akira Kuwano-Yoshida and Shoshiro Minobe https://doi.org/10.1175/JCLI-D-16-0331.1

Leonidas Tsopouridis et al.

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Short summary
Comparing simulations with realistic and smoothed SSTs, we find that the intensification of individual cyclones in the Gulf Stream and Kuroshio regions is only marginally affected by reducing the SST gradient. In contrast, we observe a reduced cyclone activity and a shift in storm tracks. Subdividing the winter climatology into dates with/without cyclones, we find that cyclones play only a secondary role in explaining the mean states differences between the SST experiments.
Comparing simulations with realistic and smoothed SSTs, we find that the intensification of...
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