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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-2019-6
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2019-6
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Sep 2019

Submitted as: research article | 13 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Weather and Climate Dynamics (WCD).

Extratropical cyclone induced sea surface temperature anomalies in the 2013/14 winter

Helen F. Dacre1, Simon A. Josey2, and Alan L. M. Grant1 Helen F. Dacre et al.
  • 1University of Reading
  • 2National Oceanography Centre

Abstract. The 2013/14 winter averaged sea surface temperature (SST) was anomalously cool in the mid-North Atlantic region. This season was also unusually stormy with extratropical cyclones passing over the mid-North Atlantic every 3 days. However, the processes by which cyclones contribute towards seasonal SST anomalies are not fully understood. In this paper a cyclone identification and tracking method is combined with ECMWF atmosphere and ocean reanalysis fields to calculate cyclone-relative net surface heat flux anomalies and resulting SST changes. Anomalously large negative heat fluxes are located behind the cyclones cold front resulting in anomalous cooling up to 0.2 K/day when the cyclones are at maximum intensity. This extratropical cyclone induced cold wake extends along the cyclones cold front but is small compared to climatological variability. To investigate the potential cumulative effect of the passage of multiple cyclone induced SST cooling in the same location we calculate Earth-relative net surface heat flux anomalies and resulting SST changes for the 2013/2014 winter period. Anomalously large winter averaged negative heat fluxes occur in a zonally orientated band extending across the North Atlantic between 40–60° N. The anomaly associated with cyclones is estimated using a cyclone masking technique which encompasses each cyclone centre and its trailing cold front. North Atlantic extratropical cyclones in the 2013/14 winter season account for 78 % of the observed net surface heat flux in the mid- North Atlantic and net surface heat fluxes in the 2013/14 winter season account for 70 % of the observed cooling in the mid-North Atlantic. Thus extratropical cyclones play a major role in determining the extreme 2013/2014 winter season SST cooling.

Helen F. Dacre et al.
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Helen F. Dacre et al.
Helen F. Dacre et al.
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Short summary
The 2013/14 winter sea surface temperature (SST) was anomalously cool in the mid-North Atlantic region. We investigate the processes by which cyclones can lead to SST cooling and their contribution towards the 2013/14 SST anomaly. We find that cyclones induce a cold wake, which extends along the cyclones cold front. Cyclones account for over half of the observed cooling in the mid-North Atlantic. Thus, cyclones play a major role in determining the extreme 2013/2014 winter SST cooling.
The 2013/14 winter sea surface temperature (SST) was anomalously cool in the mid-North Atlantic...
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