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doi:10.5194/esd-2016-67
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
15 Dec 2016
Review status
This discussion paper is under review for the journal Earth System Dynamics (ESD).
Sensitivity Experiments on the Response of Vb Cyclones to Ocean Temperature and Soil Moisture Changes
Martina Messmer1,2, Juan José Gómez-Navarro1,2,a, and Christoph C. Raible1,2 1Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland
2Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
anow at: Department of Physics, University of Murcia, Murcia, Spain
Abstract. Extra-tropical cyclones of type Vb, which develop over the western Mediterranean and move northeastward, are major natural hazards being responsible for heavy precipitation over Central Europe. To gain further understanding in the governing processes of these Vb cyclones the stu-dy explores the role of soil moisture and sea surface temperature (SST) and their contribution to the atmospheric moisture content. Thereby, recent Vb events identified in the ERA-Interim reanalysis are dynamically downscaled with the Weather Research and Forecasting model (WRF). Results indicate that a mean Vb event is mostly sensitive to an increase in the Mediterranean SSTs, e.g., an increase of +5 K leads to an average increase of 24 % in precipitation over Central Europe. This increase in precipitation is mainly induced by larger mean upward moisture flux over the Mediterranean with increasing Mediterranean SSTs. This further invokes an increase in latent energy release, which leads to an increase in atmospheric instability, i.e., in convective available potential energy. Both, the increased availability of atmospheric moisture and the increased instability of the atmosphere, which is able to remove extra moisture from the atmosphere due to convective processes, are responsible for the strong increase in precipitation over the entire region influenced by Vb events. Precipitation patterns further indicate that a strong increase in precipitation is found at the eastern coast of the Adriatic Sea for increased Mediterranean SSTs. This premature loss in atmospheric moisture leads to a significant decrease in atmospheric moisture transport to Central Europe and the northeastern flanks of the Alpine mountain chain. This leads to a reduction in precipitation in this high-impact region of the Vb event for an increase in Mediterranean SSTs of +5 K. Furthermore, the intensity of the Vb cyclones, measured as a gradient in the 850-hPa geopotential height field around the cyclone centre, indicates that an upper bound for intensity might be reached for the most intense Vb event. This fact indicates that strong cyclones are more strongly steered by the present atmospheric conditions.

Citation: Messmer, M., Gómez-Navarro, J. J., and Raible, C. C.: Sensitivity Experiments on the Response of Vb Cyclones to Ocean Temperature and Soil Moisture Changes, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2016-67, in review, 2016.
Martina Messmer et al.
Martina Messmer et al.
Martina Messmer et al.

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