Extreme midlatitude cyclones and their implications for precipitation and wind speed extremes in simulations of the Maunder Minimum versus present day conditions |
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| Authors: | C C Raible M Yoshimori T F Stocker C Casty |
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| Institution: | (1) Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland;(2) Present address: Center for Environmental Prediction, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901-8551, USA;(3) International Pacific Research Center, SOEST, University of Hawai’i, Honolulu, HI, USA |
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| Abstract: | Extreme midlatitude cyclone characteristics, precipitation, wind speed events, their inter-relationships, and the connection
to large-scale atmospheric patterns are investigated in simulations of a prolonged cold period, known as the Maunder Minimum
from 1640 to 1715 and compared with today. An ensemble of six simulations for the Maunder Minimum as well as a control simulation
for perpetual 1990 conditions are carried out with a coupled atmosphere-ocean general circulation model, i.e., the Climate
Community System Model (CCSM). The comparison of the simulations shows that in a climate state colder than today the occurrence
of cyclones, the extreme events of precipitation and wind speed shift southward in all seasons in the North Atlantic and the
North Pacific. The extremes of cyclone intensity increases significantly in winter in almost all regions, which is related
to a stronger meridional temperature gradient and an increase in lower tropospheric baroclinicity. Extremes of cyclone intensity
in subregions of the North Atlantic are related to extremes in precipitation and in wind speed during winter. Moreover, extremes
of cyclone intensity are also connected to distinct large-scale atmospheric patterns for the different subregions, but these
relationships vanish during summer. Analyzing the mean 1,000 hPa geopotential height change of the Maunder Minimum simulations
compared with the control simulation, we find a similar pattern as the correlation pattern with the cyclone intensity index
of the southern Europe cyclones. This illustrates that changes in the atmospheric high-frequency, i.e., the simulated southward
shift of cyclones in the North Atlantic and the related increase of extreme precipitation and wind speed in particular in
the Mediterranean in winter, are associated with large-scale atmospheric circulation changes. |
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