Mid latitude Atlantic SST influence on European winter climate variability in the NCEP Reanalysis |
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| Authors: | M Drévillon L Terray P Rogel C Cassou |
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| Institution: | (1) Climate Modelling and Global Change Project CERFACS/SUC URA 1875, 42, Avenue Gustave Coriolis, 31057 Toulouse Cedex, France E-mail: drevillo@cerfacs.fr, FR |
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| Abstract: | Forty one years (1958–1998) of NCEP reanalysis data are used to perform a set of statistical analyses, investigating the
interactions between the sea surface temperature (SST), the storm track activity (STA) and the time mean atmospheric circulation
in the North Atlantic-Europe (NAE) region. When the atmospheric region of study is restricted to Europe, the singular value
decomposition (SVD) lead-lag analysis between seasonal 500 hPa geopotential height (Z500) and SST captures a significant covariance
between a summer SST anomaly and a strong winter anticyclonic anomaly over Europe. The summer SST pattern is close to the
first empirical orthogonal function (EOF) of SST for the consecutive months J-A-S-O-N. The same analysis, but extending the
atmospheric area of interest to the entire NAE region, points out the same signal with a phase shift of one month. A more
zonally oriented North-Atlantic-Oscillation-like (NAO) pattern is then found as the SST structure remains practically unchanged.
This summer SST anomaly is found to persist through surface heat fluxes exchanges until winter, when it can finally have an
impact on the atmospheric circulation. Composites are made from the former SST SVD scores, showing the winter STA and different
transient and stationary eddies diagnostics associated with the extreme positive and negative events of the SST anomaly. These
suggest that the SST anomaly induces an anomalous stationary wave in winter, creating an initially small anticyclonic anomaly
over Europe. Anomalous transient eddies located over northern Europe then strengthen this anomaly and maintain it during winter,
thus acting as a positive feedback.
Received: 15 September 2000 / Accepted: 17 April 2001 |
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