Abstract
Midlatitude storm tracks are preferred regions of intense activity of synoptic eddies shaping the day-to-day weather and several aspects of surface climate. Here statistical analyses of observationally-based atmospheric data and observed Arctic sea ice concentration (SIC) in the period 1979–2017 are used to identify linkages of a dominant mode of interannual variability in wintertime upper-tropospheric storm track activity over Eurasia (STAEA mode) to the concurrent surface climate anomalies and pre-winter Arctic SIC variations. This mode explains an exceptionally large fraction (about 70% of the variance) of the North Atlantic Oscillation (NAO) and of a dominant mode of Eurasian surface air temperature variations. As more than 50% of the variance of the STAEA mode and NAO is found to be accounted for by October SIC anomalies in the Barents/Kara Sea, it is concluded that wintertime Eurasian climate variability is to some extent predictable and that this predictability might have increased after an acceleration of the sea ice cover decline in the mid 2000s. These conclusions are supported by results from leave-1-yr-out cross-validated forecast experiments.
Highlights
The extratropical weather and climate at the earth’s surface and throughout the troposphere depend profoundly on formation, propagation and decay of midlatitude, synoptic-scale, short-lived storms[1,2,3]
Previous studies on dominant regional and hemispheric modes of storm track variability, based on time series covering approximately the second half of the 20th century, have emphasised a link of the North Atlantic Oscillation (NAO) and its hemispheric generalisation, the so-called Arctic Oscillation[52], to “pulsating” modes of storm track activity (STA) variability characterised by a variable amplitude of anomalies but negligible spatial displacements[46,53]
This mode is related to the NAO index even more tightly if computed over extratropical Eurasia instead of the North Atlantic region
Summary
Midlatitude storm tracks are preferred regions of intense activity of synoptic eddies shaping the day-today weather and several aspects of surface climate. Anomalies of SAT in Asia north of 35°N (averaged over the black box in Fig. 5a) correlates even higher with the STAEA index (r = 0.79) than with the NAO index (r = 0.74) This suggests a scenario in which the anomalous upper-tropospheric circulation over Asia (“Lake Baikal” vortex) is a key agent coupling wintertime air temperature anomalies in this area to the storm track variations in the Euro-Atlantic sector. A significant relation of wintertime storm track variations over Eurasia to pre-winter sea ice cover anomalies in the northern Barents/Kara Sea is illustrated in Fig. 7a showing the pattern of October SIC anomalies regressed on the following winter STAEA index. The latter value is very close to the anomaly correlation coefficient of 0.51 between the same (domain-based DJF-mean) observed NAO index in the period 1980–2015 and its leave-1-yr-out empirical prediction from a PC-based index of the Arctic sea ice cover variability in October reported in ref.[41]
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