Interdecadal Modulations and Seasonal Dependence of the Icelandic and Aleutian Lows: Their Inter-Basin Link and Impacts on High-Latitude Climate
Abstract
The Icelandic and Aleutian lows (IL and AL, respectively) are wintertime semipermanent low-pressure systems over the North Atlantic and North Pacific, respectively. The interannual and intraseasonal IL and AL variability are closely related to the North Atlantic Oscillation (NAO) and Pacific-North American (PNA) pattern. Wintertime weather conditions in mid- to high-latitudes can be strongly influenced by variability of the two low pressure systems on multi-timescales. It has been found that an interannual seesaw-like oscillation exists between the AL and IL intensities (the AL- IL seesaw, AIS). The associated anomalies in surface air temperature (SAT) for the strong IL and weak AL are characterized as warmer conditions over the northern Europe, the southeastern US and the Far East, and colder conditions on the northern part of the North America and the Middle East. Since the seesaw formation is triggered by eastward propagation of stationary Rossby wave trains from the North Pacific into the North Atlantic, this upper-tropospheric downstream influence could be a basis for predicting climatic conditions in the Euro-Atlantic sector a month ahead. It is also known that the pronounced wintertime warming trend over landmasses observed in the recent decades is associated with concomitant deepening of the AL and IL intensities, a pattern akin to the "Cold Ocean Warm Land" (COWL) pattern, which is the opposite sense to the AIS. The associated SAT anomalies strongly reflect the recent weakening of a land-ocean contrast especially in high latitudes, suggestive of strong climatic impacts on the polar regions for the recent decades. Interestingly, these respective out-of-phase and in-phase relationships between the IL and AL can be identified as the two leading EOF modes of variability in the upper troposphere for the recent 50 or more winter seasons. Actually, interannual variability and long-term changes and "activeness" of the AIS and COWL for the last half century are essentially extracted in the two leading modes, which reflects the corresponding modulations in the strength of dynamical linkage between the North Pacific and North Atlantic in the upper troposphere. Further investigation based on more than hundred-year surface observational data set for the sea-level pressure and SAT shows that the AIS underwent multidecadal modulations and seasonal dependence during the 20th century. It was weak in the mid-1950s through the mid-1960s, while it was particularly strong during the preceding period from the 1920s to the 1940s with its impact on surface temperatures as extensive as in the recent period, although its maturity was in January. The COWL-related spatial structures and amplitudes have been also multidecadally modulated during the last century, which were not necessarily associated with the global warming trend, especially in the first half of the last century.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.U33A0024H
- Keywords:
-
- 1616 Climate variability (1635;
- 3305;
- 3309;
- 4215;
- 4513);
- 1620 Climate dynamics (0429;
- 3309);
- 3319 General circulation (1223);
- 3339 Ocean/atmosphere interactions (0312;
- 4504);
- 4215 Climate and interannual variability (1616;
- 1635;
- 3305;
- 3309;
- 4513)