Formation mechanism and multi-decadal modulation of the Aleutian-Icelandic low seesaw: Distinctive chacteristics from the annular mode

Details Formation mechanism and multi-decadal modulation of the Aleutian-Icelandic low seesaw: Distinctive chacteristics from the annular mode Formation mechanism and multi-decadal modulation of the Aleutian-Icelandic low seesaw: Distinctive chacteristics from the annular mode

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.a22d..03y&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #A22D-03

Other

3319 General Circulation, 3346 Planetary Meteorology (5445, 5739), 3349 Polar Meteorology, 3364 Synoptic-Scale Meteorology

Scientific paper

It has recently been argued that interannual variability in the atmospheric circulation over the wintertime North Atlantic, including the intensity of the Icelandic Low (IL), is strongly influenced by the Northern Hemisphere annular mode (NAM). As recently found by the authors, the North Atlantic is also under the significant influence from the North Pacific in the form of a late-winter seesaw between the IL and Aleutian Low (AL). The NAM and the upper-tropospheric manifestation of the AL-IL seesaw (i.e., a combination of the PNA pattern and NAO) were the most dominant anomaly patterns in the early and late winter periods, respectively, but their dynamics are fundamentally different. The NAM dynamics is basically the adjustment of a polar vortex through its interaction with planetary waves, whereas the seesaw formation is through propagation of stationary Rossby wave trains with the strong feedback forcing from storm tracks. The distinction is elucidated in presenting the specifics of the seesaw formation in the late January 2002, through diagnoses of wave activity propagation, eddy feedback and the stability of the zonally varying westerlies. The IL intensified as a couple of Rossby wave packets reached into the Atlantic across North America one after another, both of which had been emanated from the anticyclonic AL anomalies. Which of the two dominant anomaly patterns is more dominant has been changed on multi-decadal scales during the last century. In the 1950s and 1960s, the NAM was predominant. In such periods as the 1930s and 1940s and also since 1970s, the AL-IL seesaw was more dominant and the IL anomalies in a month of the seesaw completion tend to be significantly correlated with the AL anomalies with the opposite sign in the previous month. We will show whether the aforementioned multi-decadal modulations can be related to any modulated behavior of wave-activity propagation across North America and any modulation in the wave guide structure.

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