Cyclonic and anticyclonic regimes

Proshutinsky and Johnson [1997] document two regimes of wind-forced circulation of the Arctic Ocean. They simulated ocean currents, sea level height and ice drift on the Arctic Ocean from 1946 to 1993 using a two-dimensional, wind-forced model that includes coupling between the ocean and ice. Based on the modeled sea level and ice motion, the wind-driven circulation in the central Arctic alternates between cyclonic and anticyclonic regimes, with each regime persisting from 5 to 7 years. Anticyclonic motion appeared during 1946-52, 1958-63, 1972-9 and 1984-8. Cyclonic motion prevailed for 1953-7, 1964-71, 1980-3 and 1989-93.

The transition between these periods is evident in time series of modeled sea level gradients (slope of the sea surface) for the central Arctic Basin (Figure 11.19). During the anticyclonic periods, the Beaufort Gyre is well expressed. During the cyclonic periods, the Beaufort Gyre circulation is poorly expressed and ice motion near the Pole has a strong cyclonic component. Proshutinsky and Johnson [1997] speculate that the shift between regimes may be triggered by SST in the far northern Atlantic. Positive SST anomalies drive the formation of a tongue of low atmospheric pressure toward the Arctic that may develop into a broad cyclonic atmospheric pattern. If the SST anomaly is negative, then high pressure sets up an anticyclonic circulation. There would seem to be some relationship between the two modes and the NAO/AO. Note in particular how the change from the positive sea level gradient of 1972-9 (anticyclonic) to the generally negative gradient (1980 onwards) broadly corresponds to the upward tendency in the winter NAO/AO.

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