On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas

Abstract

Monthly and 3‐day averaged NIMBUS 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the Bering Sea and Sea of Okhotsk ice covers for the four winters 1972–1973 through 1975–1976 on the short‐term, seasonal, and interannual time scales and to define those periods for which there is an out‐of‐phase relationship between the fluctuations of the two sea ice covers. The sea ice fluctuations are shown to be related to changes in the position and intensity of quasi‐stationary high‐ and low‐pressure systems associated with large‐scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1, 2, and 3 of the sea level pressure field. On the seasonal time scale, the sea level pressure for December, the month of most rapid seasonal sea ice growth for both the Bering and Okhotsk seas, is dominated by harmonic 2, which explains almost 60% of the total sea level pressure variance on average over the four winters. The phase of harmonic 2, which is associated with the position of the Aleutian Low, shifts from 156°E in 1972–1973 to 190°E in 1975–1976, thus providing a connection between the increasingly heavy Bering Sea ice cover over these four winters and the general circulation of the atmosphere. On the short‐term, episodes of midwinter Bering Sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3. These episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165°E. This result is in excellent agreement with a study of the North Pacific Oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the Aleutian Low. It is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1, 2, and 3. Evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations. Finally, these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones.