Temporal and Spatial Scales of the Arctic Circulation

Abstract

Daily data for the years 1932?75 are used in a study of the fluctuations in the arctic circulation over time scales of several days to several months. An updated set of normal sea level pressures is constructed, and a semiannual cycle is found in the high-latitude gradient of zonally averaged pressure. July is the only month in which a mean convergence of the low-level flow into the central arctic is indicated. The high-latitude fields of sea level pressure, surface temperature and 700 mb height and temperature are represented in terms of empirical orthogonal functions in order to isolate the dominant modes of variability. The amplitudes of the functions are used to evaluate the daily persistence of arctic pressure anomalies as a function of season and to compare the persistence of arctic and midlatitude pressure anomalies. The month-to-month persistence of arctic pressure anomalies is found to be small, although the monthly persistence does exceed that expected from the lagged autocorrelations of the daily data. Cross correlations between the anomaly fields of pressure (height) and temperature at the surface and 700 mb are evaluated at lags ranging from ?8 to +8 months. The cross correlations differ substantially from zero only at 0 lag. Fluctuations in the first eigenvector of 700 mb temperature are in surprisingly good agreement with the surface temperature fluctuations reported in an earlier paper.