On Atmospheric Pressure Oscillations Along the Pacific Coast of North America, 1873–1963

Abstract

An analysis is made of 90-year sea level atmospheric pressure records along the Pacific coast of North America and in adjacent regions. An investigation of the power spectra of monthly mean and extreme pressure fluctuations in the frequency range between 0 and 6 cycles per year showed that significant periodicities were associated only with the annual and semiannual pressure oscillations, and that there have been no secular changes. The amplitude of the annual pressure oscillation varies between 1 and 7 mb, that of the semiannual one between 1 and 3 mb. Large amplitude changes over short distances are observed when proceeding from a maritime to a desert environment. The extreme pressure range at individual stations varies from 33 mb in Hawaii to 94 mb in Alaska. The mean duration of positive and negative pressure anomalies (from long term monthly means) is of the order of 2 or 3 months; the extreme duration of these anomalies varies between 10 and 20 months. The probability functions for the extremes and the mean duration agree with those expected from theory for a stationary random variable. Nonseasonal pressure oscillations along the Pacific coast are coherent over distances of 1200 to 1500 km; good coherence is also observed across coastal mountain ranges. There is a significant and inverse relationship between nonseasonal pressure and precipitation oscillations in the Pacific Northwest. Along the California coast there is a moderate and inverse relation between nonseasonal fluctuations of pressure and sea temperature at low frequencies.