Autocorrelation of Northern Hemisphere Geopotential Heights

Abstract

Local autocorrelation statistics for the Northern Hemisphere geopotential height field are presented for different seasons and tropospheric pressure levels. Values are generally much higher than those calculated from time series of outgoing infrared radiation or eddy heat fluxes. The largest one-day lag autocorrelation values are observed over the polar regions and eastern oceans. Well-defined minima exist off the cast coasts of Asia and North America. The minima are most distinct in winter, and are shifted northward and weaker during summer. Otherwise, the pattern does not change drastically with season. These geographical patterns do not change much with height, but the minima are less sharply defined at upper tropospheric levels. At longer lags, the extratropical maxima remain distinct, but the minima shift westward over the continents and cover a broader area, as the autocorrelation approaches zero with increasing lag. Values remain high over the tropics, where height anomalies tend to persist for many days. A comparison of observed autocorrelations with red noise decay suggests that geographical variations in decay rates are associated with the relative importance of baroclinic and barotropic components to the total height variability and with advective effects on the local statistics.