Persistence of Daily Geopotential Heights over the Southern Hemisphere

An analysis has been made of the persistence of geopotential heights at 1000 and 500 mb over the Southern Hemisphere for both summer and winter seasons. The focus is on lagged autocorrelation T0 the effective time between independent samples and low order autoregressive (AR) models fit to the data. A red noise AR(1) model provides the best fit to the data over most of the domain, especially in midlatitudes. However, there are substantial areas where AR(2) and AR(3) processes provide the best fit and these areas are much the same at both levels and for both seasons. Over Antarctica low-frequency trends appear to provide persistence exceeding that of the red noise process and contribute to the higher order AR processes there. However, over Austalasia the AR(2) processes fit to the data imply a damped quasi-periodicity and T0 values less than for the corresponding red noise process. Such behavior may be linked to the 40–50 day oscillation of Madden and Julian. Smallest T0 values are found over the southern oceans and especially in the main storm track regions where developing synoptic systems and rapid advection contribute to reduce the autocorrelations and T0 values. Largest persistence is found over Antarctica, in low latitudes and across Australasia Persistence in these regions is greatly enhanced by interannual variability. In part, such low frequency variability over Australasia and in the tropics is associated with the Southern Oscillation, and is thus linked to low frequency coupling between the atmospheric circulation and sea surface temperatures. The overall meridional profile of autocorrelations is similar to that in the Northern Hemisphere but persistence is less in the Southern Hemisphere in both seasons. Factors contributing to the differences are discussed.