Decadal climate variability in Australia during the twentieth century

High quality rainfall and surface temperature records for Australia during the period 1910-1993 are examined to quantify the relative importance of de cadal variability and to ascertain if there is any relationship with sea-su rface temperature (SST) variability over adjacent oceans on the same time s cale. The decadal signal was estimated by low-pass filtering detrended annu al averages of gridded data covering the entire continent to eliminate all spectral contributions with periods less than or equal to 8 years. Such var iability typically accounts for 10-60% of the total variance. Low-pass filtering does not appear to affect the structure of the leading e mpirical orthogonal functions (EOFs) of rainfall and temperature, and the v ariability of all-Australia averages of these quantities are reasonably wel l-modeled as red noise, for which there is no preference for decadal time s cales. Decadal variability in Indian Ocean SST south of 40 degrees S is associated with rainfall variability over eastern Australia. A tendency for increased Tasman Sea SST (south of 15 degrees S) to coincide with the above normal c entral and eastern Australian rainfall on both interannual and decadal time scales is also evident. The first EOF of interannual Pacific SST is associated with rainfall variab ility over Australia. This is not surprising as the EOF has an amplitude th at tends to be out of phase with the Southern Oscillation Index (SOI). A si milar relationship exists between the EOF of decadal SST variability and de cadal fluctuations in both rainfall and the SOI. The first EOF of decadal P acific SST has a broad spatial structure extending into the North and South Pacific. It has a time coefficient that is well-represented by the decadal component of the (northern) winter-time SST EOF produced in a separate stu dy, which is available back to the turn of the century. When the decadal SS T EOF warms the central Pacific, Australian rainfall is reduced, and both t he daily maximum temperature and the diurnal temperature range over Austral ia are increased. These changes are consistent with radiative and evaporati ve changes associated with fluctuations in rainfall, cloud cover and soil m oisture. Copyright (C) 1999 Royal Meteorological Society.