Decadal climate variability in Australia during the twentieth century

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 decadal variability and to ascertain if there is any relationship with sea-surface temperature (SST) variability over adjacent oceans on the same time scale. The decadal signal was estimated by low-pass filtering detrended annual averages of gridded data covering the entire continent to eliminate all spectral contributions with periods less than or equal to 8 years. Such variability typically accounts for 10-60% of the total variance. Low-pass filtering does not appear to affect the structure of the leading empirical orthogonal functions (EOFs) of rainfall and temperature, and the variability of all-Australia averages of these quantities are reasonably well-modeled as red noise, for which there is no preference for decadal time scales. Decadal variability in Indian Ocean SST south of 40°S is associated with rainfall variability over eastern Australia. A tendency for increased Tasman Sea SST (south of 15°S) to coincide with the above normal central 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 variability over Australia. This is not surprising as the EOF has an amplitude that tends to be out of phase with the Southern Oscillation Index (SOI). A similar relationship exists between the EOF of decadal SST variability and decadal fluctuations in both rainfall and the SOI. The first EOF of decadal Pacific 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 study, which is available back to the turn of the century. When the decadal SST EOF warms the central Pacific, Australian rainfall is reduced, and both the daily maximum temperature and the diurnal temperature range over Australia are increased. These changes are consistent with radiative and evaporative changes associated with fluctuations in rainfall, cloud cover and soil moisture.