Links between Tasmanian precipitation variability and the Indian Ocean subtropical high

The relationship between the Indian Ocean High (IOH) and austral autumn (March–May) precipitation variability over Tasmania during 1951–2016 is described. We present evidence that changes in autumn rainfall are influenced primarily by a strength of the Indian Ocean high pressure (IOH_P) and its longitudinal position (IOH_LN). The variation of the IOH shows a clear influence on the seasonal variability of precipitation over Tasmania. The most important factor of autumn precipitation variability is found to be IOH_P system, particularly in the regions neighboring the west coast. Positive anomalies of IOH_P are associated with less precipitation over the island. In addition, the overall eastward shift of the center of the IOH, i.e., IOH_LN, also plays a significant role in rainfall reduction. These two effects are found to be effectively statistically independent with each other. A multi-linear statistical model of autumn precipitation in Tasmania using the IOH_P and IOH_P accounts for 43% of the precipitation variability during 1951–2016. A series of well-defined atmospheric circulation composite analyses are identified during dry (wet) Tasmanian autumn mean sea level pressure, 850 hPa vector wind, and 850 hPa vertical wind velocity over the Indian Ocean. These circulations generate abnormally strong (weak) westerly winds along much of the western Tasmania which is responsible to provide more (less) moisture over Tasmania.