Anomalous rainfall over southwest Western Australia forced by Indian Ocean sea surface temperatures

作者：Ummenhofer Caroline C^*; Sen Gupta Alexander; Pook Michael J; England Matthew H

来源：Journal of Climate, 2008, 21(19): 5113-5134.

DOI：10.1175/2008JCLI2227.1

The potential impact of Indian Ocean sea surface temperature (SST) anomalies in modulating midlatitude precipitation across southern and western regions of Australia is assessed in a series of atmospheric general circulation model (AGCM) simulations. Two sets of AGCM integrations forced with a seasonally evolving characteristic dipole pattern in Indian Ocean SST consistent with observed "dry year" (P-DRY) and "wet year" (P-WET) signatures are shown to induce precipitation changes across western regions of Australia. Over Western Australia. a significant shift occurs in the winter and annual rainfall frequency with the distribution becoming skewed toward less (more) rainfall for the PDRY (P-WET) SST pattern. For southwest Western Australia (SWWA), this shift primarily is due to the large-scale stable precipitation. Convective precipitation actually increases in the P-DRY Case over SWWA forced by local positive SST anomalies. A mechanism for the large-scale rainfall shifts is proposed, by which the SST anomalies induce a reorganization of the large-scale atmospheric circulation across the Indian Ocean basin. Thickness (1000-500 hPa) anomalies develop in the atmosphere mirroring the sign and position of the underlying SST anomalies. This leads to a weakening (strengthening) of the meridional thickness gradient and the subtropical jet during the austral winter in P-DRY (P-WET). The subsequent easterly offshore (westerly onshore) anomaly in the thermal wind over southern regions of Australia, along with a decrease (increase) in baroclinicity, results in the lower (higher) levels of large-scale stable precipitation. Variations in the vertical thermal structure of the atmosphere overlying the SST anomalies favor localized increased convective activity in P-DRY because of differential temperature lapse rates. In contrast, enhanced widespread ascent of moist air masses associated with frontal movement in P-WET accounts for a significant increase in rainfall in that ensemble set.

• 出版日期2008-10
• 单位CSIRO