Is There a Relationship between the SAM and Southwest Western Australian Winter Rainfall?

Juan Feng State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, and College of Atmospheric Sciences, Lanzhou University, Lanzhou, China

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Jianping Li State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

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Yun Li CSIRO Mathematical and Information Sciences, Wembley, Western Australia, Australia

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Abstract

Previous studies have raised the possibility that the recent decline in winter rainfall over southwest Western Australia (SWWA) is related to the concurrent upward trend in the southern annular mode (SAM). On the basis of an analysis of 60-yr (1948–2007) reanalysis and observed data, the authors suggest that the apparent inverse relationship between the SAM and SWWA winter rainfall (SWR) is caused by a single extreme year—1964. It is shown that both the negative and positive phases of the SAM have little impact on SWR in the case that data for 1964 are excluded from the analysis. In addition, for periods prior to and after 1964 in the case that data for 1964 are excluded, the apparent relationship between the SAM and SWR becomes insignificant, and the circulation anomalies with respect to SWR appear to be an SAM-like pattern for which the anomalies at high latitudes are not significant. The result indicates that the SAM does not significantly influence the winter rainfall over SWWA. Instead, the variation of SWR would be more closely linked to the variability in regional circulations.

Corresponding author address: Dr Jianping Li, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China. Email: ljp@lasg.iap.ac.cn

Abstract

Previous studies have raised the possibility that the recent decline in winter rainfall over southwest Western Australia (SWWA) is related to the concurrent upward trend in the southern annular mode (SAM). On the basis of an analysis of 60-yr (1948–2007) reanalysis and observed data, the authors suggest that the apparent inverse relationship between the SAM and SWWA winter rainfall (SWR) is caused by a single extreme year—1964. It is shown that both the negative and positive phases of the SAM have little impact on SWR in the case that data for 1964 are excluded from the analysis. In addition, for periods prior to and after 1964 in the case that data for 1964 are excluded, the apparent relationship between the SAM and SWR becomes insignificant, and the circulation anomalies with respect to SWR appear to be an SAM-like pattern for which the anomalies at high latitudes are not significant. The result indicates that the SAM does not significantly influence the winter rainfall over SWWA. Instead, the variation of SWR would be more closely linked to the variability in regional circulations.

Corresponding author address: Dr Jianping Li, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China. Email: ljp@lasg.iap.ac.cn

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