A possible cause of decreasing summer rainfall in northeast Australia

Abstract

ABSTRACT:The NCEP/NCAR reanalysis and precipitation data from the Australian Bureau of Meteorology are used to analyse variability in rainfall during the austral summer (December-March, DJFM) in northeast Australia (NEA). NEA rainfall shows a marked decrease over the past 50 years, mainly in the austral summer. Our analysis reveals that the summer rainfall decrease in NEA is generally an interdecadal phenomenon. The declining trend has an imprint in the tropical Australian summer monsoon (TASM). Not only does TASM have a phase-to-phase influence on NEA summer rainfall at the interannual scale, it is also closely linked with interdecadal variation in NEA summer rainfall. Thus, the decrease in NEA at the interdecadal scale could be attributed to corresponding variation in TASM. Moreover, the coupled linkage between TASM and NEA summer rainfall appears to be largely independent of El Niño-Southern Oscillation. One possible reason for the interdecadal weakening trend in TASM is a sustained interdecadal warming trend in sea surface temperature (SST) over the Wharton Basin (100°-130°E, 20°-5°S). When the Wharton Basin is in a cold state, anomalous westerlies occur in the lower troposphere in the TASM region, and cyclonic circulation anomalies and rising flows occur in the low and middle troposphere over NEA, which are associated with a strong TASM situation, consequently favouring enhanced rainfall over NEA; the opposite occurs in the case of a warm Wharton Basin. SST over the Wharton Basin has shown a continuous warming trend over the past 60 years, contributing to the weakening of TASM and, consequently, a decrease in NEA summer rainfall.

Contrasting Impacts of Two Types of ENSO on the Boreal Spring Hadley Circulation

“…Second, the mass streamfunction (MSF) of the mean meridional circulation is adopted. The MSF is obtained by vertically integrating meridional winds in the conventional way (Li 2001) and is defined by…”

Water Discharge and Sediment Load Changes in China: Change Patterns, Causes, and Implications

“…The Asian monsoon indices were created by Li [46,47], and WI was derived from National Centers for Environmental Prediction (NCEP) reanalysis data. The TPMI was calculated from NCEP 600 mb height reanalysis data based on the method given by Wang [48].…”

Decadal-scale teleconnection between South Atlantic SST and southeast Australia surface air temperature in austral summer

“…The El Niño-Southern Oscillation (ENSO) (Taschetto and England 2009;Cai et al 2011;Ummenhofer et al 2011), Indian Ocean Dipole (IOD) (Risbey et al 2009;Cai et al 2011), Southern Hemisphere annular mode (SAM) (Hendon et al 2007;Meneghini et al 2007;Risbey et al 2009;Feng et al 2010a), sea surface temperature (SST) in the Wharton Basin (Li et al 2012a) and monsoon-like Southwest Australian circulation (SWAC) (Feng et al 2010b(Feng et al , 2015Li et al 2011) are all reported to modulate Australian rainfall on interannual time scales. On decadal time scales, positive (negative) phases of the Interdecadal Pacific Oscillation (IPO) can induce reduced (increased) rainfall in eastern Australia (Verdon et al 2004;Dong and Dai 2015).…”