A Qualitative Assessment of the Australian Tropical Region Analyses

Harry H. Hendon CSIRO, Division of Atmospheric Research, Aspendale, Victoria, Australia

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Abstract

The Bureau of Meteorology, Australia, routinely analyzes the tropospheric winds over the Australian Tropical Region (40°S–40°N, 70°–180°E). These wind data are assimilated without the use of a forecast model. While being free of any model bias, the optimum interpolation scheme imposes no dynamical constraints on the winds. To assess the realism of the Australian Tropical Region analyses, a qualitative comparison with gridded ECMWF wind data and OLR (as a proxy for tropical convection) is conducted.

In general, the depiction of the large-scale tropical circulation of the Australian Tropical Region analyses is quite reasonable. The gross features of the Australian and Asian Monsoons seem equally captured by both the ECMWF and Australian analyses. The seasonal development of the two monsoons and the relationship between the vertical structure of the divergence and zonal wind depicted in the Australian analyses agree well with previous theoretical and observational studies. Subtle differences (such as with the phase of the upper level anticyclones relative to the divergence) between the theory and the dynamics inferred from the Australian analyses are highlighted. However, we conclude that these objectively analyzed tropospheric winds are a valuable data resource for both the comparison with forecast model assimilated data and for deduction of physical processes.

Abstract

The Bureau of Meteorology, Australia, routinely analyzes the tropospheric winds over the Australian Tropical Region (40°S–40°N, 70°–180°E). These wind data are assimilated without the use of a forecast model. While being free of any model bias, the optimum interpolation scheme imposes no dynamical constraints on the winds. To assess the realism of the Australian Tropical Region analyses, a qualitative comparison with gridded ECMWF wind data and OLR (as a proxy for tropical convection) is conducted.

In general, the depiction of the large-scale tropical circulation of the Australian Tropical Region analyses is quite reasonable. The gross features of the Australian and Asian Monsoons seem equally captured by both the ECMWF and Australian analyses. The seasonal development of the two monsoons and the relationship between the vertical structure of the divergence and zonal wind depicted in the Australian analyses agree well with previous theoretical and observational studies. Subtle differences (such as with the phase of the upper level anticyclones relative to the divergence) between the theory and the dynamics inferred from the Australian analyses are highlighted. However, we conclude that these objectively analyzed tropospheric winds are a valuable data resource for both the comparison with forecast model assimilated data and for deduction of physical processes.

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