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The characterisation of orographic rainfall

Published online by Cambridge University Press:  21 November 2000

W R Gray  and
A W Seed
W R Gray
Affiliation:
National Institute of Water and Atmosphere, P.O. Box 14-901, Kilbirnie, Wellington, New Zealand
A W Seed
Affiliation:
Co-operative Research Centre for Catchment Hydrology, Bureau of Meteorology, GPO Box 1289K, Melbourne, Victoria 3001, Australia
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Abstract

The Otaki Precipitation Estimation by Radar (OPERA) programme was designed to investigate the processes that lead to enhancement of rainfall over the Tararua ranges of New Zealand. These ranges rise to 1500 m above the coastal plain and enhancement of rainfall by windflow over these hills leads to annual hill-top rainfall of over four times that upwind. The OPERA experimental campaigns aimed to characterise the enhancement processes by analysing data collected from a transect of high-resolution rain gauges and a locally deployed, high-resolution radar, supported by scanning radar and satellite observations. Measurements made during these experiments showed that orographic enhancement led to hill-top accumulations often twice that upwind, and up to as much as a factor of seven in one case. The data suggest that the most frequent occurring enhancement mechanism was triggered convection. This mechanism leads to an increase in rainfall over the hills of around a factor of two, primarily through an increase inthe duration of rain. Seeder/feeder-type enhancement occurs less frequently but leads to larger enhancements.

Type
Research Article
Information
Meteorological Applications , Volume 7 , Issue 2 , June 2000 , pp. 105 - 119
Copyright
© 2000 Cambridge University Press

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