Analysis of a scheme to dynamically model the orographic enhancement of precipitation in the UK

摘要

Gauge data in upland regions of the UK is sparse and often misrepresents intense precipitation events over small catchments. The production of flash flood warnings relies on high resolution input from the radar composite. It is therefore important that radar measurements of rainfall rate are as accurate as possible and account for the effects of orographic enhancements well. Within the Met Office, the Alpert & Shafir (1989) physically-based method of calculating the orographic enhancement of precipitation has recently replaced the previously operational climatology based one described by Hill (1983). The Alpert & Shafir model takes into account wind speed, wind direction, relative humidity, temperature and the topography of the region. The benefits of using a physical model are numerous. The corrections can be defined at much higher spatial resolution, with the possibility of introducing new fields, such as the vertical wind profile, and making further improvements to the physical model. The offline and operational trial results, as well as results from a post implementation analysis show that accuracy of the precipitation estimates is improved when using Alpert & Shafir's method.