The windfield and rainfall distribution induced within a small valley: Field observations and 2-D numerical modelling

A. Arazi, D. Sharon, A. Khain, A. Huss, Y. Mahrer

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


The distribution of rainfall over small-scale topography of uniform roughness was studied both numerically and from field observations. Field data have shown that small-scale topographic inhomogeneities (hills and valleys of a few tens of metres in height) substantially influence the rainfall distribution over the inhomogeneity itself and also some distance downwind from it. According to comprehensive rainfall measurements carried out in a small watershed, windward slopes received less conventionally-measured rain than lee-sides. Moreover, on the windward slope rainfall decreased uphill, to a pronounced minimum near the crest. In addition, 'directional' raingages, situated at the bottom of both slopes revealed a pattern suggesting a reversed surface flow on the lower slopes. This pattern persisted through a variety of background conditions. To explain the observed data, a numerical simulation of both the windfield and of drop trajectories was carried out. The windfield was generated in simulations using the Colorado State University RAMS model with a very high resolution (5 m in the horizontal). Drop trajectories were calculated using an equation for the motion of drops in a flow field that incorporates current experimental results. A strong effect of small-scale topography on drop trajectories was found. The simulation results are encouraging and help to explain many characteristic features of precipitation distributions observed in field experiments.

Original languageEnglish
Pages (from-to)349-374
Number of pages26
JournalBoundary-Layer Meteorology
Issue number3
StatePublished - 1 Jan 1997
Externally publishedYes


  • Rainfall
  • Small-scale topography
  • Windfield modelling

ASJC Scopus subject areas

  • Atmospheric Science


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