TY - JOUR
T1 - The windfield and rainfall distribution induced within a small valley
T2 - Field observations and 2-D numerical modelling
AU - Arazi, A.
AU - Sharon, D.
AU - Khain, A.
AU - Huss, A.
AU - Mahrer, Y.
N1 - Funding Information:
This study was carried out in part under project IS-14-86-88 financed by the US.-Israel Binational Research and Development Fund (BARD). Special thanks to Mr. Simon Berkowicz for his kind help in editing.
PY - 1997/1/1
Y1 - 1997/1/1
N2 - 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.
AB - 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.
KW - Rainfall
KW - Small-scale topography
KW - Windfield modelling
UR - http://www.scopus.com/inward/record.url?scp=0031407986&partnerID=8YFLogxK
U2 - 10.1023/A:1000243312103
DO - 10.1023/A:1000243312103
M3 - Article
AN - SCOPUS:0031407986
SN - 0006-8314
VL - 83
SP - 349
EP - 374
JO - Boundary-Layer Meteorology
JF - Boundary-Layer Meteorology
IS - 3
ER -