A Synoptic Study of Low Troposphere Wind at the Israeli Coast

Sigalit Berkovic,Pinhas Alpert

doi:10.2174/1874282301812010080

Abstract

Objective:This research is dedicated to the study of the feasibility of surface wind downscaling from 925 or 850 hPa winds according to synoptic class, season and hour.Methods:Two aspects are examined: low tropospheric wind veering and wind speed correlation and verification of the ERA-Interim analysis wind by comparison to radiosonde data at Beit Dagan, a station on the Israeli coast.Results:Relatively small (< 60°) cross angles between the 1000 hPa wind vector and the 925 hPa or 850 hPa wind vector at 12Z and high correlation (0.6-0.8) between the wind speed at the two levels were found only under winter lows. Relatively small cross angles and small wind speed correlation were found under highs to the west and Persian troughs.The verification of ERA-Interim analysis in comparison with radiosonde data has shown good prediction of wind direction at 12Z at 1000, 925 and 850 hPa levels (RMSE 20°-60°) and lower prediction quality at 1000 hPa at 0Z (RMSE 60°-90°). The analysis under-predicts the wind speed, especially at 1000 hPa. The wind speed RMSE is 1-2 m/s, except for winter lows with 2-3 m/s RMSE at 0Z, 12Z at all levels.Conclusion:Inference of surface wind may be possible at 12Z from 925 or 825 hPa winds under winter lows. Inference of wind direction from 925 hPa winds may be possible under highs to the west and Persian troughs. Wind speed should be inferred by interpolation, according to historical data of measurements or high resolution model.

Highlights

Deep winter cyclones over the Eastern Mediterranean are accompanied by extreme western wind events over Israel e.g [1, 2]
Under the winter lows (LE-D CLN-D CLN-S low to the west (LW) low to the east (LE-S), presented at the right 10 columns of the figures) at 12Z small CA925 (SC) values are found 77-93% of the time – (Table 3) PT’s and Hw adhere to the SC criterion in 74-100% of the cases
These relatively small Cross Angle (CA) values result from the fact that the 925 hPa level is below the boundary layer height, when mostly neutral thermal stability is dominant

Summary

Introduction

Deep winter cyclones over the Eastern Mediterranean are accompanied by extreme western wind events over Israel e.g [1, 2]. A critical effect of these extreme winds is the erosion of the coastline and the need for civil authorities to prepare for this challenge [3 - 5]. A possible way is to use weather models; this effort demands extensive resources. Statistical downscaling of extreme surface wind events is needed. Global climate models often underestimate the wind at 1000 hPa [5 - 7], and sometimes the 1000 hPa is not available [8]. The ability to infer surface winds from low troposphere data should be considered. This work examines the feasibility to employ data from

Methods

Results

Conclusion