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Hebrew University of (2017)

Characterization of convective rain-cells in the Dead Sea area using weather radar data

Belachsen, Idit

Titre : Characterization of convective rain-cells in the Dead Sea area using weather radar data

שער נוסף בעברית : איפיון תאי גשם קונבקטיביים באזור ים המלח באמצעות מכ"מ מזג אוויר‏

Auteur : Belachsen, Idit

Etablissement de soutenance : Hebrew University of Jerusalem

Grade : Master of Science (MS) 2017

Space-time patterns of rainfall are important characteristics that influence runoff generation and flash flood magnitude. Their derivation requires high-resolution measurements to adequately represent the distribution of rainfall in space and time. This need is further emphasized in dry climates, where rainfall is scarce and highly variable. This study takes advantage of 24 years of corrected and gauge-adjusted weather radar rainfall estimates to identify and characterize the spatial structure and the dynamics of convective rain cells in the dry Dead Sea region (Eastern Mediterranean). Rain cells from 424 rain events are extracted using a cell segmentation method and a tracking algorithm. A total of 10,447 rain cells and 2632 cell tracks are elicited. Rain cell properties, such as areal and maximal rain intensity, area, life span, velocity and direction, are derived. Rain events are clustered, according to several atmospheric parameters obtained from ERA-Interim reanalyses, and associated with three synoptic patterns : Cyprus low (30%), low to the east of the study region (44%) and active Red Sea Trough (26%). On average, the convective rain cells in the region are 92 km2 in size, move at velocity of 12.8 m s-1 from west to east and live for 18.1 minutes. Significant differences are observed in rain cells originated by different synoptic systems. Active Red Sea Trough events are characterized by the shortest event duration and by the highest cell mean areal rain intensity, smallest cell area, longest cell lifetime and lowest cell velocity. The area of rain cells generated by Mediterranean lows is positively correlated with the topographic height in the northern part of the study area, the number of cells is negatively correlated with the distance from the shoreline and the mean rain intensities are negatively correlated with mean annual rainfall. Rain cells related to flash-flood events are characterized by larger area, lower velocity and longer lifetime over the catchment. Rain cells with lower velocities (generally, <12 m s-1 ) and of north to north-western origins, directed downstream with the main catchment axis, lead to high magnitude flash-floods. Results from this study add insights and quantitative information to previous studies in the Dead Sea region and in other arid regions worldwide. This advocates the robustness of the methods applied and the adequacy of the radar data used to represent rainfall over the study area. The distributions of the convective rain cells characteristics extracted in this work can be used for stochastic simulations of convective rain storms and serve as input for hydrological models and for flash-flood nowcasting systems

Mots clés : Meteorological stations, Radar Rain and rainfall תחנות מטאורולוגיות, מכ"ם גשמים Dead Sea (Israel and Jordan) ים המלח (ישראל וירדן) البحر الميّت (إسرائيل والأردنّ)


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