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Application of the Lognormal Raindrop Distribution to Differential Reflectivity Radar Measurement (ZDR)

Graham FeingoldDepartment of Geophysics and Planetary Sciences, Raymond and Beverley Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel 69978

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Zev LevinDepartment of Geophysics and Planetary Sciences, Raymond and Beverley Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel 69978

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Abstract

Use of the lognormal form of raindrop size distributions in simulations of differential reflectivity (ZDR) measurements is investigated. Using two remotely measured variables and an empirical relation, the three parameters of the lognormal distribution can be deduced and the spectrum integrated to obtain rain rate. This is demonstrated by a simulation of the ZDR method using ground-based drop size distributions. Drop axis ratio and sampling time effects are also investigated and results compared to those obtained using a gamma distribution. It is shown that the lognormal representation is easily adaptable for use in the ZDR method. Using our dataset, we show that the lognormal size distribution provides lower average absolute deviations of theoretically determined rain rates from actual ones (10.7%) than those obtained using either the exponential (41.0%) or gamma distributions (11.8%).

Abstract

Use of the lognormal form of raindrop size distributions in simulations of differential reflectivity (ZDR) measurements is investigated. Using two remotely measured variables and an empirical relation, the three parameters of the lognormal distribution can be deduced and the spectrum integrated to obtain rain rate. This is demonstrated by a simulation of the ZDR method using ground-based drop size distributions. Drop axis ratio and sampling time effects are also investigated and results compared to those obtained using a gamma distribution. It is shown that the lognormal representation is easily adaptable for use in the ZDR method. Using our dataset, we show that the lognormal size distribution provides lower average absolute deviations of theoretically determined rain rates from actual ones (10.7%) than those obtained using either the exponential (41.0%) or gamma distributions (11.8%).

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