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  • Author or Editor: Graham Feingold x
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Moti Segal and Graham Feingold

Abstract

The potential impact of daytime local summer convective cloud systems on shelter air temperature is illustrated by numerical modeling and observations. Prolonged reductions in surface solar irradiance due to cloudiness result in a noticeable decrease in shelter temperature over drylands and a moderate temperature fall over wet surfaces. When cloudiness is abruptly diminished, shelter temperature increases rapidly. Numerical modeling of downdrafts associated with rainfall in a dry convective atmosphere indicates a pronounced drop in shelter temperature (as high as 12°C). The modeling results are consistent with observations. The significance of the results and their potential applications are outlined.

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Graham Feingold and Zev Levin

Abstract

Measurements of rain drop size spectra in Israel were carried out over a period of two years. It is shown that the size distribution can be best described by a lognormal distribution. With its parameters weighted by a certain choice of moments, this distribution has a better squared-error fit to the observed data than the gamma or the exponential distributions. Furthermore, this distribution is well suited for explaining drop size distribution effects in the dual-parameter remote measurement of rainfall. The lognormal distribution has the advantage that all its moments are also lognormally distributed. Its parameters, in their form presented here, have physical meaning (NT=drop concentration, Dg=the geometric mean diameter, and σ=standard geometric deviation). This facilitates direct interpretation of variations in the drop size spectrum. The different moments can easily be integrated to obtain simple expressions for the various rainfall parameters. The observed values of Dg and NT are found to depend more strongly than σ on rainfall rate (R). At high R (>45 mm h−1) the distribution tends to a steady state form (Dg and σ constant). These results suggest that the lognormal representation is suitable for a broad range of applications and can facilitate interpretation of the physical processes which control the shaping of the distribution.

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Zev Levin, Graham Feingold, Shalva Tzivion, and Albert Waldvogel

Abstract

A comparison is made between the evolution of raindrop spectra as measured at stations in the Swiss Alps separated by vertical distances of the order of 600 m, with that modeled in an axisymmetrical model including detailed microphysics. Results show that under steady rain, weak advective conditions, and rain rates greater than 2 mm h−1, the model satisfactorily reproduces the features of the observed drop spectrum. Results deteriorate for low rain rates (of the order of 1 mm h−1) since drop collisions are too few to modify the spectrum significantly. The general agreement between modeled and observed spectra suggests that further considerations of this kind are justified.

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