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  • Author or Editor: I. Zawadzki x
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I. Zawadzki, E. Torlaschi, and R. Sauvageau

Abstract

Soundings. surface pressure, temperature and humidity obtained from a standard observation network were correlated with rain rates given by raingages and radar. The correlations indicate that a single thermodynamic parameter (static potential energy) explains ∼60% of the storm-to-storm variability of the mean and the maximum rain rates. During the evolution of a precipitating system the time variation of rain rate parameters follows closely the variation of the static energy. The entire distribution of rain rates is well stratified by the energy.

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I. Zawadzki, E. Monteiro, and F. Fabry

Abstract

A model of rain development based on the quasi-stochastic coalescence equation and including the sedimentation of drops has been used to study the formation of drop size distributions in conditions of weak updraft. Comparisons with “box model” results indicate that sedimentation effects are crucial in establishing the shapes of the distribution. Under realistic conditions of cloud droplet distribution with size, the raindrop size distributions as simulated by the model compare well with observations of orographic rain made in Hawaii. On the other hand, Doppler radar measurements of drop size distributions just below a bright band confirm that the Marshall-Palmer distribution results from processes affecting particles in the solid phase rather than from the interaction of raindrops.

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I. Zawadzki and M. De Agostinho Antonio

Abstract

Observations of raindrop size distributions in Brazil were analyzed. For long lasting records and during periods when there was no evidence of rain falling through updraft, the observations indicate that equilibrium between the coalescence and the breakup processes leads to a generic shape of the distribution such that distributions for different rain rates are proportional to each other. This is in agreement with numerical solutions to the stochastic equation. In cases where there is indication that updraft was present, the drop size distributions were markedly different. The proportionality between distributions is observed in these cases as well.

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I. Zawadzki, W. Szyrmer, C. Bell, and F. Fabry

Abstract

A model of the melting snow and its radar reflectivity is presented here. The main addition to previous description of the melting layer is the explicit introduction of snow density as a variable. The model is validated with radar observations. Differences in brightband intensity for comparable precipitation rates are related here to the coexistence of supercooled cloud water (SCW) with snow above the melting level leading to riming and change in snow density. Cases where riming was suspected were selected according to the characteristics of the vertical profile of reflectivity flux above the melting layer and vertical Doppler velocities faster than expected from low-density snow. For stratiform precipitation with a melting layer, high snow-to-rain velocity ratio indicates high-density snow and consequently a small peak-to-rain reflectivity difference is expected. This relationship was computed from the model and confirmed with vertically pointing radar observations. In spite of the complexity of the physical processes present in the melting layer the model appears to capture the essential elements.

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