ISSN 1006-9895

CN 11-1768/O4

Winter Snowfall Microphysics Characterized by a 2-D Video Disdrometer (2DVD) in Beijing
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Affiliation:

1.Beijing Weather Modification Office;2.Chengdu University of Information Technology, College of Engineering (College of Meteorological Observation);3.Institute of Urban Meteorology, CMA;4.Institute of Atmospheric Physics, Chinese Academy of Sciences

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    Abstract:

    The study of snow microphysics is important to understand the mechanism of winter precipitation and to optimize the cloud microphysical parametrization scheme in the weather model. However, there are few researches on the microphysical characteristics of snowfall in China at present. In order to thoroughly understand the microphysical characteristics of snowfall in Beijing, the particle size distributions (PSDs), fall velocity (V), snow density(ρ), axis ratio (ar) and their relationship with equivalent diameter of six snowfall events observed by a 2D video disdrometer were investigated in this paper. The results showed the following: (1) The snow density with particle median volume diameter (D0) less than 1.5 mm is smaller than that reported in other regions, and the V(D) relationship is related to the snow density. The fall velocity of snow particles increases with the density and is moderately larger (smaller) than that in Colorado (Nanjing) for a given diameter. (2) The 5-minute PSDs for each case are fit with exponential and normalized gamma distribution models. The concentration intercept (N0 and Nw) and the slope (Λ) parameters for both fitting models present an almost same time series, while the errors between D0, Nt (total number concentration) and SR (snowfall rate) (SR) calculated from gamma PSD and that derived from 2DVD measurements was relatively small. (3) A directer correlation between the Nw and D0 can be observed after considering the effect of density on the Nw-D0 relation. (4) The mean aspect ratio (ar) of the snowflakes is 0.76, and the ar is close to 1 when the diameter is larger than 2.5 mm. (5) For a given SR (Ze), the decrease (increase) of Ze (SR) is accompanied with an increase of ρ and Nw while a decrease in D0. In addition, for a given Ze, the Ze–SR relationship in Nanjing overestimates snowfall rate.

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History
  • Received:July 29,2024
  • Revised:September 26,2024
  • Adopted:January 21,2025
  • Online: January 21,2025
  • Published: