Analysis of Differences in Raindrop Spectrum Characteristics of Typhoons with Similar Moving Paths When First Entering Southern Shandong
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Abstract:
The rainstorms caused by typhoons are one of the major disasters in China. The raindrop spectrum is the basic microphysical characteristic of precipitation. With the deployment of a large number of precipitation phenomena instruments, the observation and analysis of the raindrop spectrum has become an important way to study the physical characteristics of cloud precipitation. By analysing the raindrop spectrum characteristics of typhoons, the physical process and internal mechanism of cloud precipitation can be deeply explored. In order to analyse the variations in raindrop size distribution (DSD) and integrated parameters of typhoons with similar movement paths under the same geographical conditions, this study examines the heavy rainfall events triggered by typhoons “Yagi” (1814) and “In-Fa” (2106) when they first enter southern Shandong at the Taierzhuang National Meteorological Observatory. Utilising precipitation measurement instruments, automatic meteorological station data, and tropical meteorological best track datasets during the influence periods of the two typhoons, the Gamma distribution parameters, N0 (intercept parameter), μ (shape factor), and λ (slope parameter), as well as the normalised function parameters, Nw (normalised intercept parameter), Dm (mass-weighted mean diameter), NT (raindrop concentration), R (rain rate), and Z (radar reflectivity factor), are computed using the moment method. The relationships and correlations among these parameters are analysed. The results indicate that: (1) Both typhoons exhibit an unimodal raindrop size distribution with concentrations of medium and small raindrops as the main components. For “Yagi,” the increase in R is primarily influenced by an increase in Dm and secondarily by an increase in lgNw, whereas for “In-Fa,” the increase in R is mainly influenced by Dm. (2) For both typhoons,Dm increases with R, while μ and λ decrease with R. The lgNw for “Yagi” slightly increases with R, whereas for “In-Fa,” lgNw remains nearly unchanged with R. (3) The convective precipitation of “Yagi” exhibits both continental and oceanic characteristics, with formation mechanisms predominantly involving warm-rain-ice mixed and ice-phase processes. In contrast, “In-Fa” convective precipitation is primarily oceanic, with formation mechanisms mainly driven by collision-growth warm clouds, along with a minor portion of warm-rain-ice mixed processes. (4) Fitting the μ-λ relationship using the least squares method shows that the two fitted curves are close to each other, indicating minimal differences in the μ-λ relationship for the two typhoons upon their initial entry into southern Shandong. (5) Applying the formula Z=300R1.4 tends to slightly overestimate precipitation for “Yagi” while underestimating precipitation for “In-Fa.” The raindrop size distribution of “Yagi” convective clouds is characterised by atypical control, whereas “In-Fa” convective cloud precipitation is characterised by concentration-diameter mixed control.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.