| The raindrop size distribution can reflect the microphysical features of different rainfall systems thus has a great meaning helping us understand the microphysical structure and process of rainfall.Although there has been many raindrop size distribution analysis there is rarely about landfall western pacific typhon.This research is based on the national 973 program'the microphysical observation,forecast and evaluation of the landfall typhonl'.The data used in this study is collected by several raindrop disdrometer(OTT-Parsivel)set in Guangdong and Fujian Provience.The analysis of the landfall typhon Nepartak,Nida,Hato and Pakhar is based' on these observation data.The landfall typhon Nepartak,Nida,Hato and Pakhar have common features in raindrop size distribution.During the rainfall there is large raindrop size above 4mm appear in every typhon system.The number of particles for particles which has diameters between 0.5-1 mm was the highest in different typhoons.Number concentration is generally not more than 4000m-3mm-1.When precipitation of medium and small particle concentration increases suddenly,inevitably accompanied by the emergence of large particle.The typhoon the average spectrum are relatively smooth exponential distribution.The mass-weighted average diameter Dm increases with the increase of rain intensity R,and the Dm value tends to be stable after R>80mm/h.Nepartak has the smallest Dm when the rainrate is the same as other three typhons.Comparing the stratiform cloud precipitation and convective precptitation of typhoon system.Dm and log10Nw shows strong linear correlation and the fitting curve is different from the one that Bringi(2003)found for multiple stratiform cloud precipitation.It means that landfalling typhoons system has its unique physical structure.From the Dm and log10Nw of the convective cloud precipitation,typhoon Nida,Nepartak and Pakhar can be classified as matrime-like precipitation and Hato is more tend to be continental-like precipitation.Overall the Dm frequency distribution of convective precipitation in more concentrated than the stratiform cloud precipitation.In this paper,the raindrop spectral characteristics and the contribution of each scale particle to the typhoon precipitation are analyzed,and the DSD distribution difference of each typhoon is relatively small.As the precipitation rate gradually increases,the concentration of large particles gradually starts to diverge.With the increase of rainfall rate,small particles of precipitation rate gradually decreases,and the contribution of the particle medium for precipitation is increased,and when precipitation rate increases to a certain size,such as 20 mm/h,the contribution rate of medium scale particles decreases slightly.Raindrop spectrum research has important meaning for improving radar quantitative precipitation estimation,microphysical model parameterization and improve the forecast.In this paper we do a study of the Z-R relationship and the relationship between Gamma distribution shape parameter and the slope parameter X.In the Atlantic ocean typhoon Z-R relationship coefficient a,b is larger than the Pacific and Indian oceans.If we use the Atlantic typhoon Z-R relation,the rainrate might be underestimated The relationship coefficient of the four typhoons is very small,especially the coefficient of the quadratic term.The distribution of each typhoon is single peak structure,and it reaches its peak in the range of 2.5-5.In the same typhoon system,the frequency of the maximum frequency is basically the same,but the frequency of the peak is different. |
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