Abstract
Abstract. Raindrop size distribution (DSD) information is fundamental in understanding the precipitation microphysics and quantitative precipitation estimation, especially in complex terrain or urban environments which are known for complicated rainfall mechanism and high spatial and temporal variability. In this study, the DSD characteristics of rainy seasons in the Beijing urban area are extensively investigated using 5-year DSD observations from a Parsivel2 disdrometer located at Tsinghua University. The results show that the DSD samples with rain rate < 1 mm h−1 account for more than half of total observations. The mean values of the normalized intercept parameter (log 10Nw) and the mass-weighted mean diameter (Dm) of convective rain are higher than that of stratiform rain, and there is a clear boundary between the two types of rain in terms of the scattergram of log 10Nw versus Dm. The convective rain in Beijing is neither continental nor maritime, owing to the particular location and local topography. As the rainfall intensity increases, the DSD spectra become higher and wider, but they still have peaks around diameter D∼0.5 mm. The midsize drops contribute most towards accumulated rainwater. The Dm and log 10Nw values exhibit a diurnal cycle and an annual cycle. In addition, at the stage characterized by an abrupt rise of urban heat island (UHI) intensity as well as the stage of strong UHI intensity during the day, DSD shows higher Dm values and lower log 10Nw values. The localized radar reflectivity (Z) and rain rate (R) relations (Z=aRb) show substantial differences compared to the commonly used NEXRAD relationships, and the polarimetric radar algorithms R(Kdp), R(Kdp, ZDR), and R(ZH, ZDR) show greater potential for rainfall estimation.
Highlights
Raindrop size distribution (DSD) provides fundamental information on precipitation microphysics
The DSD serves as a fundamental bridge in deriving the Z–R relationships used by ground-based weather radar (Battan, 1973; Uijlenhoet and Stricker, 1999) and spaceborne radar (i.e., TRMM PR: Iguchi et al, 2000; and GPM DPR: Hou et al, 2014) for quantitative precipitation estimation (QPE)
This paper presents a comprehensive study of DSD properties using 5-year (2014–2018) continuous observations in the Beijing urban area, aiming to advance our understanding and characterizations of DSD in urban regions as well as parameterization in remote sensing retrievals and numerical weather prediction (NWP) models
Summary
Raindrop size distribution (DSD) provides fundamental information on precipitation microphysics. Understanding the DSD variability is of great importance in remote sensing observations of precipitation and microphysical parameterizations in numerical weather prediction (NWP) models. The rapid urbanization and complex topography have further exacerbated the high variability of precipitation in the Beijing urban area, posing challenges to precipitation observations and forecast (Song et al, 2014; Yang et al, 2013a, 2016) This highlights the importance of understanding local DSD characteristics to better quantify the urban precipitation. Ji et al (2019) analyzed the microphysical structure of DSD using 14-month DSD measurements from a second-generation Particle Size and Velocity (Parsivel2) disdrometer in Beijing These studies are mainly focused on summer time (June–September or July–October) or with very limited measurements from one season or two, which are not sufficient to represent local DSD characteristics, especially the monthly variability, during the rainy seasons ranging from May to October.
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