Search

In order to improve the understanding of the microphysical characteristics of raindrop size distribution (DSD) under different rainfall rates (R) classes, and broaden the knowledge of the impact of radar wavelengths and R classes on the QPE of dual-polarization radars in the Tianshan Mountains, a typical arid area in China, we investigated the microphysical characteristics of DSD across R classes and dual-polarimetric radar QPE relationships across radar wavelengths and R classes, based on the DSD data from a PARSIVEL2 disdrometer at Zhaosu in the Tianshan Mountains during the summers of 2020 and 2021. As the R class increased, the DSD became wider and flatter. The mean value of the mass-weighted mean diameters (Dm) increased, while the mean value of logarithm normalized intercept parameters (log10 Nw) decreased after increasing from C1 to C3, as the R class increased. The largest contributions to R and the radar reflectivity factor from large raindrops (diameter > 3 mm) accounted for approximately 50% and 97%, respectively, while 84% of the total raindrops were small raindrops (diameter < 1 mm). Dual-polarization radars—horizontal polarization reflectivity (Zh), differential reflectivity (Zdr), and specific differential phase (Kdp)—were retrieved based on the DSD data using the T-matrix scattering method. The DSD-based polarimetric radar QPE relations of a single-parameter (R(Zh), R(Kdp)), and double-parameters (R(Zh,Zdr), R(Kdp,Zdr)) on the S-, C-, and X-bands were derived and evaluated. Overall, the performance of the R(Kdp) (R(Kdp,Zdr)) scheme was better than that of R(Zh) (R(Zh,Zdr)) for the QPE in the three bands. Furthermore, we have for the first time confirmed and quantified the performance differences in the QPE relationship of dual-polarization radars under different schemes, radar wavelengths, and R classes in typical arid areas of China. Therefore, selecting an appropriate dual-polarization radar band and QPE scheme for different R classes is necessary to improve the QPE ability compared with an independent scheme under all R classes. [ABSTRACT FROM AUTHOR]

The performance of different quantitative precipitation estimation (QPE) relationships is examined using the polarimetric variables from the X-band polarimetric phased-array radars in Guangzhou, China. Three QPE approaches, namely, R(ZH), R(ZH, ZDR) and R(KDP), are developed for horizontal reflectivity, differential reflectivity and specific phase shift rate, respectively. The estimation parameters are determined by fitting the relationships to the observed radar variables using the T-matrix method. The QPE relationships were examined using the data of four heavy precipitation events in southern China. The examination shows that the R(ZH) approach performs better for the precipitation rate less than 5 mm h-1, and R(KDP) is better for the rate higher than 5 mm h-1, while R(ZH, ZDR) has the worst performance. An adaptive approach is developed by taking the advantages of both R(ZH) and R(KDP) approaches to improve the QPE accuracy. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of raindrop size distributions (RSDs) and polarimetric radar parameters retrieved by T-matrix for stratiform and convective precipitation in Beijing and Zhangbei (northern China), and Yangjiang (southern China) are studied and compared based on RSD data observed with PARSIVEL disdrometers in these three different climatic regions. The effects of observed and fitted RSD on scattering simulation are also discussed. The conclusions further confirm the obvious variation of RSDs in different climatic regions and rain types. There is significant regional difference in rainfall microphysical parameters for convective precipitation, and small regional difference for stratiform precipitation, instead. Convective precipitations from Beijing and Yangjiang both have higher mass-weighted mean diameter D m and log10 N w (N w : normalized intercept parameter) values than stratiform precipitations. The averaged RSDs from both rain types in Beijing and Yangjiang are in good agreement with gamma distribution while those in Zhangbei cannot be well fitted either by gamma or M–P (Marshall–Palmer) distribution. It is essential to take into account the effect of air density on raindrop fall velocity in highlands far away from sea level, such as Zhangbei. The μ–Λ relation varies with location. For a given Λ value, the fits to the data in the three regions have higher μ values than Florida relation (Zhang et al., 2003). It is robust to retrieve polarimetric radar parameters by T-matrix. There is an exponential relationship between differential reflectivity Z DR and radar reflectivity factor Z H , as well as the relation between specific differential phase K DP and Z H . The variation of the relations in different climate regions and rain types results from RSD's sensitivity to climatic regions and rain types. Observed RSD is superior to the fitted one in retrieving polarimetric radar parameters. [Copyright &y& Elsevier]

Abstract: The optical properties of spherical and non-spherical dust aerosols are calculated using the Lorenz–Mie theory and the combination of T-matrix method and an improved geometric optics method. The resulting optical properties are then applied in an interactive system that coupled a general circulation model with an aerosol model to quantitatively analyze the effect of non-spherical dust aerosol on its direct radiative forcing (DRF). Our results show that the maximum difference in dust instantaneous radiative forcing (IRF) between spherical and non-spherical particles is 0.27Wm−2 at the top of the atmosphere (TOA) and appears over the Sahara Desert due to enhanced absorption of solar radiation by non-spherical dust. The global annual means of shortwave (longwave) IRFs due to spherical and non-spherical dust aerosols at the TOA for all sky are −0.62 (0.074) Wm−2 and −0.61 (0.073) Wm−2, respectively, and the corresponding values for clear sky are −1.16 (0.092) Wm−2 and −1.14 (0.093) Wm−2, which indicates that the non-spherical effect of dust has almost no effect on their global annual mean IRFs. However, non-spherical dust displays more evident influences than above on its atmospheric- and land-temperature adjusted radiative forcing (AF) at the TOA over the Saharan Desert, West Asia, and northern China, with an approximate maximum increase of 3.0 and decrease of 0.5Wm−2. The global annual means of shortwave (longwave) AFs due to spherical and non-spherical dust aerosols are −0.55 (0.052) Wm−2 and −0.48 (0.049) Wm−2 at the TOA for all sky, respectively, and the corresponding values for clear sky are −1.07 (0.066) Wm−2 and −0.95 (0.062) Wm−2. All AFs of dust become much weaker than their corresponding IRFs. The absolute values of annual mean AF for non-spherical dust are approximately 13% (11.2%) and 6% (6%) less than those of spherical dust for the shortwave and longwave for all sky (clear sky), respectively. The results indicate that the non-spherical effect of dust can reduce their AFs more obviously than do their IRFs. [Copyright &y& Elsevier]