On the variability of the shape‐slope parameter relations of the gamma raindrop size distribution model

Abstract

[1] The gamma parameters have been derived on the ground with the disdrometer and aloft with VHF and UHF radar measurements made at Gadanki in the southwest monsoon season. They have been used to study the variability of the shape-slope (m -L) relation with the climatic regime and also as a function of height. The m -L relation obtained at Gadanki differs from that derived at Florida and Oklahoma indicating climatic differences in the relation, which could be due to the microphysical differences in the rain DSD at these two locations. However, these differences could also arise due to the use of different type of disdrometers at these locations. For the first time, an attempt has been made to study the variation of this relation with height, and the analysis clearly reveals a significant variation in the coefficients of the relation with height. The vertical variability of the relation has been ascribed to the microphysical processes occurring in the height region concerned in the present study. These results suggest that for accurate retrieval of drop size distribution from polarimetric measurements and also for studies on the microphysics of rain systems, the vertical variability of the relation needs to be accounted, in particular in an environment where the DSD variations are considerable. In addition, the reduction of the scatter in the m -L plot after filtering light rain events, suggests that the m -L relation may be pertinent to moderate to heavy rain corroborating some of the earlier reports. Citation: Narayana Rao, T., N. V. P. Kirankumar, B. Radhakrishna, and D. Narayana Rao (2006), On the variability of the shape-slope parameter relations of the gamma raindrop size distribution model, Geophys. Res. Lett., 33, L22809,

Statistical Characteristics of Multipeak Raindrop Size Distributions at the Surface and Aloft in Different Rain Regimes

“…The system description of the LAWP is given in Rao et al (2001). Important specifications of the LAWP can be found in Table 1.…”

Shape Slope Parameter Distribution Modelling of Electromagnetic Scattering by Rain Drops

“…Table 1 shows the rain categories, the coefficients of the µ-Λ relations with 95% confidence bounds and Pearson correlation coefficients. The different rain categorizations, i.e., R ≥ 5 mm/hr & drops ≥ 1000 used by Brandes et al [5], z ≥ 30 dBZ & drops ≥ 500 used by Narayana et al [12], and R ≥ 1 mm/hr used by Brawn and Upton [13], are also included in the table for comparison with other published results. As can be seen in Table 1, for the rain categories for which there are more lower rain rates included, such as R < 2 mm/hr and R ≥ 1 mm/hr, the coefficient 'C' of the polynomial fit is not only negative, but very small, with values of −0.004 and −0.005 respectively.…”

“…He concluded that the equivalence between the µ-Λ relation and Testud's function indicates the physical information in the µ-Λ relation of the constrained-gamma (C-G) model proposed by [2]. Narayana et al [12] studied the variability of the µ-Λ relation using the Joss-Waldvogel distrometer (JWD) data measured at Gadanki, India, under the conditions, reflectivity ≥ 30 dBZ and number of drops ≥ 500. They used 3rd, 4th and 6th moments to fit the gamma model.…”

“…Therefore, three different categories of rain rates, R < 2 mm/hr (stratiform), 2 mm/hr ≤ R < 10 mm/hr (stratiform, transition and convective type rain) and R ≥ 10 mm/hr (convective type rain), are considered in order to fit the µ-Λ relations for the 996 minutes of drop size data for Singapore. The rain categorization used by [5,12,13] are also considered for the µ-Λ relations fitting purposes, so as to provide a fair comparison of the different types of rains at the different climatic zones.…”

An empirical model for the variation of rain drop size distribution with rain rate at a few locations in southern India

“…However, there have not been many measurements in India. Some Verma and Jha (1996), Reddy and Kozu (2003), Sasi Kumar et al (2003), Mali et al (2003), Krishna Reddy et al (2005), Roy et al (2005), Rao et al (2006) and . We present here the measurement and derivation of a rain DSD model for 4 different locations in southern India, viz.…”