Abstract
AbstractEffect of orography on tropical rain drop size distribution (DSD), which was not well known, is evidenced through the present study. DSD is the number of raindrops/unit volume/diameter interval, which tells about the underlying physics of rainfall process. Rain DSD was studied, using a Joss–Waldvogel disdrometer, at three coastal and a hill station in the Tropics. The variation in the characteristics of three physically significant parameters derived from the DSD with rain rate clearly unraveled the effect of orography on rain physics. The orographic rain appears to have larger drops compared with nonorographic rains when rain rate is high.
Highlights
drop size distribution (DSD) corresponding to different rain rate ranges for the month of July 2005 at Thiruvananthapuram was selected as a sample and the dataset was fitted with all the three distribution functions, namely, Marshal Palmer, Gamma and lognormal
Rainfall, with high rain rates, at Kochi and SHAR is made up of more number of smaller drops compared to Thiruvananthapuram
The effect of orography on tropical rain physics is very clear from these major differences in the rain DSD between Munnar, a high-altitude station (1500 m amsl), and all other coastal stations
Summary
Understanding of rain drop size distribution (DSD) and its spatial variability is very essential and useful in the areas like cloud microphysics, microwave communication, satellite meteorology, soil erosion and landslide triggering studies (Feingold and Levin, 1986; Huggel et al, 1996; Verma and Jha, 1996; Ulbrich and Atlas, 1998; Testud et al, 2001; Liu et al, 2005; Kozu et al, 2006; Xie et al, 2006; Harikumar et al, 2008; Sasi Kumar et al, 2007). DSD corresponding to different rain rate ranges for the month of July 2005 at Thiruvananthapuram was selected as a sample and the dataset was fitted with all the three distribution functions, namely, Marshal Palmer, Gamma and lognormal. The rain DSD, and the variation of all the three derived parameters with rain rate have shown a similar trend in different months. The variation of NT with rain rate for two different months (July and August) at the same station, Thiruvananthapuram is shown in Figure 3 to convince the fact that the behavior of the variation of any derived rain parameters with rain rate in different months at a particular station is similar. Though the entire available data (total of 45 months, 1-min resolution data) from all the stations were used for the analyses, the indicative months shown in all the figures in this manuscript are July 2003 for Kochi, July 2005 for Thiruvananthapuram, July 2004 for Munnar and August 2003 for SHAR (since any July data were not available for SHAR, August data were used), as a typical sample for each station
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