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Title: Nature of light rain during presence and absence of bright band
Authors: Konwar M
Maheskumar RS
Das SK
Morwal SB
Keywords: CloudSat;hydrometeorology;precipitation (climatology);raindrop;rainfall;size distribution;stratiform cloud, India;Maharashtra;Pune
Issue Date: 2012
Publisher: Journal of Earth System Science
Indian Academy of Sciences
Source: Volume no: 121
Issue no: 4
Abstract: This paper reports the evolution of rain drop size distribution (DSD) during bright band (BB) and no-BB (NBB) conditions of low intensity rainfall events as observed by a vertically pointing Micro Rain Radar (MRR) over Pune (18.58N, 73.92E), India. The BB is identified by enhanced radar reflectivity factor Z (dBZ) at the 0C isotherm. The gradient of hydrometeor fall velocity is found to be a good indicator in identifying the melting layer when enhanced radar reflectivity at melting layer is not prominent. The storm structures as observed by the MRR are compared with CloudSat observations that provide evidence of ice hydrometeor at ~??60C with clear indication of BB at 0C. Storm heights at warmer than 0C are evident during NBB conditions from CloudSat. This suggests that warm rain processes are responsible for producing rain during NBB conditions. During BB conditions, bimodal DSDs below the melting layer are observed at lower altitudes. The DSDs of shallow warm precipitating systems of NBB conditions are monomodal at all the altitudes. Significantly, normalized DSDs are found to be bimodal for BB conditions, and monomodal for NBB conditions which confirm different dominant microphysical processes. It is found that the observed bimodal DSDs during BB conditions are mainly due to the collision, coalescence and break-up processes. During NBB conditions, number and size of large raindrops grow while reaching the ground without much breakup. The radar reflectivity and rainfall intensity R (mmh???1) relationship of the form Z = aR b are found out for BB and NBB conditions. Existing different microphysical processes lead to large coefficient in the ZR relationship with small exponent during BB conditions while during NBB conditions the coefficients are small with large exponents.
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