Examining the Use of Generalized Gamma Model to Represent the Full Rain Drop Size Distributions

2018 ◽  
Author(s):  
M. Thurai ◽  
V. Bringi
Keyword(s):  
Drop Size ◽  
Size Distributions ◽  
Gamma Model ◽  
Generalized Gamma ◽  
Rain Drop ◽  
Drop Size Distributions

scholarly journals Application of the Generalized Gamma Model to Represent the Full Rain Drop Size Distribution Spectra

2018 ◽  
Vol 57 (5) ◽  
pp. 1197-1210 ◽  
Author(s):  
Merhala Thurai ◽  
V. N. Bringi
Keyword(s):  
Goodness Of Fit ◽  
Drop Size ◽  
Nonlinear Least Squares ◽  
Shape Parameters ◽  
Gamma Model ◽  
Generalized Gamma ◽  
Rain Drop ◽  
Double Moment ◽  
Drop Size Distributions ◽  
The Stability

Abstract We report on measurements of drop size distributions (DSD) using collocated instruments (a Droplet Measurement Technologies, Inc., Meteorological Particle Spectrometer and a 2D-video disdrometer) from two locations with different rainfall climates (Greeley, Colorado, and Huntsville, Alabama, with measurements from the latter that include the outer rainbands of Hurricane Irma). The combination of the two instruments gives what we term as the “full” DSD spectra, the shape of which generally cannot be represented by the standard gamma model, but instead requires the additional flexibility of the generalized gamma model, which includes two shape parameters (μ and c). The double-moment normalization of DSDs using the third and fourth moments is used to arrive at the intrinsic shapes of the DSD with two shape parameters that are shown to capture simultaneously the drizzle mode as well as the precipitation mode, together with a “plateau” region between the two. The estimation of μ and c is done with a global search using nonlinear least squares, and the error residuals are examined to check the sensitivity of the parameters to a preselected, allowed tolerance around the minimum error in the μ, c plane. This leads to a range of plausible fits for a given normalized DSD mainly governed by the c parameter. The stability or invariance of the shape of the normalized DSDs from the two sites is examined, and on average the shapes are similar with some variability at the large normalized diameter end that is explained by the aforementioned range of plausible fits. Heuristic goodness-of-fit methods are described that demonstrate that the generalized gamma model outperforms the standard gamma model with only one shape parameter (μ).

scholarly journals Comparison of simultaneous rain drop size distributions estimated from two surface disdrometers and a UHF profiler

2000 ◽  
Vol 27 (12) ◽  
pp. 1763-1766 ◽  
Author(s):  
Christopher R. Williams ◽  
Anton Kruger ◽  
Kenneth S. Gage ◽  
Ali Tokay ◽  
Robert Cifelli ◽  
...  
Keyword(s):  
Drop Size ◽  
Size Distributions ◽  
Rain Drop ◽  
Drop Size Distributions

scholarly journals On the Realism of the Rain Microphysics Representation of a Squall Line in the WRF Model. Part II: Sensitivity Studies on the Rain Drop Size Distributions

2019 ◽  
Vol 147 (8) ◽  
pp. 2811-2825 ◽  
Author(s):  
Céline Planche ◽  
Frédéric Tridon ◽  
Sandra Banson ◽  
Gregory Thompson ◽  
Marie Monier ◽  
...  
Keyword(s):  
Drop Size ◽  
Wrf Model ◽  
Melting Process ◽  
Squall Line ◽  
Size Distributions ◽  
Line System ◽  
Stratiform Region ◽  
Rain Drop ◽  
Vertical Evolution ◽  
Drop Size Distributions

Abstract A comparison between retrieved properties of the rain drop size distributions (DSDs) from multifrequency cloud radar observations and WRF Model results using either the Morrison or the Thompson bulk microphysics scheme is performed in order to evaluate the model’s ability to predict the rain microphysics. This comparison reveals discrepancies in the vertical profile of the rain DSDs for the stratiform region of the squall-line system observed on 12 June 2011 over Oklahoma. Based on numerical sensitivity analyses, this study addresses the bias at the top of the rain layer and the vertical evolution of the DSD properties (i.e., of Dm and N0*). In this way, the Thompson scheme is used to explore the sensitivity to the melting process. Moreover, using the Thompson and Morrison schemes, the sensitivity of the DSD vertical evolution to different breakup and self-collection parameterizations is studied. Results show that the DSDs are strongly dependent on the representation of the melting process in the Thompson scheme. In the Morrison scheme, the simulations with more efficient breakup reproduce the DSD properties with better fidelity. This study highlights how the inaccuracies in simulated Dm and N0* for both microphysics schemes can impact the evaporation rate, which is systematically underestimated in the model.

scholarly journals Do We Observe Aerosol Impacts on DSDs in Strongly Forced Tropical Thunderstorms?

2011 ◽  
Vol 68 (9) ◽  
pp. 1902-1910 ◽  
Author(s):  
P. T. May ◽  
V. N. Bringi ◽  
M. Thurai
Keyword(s):  
Drop Size ◽  
Probability Distributions ◽  
Size Distributions ◽  
Cloud Properties ◽  
Median Volume ◽  
Rain Drop ◽  
Distribution Parameters ◽  
Radar Measurements ◽  
Ice Multiplication ◽  
Drop Size Distributions

Abstract Rain drop size distributions retrieved from polarimetric radar measurements over regularly occurring thunderstorms over the islands north of Darwin, Australia, are used to test if aerosol contributions to the probability distributions of the drop size distribution parameters (median volume diameter and normalized intercept parameter) are detectable. The observations reported herein are such that differences in cloud properties arising from thermodynamic differences are minimized but even so may be a factor. However, there is a clear signature that high aerosol concentrations are correlated with smaller number concentrations and larger drops. This may be associated with enhanced ice multiplication processes for low aerosol concentration storms or other processes such as invigoration of the updrafts.

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