Retrieval and Application of Raindrop Size Distributions From Polarimetric Radar and Disdrometer Data for Sub-synoptic Scale Systems Petar Bukovčić1, 3, 4, Dušan Zrnić2, Guifu Zhang 3, 4 1 Cooperative Institute for Mesoscale Meteorological Studies (CIMMS), University of Oklahoma, and NOAA/OAR National Severe Storms Laboratory, Norman, OK 2 National Severe Storms Laboratory (NSSL), University of Oklahoma, Norman 3 School of Meteorology, University of Oklahoma, Norman, OK 73072 4 Atmospheric Radar Research Center (ARRC), University of Oklahoma, Norman Croatian-USA Workshop on Mesometeorology, 19. Jun 2012, Eko park Kraš, Croatia
Overview Introduction Instrumentation and datasets • • • Methodology – DSD retrievals Case studies • • • Polarimetric KOUN radar 2 Dimensional Video Disdrometers (2 DVD) Dataset Squall line, July 13, 2005 Convective-stratiform mix, Jun 26, 2007 Convective rain, Jun 28, 2007 Summary and Discussion
Introduction • Drop Size Distributions (DSDs)- contain essential information about precipitation microphysics • Natural DSDs - high variability • Three parameter model • Gamma DSD model: much closer to natural DSDs, more flexible, 3 degrees of freedom (Ulbrich, 1983) • μ, Λ, N 0 - gamma DSD parameters • ZH, ZDR - radar measurements
Introduction • 2 measurements - 3 parameters • Constraining relation needed • Zhang (2001) proposed μ - Λ relation • μ and Λ highly correlated • D 0 and the shape of a rain drop spectrum are related → physical meaning of μ – Λ • Cao (2008) → unified μ –Λ relation for Oklahoma used for both convective and stratiform DSD retrievals
Instrumentation - KOUN • Polarimetric Radar: KOUN – Norman, OK • Provides info about hydrometeor size, shape, phase, and orientation • Allow retrieval of drop size distributions (DSDs)
Instrumentation – 2 DVD • Joanneum Research 2 D Video Disdrometer • low profile, OU • OU 2 DVDs @ KFFL (Kessler’s Farm Field Laboratory) OU 2 DVD
Instrumentation – 2 DVD • Joanneum Research 2 D Video Disdrometer • low profile, OU • OU 2 DVDs @ KFFL (Kessler’s Farm Field Laboratory) OU 2 DVD • 2 DVD directly measures the shape, size and falling velocity of precipitation particles
Dataset – Data Types • Radar Data • Disdrometer Data • ZH - horizontal reflectivity ZDR - differential reflectivity ρhv - correlation coefficient KOUN • DSDs - dropsize distributions R - rainfall rate D 0 - median volume diameter 2 DVD
Methodology – DSD retrievals • Gamma DSD • N(D) - DSD • • • N 0 (mm-1 - μ m-3) - number concentration parameter μ - the shape distribution parameter Λ (mm-1) - the slope parameter • D (mm) - the equivalent volume diameter • Constraining relation for OK rain (Cao et al. 2008)
Methodology – DSD retrievals • • • ZDR and μ-Λ relationship to find two parameters ZH to find N 0 Λ, μ and N 0 → N(D) → R, D 0 (DSD parameters)
Case Studies • Several types of storms: > Squall line, July 13, 2007; > Convective-stratiform mix, June 26, 2007; > Convective rain, June 28, 2007;
Squall line, May 13, 2005 0730 UTC ZH ZDR ρhv class. KOUN
Squall line, May 13, 2005 N(D) m(D) ZDR(D) 2 DVD
Squall line, May 13, 2005 ZH ZDR ρhv KOUN – vertical profile over 2 DVD location
Squall line, May 13, 2005 ZH R ZDR D 0 Comparison - retrievals, KOUN vs. 2 DVD
Convective-stratiform mix, June 26, 2007 1200 UTC ZH ZDR ρhv class. KOUN
Convective-stratiform mix, June 26, 2007 N(D) m(D) ZDR(D) 2 DVD
Convective-stratiform mix, June 26, 2007 ZH ZDR ρhv KOUN – vertical profile over 2 DVD location
Convective-stratiform mix, June 26, 2007 ZH R ZDR D 0 Comparison - retrievals, KOUN vs. 2 DVD
Convective rain, June 28, 2007 1230 UTC ZH ZDR ρhv class. KOUN
Convective rain, June 28, 2007 N(D) m(D) ZDR(D) 2 DVD
Convective rain, June 28, 2007 ZH ZDR ρhv KOUN – vertical profile over 2 DVD location
Convective rain, June 28, 2007 ZH R ZDR D 0 Comparison - retrievals, KOUN vs. 2 DVD
Summary and Discussion • Radar data and disdrometer measurements generally agree well for sub-synoptic scale systems • Radar retrieved R is in good agreement with 2 DVD and not too sensitive if μ –Λ changes • D 0 → highly sensitive if μ –Λ changes • Radar retrieved D 0 → slightly lower in stratiform and higher in convective stages of the storm compared to 2 DVD, but trends match very well • Convective and stratiform stages should be treated separately
Summary and Discussion • Reliable DSD retrieval technique is essential for accurate rain estimation and model parameterization • Future work • Implementation of polarimetric radar data into NWP models • Link between dynamics and microphysics (dual Doppler analysis) • μ - Λ adjustment (big drops, long tail DSDs) • Separation of convective and stratiform stages
Thank you!
Questions? petar. bukovcic@ou. edu
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