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6/26/2015 Examination of the low level polarimetric radar parameters associated with the Aug 20 2009 southern Ontario tornadic supercells Mike Leduc Sudesh Boodoo Cloud Physics and Severe Weather Research King City ON
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6/26/2015 Outline Introduce Conceptual Model of Supercell at Low levels as Seen by Polarimetric Radar. Compare features of 5 Aug 20 Supercells to this Model.
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6/26/2015
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Polarimetric Conceptual Model of Supercells Low levels of Storm
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6/26/2015 ZDR and KDP ZDR compares Z(H) and Z(V) can distinguish big drops from small drops KDP rainfall estimates proportional to D**3 –Compared with Z (D**6) can provide valuable information
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6/26/2015 Romine et al 2008 (Arc)
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6/26/2015 ZDR arc Ryzkhov – size sorting due to environmental shear. –Area nearer inflow ends up with fewer but larger drops hence higher zdr –Not only hypothesis for this effect. Claim it’s measure of strength of circulation of supercell. (?)
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KDP foot Seems to correspond to development of FFD. Does this help increase low level mesocyclone circulation? Why increase in KDP –Descending air below freezing level –hail melts large drops break up into smaller drops. KDP proportional to D**3. while Z is D**6. –At low levels in this situation KDP values would increase relative to Z In OK storm higher values of KDP accompanied by hail at surface
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6/26/2015 Evolution of Kdp Foot as tornado develops May 8 2003 OK tornadic supercell
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6/26/2015 TOR -18 min
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6/26/2015 TOR-12min
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6/26/2015 TOR-6min
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6/26/2015 TOR touchdown
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6/26/2015 TOR +6
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6/26/2015 How Does Aug 20 compare at Low Levels Look for “sharpness” of zdr shield Relationship of kdp foot to zdr shield Can we see expansion of kdp foot and cyclonic rotation as touchdown approaches –3 tornadic supercells –2 Non tornadic supercells
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6/26/2015 Tornado 1 The Newmarket Storm
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6/26/2015 R T(1)-34 MIN
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6/26/2015 T(1)-34MIN R
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6/26/2015 R T(1)-34MIN
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6/26/2015 R T(1)-14MIN
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6/26/2015 R T(1)-14MIN
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6/26/2015 R T(1)-14MIN
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6/26/2015 T(1)-4MIN R
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6/26/2015 R T(1)-4MIN
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6/26/2015 R (T1)-4MIN R
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6/26/2015 Woodbridge Tornado
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6/26/2015 T(3)-0 MIN R
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6/26/2015 T(3)-0MIN
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6/26/2015 T(3)-0MIN R
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6/26/2015 Time Series of KDP with Woodbridge Storm
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New Lowell
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6/26/2015 T-17 MIN
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KDP foot and FFD An example
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Comparing Tornadic and Non tornadic storms
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KDP foot conclusions Subjectively appears that foot does expand and that cyclonic curvature of foot occurs with tornadic storms. Again subjectively foot corresponds with FFD as defined by Doppler (divergent signature tripping micro algorithm)
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6/26/2015 Hook Echoes Indicative of RFD. –Higher Values of ZDR Smaller particles have evaporated – stronger cold pool greater chance of gusting out. Ryzhkov hypothesized tornadic supercells would have lower values of ZDR in hooks. His study 4 tornadic 5 non tornadic storms looking just prior to touchdown. –Slight evidence for hypothesis but not statistically significant.
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ZDR 10 cm vs 5 cm radar –Comparing apples and oranges here. –Further study needed on appropriate thresholds to use.
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6/26/2015 Conclusions 5 significant supercells within 60 km of polarimetric radar on Aug 20 2009 Comparison with preliminary conceptual models using polarimetric parameters. Only lowest portion of storm examined. Some “intriguing” results re potential of polarimetric radar to distinguish tornadic from non tornadic supercells Many more cases needed. Adapting conceptual models for 5 cm radar is going to be challenging.
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6/26/2015 References A dual-polarization radar based assessment of the 8May 2003 Oklahoma City Area tornadic supercell; –Glen S. Romine1, Donald W. Burgess2 and Robert B. Wilhelmson3; MWR August 2008 Microphysical differences between tornadic and non tornadic supercell rear flank downdrafts revealed by dual polarization radar measurements –Matthew R Kumjian, Alexander V. Ryzhkov; 24 th Conference on Severe Local Storms, Savannah Georgia, October 2008 Polarimetric Signatures in Supercell Thunderstorms –Matthew R Kumjian, Alexander V. Ryzhkov; Journal of Applied Meteorology and Climatology July 2008 The Operational Recognition of Supercell Thuderstorm Environments and Storm Structures –Allan Moller, Charles Doswell, Michael Foster, Gary Woodall; Weather and Forecasting September 1994
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6/26/2015 THE END
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