EnKFEnKF assimilation of mobile Doppler radar data collected in the 5 May 2007* assimilation of mobile Doppler radar data collected in the 5 May 2007*

Greensburg, Kansas Greensburg, Kansas tornadictornadic stormstormRobin L. Tanamachi Robin L. Tanamachi Robin L. Tanamachi Robin L. Tanamachi Howard B. BluesteinHoward B. BluesteinHoward B. BluesteinHoward B. Bluestein

School of Meteorology , University of Oklahoma (OU),Norman, Oklahoma

Stephen J. FrasierStephen J. FrasierStephen J. FrasierStephen J. FrasierKery HardwickKery HardwickKery HardwickKery Hardwick

Microwave Remote Sensing LaboratoryUniv. of Massachusetts – Amherst (UMass); Amherst,

Massachusetts

David DowellDavid DowellDavid DowellDavid DowellNational Center for Atmospheric Research (NCAR)

Boulder, Colorado

Louis J. WickerLouis J. WickerLouis J. WickerLouis J. WickerNational Severe Storms Laboratory (NSSL)

Norman, Oklahoma

QuestionQuestionQuestionQuestion::::DidDidDidDid thethethethe nocturnalnocturnalnocturnalnocturnal LLJLLJLLJLLJ

playplayplayplay aaaa significantsignificantsignificantsignificant roleroleroleroleinininin thethethethe tornadogenesistornadogenesistornadogenesistornadogenesis

modemodemodemode ofofofof thethethetheGreensburgGreensburgGreensburgGreensburg supercellsupercellsupercellsupercell????The Greensburg cyclicsupercell produced at

least 22 tornadoes, the

strongest of which (an

EF-5) destroyed the townof Greensburg, Kansas

and caused 11 fatalities.

In this study, we investigate the effects of the LLJ by

initializing two EnKF radar DA experiments withdifferent velocity profiles.

QuestionQuestionQuestionQuestion::::DidDidDidDid thethethethe nocturnalnocturnalnocturnalnocturnal LLJLLJLLJLLJ

playplayplayplay aaaa significantsignificantsignificantsignificant roleroleroleroleinininin thethethethe tornadogenesistornadogenesistornadogenesistornadogenesis

modemodemodemode ofofofof thethethetheGreensburgGreensburgGreensburgGreensburg supercellsupercellsupercellsupercell????The Greensburg cyclicsupercell produced at

least 22 tornadoes, the

strongest of which (an

EF-5) destroyed the townof Greensburg, Kansas

and caused 11 fatalities.

In this study, we investigate the effects of the LLJ by

initializing two EnKF radar DA experiments withdifferent velocity profiles.

*Historically speaking, the date of the Greensburg storm and tornadoes is 4 May 2007. However, the Greensburg storm occurred entirely on 5 May 2007 in UTC.

Experimental setup:Experimental setup:Experimental setup:Experimental setup:•ModelModelModelModel corecorecorecore::::WRFARW v3.0.1.1 (www.wrf-model.org)•SimulationSimulationSimulationSimulation timetimetimetime:::: 0130– 0300UTC•HorizontalHorizontalHorizontalHorizontal resolutionresolutionresolutionresolution:::: 1 km•VerticalVerticalVerticalVertical resolutionresolutionresolutionresolution:::: Stretched from 175 m near the surface (564mASL) to 1540m near the top of the model (20 km ASL)•GridGridGridGrid sizesizesizesize:::: 123x 123 x 51•ModelModelModelModel timetimetimetime stepstepstepstep:::: 5 sec•Flatbottomboundary;open lateral boundaries•No surface radiative fluxesor boundary layer physics•MicrophysicalMicrophysicalMicrophysicalMicrophysical parameterizationparameterizationparameterizationparameterization:::: Linet al. (1983)•DADADADA packagepackagepackagepackage:::: WRF-DART radar DA module(www.image.ucar.edu/DAReS/DART/), rev. 3810•AssimilationAssimilationAssimilationAssimilation cyclecyclecyclecycle:::: 120sec•DataDataDataData assimilatedassimilatedassimilatedassimilated:::: Z (σz = 5 dBZ) and Vr (σvr = 2 m s-1) from WSR-88D at Dodge City, KS (KDDC), supplemented by Vr data fromUMassX-Pol mobile radar (Tanamachiet al. 2009)•AdditiveAdditiveAdditiveAdditive noisenoisenoisenoise (Dowell and Wicker 2009):::: 1.0 m s-1 for u and v,0.5K for T and Td, every 120 sec in regionswith Z ≥ 25 dBZ•InitialInitialInitialInitial environmentenvironmentenvironmentenvironment:::: Horizontally homogeneous w/randomlyplacedthermalbubbles•EnsembleEnsembleEnsembleEnsemble:::: 48 members, generated by adding randomperturbations (~N[0,2 m s-1]) to the two velocity profiles (0100VADand 0230VAD) shownbelow.

ObservationObservationObservationObservation----space diagnostics:space diagnostics:space diagnostics:space diagnostics:

AcknowledgmentsAcknowledgmentsAcknowledgmentsAcknowledgments::::David Stensrud suggested the focus of this study. Discussions with Glen Romine, Les Lemon, Mike Umscheid,

andDaniel T. Dawson II were informative and instructive.ReferencesReferencesReferencesReferences::::Bluestein, H. B., 2009: The formation and early evolution of the Greensburg, Kansas, tornadic supercell on 4 May

2007.Wea. and Forecasting, 24242424, 899-920.Dowell, D. C., and L. J. Wicker, 2009: Additive noise for storm-scale ensemble data assimilation. J. Atmos. and

Oceanic Tech., 26262626, 911-927.Lemon, L. R. and M. Umscheid, 2008: The Greensburg, KS tornadic storm: a storm of extremes. Preprints, 24th

Conf. on Severe Local Storms. Savannah,Georgia, AmericanMeteorological Society, 2.4.Lin, Y.-L., R. D. Farley, and H. D. Orville, 1983. Bulk parameterization of the snow field in a cloud model. J. Appl.

Meteor., 22222222, 1065 – 1092.Tanamachi, R. L., D. C. Dowell, L. J. Wicker, H. B. Bluestein, S. J. Frasier, K. Hardwick, 2009: Numerical simulation

of a cyclic tornadic thunderstorm augmented by EnKF assimilation of mobile Doppler radar data. Preprints,34thConf. on RadarMeteorology, Williamsburg, Virginia, AmericanMeteorological Society, 14.1.

from Lemon and

Umscheid (2008)

Tornado tracks Tornado tracks Tornado tracks Tornado tracks associated with the associated with the associated with the associated with the Greensburg Greensburg Greensburg Greensburg supercellsupercellsupercellsupercell

Greensburg struck at 0245 UTC

UMassX-Pol

Surface

Surface

h = 1.2 km AGL

Surface

Surface

Surface

Surface

Surface

Surface

h = 7 km AGL

h = 7 km AGL

h = 7 km AGL

0100 VAD

0230 VAD

Difference fields

0230 -0100 VAD

Ensemble mean fields at 0231 UTC

Spurious

Spurious

Relatively uncontaminated LLJ

Transient“warm”downdraft

ResultsResultsResultsResults::::•The initial wind profile does not appear to exert much influence onthe overall storm structure or observation-space diagnostics. The

locations of the main supercell updraft and Greensburg tornado-like vortex are similar in both experiments.

•In time-height cross sections of max.vertical vorticity in the simulatedGreensburg storm (left), it can be seenthat vortices are generated earlier in the0100 VAD experiment, but that thevortex in the 0230 VAD experiment isdeeper, more persistent, and more

intense, particularly near the surface.•RMSI values (right) indicate that the assumed observation error forVr (σvr = 2 m s

-1) may be too small.•The consistency ratio (Dowell and Wicker 2009) is slightly lessthan 1 at most times, indicating insufficient model spread.

ResultsResultsResultsResults::::•The initial wind profile does not appear to exert much influence onthe overall storm structure or observation-space diagnostics. The

locations of the main supercell updraft and Greensburg tornado-like vortex are similar in both experiments.

•In time-height cross sections of max.vertical vorticity in the simulatedGreensburg storm (left), it can be seenthat vortices are generated earlier in the0100 VAD experiment, but that thevortex in the 0230 VAD experiment isdeeper, more persistent, and more

intense, particularly near the surface.•RMSI values (right) indicate that the assumed observation error forVr (σvr = 2 m s

-1) may be too small.•The consistency ratio (Dowell and Wicker 2009) is slightly lessthan 1 at most times, indicating insufficient model spread.

0-1 km

“Deep”

UMassX-Pol

volumes

“Shallow” UMass

X-Pol volumesNo UMass

X-Pol data

7-8 km

“Deep”

UMassX-Pol

volumes

“Shallow” UMass

X-Pol volumes

No UMass

X-Pol data

LLJ0230 UTC VAD

0100 UTCVAD Heights are

in km AGLCAPE =4600 J kg-1

Comparison of initial wind profiles