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Numerical Simulation and Prediction of Supercell Tornadoes
Ming XueSchool of Meteorology and
Center for Analysis and Prediction of StormsUniversity of Oklahoma
February 2008
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Outline of Talk
LES-resolution simulation of supercell tornado
Prediction of real tornados with radar data assimilation
Sensitivity of tornado prediction to microphysics
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Tornadogenesis and Tornado Dynamics as Revealed by LES-resolution Numerical
Simulations of Supercell Storm
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Numerical Simulation of Supercell Tornado using up to 12.5 m Grid Spacing
Using the Advanced Regional Prediction System (ARPS, Xue et al 2000, 2001, 2003) of CAPS
1977 Del City, OK sounding (~3300 J/kg CAPE) 2000 x 2000 x 83 point uniform resolution covering 50 x 50 km2. x = 25 m, zmin = 20 m, dt = 0.125 s.
x = 12.5 m in a 20 x 20 km subdomain, dt = 0.05 s.
Warmrain microphysics with surface friction at the later stage Simulations up to 5 hours Using 2048 Alpha Processors at Pittsburgh Supercomputing Center 60TB of data generated by one 25m simulation over 30 minutes, output
at 1 second intervals
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Sounding for May 20, 1977 Del City, Oklahoma tornadic supercell storm
CAPE=3300CAPE=3300J/kgJ/kg
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Full Domain Surface Fields of 50m simulation
t =3 h 44 mint =3 h 44 min
Red – positive Red – positive vertical vorticityvertical vorticity
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Near surface vorticity, wind, reflectivity, and temperature perturbation from 25-m run
2 x 2 km2 x 2 km
Vort ~ 2 sVort ~ 2 s-1-1
Movie
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Near surface vorticity, wind, reflectivity, and temperature perturbation from 12.5 m grid
1.5 x 1 km1.5 x 1 kmdomaindomain
Vort > 4 sVort > 4 s-1-1
Movie
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Near surface vorticity, wind and p' felds- evolution from single to multiple vortices
t=13447 s t=13661s
Vort_max=3.27 /s Vort_max=3.28 /s
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Movie of Cloud Water Field25 m, 7.5x7.5km domain, 30 minutes
Movie of Cloud Water Field. dx=25m 7.5x7.5km domain, 30 min.
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130m/s
-100mb
>120m/s max >120m/s max surface windssurface winds
>90mb p drop>90mb p drop +60m/s speed +60m/s speed increase in ~2minincrease in ~2min
220min 236min220min 236min
Max sfc wind speedMin. sfc perturb. p220min 236min220min 236min
Maximum surface wind speed and pressure drop in 12.5 m simulation
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What is the main source of air parcel and vorticity feeding the tornado?
Trajectory calculations based on 1-s model output
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View from SouthView from Southt=13250st=13250sbeginning of beginning of vortex intensificationvortex intensification
z = 3 kmz = 3 km
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View from NortheastView from Northeast
3km3km
RFD of1st cell
RFD of2nd cell
Inflowfrom east
Low-level jump flowLow-level jump flow
East West
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Diagnostics along Trajectories
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Orange portion t=13250-500s – 13250+200s
t=13250sBeginning of low-level spinup
14km14km
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X Y Z
8km8km
WVh
Streamwise Vort.Cross-stream Vort.Horizontal Vort.
Vertical Vort.Vertical Vort.Total VortTotal Vort..
13250132501275012750 1345013450
Vorticity components along trajectory
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Force along trajectoryForce along trajectory
BuoyancyBuoyancyVert. PgradVert. PgradSum of the twoSum of the two
Perturbation pressurePerturbation pressure-76mb-76mb
55
-5-5
1325013250
~2 m s~2 m s-2-2
+b' due to -p'+b' due to -p'
Forces along trajectory
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Can we numerically predict real tornadoes?
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May 8th, 2003 OKC tornado
OKC tornado2210-2238 UTC
30 km long path
F4
(Hu 2005; Hu and Xue 2007)
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DA cycles on 1-km Grid3DVAR+Cloud Analysis Forecast
2030 UTC 2140 UTC
4 nested grids
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Observed v.s. Predicted Z and Vr at 1.45° of the supercell storm
Observation 1 km Forecast
From 2140 to 2240 UTC every 5-min
Reflectivity
Radial velocity
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What about the prediction of embedded tornado?
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50-m Grid Forecast v.s. Observation
Forecast Low-level Reflectivity Observed Low-level Reflectivity
Movie
43 minute forecast
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50-m Grid Forecast v.s. Observation
Forecast Low-level Reflectivity Observed Low-level Reflectivity
Movie
43 minute forecast
43 min. forecast on 100m grid
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t=34 min
t=40 min
Sfc vert. vort., and p’ E-W x-sections of vert. vort. and w
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A case from CASA 2007 Spring Experiment
CASA – an NSF ERC for Collaborative Adaptive Sensing of Atmosphere
- Low cost, high density, adaptively scanning radars
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© KSWO TV
© Patrick Marsh
May 8-9, 2007
A series of low-levelcirculations.
NWS TornadoWarnings: 7:16pm,7:39pm, 8:29pm
7:21pm (0021Z)
8:30pm (0130Z)
9:54pm
10:54pm (0354 Z) Minco Tornado
A Case from 2007 CASA Spring Experiment
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dx = 400 m 115-min. prediction of sfc winds, Z (color), and vertical vorticity at 0355 UTC. Both WSR-88D and CASA IP1 data were assimilated very 5 min. for 1 h. The black triangle indicates the location of observed Minco tornado.
0:00Z 0:30Z 1:00Z 1:30Z 2:00Z
0Z Analysis1 hr. spin-up period 1 hr. assimilation window
with 5 min assimilation intervals
Forecast to 0500 UTC
0:00Z 0:30Z 1:00Z 1:30Z 2:00Z
0Z Analysis1 hr. spin-up period 1 hr. assimilation window
with 5 min assimilation intervals
Forecast to 0500 UTC
Predicted sfcVort. max
115-min sfc forecastMinco tornado
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Importance and/or Uncertainties of Microphysics?
Daniel Dawson’s Poster Yesterdayusing multi-moment microphysics
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Impact of Microphysics on Prediction of Tornadic Supercell Storm
May 3, 1999 Moore – OKC F-5 Tornado Case
Daniel Dawson’s Poster Yesterdayusing multi-moment microphysics
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Surface ’gray shading), Z (blue contours), vertical vorticity (color shading), and wind vectors at the time of largest vertical vorticity using 100 m resolution and with MY1 (a) and MY2 (b) schemes.
HP storm LP storm
100 m simulations with MY1 and MY2 schemes
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Vis5D visualization of the cloud field (gray surface), and 0.3 s-1 vertical vorticity iso-surface (yellow) from the 100
m simulations using MY1 (left) and MY2 (right) schemes.
MY Single-moment MY two-moment
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Greensburg, Kansas Tornado, 5 May 2007
Numerical prediction of tornados - has its time come?
What is the predictability of tornadoes?