jim marquis , yvette richardson, paul markowski , david dowell,
DESCRIPTION
Analysis of the Goshen County, Wyoming, tornadic supercell on 5 June 2009 during VORTEX2 using EnKF assimilation of mobile radar observations . Jim Marquis , Yvette Richardson, Paul Markowski , David Dowell, Josh Wurman , Karen Kosiba , and Paul Robinson. Photo by Sean Waugh. - PowerPoint PPT PresentationTRANSCRIPT
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Analysis of the Goshen County, Wyoming, tornadic supercell on 5 June 2009 during
VORTEX2 using EnKF assimilation of mobile radar observations
Jim Marquis, Yvette Richardson, Paul Markowski,
David Dowell,
Josh Wurman, Karen Kosiba, and Paul RobinsonPhoto by Sean Waugh
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Goals of EnKF analysis• Increase availability of 3-D kinematic and
thermodynamic data (dual-Doppler and in situ obs are spatially/temporally limited).
Paul MarkowskiCourtesy www.vortex2.org
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Goals of Data Assimilation• We want a set of realistically evolving analyses (i.e., We are not using DA to initialize a forecast).
• Analyze roles that mesocyclone-scale processes play in tornadogenesis, maintenance, and decay:
- trajectory analysis,- vorticity, momentum budgets,- complete thermodynamic fields,- mid-upper level features,
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Model Specifics• WRF-ARW 3.2.1:
-Δx,y = 500 m, 80m < Δz < 2km, [120 x 80 x 20] km3 -LFO microphysics (χrain= 8x106, χgraup= 4x103 m-4 ; ρgraup= 900 kg/m3),-open lateral BCs,-no surface fluxes, no radiation, flat terrain.
Homogeneous environment:
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DA Specifics• DART (Anderson et al. 2009):– Ensemble adjustment filter,
– 50 members,– Localization:
• Gaspari-Cohn (1999) = 0 @ r = 6 km– Ensemble initiation:
• 10 randomly placed warm bubbles at model t0 for each member
– Ensemble spread maintained with:• Additive noise added to T, Td, U, V every 5 min where radar
reflectivity is > 25 dBZ, (Dowell and Wicker 2009) • Perturbations smoothed to 4 km (horiz), 2 km (vert) scales
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Courtesy www.vortex2.org
σ2obs = (2 m/s)2
• Radar velocities assimilated every 2 minutes
•
• OBAN: Cressman weighting
500 m horizontal grid spacing (for 500m-model grid experiment)
data along conical slices
Experiment timeline
“synthetic Data”
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ζradarsDu
al-D
oppl
erEn
KF
Wm/s
Z = 400 m AGL
Dual-Doppler – EnKF (posterior) kinematics comparison
X (km)
Y (k
m)
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Comparison of temperature observations and EnKF analyses near the ground:
Z = 50 m AGL
θv(K)
ζ
Mobile mesonet Observations (not assimilated)Surface gust fronts
’
• Greatest differences early in the assimilation period. They get smaller with time.
X (km)
Y (k
m)
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Pressure fields
do
mdo pRppWRF diagnostic pressure:
• Want pressure for: ...''1
Bzp
zp
dtdw db
Important to supercells
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Pressure diagnosed using individual members vs. retrieval using ensemble mean posteriors kinematic fields (e.g., Gal-Chen 1978,
Hane and Ray 1985):
Sfc gust front z = 250 m
Y (k
m)
X (km)
do
mdo pRpp
Retrieved from horiz. momentum eqns
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2211 UTC
Trajectories (storm-rel.) calculated from ens. mean analyses
Ring (radius = 1 km) of 20 parcels centered on peak ζ at z = 700 m at 2211 UTC, integrated backward in time to 2143 UTC
Sfc gustfront
θρ(K)’
(Note: Trajectories curtailed because they encounter edges of dual-Doppler coverage)
X (km)
Y (k
m)
z = 200 m
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=
=
=
Tilting Stretching Baroclinicgeneration
Boussinesq, inviscid, coriolis-free 3-D Vorticity Equation:=
𝐵=𝑔𝜃−𝜃𝑒𝑛𝑣
𝜃𝑒𝑛𝑣
Ultimately important for generation of low-level mesocyclone
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=
=
=
More verification: Does ensemble mean vorticity along parcel trajectories match predicted (i.e., integrated) tendency?
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Ens. mean interpolatedto trajectory ∫(𝒕𝒊𝒍𝒕+𝒔𝒕𝒓+𝒃𝒂𝒓𝒐 )𝒅𝒕 ∫(𝒕𝒊𝒍𝒕+𝒔𝒕𝒓 )𝒅𝒕
Lagrangian 3-D vorticity budget for a parcel entering mesocyclone:
z = 200 m
X (km)
Y (k
m)
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ρ
Ens. mean interpolatedto trajectory ∫ (𝒕𝒊𝒍𝒕+𝒔𝒕𝒓+𝒃𝒂𝒓𝒐 )𝒅𝒕 ∫(𝒕𝒊𝒍𝒕+𝒔𝒕𝒓 )𝒅𝒕
Lagrangian 3-D vorticity budget for a parcel in the forward flank:
X (km)
Y (k
m)
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Summary: Utility of EnKF analysis • EnKF Kinematic Analyses:
- Compare well with dual-Doppler fields.
- Most trajectories seem believable;though, Lagrangian vorticity budgets have some problems in some areas of the storm.
• EnKF Thermo Analyses: - Mixed success with comparisons to in situ obs.
• Pressure fields seem unusable.
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Acknowledgements• The EnKF experiments were performed using NCAR CISL
supercomputing facilities (bluefire) with the Data Assimilation Research Testbed (DART) and WRF-ARW software.
• Thanks to: Glen Romine, Lou Wicker, Chris Snyder, Nancy Collins, Jeff Anderson, Don Burgess, Dan Dawson, Robin Tanamachi, Bruce Lee, Cathy Finley, Altug Aksoy, Fuqing Zhang, and Matt parker for consulting.
• Thanks to all VORTEX2 crew for their dedication while collecting data on 5 June 2009.
• This research is funded by NSF grants: NSF-AGS-0801035, NSF-AGS-0801041. The DOW radars are NSF Lower Atmospheric Observing Facilities supported by NSF-AGS-0734001.
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Extras
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Surface gust front
ζ
Pressure diagnosed with posterior ensemble mean thermodynamic variables vs. Pressure retrieved from posterior ensemble mean kinematic fields (e.g., Hane and Ray 1985, Majcen et al. 2008):
Diag
nose
d p’
Retr
ieve
d p’
• Posterior diagnosed pressure doesn’t seem right.
• Retrieved pressure fields seemingly more realistic, but vertical gradients still not trustworthy.
z = 250 mX (km)
Y (k
m)
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do
mdo pRpp
W>0
Pressure fields diagnosed with posterior means, prior means, and individual members :
z = 250 m
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Model errors/idealized conditions require DA for a good storm.
Storm structure with/without radar assimilation:
Top row: Series of Posterior ens. mean analyses.
Bottom row: Single member forecasted forward from 2157 (no DA).
ζ
Z = 150 m
X (km)
Y (k
m)
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Difference between surface obs and near-surface EnKF analyses of thermodynamic fields:
θe
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Time UTC
RMS Innovation
Total Spread
Consistency Ratio
Some obs-space statistics
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Comparison of Dual-Doppler – EnKF (ensemble mean) horizontal vorticity
EnKF
Dual
-Dop
Dual
-Dop
pler
EnKF
Horizontal vorticity vector pattern is similar, though magnitude of EnKF vorticity is greater
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ζ
θ(K)’
X (km)
Y (k
m)
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Surface & mid-upper-level features
(pre-tornado/tornadogenesis) (tornado mature)
(tornado weakening) (tornado dissipated)
W > 5 m/s(z = 5km)
ζ(z = 300m)Surface gust front
Low-level meso cyclone/tornado stays beneath mid-level updraft
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W (m/s)
ζ
Z = 400 m AGL
Dual-Doppler – EnKF (ensemble mean) kinematics comparison(DOW6 & NOXP)
ζ
Wm/s
X (km)
Y (k
m)
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θ’(K)
Low-level wmax trace: MM obs:
ζ
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