analysis and prediction of convective initiation on 24 may, 2002
DESCRIPTION
Analysis and Prediction of Convective Initiation on 24 May, 2002. June 14, 2004 Toulouse 2 nd IHOP_2002 Science Meeting. Ming Xue, William Martin and Geoffrey Stano School of Meteorology and Center for Analysis and Prediction of Storms University of Oklahoma. - PowerPoint PPT PresentationTRANSCRIPT
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Analysis and Prediction of Convective Initiation on 24 May, 2002
June 14, 2004Toulouse 2nd IHOP_2002 Science Meeting
Ming Xue, William Martin and Geoffrey StanoSchool of Meteorology and Center for Analysis and Prediction of Storms
University of Oklahoma
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Our work on May 24, 2002 CI Case
• MS Thesis work of Geoffrey Stano: Multi-scale study based-on ADAS analyses including special IHOP data sets, and by examining observations directly.
• High-resolution simulation study (focus of this talk)
• Very large (~2000) ensemble and adjoint I.C. sensitivity study. dP/dqv sensitivity fields.
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Objectives
• Understand convective initiation in this case
• Predict and understand the convective systems involved
• Assess the sensitivity of precipitation forecast to initial conditions
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Methodology
• Make use of special data sets collected during IHOP
• Create high-resolution gridded data to perform diagnostic analysis and for model initialization
• Verify model simulations against available data
• Analyze realistic high-resolution model simulations to understand CI process
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Synopsis of the Event
• Convection started between 20:00 and 20:30 UTC in Texas panhandle area along a dryline. An intensive observation of IHOP_2002.
• Rapidly developed into a squall line and advanced across Oklahoma and northern Texas
• SPC reported almost 100 incidents of large hail, 15 wind reports, and two tornadoes in central Texas
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Time and Location of Initiation(17UTC – 22 UTC)
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Isotach Analysis: 250mb
TX Panhandle located at left-rear of upper level jetA short wave trough moved over western TX
19 UTC 20 UTC
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CIN and CAPE AnalysesCIN 19UTC
CAPE 19UTC CAPE 20UTC
CIN 20UTC
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Results of Stano’s diagnostic study
• Favorable condition pointing to initial initiation near Childress, TX– Placement of 250mb jet max and minimum– Surface heating and high surface dew points– Low Convective Inhibition values
• Causes for initiation– Weakening of cap over the boundary layer by turbulently
mixing – Break down of cap led to higher CAPE values– Convergence along the dryline or possibly from the cold
front approaching dryline
• More specifics limited by data resolutions
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Model Simulation Study
• Model can provide much more complete data in both space and time
• Easier to examine cause and effect
• Model fields are dynamically consistent
• Caution - model solution may deviate from truth therefore verification against truth is necessary
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Forecast Grids
4
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Model Configurations
• 1 km grid nested inside 3 km one• ADAS analyses for ICs and 3 km BCs• NCEP ETA 18UTC and 00UTC analyses and
21UTC forecast used as analysis background• ARPS model with full physics, including ice
microphysics + soil model + PBL and SGS turbulence
• LBCs every 3h for 3km grid and every 15min for 1 km grid
• 6 hour simulation/forecast, starting at 18 UTC
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OBS Used by ADAS
• ARM• COAG• IHOP Composite Upper Air - rawinsondes• KS Ground Water District 5• OK Mesonet• SAO• SW Kansas Mesonet• Western TX Mesonet• Profiler data absent
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Surface Data Sets
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Upper-Air Observing Sites
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Dropsondes on 20 UTC Isodrosotherms
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20:02UTC
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20:32UTC
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21:02UTC
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21:32UTC
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22:02UTC
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22:58UTC
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23:58UTC
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Animation 20UTC-00UTC, KLBB radar
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Animation 20UTC-00UTC, KFRD radar
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3km model simulation/forecast
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1 km simulation
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T=2.5h20:30UTC
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T=3.0h21:00UTC
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T=3.5h21:30UTC
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T=4.0h22:00UTC
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T=4.5h22:30UTC
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T=5h23:00Z
T=5h23:00Z
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T=5.5h23:30Z
T=5h23:00Z
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Animations
• Surface reflectivity
• 2km level w, winds
See movies(18:30 UTC – 00:00 UTC)
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See Movies
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19:16UTC
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19:45UTC
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20:30UTC
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23:00UTC
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Vertical cross-section animations
• w and • w and qv• qv and e
See Movies
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See Movies
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X-section at y=170 km
See movie
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Conclusions
• Dryline convection occurred in favorable synoptic-scale environment (upper jet, sfc trough, convergence, moisture supply, CAPE, etc.)
• Realistic CI predicted by the model, especially at 1 km resolution
• Model CI associated with dryline was ~ 30min-1h late (related to spinup?)
• Active development of BL eddies observed before C.I. in convergence zone (50-100km wide) and in the moist air (underneath CAP)
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Conclusions – continued
• A number of successfully penetration by B.L. parcels through the CAP before sustained convection is achieved
• Sustained convection occurred on the moist side near but not in the well mixed convergence zone or at the location of strong Td gradient
• Sloping terrain and surface heating played key roles• Cold frontal convection started earlier, due to lifting• Cold front or the triple point did not directly trigger dryline
convection – dryline did it on its own and initiated convection further south
• Cold air surge to the N.W. of dryline did not directly trigger convection (was in dry air, no CAPE)
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Conclusions - continued
• Role of surface wind convergence induced by mixing unclear to C.I. – perhaps indirectly by destabilizing the zone
• B.L. depth increases with time, so does its temperature, due to surface heating and eddy mixing)
• Any role of played by gravity waves or their interaction with B.L. eddies – not clear.
• Eddies organize into rolls/cloud streets near the edges of the convergence zone, where background wind is present
• Fine westward-propagating echoes observed by KLBB radar at the low levels are associated with the rearward propagating outflow boundary
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Comments very welcome!
Like to compare with fine-scale observations
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Posters
• Dawson and Xue: Data sensitivity study on June 16 MCS case
• Liu and Xue: 3DVAR assimilation GPS slant path water vapor data with an isotropic spatial filter. Tested on simulated data from June 18, 2002 dryline case.
• Tanamachi: June 12, 2002 boundary layer water vapor oscillation case - undular bore? Observation and simulation study
• Sensitivity Study – Title Slide
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TANGENT-LINEAR AND ADJOINT MODELS VERSUS PERTURBED FORWARD MODEL
RUNS
William J. MartinMing Xue
Center for Analysis and Prediction of Storms and the
University of Oklahoma, Norman, Oklahoma
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6 hr. forecast total accumulated precipitation
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• The sensitivity of a defined response function, J, such as the total rainfall in some area, is sought as a function of the initial fields.
• This is done by making a large number of forward model runs, each with a perturbation in a different location. The location of the perturbation is varied so as to tile a 2-D slice of the model domain.
• dx=dy=9km, no Cb parameterization
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1 g/kg qv pert
Example of an initial perturbation
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i
i vi
yx
yxqJ
)(
Response Function Defined As:
)),((1000),( controlJyxJyxS
Sensitivity Defined As:
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Sensitivity field for the dependence of total PPT on initial boundary layer moisture perturbations
+1 g/kg perturbations