BOUNDARY LAYER ENERGY POTENTIAL (BLEP): AN OPERATIONAL ... · boundary layer energy potential...

BOUNDARY LAYER ENERGY POTENTIAL (BLEP): BOUNDARY LAYER ENERGY POTENTIAL (BLEP): AN OPERATIONAL TOOL TO ESTIMATEAN OPERATIONAL TOOL TO ESTIMATEMAXIMUM SURFACE WIND SPEEDS IN MAXIMUM SURFACE WIND SPEEDS IN

CONVECTIVE STORMS?CONVECTIVE STORMS?

Bill NicholsBill NicholsLead Forecaster, WFO DVN Quad CitiesLead Forecaster, WFO DVN Quad Cities

OVERVIEWOVERVIEW

Purpose Of BLEPPurpose Of BLEPGeneral Science Of Updrafts and DowndraftsGeneral Science Of Updrafts and DowndraftsSupporting Studies Identifying Key ProcessesSupporting Studies Identifying Key ProcessesBLEP DescribedBLEP Described----How Captures Major ProcessesHow Captures Major ProcessesBLEP (Operational Equation) BLEP (Operational Equation) Results (So Far)Results (So Far)FindingsFindingsOperational ChallengesOperational ChallengesConclusions/Future WorkConclusions/Future Work

Purpose of BLEPPurpose of BLEP

NEED: NEED: Limited Operational Tools Exist forLimited Operational Tools Exist forAssessing High Winds For ConvectiveAssessing High Winds For ConvectiveStorms (WINDEX, CAPE, DCAPE)Storms (WINDEX, CAPE, DCAPE)

PURPOSE: Operationally Capture MajorPURPOSE: Operationally Capture MajorAtmospheric Processes ResponsibleAtmospheric Processes ResponsibleFor Winds In Convective Storms For Winds In Convective Storms

DERIVED: Identified Key Parameters Responsible DERIVED: Identified Key Parameters Responsible For For Winds From Theory/StudiesWinds From Theory/Studies----Then Then Modified Modified From From Observational DataObservational Data

Purpose of BLEPPurpose of BLEP

MUST BE ABLE TO:MUST BE ABLE TO:Apply To Full Spectrum Of ConvectiveApply To Full Spectrum Of Convective

High Wind PhenomenaHigh Wind Phenomena

Straight Line WindsStraight Line Winds----Pulse Pulse MicroburstsMicrobursts, Squall, SquallLines, Bow Echoes, Lines, Bow Echoes, DerechoesDerechoes

Rotational WindsRotational Winds----Tornadoes, Near SurfaceTornadoes, Near SurfaceMesocyclonesMesocyclones, Intense Comma Head Vortex, Intense Comma Head Vortex

Readily Calculated Using Available Readily Calculated Using Available Thermodynamic Thermodynamic ParametersParameters

Basic Science Basic Science ---- Updrafts & Updrafts & DowndraftsDowndrafts

Static StabilityStatic Stability

Governed by Vertical Distribution Of Governed by Vertical Distribution Of Temperature and MoistureTemperature and Moisture

Adiabatic Vertical DisplacementsAdiabatic Vertical DisplacementsUpdraftUpdraft----Parcel Becomes Warmer Than Parcel Becomes Warmer Than Environment Environment

DowndraftDowndraft----Parcel Becomes Cooler Than Parcel Becomes Cooler Than Environment Environment


Strength Of DowndraftStrength Of DowndraftPrecipitation LoadingPrecipitation Loading

Evaporative CoolingEvaporative Cooling

Strength Of UpdraftsStrength Of UpdraftsPrecipitation LoadingPrecipitation Loading

Latent Heat ReleaseLatent Heat Release


Importance of Mixing (Parcel w/ Environment)Importance of Mixing (Parcel w/ Environment)Thermodynamic Differences Drive Vertical MotionsThermodynamic Differences Drive Vertical Motions

Dry Air Entrainment and Detrainment Accelerate Dry Air Entrainment and Detrainment Accelerate Parcels Parcels

Mixing Theories (Shear and/or Buoyancy Driven)Mixing Theories (Shear and/or Buoyancy Driven)K Theory (Simplest, 1K Theory (Simplest, 1stst Order)Order)

Mixing LengthMixing Length----PrandtlPrandtl, Taylor (Sophisticated, 2, Taylor (Sophisticated, 2ndnd

Order)Order)

Turbulence TheoriesTurbulence Theories----TKE (More Sophisticated, 3TKE (More Sophisticated, 3rdrd

Order)Order)

Richardson NumberRichardson Number----Ratio of Buoyancy/ShearRatio of Buoyancy/Shear----BRN BRN


Theory and Observations of Mixing Driven Theory and Observations of Mixing Driven by:by:

Vertical ShearVertical Shear

Atmospheric Motions Governed by Atmospheric Motions Governed by Temperature Differences (Planetary to Temperature Differences (Planetary to Molecular ScalesMolecular Scales))

Greater Latent Heat Release and Evaporative Greater Latent Heat Release and Evaporative CoolingCooling

Greater Mixing with Surrounding EnvironmentGreater Mixing with Surrounding Environment

How Operationally?? Use Of THETA-E (θ) Changes With Height•By Definition: ∆ Theta-e Describes Vertical Distribution Of Moisture & Temperature•Most Importantly--Adjusts For Parcel Latent Heat Release Then Brought Dry Adiabatically To Surface


Mixing (NonMixing (Non--Adiabatic Process) Major Model Limitation! Adiabatic Process) Major Model Limitation! (Rough,(Rough,

Indirectly Inferred through Parameterization) Indirectly Inferred through Parameterization) Existing Models Too Coarse Grid Scales Existing Models Too Coarse Grid Scales Limited UnderstandingLimited Understanding----Cloud Microphysics, Radiative Cloud Microphysics, Radiative Feedbacks, Mixing/EddiesFeedbacks, Mixing/EddiesInconsistent Model Results with Observations and/or Inconsistent Model Results with Observations and/or Between ModelsBetween ModelsCascade Of Energy Problems (Emanuel 1994, Zhang 2002, Cascade Of Energy Problems (Emanuel 1994, Zhang 2002, Kain 2003)Kain 2003)Model Sensitivities Increase at Smaller ScalesModel Sensitivities Increase at Smaller Scales

BOTTOM LINE: Model DataBOTTOM LINE: Model Data----Qualitative RelationshipsQualitative RelationshipsVersus Quantitative (Adequate to Confirm Major Processes)Versus Quantitative (Adequate to Confirm Major Processes)Compared With Observational Data Compared With Observational Data

Supporting Studies Identifying Key Supporting Studies Identifying Key ProcessesProcesses

Several Studies (Many Recent) Indicate IncreasingSeveral Studies (Many Recent) Indicate IncreasingImportance Sub Cloud (SCL) Instability EnhancingImportance Sub Cloud (SCL) Instability EnhancingDowndrafts to Surface and/or TornadogenesisDowndrafts to Surface and/or Tornadogenesis

CAPE CAPE –– By Definition Doesn’t Apply To SCLBy Definition Doesn’t Apply To SCLUpdraft Motions above Level Of Free ConvectionUpdraft Motions above Level Of Free ConvectionGeneral Relationship Between Amount CAPE and General Relationship Between Amount CAPE and Strength Of UpdraftsStrength Of Updrafts

1980s1980s----Early Models Suggest Greater SCL Lapse Early Models Suggest Greater SCL Lapse RatesRates

& Amount SCL Dry Air& Amount SCL Dry Air----Stronger Downdrafts Stronger Downdrafts ((SrivastavaSrivastava


Some Recent Studies Supporting SCL Some Recent Studies Supporting SCL ProcessesProcessesAtkins 1991Atkins 1991----ObservationsObservations----Importance of Change THETAImportance of Change THETA--E E MicroburstsMicroburstsMarkowskiMarkowski 20022002----ObservationsObservations----Importance SCL Importance SCL BouyancyBouyancy To To TornadoesTornadoesWakimotoWakimoto 19941994----ObservationsObservations----Maximum Downdrafts @ Maximum Maximum Downdrafts @ Maximum CoolingCoolingProctor 1989Proctor 1989----Modeled Downdrafts Compared to Observed Modeled Downdrafts Compared to Observed MicroburstsMicrobursts

Evaporative CoolingEvaporative Cooling----Primary Contributor to DowndraftsPrimary Contributor to DowndraftsMaximum Evaporative CoolingMaximum Evaporative Cooling----Directly Related to Increased SCL ∆ THETADirectly Related to Increased SCL ∆ THETA--E E

McCaulMcCaul 20012001----Modeled Storm EnvironmentModeled Storm Environment----SCL Buoyancy/Shear Drive SCL Buoyancy/Shear Drive IntensityIntensityMarkowskiMarkowski 2002/22002/2----Observed/Modeled RFDObserved/Modeled RFD----Increased Buoyancy Increased Buoyancy Increased Chances for TornadoesIncreased Chances for Tornadoes

l d l d d f / d


Atkins & Wakimoto, 1991


Davies-Jones, 1986


Wurman & Gill, 2000 Wurman & Gill, 2000


Evans & Doswell,


Evans & Doswell, 2001


Gilmore & Wicker, 2000


Summary Of Key Environmental ParametersSummary Of Key Environmental ParametersGreater Low Level SCL InstabilityGreater Low Level SCL Instability----Greater DowndraftsGreater DowndraftsDry Air at SCL and Up To Melting LevelDry Air at SCL and Up To Melting Level----Greater Greater DowndraftsDowndraftsLarger Mixing in Larger Mixing in SubsaturatedSubsaturated EnvironmentEnvironment----Greater Greater Downdraft Downdraft Larger Precipitation LoadingLarger Precipitation Loading----Greater Evaporation & Greater Evaporation & DowndraftDowndraftGreater SCL Lapse Rate to Melting LevelGreater SCL Lapse Rate to Melting Level----Greater DowndraftGreater DowndraftGreater Updraft with More SCL BuoyancyGreater Updraft with More SCL Buoyancy----Larger Latent Larger Latent Heat ReleaseHeat ReleaseHigher LCLHigher LCL----Supports Stronger DowndraftsSupports Stronger DowndraftsLower LCLLower LCL----Supports Greater Mixing & Rotation Supports Greater Mixing & Rotation


Explains Limitation Of Existing Tools by Not Depicting Key Explains Limitation Of Existing Tools by Not Depicting Key SCLSCL

Processes Processes

WINDEXWINDEXNo Variance in SCLNo Variance in SCL Moisture and Buoyancy ProfilesMoisture and Buoyancy Profiles----Limited Limited Adjustments for MixingAdjustments for Mixing----No Assessment Directly For Changes In No Assessment Directly For Changes In Evaporative CoolingEvaporative CoolingSimilar to using 540 Thickness for Rain/SnowSimilar to using 540 Thickness for Rain/Snow----Worse Due To NonWorse Due To Non--Linear Effects? Linear Effects? No Incorporation of Unidirectional ShearNo Incorporation of Unidirectional Shear

DCAPEDCAPENo Change in SCL Moisture and BuoyancyNo Change in SCL Moisture and Buoyancy----No MixingNo MixingNo Evaporative Cooling Effects (Dilution)No Evaporative Cooling Effects (Dilution)No Incorporation of Unidirectional ShearNo Incorporation of Unidirectional Shear

BLEP (Operational Equation)BLEP (Operational Equation)

KinematicKinematic ProcessesProcesses→ → →→ → →[[VVsfcsfc ± ± CosCos (V(VLCL LCL + V+ V700700)] · M)] · M

Where Where For ∆For ∆θθe e ((SfcSfc--LCL)LCL)M= 1.0M= 1.0 GTE GTE --1818M=.8M=.8--.9.9 --15 to 15 to --1717M=.6M=.6--.7.7 --11 to 11 to --1414M=.4M=.4--.5.5 --8 to 8 to --1010M=.2M=.2--.3.3 --4 to 4 to --77M=.1M=.1 --2 to 2 to --33


Potential ProcessesPotential Processes (Straight Line Winds)(Straight Line Winds)→→

∆∆θθe e · K (· K (VVDowndraftDowndraft LCL) LCL) ))

Where Where For ∆For ∆θθe e ((SfcSfc--LCL)LCL)K=.3K=.3 --1 to 1 to --33K=.7K=.7 --4 to 4 to --77K=1.0K=1.0 --8 to 8 to --1010K=1.5K=1.5 --11 to 11 to --1414K=2.0K=2.0 --15 to 15 to --1818K=3.0K=3.0 --18 to 18 to --2121K=5.0K=5.0 GT GT --2121


Potential ProcessesPotential Processes (Rotational Winds)(Rotational Winds)

→→S · (S · (VVDowndraftDowndraft LCL) LCL) ))

Where Where SfcSfc –– LCL Shear (LCL Shear (KtsKts))

S=1.0S=1.0 6 to 9 6 to 9 KtsKts

S=1.5S=1.5 11 to 14 11 to 14 KtsKts

S=2.0S=2.0 15 to 18 15 to 18 KtsKts

S=3.0S=3.0 19 to 22 19 to 22 KtsKts

S=5.0S=5.0 GT 23 GT 23 KtsKts


Strength Of Downdraft at Base Of CloudStrength Of Downdraft at Base Of Cloud---- Further Adjusted For:Further Adjusted For:

------ Height Of LCL (Straight Line Winds)Height Of LCL (Straight Line Winds)-------- ~ 20~ 20--25% Of 25% Of WWmaxmax derived from derived from

CAPECAPE-------- If LCL 2If LCL 2--3,000’ AGL3,000’ AGL----75% Of Value75% Of Value-------- If LCL LT 2,000’ AGLIf LCL LT 2,000’ AGL----50% Of Value50% Of Value

------ Downdraft Strength at LCL IncreasedDowndraft Strength at LCL Increased-------- Steep Lapse LCL to 700 Steep Lapse LCL to 700 mbmb (+30%)(+30%)-------- Dry Air Above LCL (+10%)Dry Air Above LCL (+10%)


Strength Of Downdraft at Base Of Cloud Strength Of Downdraft at Base Of Cloud (cont.)(cont.)

------ Height Of LCL (Rotational Winds)Height Of LCL (Rotational Winds)

-------- LCL 2LCL 2--3,000’3,000’----80% Of Value 80% Of Value

-------- LCL GT 3,000’LCL GT 3,000’----67% Of Value67% Of Value

BLEP RESULTSBLEP RESULTS

Methodology Of Verification Of BLEP ValuesMethodology Of Verification Of BLEP Values

WindsWindsStorm ReportsStorm ReportsASOS/AWOS and Other Estimated SourcesASOS/AWOS and Other Estimated Sources

TornadoesTornadoesFF--ScaleScale----Estimated Wind Strength (Damage)Estimated Wind Strength (Damage)Path LengthPath Length----Estimated Wind Strength Estimated Wind Strength Other Sources?Other Sources?

Initial Results Initial Results

25/26 Cases25/26 Cases----BLEP Within 20% Of Estimated Wind StrengthBLEP Within 20% Of Estimated Wind Strength

BLEP Performed in a Spectra of Environments/Time BLEP Performed in a Spectra of Environments/Time (Pulse, SC, LTSC, Squall, Bow Echo, (Pulse, SC, LTSC, Squall, Bow Echo, DerechoDerecho, No, No--CAPE CAPE Convective Events)Convective Events)

Best Agreements Straight Line Winds Less Than 110 Best Agreements Straight Line Winds Less Than 110 KtsKts

Adequate Agreement (30%) Straight Line Greater Than 110 Adequate Agreement (30%) Straight Line Greater Than 110 KtsKts

BLEP Calculated Values Consistent With Estimated FBLEP Calculated Values Consistent With Estimated F--Scale Scale Best Agreement Best Agreement ---- F0 to F3 (Less than 20%)F0 to F3 (Less than 20%)

Adequate Agreement Adequate Agreement ---- F4/F5 (~20%)F4/F5 (~20%)

BLEP Very Useful for Severe Threshold 58 Knots BLEP Very Useful for Severe Threshold 58 Knots –– 6/6 6/6 EventsEvents

~75% of BLEP Cases from DVN Warning Area~75% of BLEP Cases from DVN Warning Area

Operational ChallengesOperational Challenges

Must Be Able to Anticipate Surface and Near Must Be Able to Anticipate Surface and Near Surface Temperature and Moisture ProfileSurface Temperature and Moisture Profile

Severe Weather Checklist To Calculate Severe Weather Checklist To Calculate ThermodynamicThermodynamic

ParametersParameters

Importance of SkewImportance of Skew--T Log P DiagramT Log P Diagram

Most EffectiveMost EffectiveCalculate Winds for a Suite of Surface T/TCalculate Winds for a Suite of Surface T/Td d

Determine “Crossover Point” from Severe to NonDetermine “Crossover Point” from Severe to Non--SevereSevere

Conclusions/Future WorkConclusions/Future Work

BLEPBLEP----Step In Assessing Max Winds At SurfaceStep In Assessing Max Winds At SurfaceDowndrafts Through Evaporative and Momentum Downdrafts Through Evaporative and Momentum TransferTransferRotationRotation----SCL SCL VorticityVorticity/Buoyancy/Buoyancy----Updrafts/DowndraftsUpdrafts/Downdrafts

Initial Results PromisingInitial Results PromisingBLEP Adjusts For SCL T/TBLEP Adjusts For SCL T/Tdd Profiles (∆ THETAProfiles (∆ THETA--E)E)BLEP Incorporates Key Processes Identified BLEP Incorporates Key Processes Identified Damaging WindsDamaging WindsSatisfies CriteriaSatisfies Criteria----Gilmore & Wicker (98) for WindsGilmore & Wicker (98) for WindsMore Rigorous Studies NeededMore Rigorous Studies Needed----BAMEX/Office 2003BAMEX/Office 2003Refine Operational ApplicationsRefine Operational Applications

Adjust BLEP for Dry Adjust BLEP for Dry MicroburstsMicroburstsAdjust BLEP for Adjust BLEP for KatabaticKatabatic WindsWinds

Put Cases and Theory On WebPut Cases and Theory On Web

BOUNDARY LAYER ENERGY POTENTIAL (BLEP): AN OPERATIONAL ... · boundary layer energy potential...

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