The Role of Boundary Layer Variability in Aviation Forecasting

Across Eastern New York and Western New England

Ian LeeNOAA/NWS Albany, NY

Dave Fitzjarrald, Jeff FreedmanSUNY Albany ASRC

NROW XIV10 December 2013

MotivationMotivation• Aviation IFR occurrence key Government Performance Aviation IFR occurrence key Government Performance

and Results Act (GPRA) performance measureand Results Act (GPRA) performance measure• WFO ALY has tried various methodologies and training WFO ALY has tried various methodologies and training

to improve IFR forecastingto improve IFR forecasting• Distance Learning Aviation Course (DLAC)Distance Learning Aviation Course (DLAC)• Utility of MOS/LAMP guidanceUtility of MOS/LAMP guidance• Crossover temperatureCrossover temperature

• How important is the planetary boundary layer (PBL) How important is the planetary boundary layer (PBL) profile?profile?• Specifically, static stability profileSpecifically, static stability profile

Why the Boundary Layer?Why the Boundary Layer?

• Friction results in ~10-50% reduction of kinetic Friction results in ~10-50% reduction of kinetic energy in the boundary layerenergy in the boundary layer• However, surface fluxes can compensate (turbulence)However, surface fluxes can compensate (turbulence)

• Heat transfer, evapotranspiration, diurnal dragHeat transfer, evapotranspiration, diurnal drag

• IFR CIG and VIS are tied to boundary layer IFR CIG and VIS are tied to boundary layer fluctuationsfluctuations• Fog occurs near surfaceFog occurs near surface• Stratus often occurs near the top of a moist boundary Stratus often occurs near the top of a moist boundary

layerlayer

The Role of Static StabilityThe Role of Static Stability

• So what is the driving force behind IFR?So what is the driving force behind IFR?

• Static stability profileStatic stability profile• Similar in concept to frictionSimilar in concept to friction• Controls an air parcel’s energy (buoyancy) Controls an air parcel’s energy (buoyancy) • Distribution of this profile directly affects PBL orientation of:Distribution of this profile directly affects PBL orientation of:

• MoistureMoisture• WindWind• Momentum (aka turbulence)Momentum (aka turbulence)

θθ θθ θθ

unstableunstable well-mixedwell-mixed stablestableriserise

riserisesinksink

sinksink

Steady unless acted Steady unless acted upon by an upon by an outside forceoutside force

Static Stability Profile Cont.Static Stability Profile Cont.• Wind effectsWind effects

• Subgeostrophic daytime profileSubgeostrophic daytime profile• Supergeostrophic nocturnal low-level jet (LLJ)Supergeostrophic nocturnal low-level jet (LLJ)

• Near-surface winds largely follow logarithmic profileNear-surface winds largely follow logarithmic profile

• Controls distribution/orientation of turbulent eddiesControls distribution/orientation of turbulent eddies• Bulk Richardson NumberBulk Richardson Number

RRii = g*(∂ = g*(∂θθ//ΔΔZ)/Z)/θθ*(∂u/*(∂u/ΔΔz)z)22

*Critical Ri varies depending *Critical Ri varies depending

on resolutionon resolution

(Oke 1978)(Oke 1978)

*0.25 used in this research*0.25 used in this research

> 0.25: inhibits turbulence> 0.25: inhibits turbulence

0-0.25: turbulence possible0-0.25: turbulence possible

< 0: turbulence favored< 0: turbulence favored

DataData• Analyzing 2012 sounding data for KALYAnalyzing 2012 sounding data for KALY• Found every occurrence of IFR VIS and CIG from Found every occurrence of IFR VIS and CIG from

hourly ASOS datahourly ASOS data• Multiple IFR occurrences in a single day counted as only 1 Multiple IFR occurrences in a single day counted as only 1

eventevent• IFR VIS (< 3 SM) IFR VIS (< 3 SM) • 102 events102 events

• IFR CIG (< 1000 ft)IFR CIG (< 1000 ft)• 88 events88 events

Data ResolutionData Resolution

• For each occurrence, gathered previous and For each occurrence, gathered previous and precluding soundingsprecluding soundings• KALY hi-res (1 second interval) sounding dataKALY hi-res (1 second interval) sounding data

• Goal is to recreate what the boundary layer may Goal is to recreate what the boundary layer may have “looked” like at time of IFR occurrencehave “looked” like at time of IFR occurrence

• Initially, using only observed soundingsInitially, using only observed soundings• Differing degrees of model unrepresentativenessDiffering degrees of model unrepresentativeness

• ResolutionResolution• Parameterization schemes (boundary layer, surface model, Parameterization schemes (boundary layer, surface model,

radiative transfer)radiative transfer)

MethodologyMethodology• Focus on variations in the PBLFocus on variations in the PBL• DaytimeDaytime• Convective boundary layer/mixed layer (CBL)Convective boundary layer/mixed layer (CBL)

• Role of turbulent transport of sensible heat, latent heat, and momentum Role of turbulent transport of sensible heat, latent heat, and momentum fluxes fluxes

• Entrainment effects within the inversion transition zone (ITZ) of the free Entrainment effects within the inversion transition zone (ITZ) of the free atmosphere (FA) atmosphere (FA)

• NighttimeNighttime• Nocturnal stable boundary layer (NBL) and residual layer (RL)Nocturnal stable boundary layer (NBL) and residual layer (RL)

• Role of decouplingRole of decoupling

Diurnal PBL EvolutionDiurnal PBL Evolution

(Stull 1988)

““Normal” PBL Profile - DayNormal” PBL Profile - Day

(Stull (Stull 2000)2000)

““Normal” PBL Profile - NightNormal” PBL Profile - Night

f

The Surface Layer – aka NBLThe Surface Layer – aka NBL

• A more stable, “mini” version of the CBLA more stable, “mini” version of the CBL• Turbulence, mixing occur near the surfaceTurbulence, mixing occur near the surface• Critical for moisture distributionCritical for moisture distribution• Fog? Low stratus? Dew? Any clouds?Fog? Low stratus? Dew? Any clouds?

Specific Humidity q

Saturation Specific Humidity qs

(Fitzjarrald and Lala 1989)

Mixed NBL– Radiative CoolingMixed NBL– Radiative Cooling

Radiative cooling Radiative cooling initially concentrated initially concentrated near the surface, near the surface, increasing in depth increasing in depth through the nightthrough the night

Initial radiative cooling in Initial radiative cooling in shallow NBLshallow NBL

Radiative cooling dispersed Radiative cooling dispersed through mixed NBLthrough mixed NBL

Determining Top of PBLDetermining Top of PBL

• Must satisfy three criteria:Must satisfy three criteria:• Increase in potential temperatureIncrease in potential temperature• Decrease in mixing ratioDecrease in mixing ratio• Top must be lower than LCL heightTop must be lower than LCL height

• If these criteria coincide = top of PBLIf these criteria coincide = top of PBL• Multiple criteria used to decrease influence of Multiple criteria used to decrease influence of

subjective analysissubjective analysis• Top of PBL corresponds to base of ITZTop of PBL corresponds to base of ITZ

Inflection pointInflection point

Data Analysis/TermsData Analysis/Terms• Scaling approachScaling approach

h/zh/zi i (day) and (day) and

h/zh/zr,sr,s (night) (night)

hh22/z/zi,ri,r

ΔθΔθmm = z = zii – h – hsfc sfc (day) (day)

ΔθΔθrr = z = zrr - z - zss (night) (night)

ΔθΔθss = z = zss - h - hsfcsfc where…where…

zzii = value at top of CBL = value at top of CBL

zzrr = value at top of RL = value at top of RL

zzss = value at top of NBL = value at top of NBL

h = data level to be scaledh = data level to be scaledhh22 = 1.5h (ITZ depth approx) = 1.5h (ITZ depth approx)

ΔθΔθm,r,sm,r,s = depth of mixed, residual, and surface layers = depth of mixed, residual, and surface layers

• Statistical/graphical analysis performed using R, Excel software Statistical/graphical analysis performed using R, Excel software Adapted from (Stull 2000)

zzi,ri,r

hh22

zzss

hh

ΔΔθθrr

ΔΔθθmm

ITZITZ

Free AtmosphereFree Atmosphere

Preliminary Results/ApplicationsPreliminary Results/Applications

IFR VIS OccurrenceIFR VIS Occurrence

IFR CIG OccurrenceIFR CIG Occurrence

Hourly OccurrenceHourly Occurrence• Peak occurrence between 00-12 UTCPeak occurrence between 00-12 UTC• Coinciding with stable NBLCoinciding with stable NBL

Example - IFRExample - IFR

Onset of nocturnal LLJ

Increased stability, “spike” in moisture

Onset of NBL

Example - VFRExample - VFR

Well-mixed stability profile

Super-adiabatic layer

Favorable turbulence profile

Example – IFR Stratus or Fog?Example – IFR Stratus or Fog?

Distribution of moisture profile can provide clues to fog or stratus potential

Other Potential ApplicationsOther Potential Applications• Wind ForecastingWind Forecasting

• Example: Hurricane SandyExample: Hurricane Sandy• High Wind Warning in effect for much of area from High Wind Warning in effect for much of area from 13 UTC 10/29/12 – 15 UTC 10/30/1213 UTC 10/29/12 – 15 UTC 10/30/12• Did not get as strong of winds as forecasted at KALB and other Did not get as strong of winds as forecasted at KALB and other

valley locations (sub-verification criteria)valley locations (sub-verification criteria)• Peak wind gust at KALB only 37 kts (43 mph)Peak wind gust at KALB only 37 kts (43 mph)• Higher terrain locations received stronger winds (Hancock, MA in Higher terrain locations received stronger winds (Hancock, MA in

Berkshires had a gust to 67 kts/77 mph)Berkshires had a gust to 67 kts/77 mph)

• Why did valley locations not verify, despite intense synoptic-Why did valley locations not verify, despite intense synoptic-scale pressure gradient?scale pressure gradient?

Top of PBL*

Critical Ri (0.25)

Critical Ri (0.25)

Available ToolsAvailable Tools• Can be utilized operationally using AWIPSCan be utilized operationally using AWIPS• Available through Volume BrowserAvailable through Volume Browser• Load Var vs. HeightLoad Var vs. Height• Select Point (make sure centered over TAF site)Select Point (make sure centered over TAF site)

• Potential Temperature, RH, Specific Humidity Potential Temperature, RH, Specific Humidity available in hourly resolution available in hourly resolution • NAM BufrNAM Bufr• GFS Bufr (3 hourly resolution)GFS Bufr (3 hourly resolution)

• Moisture Flux Divergence can be used as a proxy for Moisture Flux Divergence can be used as a proxy for turbulence distributionturbulence distribution

Available Tools – Potential TempAvailable Tools – Potential Temp

Available Tools – CompleteAvailable Tools – Complete

*Consists of:*Consists of:•Potential Potential temperaturetemperature•WindspeedWindspeed•RHRH•Specific Specific humidityhumidity

Available Tools - MoistureAvailable Tools - Moisture

*NWS Albany *NWS Albany has an office has an office procedure that procedure that incorporates incorporates some of these some of these variables:variables:IRLAviationIRLAviation

Specific HumiditySpecific Humidity TemperatureTemperature

Moisture Flux Moisture Flux DivergenceDivergenceWind SpeedWind Speed

BUFKITBUFKIT

Future WorkFuture Work• Continue statistical/graphical analysisContinue statistical/graphical analysis• Expand datasetExpand dataset• December 2011 (to capture winter 2011-2012 season)December 2011 (to capture winter 2011-2012 season)• January 2013 – March 2014 (to capture winter 2013-2014 January 2013 – March 2014 (to capture winter 2013-2014

season)season)

• Differentiate data furtherDifferentiate data further• Season, precip vs. non-precip, types of precipSeason, precip vs. non-precip, types of precip

Future WorkFuture Work

• Creation of forecasting methodologyCreation of forecasting methodology• Develop training/articulate presentations on aviation Develop training/articulate presentations on aviation

boundary layer principlesboundary layer principles• Develop algorithm that computes probability of IFR Develop algorithm that computes probability of IFR

VIS and/or CIG occurrenceVIS and/or CIG occurrence• Utilizing NAM/GFS Bufr files, KALY soundingsUtilizing NAM/GFS Bufr files, KALY soundings

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• Fitzjarrald, David R., Michael Garstang, 1981: Boundary-Layer Growth over the Tropical Ocean. Fitzjarrald, David R., Michael Garstang, 1981: Boundary-Layer Growth over the Tropical Ocean. Mon. Wea. Rev.Mon. Wea. Rev., , 109109, 1762–1772., 1762–1772.

• Fitzjarrald, Dayid R., Michael Garstang, 1981: Vertical Structure of the Tropical Boundary Layer. Fitzjarrald, Dayid R., Michael Garstang, 1981: Vertical Structure of the Tropical Boundary Layer. Mon. Wea. Rev.Mon. Wea. Rev., , 109109, 1512–1526., 1512–1526.

• Fitzjarrald, David R., G. Garland Lala, 1989: Hudson Valley Fog Environments. Fitzjarrald, David R., G. Garland Lala, 1989: Hudson Valley Fog Environments. J. Appl. Meteor.J. Appl. Meteor., , 2828, 1303–1328., 1303–1328.

• Hanna, S.R., Burkhart, C.L., Paine, R.J., 1985. Mixing height uncertainties. Proceedings of 7th AMS Symposium on Turbulence and Diffusion, Boulder, Hanna, S.R., Burkhart, C.L., Paine, R.J., 1985. Mixing height uncertainties. Proceedings of 7th AMS Symposium on Turbulence and Diffusion, Boulder, pp. 82-85.pp. 82-85.

• Mahrt, L., 1985: Vertical Structure and Turbulence in the Very Stable Boundary Layer. Mahrt, L., 1985: Vertical Structure and Turbulence in the Very Stable Boundary Layer. J. Atmos. Sci.J. Atmos. Sci., , 4242, 2333–2349., 2333–2349.

• Martin, C. L., D. Fitzjarrald, M. Garstang, A. P. Oliveira, S. Greco, and E. Browell, 1988: Structure and growth of the mixing layer over the Amazonian Martin, C. L., D. Fitzjarrald, M. Garstang, A. P. Oliveira, S. Greco, and E. Browell, 1988: Structure and growth of the mixing layer over the Amazonian rain forest. rain forest. J. Geophys. ResJ. Geophys. Res., ., 9393, 1361–1375., 1361–1375.

• Oke, T.R., 1978: Oke, T.R., 1978: Boundary Layer ClimatesBoundary Layer Climates, Halsted Press, 372 pp., Halsted Press, 372 pp.

• Stull, R.B., 1988: Stull, R.B., 1988: An Introduction to Boundary Layer Meteorology.An Introduction to Boundary Layer Meteorology. Volume 13. Kluwer Academic Publishers, 670 pp. Volume 13. Kluwer Academic Publishers, 670 pp.

• Stull, R.B., 1991: Static Stability - An Update. Stull, R.B., 1991: Static Stability - An Update. Bull. Amer. Meteorol. SocBull. Amer. Meteorol. Soc. 72, 1521-1529.. 72, 1521-1529.

• Stull R.B., 2000: Stull R.B., 2000: Meteorology for Scientists and Engineers.Meteorology for Scientists and Engineers. 2 2ndnd Edition. Cengage Learning, 528 pp. Edition. Cengage Learning, 528 pp.

Questions?/Comments?Questions?/Comments?