Geophysical Disaster Computational Fluid Dynamics Center • University of British Columbia – Vancouver • Dept. of Earth, Ocean & Atmospheric Sciences • Weather Forecast Research Team • Directed by Prof. Roland Stull • Atmospheric Boundary
Layers, Turbulence & Topics: 1. Boundary Layer Basics Dispersion 2. Static Stability (A Review for the BC Ministry of Environment) 3. BL Evolution 4. Turbulence Generation 5. Turb. Kinetic Energy Roland Stull 6. TKE & Dispersion University of British Columbia (UBC) Vancouver, Canada 7. Pile-burn Case Study March 2017 8. Clarifications of Your Issues
If requested, if time: 9. Dispersion in the Convective ML
1 Survey Results
1) PBL expertise: 1 high , 7 medium, 0 low 2) Turbulence : 1 high , 5 medium , 2 low 3) Plume dispersion: 2 high , 6 medium , 0 low 4) Thermo diagram: 2 tephi, 3 skew-T , 4 not use 5) Potential temperature: 2 high , 4 medium , 2 low 6) Virtual temperature: 1 high , 2 medium , 5 low
7) 6 AERMOD , 3 Hysplit , 7 CALPUFF , 1 CMAQ , 1 GEM-MACH , 1 CAMx 8) Complex terrain: 6 high , 1 medium , 1 low Survey Results - Clarification Desired • PBL formation and breakdown • winter PBLs • PBL in valleys. Also valley clouds vs. inversions • PBL vs smoke dispersion • dispersion prediction days in advance • using soundings to anticipate dispersion • how to understand Weinstein’s Air Qual. Advisory fcsts. • surface roughness • venting: roles of shear and buoyancy • how fine a resolution in NWP is numerically stable • using weather forecasts to anticipate episodes of poor air quality 1. Atmospheric Boundary Layer (ABL)
Some Definitions:
ABL = the portion of the atmosphere that feels the effects of the Earth’s surface, on a timescale of roughly an hour —————————-> {
PBL = planetary boundary layer = ABL
ML = mixed layer (or mixing layer), when the ABL is so strongly mixed by turbulence that conserved properties (humidity, pollutant concentration, potential temperature) are roughly uniform with height. 4 Evolution of Thoughts about the Atmospheric Boundary Layer (ABL)
(a) No height limit. Doesn’t apply in general to the whole ABL, but works for initial growth of atmos. internal boundary layer (IBLs).
(b) Based on theoretical Ekman spiral, assuming molecular diffusion on a rotating planet. Doesn’t work in real atmos. (not even for neutral ABLs)
(c) Based on thermodynamics. where: z = height h = ABL height temperature inversion x = downwind distance M = wind speed u* = friction velocity (a measure of surface stress) fc = Coriolis parameter (1/s) (related to Earth’s rotation) θ = potential temperature 5 Evolution of Thoughts about the Atmospheric Boundary Layer (ABL)
(a) No height limit. Doesn’t apply in general to the whole ABL, but works for initial growth of atmos. internal boundary layer (IBLs).
(b) Based on theoretical Ekman spiral, assuming molecular diffusion on a rotating planet. Doesn’t work in real atmos. (not even for neutral ABLs)
(c) Based on thermodynamics. where: z = height h = ABL height temperature inversion x = downwind distance M = wind speed u* = friction velocity (a measure of surface stress) fc = Coriolis parameter (1/s) (related to Earth’s rotation) θ = potential temperature 5 Evolution of Thoughts about the Atmospheric Boundary Layer (ABL)
(a) No height limit. Doesn’t apply in general to the whole ABL, but works for initial growth of atmos. internal boundary layer (IBLs).
(b) Based on theoretical Ekman spiral, assuming molecular diffusion on a rotating planet. Doesn’t work in real atmos. (not even for neutral ABLs)
(c) Based on thermodynamics. where: z = height h = ABL height temperature inversion x = downwind distance M = wind speed u* = friction velocity (a measure of surface stress) fc = Coriolis parameter (1/s) (related to Earth’s rotation) θ = potential temperature 5 Evolution of Thoughts about the Atmospheric Boundary Layer (ABL)
(a) No height limit. Doesn’t apply in general to the whole ABL, but works for initial growth of atmos. internal boundary layer (IBLs).
(b) Based on theoretical Ekman spiral, assuming molecular diffusion on a rotating planet. Doesn’t work in real atmos. (not even for neutral ABLs)
(c) Based on thermodynamics. where: z = height h = ABL height temperature inversion x = downwind distance M = wind speed u* = friction velocity (a measure of surface stress) fc = Coriolis parameter (1/s) (related to Earth’s rotation) θ = potential temperature 5 • Turbulence Creates the ABL. • The ABL Traps Turbulence. Thus: feedback. θ = T + Γ z = potential temperature, where Γ = 9.8 °C/km = dry adiabatic lapse rate
Stratosphere 12 Tropopause 10
Troposphere 8
6
Free
Height, z (km) 4 Atmosphere
2 Capping Inversion zi Turbulent Boundary Layer 0 10 20 30 40 50 60 Potential Temperature (°C) 2 Capping Inversion z zi (km) Turbulent Boundary Layer 0 10 20 30 40 50 60 Potential Temperature (°C) There is always a capping inversion at the top of the ABL. Let zi be the inversion height.
Free Atmosphere ers Troposphere g Inv ion pin ~11 km ap er C ry Lay nda Height, z ou ~2 km zi B Earth Horizontal distance, x 2. Static Stability
Little or no pollutant dispersion if the flow is not turbulent.
<— use thermo diagram to determine static stability 2. Static Stability
Little or no pollutant dispersion if the flow is not turbulent.
<- Vigorous pollutant dispersion <- No pollutant dispersion <- Modest pollutant dispersion
<— use thermo diagram to determine static stability Thermo Diagrams (Give handouts. Choice: skew-T or tephigram) .JYJOH3BUJP HLH 4LFX5-PH1%JBHSBN $PQZSJHIU¥CZ3PMBOE4UVMM 'SFFDPQJFTPGUIJTQBHFQFSNJUUFE GSPN i1SBDUJDBM.FUFPSPMPHZ"O"MHFCSBCBTFE4VSWFZ $ $ $ $ $ $%SZ"EJBCBU
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3 km of the atmosphere. 5 m$JTPUIFSN )FJHIU LN 1SFTTVSF L1B
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HLH
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Free downloads: search on “Practical Meteorology Stull”. See end of Chapter 5. Next: step by step instructions on how to determine static stability from a sounding
(using a contrived example) Step 1 find kinks in the sounding (including top and bottom end points) Step 1 find kinks in the sounding (including top and bottom end points) Step 2 from each kink, conceptually lift an air parcel following a dry adiabat.
If buoyancy force is in the same direction as your lifting, then label with “U” for unstable.
If buoyancy would return it to its starting point, then label as “S” for stable.
Otherwise, “N” for neutral. Step 3 from each kink, conceptually lower an air parcel following a dry adiabat.
If buoyancy force is in the same direction as your initial motion, then label with “U” for unstable.
If buoyancy would return it to its starting point, then label as “S” for stable.
Otherwise, “N” for neutral. Step 4 for all the motions labeled with “U”, continue moving the parcial dry adiabatically until it hits the sounding or the ground.
The superposition of these “U” domains identifies all the Unstable layers in the atmos.
Unstable always wins. Step 4 forac all castellanus the motions labeled with “U”, continue moving the parcial dry adiabatically untilBide CCit hits BY-SA 3.0 Wikipedia the sounding or the ground.
The superposition of these “U” domains identifies all the Unstable layers in the atmos.
Unstable always wins. Step 4 forac all castellanus the Remember: motions labeled Unstable with “U”, continue regions moving the cause parcial dry rapid adiabatically dispersion. untilBide CCit hits BY-SA 3.0 Wikipedia the sounding or the ground.
The superposition of these “U” domains identifies all the Unstable layers in the atmos.
Unstable always wins. Step 5 all remaining portions of “S” regions that are not unstable are STABLE, and all remaining portions of “N” regions that are not unstable are NEUTRAL. 72265 MAF Midland 100 16340 m SLAT 31.93 SLON SELV 874.0 SHOW 13.39 LIFT 13.07 LFTV 12.98 SWET 110.9 KINX 4.30 13850 m CTOT 7.30 VTOT 21.30 TOTL 28.60 CAPE 0.00 CAPV 0.00 CINS 0.00 200 12050 m CINV 0.00 EQLV −9999 EQTV −9999 LFCT −9999 LFCV −9999 10620 m BRCH 0.00 BRCV 0.00 LCLT 265.2 LCLP 693.2 300 9410 m MLTH 294.5 MLMR 3.06 THCK 5561. PWAT 7.89
400 7400 m Midland, TX
500 5750 m Q: The approx. static stability of the shaded 600 layer is
A) stable dry adiabat 700 3121 m B) neutral C) conditionally unstable 800 D) unstable 1562 m E) not enough info 900 856 m 1000 189 m 0.4 1 2 4 7 10 16 24 32 40g/kg
−40 −30 −20 −10 0 10 20 30 40 00Z 23 Oct 2008 T (°C) University of Wyoming 72265 MAF Midland 100 16340 m SLAT 31.93 SLON SELV 874.0 SHOW 13.39 LIFT 13.07 LFTV 12.98 SWET 110.9 KINX 4.30 13850 m CTOT 7.30 VTOT 21.30 TOTL 28.60 CAPE 0.00 CAPV 0.00 CINS 0.00 200 12050 m CINV 0.00 EQLV −9999 EQTV −9999 LFCT −9999 LFCV −9999 10620 m BRCH 0.00 BRCV 0.00 LCLT 265.2 LCLP 693.2 300 9410 m MLTH 294.5 MLMR 3.06 THCK 5561. PWAT 7.89
400 7400 m Midland, TX
500 5750 m Q: The approx. static stability of the shaded 600 layer is
A) stable dry adiabat 700 3121 m B) neutral dry adiabat C) conditionally unstable unstable 800 D) unstable 1562 m E) not enough info 900 856 m 1000 189 m 0.4 1 2 4 7 10 16 24 32 40g/kg
−40 −30 −20 −10 0 10 20 30 40 00Z 23 Oct 2008 T (°C) University of Wyoming 72265 MAF Midland 100 16340 m SLAT 31.93 SLON SELV 874.0 SHOW 13.39 LIFT 13.07 LFTV 12.98 SWET 110.9 KINX 4.30 13850 m CTOT 7.30 VTOT 21.30 TOTL 28.60 CAPE 0.00 CAPV 0.00 CINS 0.00 200 12050 m CINV 0.00 EQLV −9999 EQTV −9999 LFCT −9999 LFCV −9999 10620 m BRCH 0.00 BRCV 0.00 LCLT 265.2 LCLP 693.2 300 9410 m MLTH 294.5 MLMR 3.06 THCK 5561. PWAT 7.89
400 7400 m Midland, TX
500 5750 m Q: The approx. static stability of the shaded 600 layer is Near neutral
A) stable dry adiabat 700 3121 m B) neutral dry adiabat C) conditionally unstable unstable 800 D) unstable 1562 m E) not enough info 900 856 m 1000 189 m 0.4 1 2 4 7 10 16 24 32 40g/kg
−40 −30 −20 −10 0 10 20 30 40 00Z 23 Oct 2008 T (°C) University of Wyoming 72265 MAF Midland 100 16340 m SLAT 31.93 SLON SELV 874.0 SHOW 13.39 LIFT 13.07 LFTV 12.98 SWET 110.9 KINX 4.30 13850 m CTOT 7.30 VTOT 21.30 TOTL 28.60 CAPE 0.00 CAPV 0.00 CINS 0.00 200 12050 m CINV 0.00 EQLV −9999 EQTV −9999 LFCT −9999 LFCV −9999 10620 m BRCH 0.00 BRCV 0.00 LCLT 265.2 LCLP 693.2 300 9410 m MLTH 294.5 MLMR 3.06 THCK 5561. PWAT 7.89
400 7400 m Midland, TX
500 5750 m Q: The approx. static stability of stable the shaded 600 layer is Near neutral
A) stable dry adiabat stable 700 3121 m B) neutral dry adiabat C) conditionally unstable unstable 800 D) unstable 1562 m E) not enough info 900 856 m 1000 189 m 0.4 1 2 4 7 10 16 24 32 40g/kg
−40 −30 −20 −10 0 10 20 30 40 00Z 23 Oct 2008 T (°C) University of Wyoming Scenario: nighttime over a forest. Calm winds. Clear skies. .JYJOHSBUJP HLH 4LFX5-PH1%JBHSBN "#- $PQZSJHIU¥CZ3PMBOE4UVMM Sounding 'SFFDPQJFTPGUIJTQBHFQFSNJUUFE GSPN Work in teams to i1SBDUJDBM.FUFPSPMPHZ"O"MHFCSBCBTFE4VSWFZ PG"UNPTQIFSJD4DJFODFu R R 5 plot this sounding, P (kPa) T (°C) r4UBUFMJOFTBSFUIJO 8 r1SPDFTTMJOFTBSF UIJDL BOEBSFMBCFMFE & identify the altitudes 80 8 XJUIUFNQFSBUVSFXIFSF UIFZDSPTT1 L1B R XFUCVMCQPUFOUJBMUFNQ $ 8 (top and bottom) 84 6 of stable, neutral, and R 90 11 $
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Height, z HLH d
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m m 5FNQFSBUVSF $ 3. Boundary Layer Evolution (a) DAY Boundary z z z FA Layer zi EZ Evolution ML Height, z SL additional T θ q VBL G V variables (b) NIGHT z z z FA
zi CI
RL
Height, z SBL
T θ q G V Boundary Layer Evolution - Summer, Fair Wx Boundary Layer Evolution - Winter, Fair Wx
16
16 Boundary Layer Evolution - Inversions & Clouds
Free Atmosphere
E.Z. Capping Inversion
Residual
Height, z Layer Mixed Layer Stable BL
Day 1 Night 1 Day 2 Boundary Layer Evolution - Inversions & Clouds
Phase 1 Phase 2 Phase 3 Nocturnal Rapid Quasi- Inversion Rise steady Burn-off Height, z clouds ~1 km LCL
zi
sunrise mid morning mid afternoon Boundary Layer Evolution - Synoptic Variations
tropopause tropopause clouds (a)
deep subsidence clouds Height, z updrafts clouds fro zi ntal in vers top yer ion of boundary la zi zi warm air z cold BL divergence convergence BL air x frontal High Low zone
z Tropopause
poor air quality Venting by
(b) thunderstorms y H L x Venting y by fronts
x Take a 5 minute “stretch” break 4. Turbulence Generation in ABL three mechanisms: 1) Buoyancy (warm air rising or cold air sinking as thermals) => thermal generation of turbulence in UNSTABLE ABL.
z Clean (km)
thermal diameter ≈ height Polluted
Time Vertical pointing lidar. Image by Shane Mayor Turbulence Generation in ABL three mechanisms: 2. Wind shear (change of wind speed or direction with z) => mechanical generation of turb. in neutral & stable ABL. boundary shear free shear at the ground across a temperature inversion z z 20 m 2 km
inversion layer
M is wind speed T M Turbulence Generation in ABL three mechanisms: 2. Wind shear (change of wind speed or direction with z) => mechanical generation of turb. in neutral & stable ABL. boundary shear free shear at the ground across a temperature inversion z z 20 m 2 km KH wave cloud inversion layer
May Wong 2016
M is wind speed T M Turbulence Generation in ABL three mechanisms:
3) Obstacle wakes (behind trees, bldgs, mountains, cars) => mechanical generation of turbulence wind
banner cloud
wake turbulence ABL Wind- Turbulence Feedbacks
Buoyantly generated turbulence behaves in a special way. Thus, pollutant dispersion also behaves in a special way in convective mixed layers. Turbulence = gustiness Standard Deviation: Anisotropic (not isotropic) σw > σu examples:
σu > σw Why do we care about σz σz sigma- velocity?
Greater σw causes faster spread σz.
Greater σv causes faster spread σy.
Greater σu causes faster spread σx. Anisotropy and Dispersion 5.
A statistic tells us about turbulent energy. TKE Budget
Flux Richardson Number:
a measure of dynamic stability In a nutshell: TKE S Increases as wind shear increases Budget B positive when warm thermals are rising or when cold “thermals” are sinking. (this happens in statically unstable air)
B negative when warm air tries to sink, or cold air tries to rise. (this happens in statically stable air)
ε always causes TKE to decrease. Turbulence is NOT conserved. TKE will decay exponentially toward zero. Turbulence can be maintained ONLY if it is continually generated. 6. TKE and Dispersion S Shear Generation Rate (m2/s3)
0.006
0.004
0.002
0 –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Buoyant Generation Rate (m2/s3) S TKE more turb. Shear Generation Intensity Rate (m2/s3) 0 0.006 less turb.
0.004 Turbulence NO 0.002
0 –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Buoyant Generation Rate (m2/s3) Static Stability & S Flow Type Shear Generation Rate (m2/s3) forced convection 0.006 neutral SST free convection 0.004
unstable
0.002 Turbulence waves NO
stable
0
Flow –0.006 -> –0.004 –0.002 0 0.002 0.004 0.006 B Buoyant Generation
Static Stab -> Rate (m2/s3) Richardson S Number Shear Generation Rate (m2/s3)
0.006
0.004 Rf=0
Rf=1 Rf=–1 0.002
0 Rf=∞ Rf=–∞ –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Buoyant Generation Rate (m2/s3) Dynamics S Stability Shear Generation Rate (m2/s3)
0.006
0.004 Rf=0 Dynamically Stable Rf=1 NO Turbulence Dynamically Unstable Rf=–1 0.002 & Turbulent
0 Rf=∞ Rf=–∞ –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Buoyant Generation Rate (m2/s3) Pasquill-Gifford Turbulence Type Pasquill-Gifford S Turbulence Type Shear Generation Rate (m2/s3) forced convection 0.006 D E neutral C SST free convection 0.004 F
unstableB G 0.002 waves stable A
0 –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Pasquill Buoyant Generation Rate (m2/s3) Gifford Turb. Type Smoke Plume S Cross Section Shear Generation Rate (m2/s3) forced convection 0.006 D E neutral C SST free convection 0.004 F
unstableB G 0.002 waves stable A
0 –0.006 –0.004 –0.002 0 0.002 0.004 0.006 B Pasquill Buoyant Generation Rate (m2/s3) Gifford Turb. Type
Take a 5 minute “stretch” break 7. Pile-burn Case Study. Sep 2016 near Smithers thanks to Ben Weinstein
“A forest company burned 400+ industrial slash piles < 20 km from Smithers. The venting forecast was ‘good’, however the plume was trapped aloft and had a defined top and bottom (see pictures). It ended up descending into town in the evening and led to high exposure for a short time, causing me much grief and extra workload.”
Morning or Mid-day
photos provided by Ben Weinstein Morning or Mid-day
photos provided by Ben Weinstein Evening. Photos provided by Ben Weinstein One possible explanation.
Cap. Inversion
RL EZ ML
Discussion? Thoughts? 8. Clarifications of Some of Your Issues
• PBL formation and breakdown • winter PBLs • PBL in valleys. Also valley clouds vs. inversions • PBL vs smoke dispersion • dispersion prediction days in advance • using soundings to anticipate dispersion • how to understand Weinstein’s Air Qual. Advisory fcsts. • surface roughness • venting: roles of shear and buoyancy • how fine a resolution in NWP is numerically stable • using weather forecasts to anticipate episodes of poor air quality • how fine a resolution in NWP Clarifications is numerically stable? • We run NWP models at ∆x = 1.3 km every day, & 0.44 km for case studies. • “Resolution” = 7 ∆x in most NWP • Our “nowcasting” map combines NWP, station data, and very-high res. DEM.
Nowcast created by Nadya Moisseeva Clarifications • Valley PBLs, inversions & dispersion See Chapter 17 of Stull 2015: Practical Meteorology. Anabatic & katabatic winds during fair weather.
anabatic winds
valley winds (a) Clarifications • Valley PBLs, inversions & dispersion See Chapter 17 of Stull 2015: Practical Meteorology. Valley inversions in fair weather. Gap winds.
needs cold air under warm Clarifications • Valley PBLs, inversions & dispersion See Chapter 17 of Stull 2015: Practical Meteorology. For synoptically windy conditions. Mountain waves Barrier Jet.
Fr = λ/2W ∝ M/(W·NBV) = Froude Number
W Clarifications • Valley PBLs, inversions & dispersion See Chapter 17 of Stull 2015: Practical Meteorology. Downslope winds Bora Foehn = Chinook
Channeled flow. Survey Results - Clarification Presented
✓ PBL formation and breakdown ✓ winter PBLs ✓ PBL in valleys. Also valley clouds vs. inversions ✓ PBL vs smoke dispersion • dispersion prediction days in advance (use NWP) ✓ using soundings to anticipate dispersion • how to understand Weinstein’s Air Qual. Advisory fcsts. • surface roughness (rougher terrain causes slower winds but greater turbulence intensity near the ground) ✓ venting: roles of shear and buoyancy (greater shear & buoyancy increase dispersion rate, but other factors for venting include inversion height and wind speed) ✓ how fine a resolution in NWP is numerically stable ✓ using weather forecasts to anticipate episodes of poor air quality Geophysical Disaster Computational Fluid Dynamics Center • University of British Columbia – Vancouver • Dept. of Earth, Ocean & Atmospheric Sciences • Weather Forecast Research Team • Directed by Prof. Roland Stull •
Topics: Atmospheric Boundary 1. Boundary Layer Basics 2. Static Stability Layers, Turbulence & 3. BL Evolution Dispersion 4. Turbulence Generation 5. Turb. Kinetic Energy Prof. Roland Stull, CCM, CFII 6. TKE & Dispersion Dept. of Earth, Ocean & Atmospheric Sciences University of British Columbia (UBC) 7. Pile-burn Case Study 2020-2207 Main Mall 8. Clarifications of Your Issues Vancouver, BC V6T 1Z4 Canada If requested, if time: [email protected] 9. Dispersion in the +1 604 822 5901 Convective ML
For free book online: https://www.eoas.ubc.ca/books/Practical_Meteorology/ the end 61 9. Dispersion in a Convective Mixed Layer Jim Deardorff
Snapshots
Time Average
Strangely, for a convective ML, the centreline can descend. (show Deardorff tank movie if time) Time-averaged Centreline Height (ZCL) vs. Downwind Distance (x)
FH = surface heat flux, zi = mixed layer depth, M = wind speed Cross-wind Integrated Concentration, Cy Cy vs. z and x, for various effect stack heights