The impact of mesoscale PBL parameterizations

on the evolution of mixed-layer processes important for fire weather

Joseph J. CharneyUSDA Forest Service, Northern Research Station, East Lansing, MI

Daniel KeyserDepartment of Atmospheric and Environmental Sciences, University at

Albany, Albany, NY

1. Background

2. WRF model configuration

3. Double Trouble State Park (DTSP) wildfire case study

4. Summary and future work

Organization

• Mesoscale models are important tools for fire-weather forecasting and research applications.

• The surface-based mixed layer can profoundly influence fire–atmosphere interactions.

• Mixed-layer profiles of temperature, moisture, and wind strongly affect the evolution of a wildland fire.

• Mixed-layer processes are incorporated into mesoscale models through the planetary boundary layer (PBL) parameterization scheme.

Background

• WRF version 3.1

• 4 km nested grid

• 51 sigma levels, with 21 levels in the lowest 2000 m

• NARR data used for initial and boundary conditions

• Noah land-surface model

• RRTM radiation scheme

• MRF, YSU, MYJ, MYNN PBL schemes

WRF model configuration

PBL schemes

• MRF (Hong and Pan 1996): MRF PBL; predecessor to YSU scheme with implicit treatment of entrainment layer.

• YSU (Hong et al. 2006): update of MRF scheme; explicit entrainment layer, reduced mixing in high wind regimes, more realistic diurnal PBL growth.

• MYJ (Janjić 1990, 1994): TKE-based PBL prediction scheme used in Eta and MM5 models; Mellor–Yamada level 2.5 turbulence closure and local vertical mixing.

• MYNN (Nakanishi and Niino 2004): update to the MYJ scheme; deeper mixed layer, better representation of vertical moisture gradients.

WRF model configuration

Surface physics schemes

• MRF: MM5 similarity scheme

• YSU: MM5 similarity scheme

• MYJ: Eta similarity scheme

• MYNN: updated version of Eta similarity scheme

WRF model configuration

Surface physics schemes

• Simulations with the MYNN PBL scheme were rerun using the surface physics schemes for the MRF, YSU, and MYJ PBL schemes.

• Changing the surface physics scheme results in relatively minor differences compared with the differences that arise from changing the PBL scheme.

WRF model configuration

DTSP wildfire case study

DTSP wildfire event

• Occurred on 2 June 2002 in east-central NJ• An abandoned campfire grew into a major wildfire by

1800 UTC• Burned 1,300 acres• Forced closure of the Garden State Parkway• Damaged or destroyed 36 homes and outbuildings• Directly threatened over 200 homes• Forced evacuation of 500 homes• Caused ~$400,000 in property damage

DTSP wildfire event

Fire location

OKXupper air station

KWRI surface station

New Brunswick wind profiler

DTSP wildfire observations

Observed skew T–log p sounding at Upton, NY (OKX), valid at 0000 UTC 3 June 2002

Simulated skew T–log p sounding at OKX valid at 0000 UTC 3 June 2002

MRF

DTSP wildfire simulationsWRF simulations initialized at 1200 UTC 1 June 2002

Simulated skew T–log p sounding at OKX valid at 0000 UTC 3 June 2002

YSU

DTSP wildfire simulations

MYJ

Simulated skew T–log p sounding at OKX valid at 0000 UTC 3 June 2002

DTSP wildfire simulations

MYNN

Simulated skew T–log p sounding at OKX valid at 0000 UTC 3 June 2002

DTSP wildfire simulations

Wind profiler observations at New Brunswick, NJ, from 1100 UTC to 2100 UTC 2 June 2002

DTSP wildfire observations

MRF

DTSP wildfire simulations

Simulated skew T–log p sounding at the fire location valid at 1800 UTC 2 June 2002

YSU

DTSP wildfire simulations

Simulated skew T–log p sounding at the fire location valid at 1800 UTC 2 June 2002

MYJ

DTSP wildfire simulations

Simulated skew T–log p sounding at the fire location valid at 1800 UTC 2 June 2002

MYNN

DTSP wildfire simulations

Simulated skew T–log p sounding at the fire location valid at 1800 UTC 2 June 2002

surface temperature (°C)

21.0022.00

23.0024.00

25.0026.00

27.0028.00

29.0030.00

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

MRF

YSU

MYNN

MYJ

OBS - McGuire AFB

DTSP wildfire simulations

Time series at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated surface temperature

surface mixing ratio (g kg−1)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

MRF

YSU

MYNN

MYJ

OBS - McGuire AFB

DTSP wildfire simulations

Time series at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated surface mixing ratio

surface wind speed (m s−1)

0.001.002.003.004.005.006.007.008.009.00

10.00

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

MRF

YSU

MYNN

MYJ

OBS - McGuire AFB

DTSP wildfire simulations

Time series at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated surface wind speed

MRF temperature profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

temperature (°C)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated temperature

YSU temperature profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

temperature (°C)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated temperature

MYJ temperature profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

temperature (°C)

he

igh

t (k

m)

1200

1300

1400

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1600

1700

1800

1900

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2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated temperature

MYNN temperature profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

temperature (°C)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated temperature

MRF mixing ratio profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00

mixing ratio (g kg−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated mixing ratio

YSU mixing ratio profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00

mixing ratio (g kg−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated mixing ratio

MYJ mixing ratio profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00

mixing ratio (g kg−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated mixing ratio

MYNN mixing ratio profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00

mixing ratio (g kg−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated mixing ratio

MRF wind speed profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

wind speed (m s−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated wind speed

YSU wind speed profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

wind speed (m s−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated wind speed

MYJ wind speed profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

wind speed (m s−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated wind speed

MYNN wind speed profiles

0

0.5

1

1.5

2

2.5

3

3.5

0.00 5.00 10.00 15.00 20.00 25.00 30.00

wind speed (m s−1)

he

igh

t (k

m)

1200

1300

1400

1500

1600

1700

1800

1900

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2100

DTSP wildfire simulations

Vertical profiles at fire location valid from 1200 UTC to 2100 UTC 2 June 2002 of simulated wind speed

• An intercomparison of the MRF, YSU, MYJ, and MYNN PBL schemes in WRF version 3.1 for the DTSP wildfire event indicates that the behavior of these schemes is consistent with that documented in the literature.

• The MRF and YSU schemes produce less directional wind shear than the MYJ and MYNN schemes.

• The diurnal growth of the mixed layer is more gradual in the YSU, MYJ, and MYNN schemes than in the MRF scheme.

• The YSU and MYNN PBL schemes exhibit a deeper mixed layer than the MYJ scheme.

Summary

Future work

• The methodology developed for the DTSP wildfire event will be extended to additional events.

• Candidates include the Warren Grove (NJ, 2007), Evans Road (NC, 2008), and Cottonville (WI, 2005) wildfires.

• Aspects to be examined for these events:

1) effects of the entrainment formulation on mixed-layer growth

2) sensitivity of mixing ratio profiles in the mixed layer to the choice of PBL scheme

3) performance of the PBL schemes in high-wind regimes