Fire P lume K inematic S tructure O bserved U sing Doppler W ind L idar

Fire Plume Kinematic Structure Observed Fire Plume Kinematic Structure Observed Using Doppler Wind LidarUsing Doppler Wind Lidar

Allison Charland, Craig Clements, Daisuke SetoDepartment of Meteorology and Climate Science

San José State UniversitySan José, CA

American Meteorological SocietyNinth Symposium on Fire and Forest Meteorology

19 October 2011

San José State UniversityFire Weather Research Laboratory

Overview

• Introduction• Experimental Design• Observations• Preliminary Results


Introduction

• A prescribed burn was conducted in complex terrain on 13 July 2011

• The burn unit included ~660 total acres – Oak woodland


Goals

• To observe structure of the velocity field in the vicinity of a fire

• Test the performance of the Doppler wind lidar for wildland fire applications


Experimental Site

San Jose

San Francisco

Diablo RangeSanta Cruz M

ountains

Instrumentation

• 2 Remote Automated Weather Stations (RAWS)• T, RH, WS, WD, P

• 6.7-m In situ Tower• 3D winds at 6.5 m• Turbulence• Sensible and Radiant Heat flux

• 2 Radiosonde Sounding Systems• GRAW GS-E• Vaisala, Inc., DigiCora MW31


Neal Waters Photography

Instrumentation• MiniSoDAR

• Atmospheric Systems Corporation (ASC)• 10 min, 20-200 m AGL

• Doppler wind lidar • Halo Photonics, Ltd. Stream Line 75 • 1.5 micron• Eye-safe• 75 mm aperture all-sky optical

scanner • Min Range: 80 m• Max Range: 10km• 550 user defined range gates (24 m)• Temporal resolution: 0.1-30 s

• Profiling Radiometer• Radiometrics, Inc., MP-3000A



Experimental Design• Total of ~ 660 acres in the

burn unit• Prevailing wind from the

northwest• Ignited at the Northeast

corner of the burn unit at 11:43 PST

• Lidar placed upwind of burn area

• Sodar placed downwind • Tower within the burn unit• RAWS near the lidar and the

other higher on the ridge• Radiosondes launched at

different times from along the ridge near the sodar and from near the lidar

RAWS

Radiosonde

Radiosonde

Lidar Scanning Techniques• Multiple elevation and azimuth

angles were adjusted throughout the experiment to obtain the best scan through the fire plume.– Stare: Vertically pointing beam– Wind Profile– RHI (Range Height Indicator):

• Fixed azimuth angle with varying elevation angles

– PPI (Plan Position Indicator):• Fixed elevation angle with

varying azimuth angles


95o

30o

70o

Weather Conditions• Slight drizzle in the morning before the burn.• Morning soundings show a moist layer extending to 900 hPa drying out by

noon.

-10 -5 0 5 10 15

700

750

800

850

900

950

Temperature (oC)

Pre

ssur

e (h

Pa)

-15 -10 -5 0 5 10 15 20

700

750

800

850

900

950

Temperature (oC)

Pre

ssur

e (h

Pa)

13 July 2011 0900 PST 13 July 2011 1149 PST

Background Soundings


Surface Conditions• Relative humidity between 50-70% during the time of the burn.• Wind speeds from 1-4 ms-1

• With moisture in the morning and light wind speeds throughout the day, the fire intensity was fairly low for this particular burn.


09 10 11 12 13 14 15 16 17 180

1

2

3

4

5

Win

d Sp

eed

(ms-1

)

09 10 11 12 13 14 15 16 17 180

90

180

270

360W

ind

Dire

ction

(deg

)

Time (PST)

09 10 11 12 13 14 15 16 17 1810

15

20

25

Tem

pera

ture

(o C)

09 10 11 12 13 14 15 16 17 1840

60

80

100

Rela

tive

Hum

idity

(%)

Time (PST)

12:00 13:00 14:000

2

4

6

Time (PST)

Heat Flux (kWm-2)

Total heat flux

Radiative heat flux

12:00 13:00 14:00-4

-2

0

2

4

Vertical Velocity (ms-1)

w


Tower Measurements• Increased heat flux to 4

kWm-2 as the fire passes the tower.

• No signature in the vertical velocity as normally seen, due to lower intensity of the fire.

13 July 2011 1237 PST 13 July 2011 1644 PST

Thermodynamic Plume Properties: Ridge Top Soundings


• Warming near the surface through the fire plume ~4 K.• Enhanced moisture in the plume of 1 gkg-1.

2 4 6 80

100

200

300

400

500

600

Mixing Ratio

Hei

ght

(m A

GL)

294 296 298 3000

100

200

300

400

500

600

Potential Temperature (K)

2 4 6 80

100

200

300

400

500

600

Mixing RatioH

eigh

t (m

AG

L)

294 296 298 3000

100

200

300

400

500

600

Potential Temperature (K)(gkg-1) (gkg-1)

Time (PST)

TKE (m2s-2)H

eigh

t (AG

L)

11:00 11:10 11:20 11:30 11:40 11:50 12:00 12:10 12:20 12:30 12:40 12:50 1:0020

40

60

80

100

120

140

160

180

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

-0.75

-0.75

-0.5

-0.5-0.25 -0.25

0

0 0

0

0

00

0 0

0

0

0

0.25

0.25

0.25

0.25

0.25

0.250.5

0.5

0.5

0.50.5

0.5

0.5

0.50.75

0.750.75

1

1

11

1

1.251.25

Vertical Velocity (ms-1)

Heig

ht (A

GL)

11:00 11:10 11:20 11:30 11:40 11:50 12:00 12:10 12:20 12:30 12:40 12:50 1:0020

40

60

80

100

120

140

160

180

Kinematic Plume Properties: SoDAR

• Time-height contours of vertical velocity and TKE

• Downward motion shortly after ignition

• Vertical motion above 100 m at 12:20

• Increased turbulence within the plume

Ignition

Lidar: RHI Scans• Backscatter intensity and radial

velocity vertical cross sections • 7.5-45o elevation angle with

increments of 2.5o and at a 95o azimuth angle for the time period of 1701-1830 PST.

95o


1804 PST

x

z

Lidar: RHI ScansBackscatter Intensity (dB) Doppler Radial Velocity (ms-1)

1751 PST1751 PST

1746 PST 1746 PST

Strong radial velocity underneath and within the plume

Entrainment of the plume

Weaker velocity aloft

Lidar was able to penetrate through

the plume

1759 PST1759 PST

Lidar: RHI ScansBackscatter Intensity (dB) Doppler Radial Velocity (ms-1)

1805 PST1805 PST

Weaker radial velocity with dispersion

of the plume


Lidar: PPI Scans 1755 PST

X (m)

Y (

m)

Backscatter Intensity (dB)

200 400 600 800 1000 1200 1400 1600

200

400

600

800

1000

1200

1400

1600

-60

-50

-40

-30

-20

-10

0

200 400 600 800 1000 1200 1400 1600

200

400

600

800

1000

1200

1400

1600

X (m)

Y (

m)

Doppler Radial Velocity (m/s)

-8

-6

-4

-2

0

2

4

6

8

Maps at 30-70o azimuth angle with increments of 1.0o at a 10o elevation angle.Lidar penetrates through the most intense part of the plume but is attenuated at times.

Increased velocity in the intense part of the plume.

Plume blocking the ambient wind.

Summary•Moisture in the morning combined with low wind speeds throughout the day kept the fire intensity low for the prescribed burn.•LIDAR performed well, able to penetrate main convection core of the plume.•Increased turbulence within the plume.•Strong radial velocities beneath and within the plume.•Reduced velocities observed downwind of the plume indicating ambient wind modification.


Future Work

• Further processing of Lidar data • Comparisons of Lidar measurements and in situ

measurements• Collect Lidar data on more fires


Acknowledgements

• CalFire– Battalion Chief Dave McLean

• NSF Grant #0960300

• USDA #07-JV-11242300-073



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Fire P lume K inematic S tructure O bserved U sing Doppler W ind L idar

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