Fire Plume Kinematic Structure Observed Using Doppler Wind Lidar Allison Charland, Craig Clements, Daisuke Seto Department of Meteorology and Climate Science San José State University San José, CA American Meteorological Society Ninth Symposium on Fire and Forest Meteorology 19 October 2011 San José State University Fire Weather Research Laboratory

Overview Introduction Experimental Design Observations Preliminary Results San José State University Fire Weather Research Laboratory

Introduction A prescribed burn was conducted in complex terrain on 13 July 2011 The burn unit included ~660 total acres Oak woodland San José State University Fire Weather Research Laboratory

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 San José State University Fire Weather Research Laboratory

Diablo Range Santa Cruz Mountains San Francisco Experimental Site San Jose

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 San José State University Fire Weather Research Laboratory

Instrumentation MiniSoDAR Doppler wind lidar Profiling Radiometer 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 Neal Waters Photography San José State University Fire Weather Research Laboratory

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 Radiosonde RAWS 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 30o 70o 95o San José State University Fire Weather Research Laboratory

Weather Conditions Background Soundings Slight drizzle in the morning before the burn. Morning soundings show a moist layer extending to 900 hPa drying out by noon. Background Soundings 13 July 2011 0900 PST 13 July 2011 1149 PST San José State University Fire Weather Research Laboratory

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. San José State University Fire Weather Research Laboratory

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. San José State University Fire Weather Research Laboratory

Thermodynamic Plume Properties: Ridge Top Soundings 13 July 2011 1237 PST 13 July 2011 1644 PST (gkg-1) (gkg-1) Warming near the surface through the fire plume ~4 K. Enhanced moisture in the plume of 1 gkg-1. San José State University Fire Weather Research Laboratory

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 x z 1804 PST San José State University Fire Weather Research Laboratory

Lidar: RHI Scans Lidar was able to penetrate through the plume Backscatter Intensity (dB) Doppler Radial Velocity (ms-1) 1746 PST 1746 PST Strong radial velocity underneath and within the plume Weaker velocity aloft 1751 PST 1751 PST Entrainment of the plume

Weaker radial velocity with dispersion Lidar: RHI Scans Backscatter Intensity (dB) Doppler Radial Velocity (ms-1) 1759 PST 1759 PST Weaker radial velocity with dispersion of the plume 1805 PST 1805 PST

Lidar: PPI Scans 1755 PST 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. San José State University Fire Weather Research Laboratory

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. San José State University Fire Weather Research Laboratory

Future Work Further processing of Lidar data Comparisons of Lidar measurements and in situ measurements Collect Lidar data on more fires San José State University Fire Weather Research Laboratory

Acknowledgements CalFire Battalion Chief Dave McLean NSF Grant #0960300 USDA #07-JV-11242300-073 Neal Waters Photography San José State University Fire Weather Research Laboratory