Use of Lidar Backscatter to Determine the PBL
Use of Lidar Backscatter to Determine the PBL Heights in New York City, NY Jia-Yeong Ku, Chris Hogrefe, Gopal Sistla New York State Department of Environmental Conservation Albany, NY 12233 And Shuki Chaw, Leona Charles, Barry Gross City College of City University of New York, NY 10031
Objective • Analyze Lidar Backscatter to determine PBL Heights using Wavelet method • Demonstrate the potential of applying Lidar Backscatter in the air quality forecast evaluation
Data • Lidar measured backscatter signal • PBL heights and aerosol extinction coefficients out of WRF/CMAQ air quality forecast system
Lidar System • Lidar (Light Detection And Range) measures the intensity of backscattered light as a function of distance • The primary contribution of scattering is from aerosol particles suspended in the air
Lidar Backscatter C: calibration constant β: backscatter coefficient α: extinction coefficient
CCNY Lidar Setup Lidar data: 1064 nm channel Temporal resolution: 1 minute Vertical resolution: 37. 5 m
WRF/CMAQ Forecast System • Meteorology/Emission: Based on NECP/NWS 48 -hr WRF forecasts initialized at 12: 00 UTC and 2002/2004 emission inventory, processed with PREMAQ • Photochemical Model: CMAQ (ver 4. 51) Horizontal resolution: 12 km vertical resolution: 22 layers, lowest layer ~40 m • Study periods: July 31 – August 2, 2006
EDST NWS Eta 12 km 48 hr Forecast Initialized at 12: 00 UTC NWS Product Generator (horizontal interpolation) NWS Eta-Post (vertical interpolation) NWS CMAQ-Eta 12 km O 3 forecasts for Northeast (NE) domain NWS Eta for CMAQ 22 sigma layer, 12 km, Lambert-Conformal 08: 00 10: 00 13: 00 Location: National Weather Service (NWS) EPA stores emission input files at EPA NESC EPA gets NOAA AQ forecasting output (NE domain) and archives at EPA NESC Location: EPA RTP Atmospheric Modeling Division National Environmental Supercomputing Center (NESC) EPA gets Eta for CMAQ to EPA NESC NYSDEC runs PREMAQ at EPA NESC to generate model-ready meteorology and emissions Location: NY State Department of Environmental NYSDEC brings PREMAQ output (model-ready Conservation (NYSDEC) 18: 00 20: 00 21: 00 23: 00 emissions and meteorology) back to their Linux cluster NYSDEC runs CMAQ using PREMAQ model-ready emissions and meteorology for near-realtime O 3 and PM forecasts on NYSDEC Aspen Linux Cluster. Postprocessing finishes by 05: 30 EDST Research Mode: Run alternate CMAQ version from 5. 30 to 9. 30 EDST 01: 00 05: 30
Modeling Domain
Analyze Lidar Backscatter for PBL Heights • Boundary layer usually has much higher aerosol concentration than free troposphere above. • The significant change in the backscatter across the top of the BL provides a means of determining PBL heights. • Wavelet provides a scale-dependent approach to determine PBL height.
Wavelet Covariance Transform
The key of the wavelet analysis is the selection of an appropriate dilation (vertical scale).
Compare PBL heights of Lidar measured and Model predicted • Lidar measures aerosol layers • Model determines vertical mixing based on some meteorological parameters, such as temperature and wind field
Compare Lidar Backscatter and CMAQ Extinction Coefficient • Hourly and vertical averaged Lidar Backscatter signal • Hourly extinction coefficient of CMAQ outputs • A qualitative comparison; both backscatter and extinction coefficient reflect the aerosol and humidity loading in the atmosphere
July 31, 2006
August 1, 2006
August 2, 2006
Summary • A wavelet technique is applied to analyze the PBL height using lidar backscatter measured in New York City • WRF/CMAQ forecast system keeps track the lidar measured PBL development well • WRF/CMAQ forecast system predicted the vertical PM profile (in terms of extinction coefficient) resemble to the backscatter vertical profile under cloud free conditions • Development in the areas that we can directly compare the aerosol optical products between Lidar and model.
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