1. ACKNOWLEDGEMENTS: Rob Albee, Jim Wendell, Stan Unander, NOAA Climate Forcing program, DOE ARM program, NASA, Met. Service Canada, Chinese Met. Agency, Korean Met. Agency, South African Weather Service, University of Puerto Rico. Comparison of aerosol vertical profiles from CALIOP with in-situ measurements John Ogren, Patrick Sheridan, NOAA Earth System Research Laboratory Elisabeth Andrews, NOAA/ESRL and Univ. of Colorado Tad Anderson, Univ. of Washington I.II. III.IV. QUESTIONS What is the vertical distribution of aerosol optical properties in the midwest United States? To what extent do surface aerosol measurements represent the column aloft? What level of aerosol light extinction is detectable by CALIOP? How frequently are aerosol loadings undetectable by CALIOP? NOAA/ESRL Airborne Aerosol Observatory, showing orientation of inlet and major measurement systems. MEASUREMENTS Aerosol optics (light scattering, absorption, hygroscopic growth) Aerosol size distribution and number concentration Aerosol chemistry (major ions) Gases (O 3, carbon-cycle flasks) Inlet RH is maintained below 40% by gentle heating. APPROACH 2-3 flights weekly with an instrumented airplane, starting June, 2006. 15-30 km long horizontal legs at 10 altitudes from 0.5-4.6 km asl (lowest leg is 0.2 km agl) Primary profile location near Bondville, Illinois aerosol monitoring station Co-locate profiles with A-Train flight tracks when weather permits (map) Four-nephelometer optics rack. The three small nephelometers are operated at different relative humidities. IN-SITU: SFC VS. ALOFT Plots (right) show 5 th and 95 th percentiles (whiskers), quartiles (boxes), and median at each sampling altitude. Light extinction decreases at higher altitudes. Surface measurements of light extinction are representative of aerosols in the lowest 1 km. Climatology of single- scattering albedo shows little variation in the vertical. Note that individual profiles can show much more vertical structure. Statistical distributions of aerosol light extinction and single-scattering albedo from 130 flights over Illinois (June 2006- Oct. 2007). Measurements at 40% RH and 550 nm wavelength. Yellow box shows results from surface site. Detection of Aerosol Layers: CALIOP vs. In-situ Qualitative comparison of profiles of attenuated backscatter and aerosol light scattering coefficient indicates that CALIOP is –unlikely to detect layers with scattering below 10 Mm -1 –likely to detect layers with scattering above 25 Mm -1. Precise determination of a CALIOP detection threshold from comparison with in-situ data is complicated by several factors: –conversion of “dry” scattering to ambient conditions (amenable to further analysis using measured RH and aerosol hygroscopic growth) –Variations in ratio of aerosol backscatter to scattering coefficient (amenable to further analysis using measured aerosol size distribution and hemispheric backscattering coefficient) –Different spatial averaging, 80 km for lidar vs. 30 km (high altitude) or 15 km (low altitude) for in-situ 11 comparison cases (21 total, 10 excluded due to overcast high cloud) CALIOP: 80-km mean, cloud- cleared profile of attenuated backscatter at 532 nm (red line) In-situ: dry scattering coefficient for submicrometer particles, at 550 nm, at STP. Black line is estimated profile of molecular backscatter. Probability of Detection Plot (lower right) summarizes long-term results from global network measuring aerosol light scattering (map). Median value of scattering at Bondville is 40 Mm -1, suggesting that CALIOP should be able to detect the aerosol there about 70% of the time Bondville (BND) NIM KOS CONCLUSIONS Surface aerosol climatologies at continental sites can be used to guide and evaluate CALIOP algorithms. Comparison of CALIOP with in- situ measurements indicates that the satellite-borne lidar should be able to detect continental aerosols more than half of the time. CLOUD THRESHOLD Surface aerosol climatologies can be used to guide choice of threshold for aerosol-cloud separation. Dry scattering levels are rarely above 500-1000 Mm -1 (below). altitude (km asl)