References

1. Intercomparison of Ground-based Column Ozone Measurements with Aura Satellite Retrievals over Richland, WA during INTEX-B/IONS-06 Wan Ching Jacquie Hui1, Brett Taubman2, Anne Thompson1, Mark Schoeberl3, and Eugene Clothiaux1 1Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA, amt16@psu.edu, 2Appalachian State University, 3NASA/GSFC INTRODUCTION RESULTS AND DISCUSSIONS I RESULTS AND DISCUSSIONS II (Shadowband Radiometer) Total Ozone Comparison The Ozone Monitoring Instrument (OMI) on board the NASA Earth Observing System Aura Satellite provides the greatest spatially resolved ozone retrievals on a global scale. While the space-borne instrument provides good horizontal spatial coverage, it is relatively insensitive to tropospheric chemical concentrations and therefore requires validation from ground-based observations. The Pennsylvania State University Department of Meteorology NATIVE (Nittany Atmospheric Trailer and Integrated Validation Experiment, http://www.meteo.psu.edu/~btaubman/Webpage/native.html) facility is a mobile atmospheric research facility that was deployed in Richland, WA (46.2oN, 119.16oW) from April 21, 2006 through May 15, 2006 as part of the INTEX-B (Intercontinental Chemical Transport Experiment) campaign. Soundings were part of the IONS-06 (Thompson et al., 2007). During this period, NATIVE made column and vertical profile ozone measurements using ozonesondes, a Microtops ozonometer, and a UV-MFR (Ultraviolet Multifilter Radiometer). These measurements were compared with OMI total column ozone (TCO) and tropospheric ozone residual (TOR). • Sonde-retrieved total ozone is on average 13 DU higher than OMI-retrieved values over Richland • Shadowband values (SR-JPL06 and SR-BP85) are computed with the same sets of V0, (top of the atmosphere solar irradiance). The wavelength pairs are (310.7, 323.7 nm) and (316.8, 331.7 nm). • Intercomparison among various instruments indicate they are highly correlated with each other. Among those, total OMI and shadowband radiometer give the highest correlation of 0.98 • Total column ozone obtained from the shadowband radiometer requires an accurate estimate of V0 and ozone absorption coefficients • V0 is estimated through Langley analysis on data taken on clear days. Reference to AERONET helped to eliminate days when there are large aerosol changes within the day Fig 3. The Langley plot of ln(I) (spectral irradiance) versus air mass in the morning of May 4th 2006 for 310.7nm. ln(I0) can be extrapolated to zero air mass and yield the irradiance at the top of the atmosphere. The slope of the line is the total optical depth for the particular time period. The quality of the analysis is best on clear stable days. • Due to the limited time period in the campaign and the weather condition of the sites, we cannot obtain a set of V0’s that are close to the measurements from other instruments • The wavelength pairs used in the double-wavelength formula also affect TCO (not shown) • Optimization of V0’s • Using four sets of O3 absorption coefficients (JPL 2006, Brion 1985, Bass & Paur 1985, and Voigt 2001), we try to minimize the sum of errors between sonde and shadowband values. Fig 1.Comparison of total ozone with OMI, ozonesonde, Microtops, and shadowband radiometer (SR) values during the campaign over Richland. SR-JPL and SR-BP85 are the shadowband radiometer measurements derived using JPL 2006 and Bass & Paur 1985 ozone absorption coefficients respectively. DATA AND METHODS Table 1.Correlation coefficients of column ozone retrieved with the different instruments during the campaign. • Instrumentation • Ozonesondes: ozone profiles were taken during INTEX and IONS-06 with En-Sci Electrochemical Concentration Cell (ECC) Ozonesondes. Total column ozone is calculated by integrating the profiles up to a pressure level of 7mb (~35km) and adding climatological ozone from satellite SBUV (solar backscattered UV) above 7mb. • The UVMFR-7 Shadowband radiometer measures atmospheric ozone content based on the absorption efficiencies at an 2-nm FWHM centered on 300, 305.5, 311.5, 317.5, 325, 332.5, and 368 nm. To obtain total column ozone, a double-wavelength radiative transfer formula is used (Gao et. al., 2001). • Microtops II Ozonometer: borrowed from G. Labow of NASA/GSFC. It uses five UV channels to measure total column ozone. The instrument outputs column ozone and aerosol optical depths. • OMI: Total column ozone is based on the TOMS v8 algorithms. Also onboard the Aura, the Microwave Limb Sounder (MLS), measures stratospheric ozone with high vertical resolution. • TOR: derived by subtracting the MLS SCO (stratospheric column ozone) from the TCO, according to Schoeberl et al., 2007. Sonde estimate of TOR is obtained from integrating the O3 profile from surface to the tropopause height. FUTURE WORK TOR Comparison • Average absolute difference in TOR: 11.8 DU • Average % error (absolute): 32.7%  difference/sonde TOR on a specific day • Average underestimate by OMI TOR relative to sonde: 11.6 DU (31% error, 19 out of 24 cases) • Average overestimate by OMI TOR relative to sonde: 12.6 DU (39% error, 5 out of 24 cases) • Apr 27-29 has relatively low ozone mixing ratio but high overestimates of OMI TOR, yet good estimates in total column ozone Continuing optimization on V0 for the shandowband radiometer Case studies will be used to investigate discrepancies among the measurements of OMI (TCO and TOR), shadowband radiometer, and ozonesonde Extend current study to other IONS data. (e.g. WAVES at Beltsville) Longer time period in future campaigns would be needed for better comparisons and validation of satellite retrievals References Bhartia, P. K. (2002), OMI Algorithm Theoretical Basis Document, Vol II, OMI Ozone Products, ATBD-MI-02, Version 2.0. NASA Goddard Space Flight Center, Greenbelt, MD, USA. Gao, W. J., J. R. Slusser, J. H. Gibson, G. Scott, D. S. Bigelow, J. Kerr, and B. McArthur (2001), Direct-Sun column ozone retrieval by the Ultraviolet Multi-filter Rotating Shadow-band Radiometer and comparison with those from Brewer and Dobson spectrophotometers, Appl. Opt. 40(19), 3149–3155 Thompson A. M., et al. (2007), Intercontinental Chemical Transport Experiment Ozonesonde Network Study (IONS) 2004: 1. Summertime upper troposphere/lower stratosphere ozone over northeastern North America, J. Geophys. Res., 112, D12S12, doi:10.1029/2006JD007441. M. R. Schoeberl, J. R. Ziemke, B. Bojkov, N. Livesey, B. Duncan, S. Strahan, L.  Froidevaux, S. Kulawik, P. K. Bhartia, S. Chandra, P. Levelt, J. C. Witte, A. M. Thompson, A Trajectory Based Estimate of the Tropospheric Column Ozone Column Using the Residual Method, J. Geophys. Res., doi:10.1029/2007JD008873, in press, 2007. Fig 2. Comparison of differences in total ozone, TOR, and SCO between OMI and ozonesonde values.