Retrieval of ozone column content from airborne Sun photometer measurements during SOLVE II: comparison with coincident satellite and aircraft measurements

摘要

During the 2003 SAGE (Stratospheric Aerosol and Gas Experiment) III OzoneLoss and Validation Experiment (SOLVE) II, the fourteen-channel NASA AmesAirborne Tracking Sunphotometer (AATS-14) was mounted on the NASA DC-8aircraft and measured spectra of total and aerosol optical depth (TOD andAOD) during the sunlit portions of eight science flights. Values of ozonecolumn content above the aircraft have been derived from the AATS-14measurements by using a linear least squares method that exploits thedifferential ozone absorption in the seven AATS-14 channels located withinthe Chappuis band. We compare AATS-14 columnar ozone retrievals withtemporally and spatially near-coincident measurements acquired by the SAGEIII and the Polar Ozone and Aerosol Measurement (POAM) III satellite sensorsduring four solar occultation events observed by each satellite. RMSdifferences are 19 DU (7% of the AATS value) for AATS-SAGE and 10 DU(3% of the AATS value) for AATS-POAM. In these checks of consistencybetween AATS-14 and SAGE III or POAM III ozone results, the AATS-14 analysesuse airmass factors derived from the relative vertical profiles of ozone andaerosol extinction obtained by SAGE III or POAM III.

We also compare AATS-14 ozone retrievals for measurements obtained duringthree DC-8 flights that included extended horizontal transects with totalcolumn ozone data acquired by the Total Ozone Mapping Spectrometer (TOMS)and the Global Ozone Monitoring Experiment (GOME) satellite sensors. Toenable these comparisons, the amount of ozone in the column below theaircraft is estimated either by assuming a climatological model or bycombining SAGE and/or POAM data with high resolution in-situ ozonemeasurements acquired by the NASA Langley Research Center chemiluminescentozone sensor, FASTOZ, during the aircraft vertical profile at the start orend of each flight. Resultant total column ozone values agree withcorresponding TOMS and GOME measurements to within 10-15 DU (~3%)for AATS data acquired during two flights - a longitudinal transect fromSweden to Greenland on 21 January, and a latitudinal transect from 47° Nto 35° N on 6 February. For the round trip DC-8 latitudinal transectbetween 34° N and 22° N on 19-20 December 2002, resultant AATS-14ozone retrievals plus below-aircraft ozone estimates yield a latitudinalgradient that is similar in shape to that observed by TOMS and GOME, butresultant AATS values exceed the corresponding satellite values by up to 30 DUat certain latitudes. These differences are unexplained, but they areattributed to spatial and temporal variability that was associated with thedynamics near the subtropical jet but was unresolved by the satellitesensors.

For selected cases, we also compare AATS-14 ozone retrievals with valuesderived from coincident measurements by the other two DC-8 based solaroccultation instruments: the National Center for Atmospheric Research Directbeam Irradiance Airborne Spectrometer (DIAS) and the NASA Langley ResearchCenter Gas and Aerosol Monitoring System (GAMS). AATS and DIAS retrievalsagree to within RMS differences of 1% of the AATS values for the 21January and 19-20 December flights, and 2.3% for the 6 February flight.Corresponding AATS-GAMS RMS differences are ~1.5% for the 21January flight; GAMS data were not compared for the 6 February flight andwere not available for the 19-20 December flight. Line of sight ozoneretrievals from coincident measurements obtained by the three DC-8 solaroccultation instruments during the SAGE III solar occultation event on 24January yield RMS differences of 2.1% for AATS-DIAS and 0.5% forAATS-GAMS.