HR: 17:15h
AN: A54A-06    [Abstracts]
TI: Lessons Learned From the POLARIS and TOMS$^3$-F Ozone Intercomparisons, With Applications to Aura Validation at High Latitudes
AU: * Lloyd, S A
EM: Steven.Lloyd@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory (JHU/APL), 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: Labow, G J
EM: labow@qhearts.gsfc.nasa.gov
AF: Science Systems and Applications, Inc.(SSAI), Code 916, NASA Goddard Space Flight Center (GSFC), Greenbelt, MD 20771 United States
AU: Cede, A
EM: cede@chescat.gsfc.nasa.gov
AF: Science Systems and Applications, Inc.(SSAI), Code 916, NASA Goddard Space Flight Center (GSFC), Greenbelt, MD 20771 United States
AU: McPeters, R D
EM: mcpeters@wrabbit.gsfc.nasa.gov
AF: Code 916, NASA Goddard Space Flight Center (GSFC), Greenbelt Road, Greenbelt, MD 20771 United States
AB: High-latitude ozone is important because this is the region where most of the global ozone loss occurs. Data from the POLARIS and TOMS$^3$-F field campaigns based in Fairbanks, AK raised the concern that Dobson spectrometers systematically underestimate total column ozone under conditions of high ozone and high solar zenith angles, exactly the conditions under which the sudden springtime loss of polar ozone occurs. Total ozone when measured at very high solar zenith angles ($>$80$\deg$) has never been rigorously validated in an absolute sense, either by satellite- or ground-based instruments or their intercomparison. UV/visible retrieval algorithms for ozone at very high solar zenith angles are complex for a variety of reasons, including low light levels and the fact that multiple scattering dominates the UV radiation field used in TOMS, OMI, Dobson and Brewer spectrometer algorithms. The validation of OMI total column ozone at high solar zenith angles is a high priority for Aura validation. While many science and technical issues were addressed and/or resolved by the POLARIS and TOMS$^3$-F campaigns, we learned a number of practical lessons on how to optimize the collection of data during intercomparisons between satellite and balloon- and ground-based instruments. Perhaps the most important issue was obtaining truly coincident observations in time and space; simple co-location of the instruments and making measurements on the same date is not sufficient for rigorous validation of satellite observations. Comparisons with POAM III observations illustrated that even near-coincident observations can have significant differences in the ozone profile between the peak of the ozone concentration and the tropopause due to dynamical activity in the lowermost stratosphere. Variability on much shorter timescales was identified by the comparison of Dobson and Brewer total ozone observations, indicating that the atmosphere can be active even on days that are relatively cloud-free and apparently quiescent to the naked eye. The use of GPS transmitters on the ozonesondes and timing the launch of the balloon sondes such that they are at the peak of the ozone layer at the time of the satellite overpasses allowed us to further narrow the definition of ``coincident'' observations. Future ozone validation campaigns should plan to include laboratory observations on the actual field instruments (measuring the instrument's wavelength-dependent slit function, stray light, and forward-scattered light through the entrance optics), which along with the atmospheric observations can yield a quantitative means of correcting Dobson and single-pass Brewer data to better match the double-pass Brewer and satellite instrument observations obtained under conditions of high slant column ozone ($>$800 DU). Post-campaign re-processing of the raw data should include taking into account the actual stratospheric temperature profile in the Dobson retrievals, making use of sonde profiles in the satellite retrievals, assessing the impact of ozone field inhomogeneity using simultaneous vertical ozone profiling instruments (sondes or lidar) co-located with ground-based solar viewing spectrometers (Dobson, Brewer, SAOZ, etc.), all of which might result in an improved agreement between satellite and ground-based observations.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0340 Middle atmosphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting