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PMC Detection and Mapping Using Aura OMI Measurements

PMC Detection and Mapping Using Aura OMI Measurements. Matthew DeLand ( SSAI ) Eric Shettle ( NRL ) Gary Thomas ( LASP/U. Colorado ) John Olivero ( Embry-Riddle ) 8 th International Workshop on Layered Phenomena in the Mesopause Region Fairbanks, Alaska 20-23 August 2007.

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PMC Detection and Mapping Using Aura OMI Measurements

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  1. PMC Detection and Mapping Using Aura OMI Measurements Matthew DeLand (SSAI) Eric Shettle (NRL) Gary Thomas (LASP/U. Colorado) John Olivero (Embry-Riddle) 8th International Workshop on Layered Phenomena in the Mesopause Region Fairbanks, Alaska 20-23 August 2007

  2. Satellite Measurements • All instruments prior to AIM not designed with PMC measurements in mind  some compromises in data sampling or quality are inevitable. • Various observation techniques are represented here: limb scattering (UV and visible), occultation (visible and IR), nadir backscattering (UV).

  3. SBUV/2 Detection Method • Useful in UV (λ < 300 nm) where Earth albedo is (relatively) low. • Identify PMC using enhancement above background, spectral dependence of 5 shortest wavelengths. • Uncertainty in derived background due to ozone variability limits PMC detections to brightest 15% of overall population. NOAA-16 SBUV/2 data DeLand et al. [2003]

  4. Typical SBUV/2 PMC Results

  5. Long-Term Variations • Combine albedo data from multiple SBUV instruments to examine secular and periodic behavior. Adjust data for local time effects. • Results show increasing brightness with time at all latitudes, both hemispheres. • Multiple regression fits also find anti-correlation with solar activity (0-1 year phase lag), stronger response at higher latitudes. DeLand et al. [2007, J. Geophys. Res.]

  6. OMI Summary • Launched on NASA Aura satellite 15 July 2004. • Hyperspectral instrument designed for measuring total ozone and stratospheric profile ozone. • Nadir pointing, wide field of view telescope (114º cross-track)  full global coverage at equator, lots of overlap at high latitudes. • Wavelength range = 264-504 nm using three overlapping detectors (UV1 = 264-311 nm, UV2 = 307-383 nm, visible = 378-504 nm). • Detector = 2-D CCD. Ground resolution = 13 km x 24 km pixels at nadir (UV2, visible) with full spectral information for each pixel. UV1 data doubles pixel width for improved signal-to-noise quality.

  7. OMI Viewing Geometry

  8. OMI Advantages for PMC Detection • Smaller pixels (13x48 km2 in UV1 data) increase chance of being filled with PMC  more contrast to background. • Cross-track observations can show horizontal structure over large geographic regions. • First regular measurements up to 90º latitude. • Overlapping measurements at high latitude allow study of short-term (orbit to orbit) variability, planetary waves. • Spectral information with each pixel holds potential to address particle size questions. • Many more opportunities for coincidence analysis with ground-based data.

  9. OMI Detection Algorithm • Adapt SBUV/2 approach. Use 267 nm as shortest wavelength (less cross-track variation). • Initial tests use all pixels, 5 wavelengths (same number as SBUV/2), sample day of Level 1B data. • Process each swath independently due to cross-track albedo variations. • Raw albedo data show clear along-track structure (nadir swath shown). PMC brightness is higher than SBUV/2.

  10. OMI Results: Single Orbit

  11. OMI Results: Multiple Orbits

  12. Single Day – All SBUV/2

  13. Single Day - OMI

  14. OMI Variability: Single Day

  15. OMI Variability: Three Days

  16. Coincidence Analysis • Low latitude NLC (< 50º) detections increasing in frequency, but still rare. Would like quantitative evaluation of these clouds with satellite data. • NLC and SBUV-type PMC observations not simultaneous by definition. • SBUV/2 orbit tracks are far apart at mid-latitudes (22º longitude = 1000 km)  hard to get useful samples. • Work in progress for 2003-2005 seasons using Canadian-American NLC network and SBUV/2 data. • OMI cross-track coverage and smaller pixels will allow tighter windows on geographic, temporal coincidence tests.

  17. Can Am Network + SBUV/2 Courtesy of J. Barker-Tvedtnes and M. Taylor [Utah State Univ.]

  18. OMI at Single Location

  19. Further OMI Algorithm Work • Calculate revised PMC detection thresholds using OMI data. • Implement adjustment for cross-track albedo variations (wavelength-dependent?). • Modify background calculation to analyze multiple swaths together. • Test algorithm performance with alternate wavelength sets, spectral averaging. • Create larger spatial bins for quantitative comparisons with SBUV/2 instruments. • Analyze PMC detections for particle size information.

  20. Conclusions • OMI data can be used to continue the unique PMC database developed from SBUV and SBUV/2 instruments. • The improved measurement capabilities of OMI will give tremendous advances in our understanding of PMC morphology and evolution. • Aura MLS temperature and water vapor profiles can provide valuable background information. • OMI measurements can specifically address the recent increase in low-latitude PMC detections. • Public release of all reprocessed OMI Level 1B data will occur in Fall 2007. • OMI data will help to validate measurements from the CIPS instrument on AIM.

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