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Development of an OMPS cloud pressure algorithm

Development of an OMPS cloud pressure algorithm. Alexander Vasilkov , Joanna Joiner, Colin Seftor , and Jason Li OMPS Science Team Meeting December 5, 2013. Rotational-Raman scattering cloud algorithm basics.

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Development of an OMPS cloud pressure algorithm

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  1. Development of an OMPS cloud pressure algorithm Alexander Vasilkov, Joanna Joiner, Colin Seftor, and Jason Li OMPS Science Team Meeting December 5, 2013

  2. Rotational-Raman scattering cloud algorithm basics • Cloud pressures are retrieved from the high-frequency structure of TOA radiance caused by RRS. • The Mixed Lambertian Equivalent Reflectivity (MLER) method. • Fixed solar irradiance of Day1 to calculate normalized radiances • Lookup tables generated with a synthetic high-resolution solar spectrum. The OMPS solar data did not work well. • Spline interpolation of TOA normalized radiance over the lookup table wavelength grid. Linear interpolation did not work at all. • Fitting window 345.5 to 354.5 nm. Reflectivity/Effective cloud fraction at 354.1 nm. • Soft calibration is a key element of the algorithm.Over Antarctic Plateau the scene pressure is assumed be equal to the surface pressure. • Compute spectral residuals (observed minus calculated radiances) for each swath position • Use the calculated residuals to correct TOA radiances • Determined from Dec. 2012 data

  3. Tropical total ozone:Comparison of the use of retrieved OCP (OMI), OCP climatology (NASA OMPS), & CTP (1st 1.5 years IDPS) The use of cloud-top pressures (red curve) leads to unphysical increase of total ozone for bright deep convective clouds Monthly gridded OMI OCP climatology captures much of the variability in cloud OCP

  4. OMPS solar flux Expected solar flux based on convolution of high resolution spectrum with OMPS band passes Actual measured OMPS solar flux • Dots are for different cross track positions • Each cross track position has a different set of wavelengths and a different band pass

  5. Rotational-Raman scattering effect on TOA radiances • OMPS less sensitive to effects of rotational-Raman scattering (RRS) than OMI owing to its lower spectral resolution • Good for SO2 & O3retrievals, not so good for RRS cloud pressure retrievals Percentage effect of RRS on OMPS radiances at the total ozone algorithm wavelengths

  6. Soft calibration of TOA radiance Corrections to TOA radiances are within  1%. Depend on wavelength and cross-track position Spectral corrections that are applied to measured TOA OMPS radiances as derived from data over Antarctica. Each curve is for a particular OMPS cross-track position.

  7. Comparison of OMPS and OMI Cloud pressure retrievals of Jan 07, 2013 OMPS 1. Most cloud OCP patterns are same 2. OMI OCP retrievals are somewhat lower than OMPS particularly in the tropics OMI

  8. Comparison of PDFs of effective cloud fraction PDFs are practically same.Not anticipated because of different sizes of the OMI and OMPS footprint.

  9. Comparison of PDFs of cloud pressure Tropics Northern mid-latitudes Southern mid-latitudes - In general, OMI retrieves somewhat lower cloud OCPs than OMPS does. Differences are most pronounced in the tropics. - The differences might be attributed to the absence of stray light correction.

  10. Comparison of PDFs of cloud pressure, OMI O2-O2 added Southern mid-latitudes Northern mid-latitudes Tropics - Differences between OMI RRS and OMPS cloud pressures appear to be similar to differences between OMI RRS and OMI O2-O2 except for the differences in the tropics.

  11. Stray light correction Comparison of PDFs of cloud pressures retrieved with and without the stray light correction shows insignificant differences only.

  12. Wavelength shift Wavelength shift as a function of OMPS orbit scan position Wavelength shift as a function of OMPS cross-track position The retrieved wavelength shift agrees well with that reported by NOAA

  13. Total column ozone: OCP climatology vs retrieved OCP Ozone differences: - mostly positive - up to 5% - well correlated with bright clouds Reflectivity

  14. Comparisons with OMI OCP climatology Retrieved OCPs improve OMPS – OMI comparison Retrieved OCP

  15. Conclusions • OMPS less sensitive to effects of rotational-Raman scattering than OMI owing to its lower spectral resolution; • good for SO2 & O3 retrievals, not so good for cloud OCP retrievals • Comparisons of cloud OCPs from OMI and OMPS show that OMPS retrieves somewhat higher cloud OCPs than OMI does, particularly in the tropics • PDFs of effective cloud fraction retrieved from OMI and OMPS are practically same • Monthly gridded OMI OCP climatology captures much of the variability in cloud OCP, good for both NP and TC • The use of actual cloud OCPs improves total column O3 estimates • Differences up to 5% • Differences well correlated with bright clouds • Makes OMPS total column ozone retrievals be closer to OMI

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