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Simulation of an IHOP Convective Initiation Case for GIFTS Preparation

Explore the potential of GIFTS in observing convective initiation by simulating atmospheric conditions, obtaining radiances, and retrieving temperature, humidity, and wind data.

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Simulation of an IHOP Convective Initiation Case for GIFTS Preparation

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  1. Simulation of an IHOP Convective Initiation Casefor GIFTS Preparation Derek J. Posselt1, Erik Olson1, Wayne F. Feltz1, Russ Dengel1, Gail Dengel1, John R. Mecikalski1, Robert Aune1, Brian Osborne1, Robert O. Knuteson1, and William L. Smith2 1Cooperative Institute for Meteorological Satellite Studies, Space Science and Engineering Center, University of Wisconsin–Madison 2NASA Langley Research Center IHOP Spring Workshop

  2. Outline • Introduction to GIFTS • Choice of case: 12 June 2002 • Evaluation of CI simulation • GIFTS simulated radiances • Uses of simulated radiances and retrievals • Future Work IHOP Spring Workshop

  3. Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) GIFTS Details: • Next generation geostationary imager/sounder with launch as early as 2006 • Spectral resolution as high as 0.625 cm-1 • Designed for horizontal resolution of 4 km, vertical resolution of 1-2 km, and maximum temporal resolution of 11 seconds • Potential for much more rapid and high-resolution retrievals of temperature, moisture, and wind than are available with any current geostationary instrument. Pre-Launch Tasks: • Produce simulations of several different atmospheric cases • Use simulated atmosphere in the GIFTS forward radiative transfer model to obtain top of the atmosphere radiances • Retrieve temperature, water vapor and winds from these radiances, and compare them with the original simulated atmosphere to assess retrieval accuracy • Develop uses for radiance observations and retrieved quantities in advance of launch IHOP Spring Workshop

  4. GIFTS IHOP 2002 CI Objectives GIFTS high spatial and temporal resolution water vapor measurements indicate vast potential for early detection and diagnosis of CI IHOP Case Objectives: • Produce simulated atmosphere to be used for GIFTS preparation • Demonstrate GIFTS potential to observe moisture convergence prior to convective initiation • Demonstrate GIFTS usefulness for observation of fine-scale rapidly-evolving water vapor structures • Develop GIFTS data analysis techniques for CI applications IHOP Spring Workshop

  5. Case: 12 June 2002 Convective initiation occurred at approximately 2100 UTC along a weak low-level trough stretching southwest to northeast through the Oklahoma panhandle • Case Specifics for GIFTS Simulation: • Environment mostly clear preceding convection • CI occurred associated with strong, but small-scale water vapor gradient • CI well-predicted and well-forced, leading to relative ease of simulation • Occurred during a day specifically targeted for study of convective initiation during IHOP 2002 King Air P3 Proteus IHOP Spring Workshop

  6. GOES-11 Imagery 10-minute (approximate) 10.7 micron GOES-11 imagery clearly depicting wind-shift boundary and CI IHOP Spring Workshop

  7. MM5 Configuration Simulated atmospheric fields generated using the 5th generation Penn State/NCAR Mesoscale Modeling system (MM5) initialized from 10 km RUC analyses Configuration details: • 4 km grid spacing, 60 vertical levels • Initialized 0600 UTC, 24-hour duration • Goddard microphysics • MRF boundary layer • No cumulus parameterization • RRTM radiation • OSU-Land surface model • Nudged toward RUC analyses during 6-hour spin-up period IHOP Spring Workshop

  8. Simulation Results Cloud and water vapor features • Color-shaded plot depicts 2-meter mixing ratio • White iso-surfaces encompass cloud boundaries • Wind vectors valid at 1.5 km height IHOP Spring Workshop

  9. Observed GOES-11 imagery Simulated GOES-11 imagery Simulation Results 1900 UTC 1900 UTC IHOP Spring Workshop

  10. Observed GOES-11 imagery Simulated GOES-11 imagery Simulation Results 2000 UTC 2000 UTC IHOP Spring Workshop

  11. Observed GOES-11 imagery Simulated GOES-11 imagery Simulation Results 2100 UTC 2100 UTC IHOP Spring Workshop

  12. Observed GOES-11 imagery Simulated GOES-11 imagery Simulation Results 2200 UTC 2200 UTC IHOP Spring Workshop

  13. Observed GOES-11 imagery Simulated GOES-11 imagery Simulation Results 2300 UTC 2300 UTC IHOP Spring Workshop

  14. Model Atmosphere Forward Model Radiances GIFTS Simulated Radiances and Retrievals Procedure • Generate simulated atmospheric fields representative of desired case • Using GIFTS forward radiative transfer model, produce top of atmosphere radiances from simulated atmospheric fields • Retrieve temperature and water vapor from top of atmosphere radiances • Compare retrievals with “truth” atmosphere to assess accuracy of retrieval method • Develop applications based on simulated radiances and retrievals IHOP Spring Workshop

  15. Top of Atmosphere Brightness Temperatures Output from GIFTS forward radiative transfer model: 10.7 micron brightness temperatures 10-min time resolution 1800-2200 UTC IHOP Spring Workshop

  16. Simulated vs. Retrieved Water Vapor: 700 hPa “True” mixing ratio: 1800 UTC Retrieved mixing ratio: 1800 UTC IHOP Spring Workshop

  17. Simulated vs. Retrieved Water Vapor: 700 hPa “True” mixing ratio: 1830 UTC Retrieved mixing ratio: 1830 UTC IHOP Spring Workshop

  18. Simulated vs. Retrieved Water Vapor: 700 hPa “True” mixing ratio: 1900 UTC Retrieved mixing ratio: 1900 UTC IHOP Spring Workshop

  19. Simulated vs. Retrieved Water Vapor: 700 hPa “True” mixing ratio: 1930 UTC Retrieved mixing ratio: 1930 UTC IHOP Spring Workshop

  20. Simulated vs. Retrieved Water Vapor: 700 hPa “True” mixing ratio: 2000 UTC Retrieved mixing ratio: 2000 UTC IHOP Spring Workshop

  21. Uses of Simulated Data • Band differencing for CI detection • John Mecikalski and Kris Bedka • Subtraction of one spectral band from another to detect features associated with CI • Wind retrievals • Chris Velden, Dave Stettner, Russ Dengel, Gail Dengel • Tracking retrieved water vapor gradients to produce derived winds IHOP Spring Workshop

  22. Band Differencing: 5.9-11 micron 5.9 micron weighting function peaks in upper troposphere (~300 mb) 11 micron window channel much less sensitive to water vapor absorption Details: • Low clouds or clear scene: brightness temperature difference usually << 0 • High, cold clouds: difference = 0 • Cloud top at or above tropopause: difference may be > 0 • Has been used to locate overshooting tops in geostationary satellite imagery and to monitor temporal trends in cloud top height • Large temporal change in this band difference often an indicator of CI 1800-2200 UTC IHOP Spring Workshop

  23. Band Differencing: 8.5-11 micron Key: Differences in real and imaginary indices of refraction for liquid vs. ice • Very small difference at 8.5 microns • Maximum difference at 11 microns • Band combination used in MODIS cloud phase product 1800-2200 UTC Details: • Ice clouds: positive difference • Water clouds: slightly negative difference • Mixed phase: values near zero • Clear sky: strongly negative differences, due to contribution of terrestrial radiation at 11 microns • Band combination also highly dependent on effective radius of the size distribution • Ice clouds with smaller particles: greater (positive) differences. IHOP Spring Workshop

  24. Winds From GIFTS Simulated Retrievals Using existing techniques, simulated water vapor retrievals are being used to obtain water vapor gradient-track winds 700 hPa 500 hPa Mixing ratio (gray shaded), model winds (streamlines), and retrieved winds (barbs) IHOP Spring Workshop

  25. Future Work • Rerun initializing from IHOP reanalyses • Continued assessment of GIFTS utility for CI detection • Rerun GIFTS forward model with improved cloud microphysics (improved scattering, multiple ice habits) • Develop derived products from simulated data (stability, etc) • Simulation of other cases (THORPEX) IHOP Spring Workshop

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