P2.36 Generation of Simulated Top of Atmosphere Radiance Datasets for GIFTS/HES Algorithm Development Jason A. Otkin*, Derek J. Posselt, Erik R. Olson, James E. Davies, Wayne F. Feltz, Robert O. Knuteson, and John R. Mecikalski Cooperative Institute for Meteorological Satellite Studies, Space Science and Engineering Center, University of Wisconsin–Madison 1. INTRODUCTION 4. MM5 SIMULATIONS: SENSITIVITY STUDIES 6. SIMULATED RADIANCE DATA The anticipated launch of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) represents a significant advance in our ability to image and sound the atmosphere from a geosynchronous orbit. GIFTS is targeted at a horizontal resolution of 4 km, a vertical resolution of 1-2 km, and a maximum temporal resolution of 10 seconds. As such, it will produce retrievals of temperature, moisture, and wind with much greater temporal and vertical resolution than is currently available from any existing geostationary instrument. SSEC/CIMSS is currently tasked with testing and developing the GIFTS fast forward radiative transfer model and retrieval algorithms. In support of this work, numerical model simulations with high spatial and temporal resolution are used to produce a “truth” atmosphere that is then passed through the GIFTS fast forward radiative transfer model to generate simulated top of the atmosphere (TOA) radiances. Retrievals of temperature and water vapor generated from these radiances are subsequently compared with the original simulated atmosphere to assess retrieval accuracy. Extensive sensitivity testing was undertaken in order to determine the optimal configuration of physical parameterizations for this simulation. Each simulation was initialized at 1200 UTC 11 March 2003 and allowed to spin-up for 33 hours before the start of the ER-2 flight at 2100 UTC on 12 March 2003. Such a long spin-up period was chosen in order to allow sufficient time for the MM5 simulation to properly generate realistic fine-scale cloud and moisture features from the original coarse-resolution GDAS analyses. Simulated IR fields at 2100 UTC on 12 March 2003 are shown below for each sensitivity test. Configuration details for each sensitivity run: All simulations were run on a Lambert Conformal conical projection grid with 50 vertical levels and fully explicit convection on the innermost 4-km domain. Control: Goddard microphysics, RRTM/Dudhia radiation, MRF boundary layer scheme, and Grell cumulus convection scheme on the outer two domains. ETA: as for the control simulation, but with the ETA boundary layer scheme in place of the MRF scheme. KAIN-FRITSCH: as for the ETA simulation, but with the Kain-Fritsch cumulus parameterization scheme used in place of the Grell scheme on the outer two domains. NUDGED: as for the ETA simulation but nudged toward the GDAS analyses using the MM5 four-dimensional data assimilation system. The outermost 36-km domain was nudged during the first 24 hours of the simulation while the inner 12-km domain was nudged for the first 12 hours. Each domain then had a 3-hour period after their respective "nudging periods" during which the nudging coefficients were ramped down to zero in order to allow the model simulation to transition gracefully between the forced and freely-evolving states. The innermost 4-km domain was not nudged during any portion of the simulation. UW-CIMSS has developed a fast forward radiative transfer model that ingests atmospheric profiles of temperature, water vapor mixing ratio, liquid and ice cloud, and ozone, and generates top of atmosphere radiances in the GIFTS spectral range. GIFTS Spectrum: Clear Sky Observed and Simulated GOES-10 10.7 micron Brightness Temperatures 2. CASE DESCRIPTION GIFTS Spectrum: Low-Level Cloud Current work involves a high-resolution MM5 simulation of an intense upper-tropospheric jet streak that occurred over the north-central Pacific Ocean during 12-13 March 2003. This particular jet streak case was selected because it occurred during a day specifically targeted for the study of jet streak dynamics during the Pacific THORPEX Observational Science Test 2003. Observational datasets collected during a NASA ER-2 flight between 2100 UTC 12 March and 0400 UTC 13 March included remotely-sensed observations from the NPOESS Aircraft Sounder Testbed-Interferometer (NAST-I), Scanning High-resolution Interferometer Sounder (SHIS), MODIS Airborne Simulator (MAS), and Cloud Physics Lidar (CPL), as well as dropsondes across the jet streak core. Case specifics: Maximum analyzed zonal wind speed at 300 hPa was over 90 m s-1 Upper-tropospheric jet streak was characterized by very strong horizontal and vertical wind shear Observation/Analysis Control ETA KAIN-FRITSCH NUDGED GIFTS Spectrum: Upper-Level Cloud The goal of this simulation was to achieve a high degree of realism between the observed and MM5-simulated cloud fields. Since observations of cloud microphysical properties are not available for this case, a subjective comparison between the simulated and observed GOES IR fields was undertaken in order to determine which MM5 simulation performed best. Examination of the simulated IR fields indicates that both the ETA and Kain-Fritsch simulations most realistically depicted the cellular cumulus cloud field observed across the southern three quarters of the domain while still maintaining the cirrus cloud shield associated with the cyclone along the northern periphery of the domain. Since the Kain-Fritsch cumulus scheme has been shown in prior studies to have some difficulty simulating clouds over the ocean, it was determined that the ETA simulation most faithfully represented the observed GOES IR imagery across the region of interest. 5. MM5 SIMULATION: RESULTS The observed GOES-10 IR brightness temperatures and the simulated brightness temperatures from the ETA simulation are shown below. Comparison between the observed and simulated IR fields indicates that the ETA simulation accurately portrays the location of the cloud field associated with the northern cyclone as well as realistically depicts the low-level cumulus cloud field to the south of this cyclone. It is also evident that the fairly smooth appearance of the observed IR field along the southern portion of the domain is adequately portrayed in the simulated IR field by the relatively large spatial scale of the individual components of the stratus cloud deck within this region. One notable difference, however, between the observed and simulated IR fields is the absence of upper-level cirrus within the southwestern portion of the simulated IR field. Even with this error, the fact that the MM5 simulation was able to realistically simulate much of the observed cloud field renders it a useful example to generate simulated GIFTS top of the atmosphere radiances over a maritime atmosphere characterized by strong horizontal and vertical wind shear. Simulated radiances from the GIFTS forward model with spectra in the GIFTS longwave band for clear (top), low cloud (middle) and high cloud (bottom) regions. 7. ATMOSPHERIC RETRIEVALS 300 hPa zonal wind isotachs (m/s) at 0000 UTC 13 March 2003 Meridional cross-section of zonal wind isotachs (m/s) at 0000 UTC 13 March 2003 Top of the atmosphere radiances generated by the fast forward radiative transfer model are used to retrieve profiles of atmospheric temperature and water vapor. Horizontal fields constructed from these profiles are then compared to the original atmospheric fields to assess the robustness of the retrieval method. A comparison of the simulated and retrieved (with double noise added) water vapor mixing ratio fields at 750 hPa is shown below. Observed GOES-10 10.7 micron Brightness Temperatures 3. MM5 SIMULATIONS: DATA INGEST Simulated atmospheric fields were generated using version 3.5 of the 5th generation Penn State/NCAR Mesoscale Modeling system (MM5). Atmospheric fields required to initialize the MM5 and provide lateral boundary conditions during the subsequent simulation were obtained from six-hourly GDAS analyses with 1° x 1° horizontal grid spacing. Each six-hourly GDAS file contained three-dimensional fields of temperature, zonal and meridional components of the horizontal wind, geopotential height, and relative humidity on 26 pressure levels between 1000 and 10 hPa. The GDAS analyses of skin temperature, sea level pressure, soil temperature, soil moisture, surface height and other near-surface atmospheric fields provided the lower boundary conditions for the MM5 simulations. Simulated GOES-10 10.7 micron Brightness Temperatures Geographical region covered by the three two-way interactive nested domains used for each simulation. Horizontal grid spacings for each domain were 36 km, 12 km, and 4 km, respectively. Only atmospheric fields from the innermost 4-km domain were used to produce the simulated TOA radiances. Simulated (left) and retrieved (right) water vapor at 750 hPa, 0000 UTC 13 March 2003 ACKNOWLEDGEMENTS This work was funded by NASA NMP contract NAS1-00072 *Contact: Jason A. Otkin • Address: 1225 W. Dayton Street • Madison, WI 53706 • Phone: 608/265-2476 • Email: jason.otkin@ssec.wisc.edu