27th Conference abstracts
A summary of recent GFDL model upgrades and plans for 2006
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A summary of recent GFDL model upgrades and plans for 2006Morris A. Bender, NOAA/GFDL, Princeton, NJ; and T. Marchok, I. Ginis, B. Thomas, and I.-J. Moon Since 1995 the GFDL Hurricane Prediction System has provided operational guidance for forecasters at TPC in both the Atlantic and East Pacific ocean basins. With the installation of a new generation computer at the National Centers for Environmental Prediction (NCEP), the computer power available for operational models was significantly increased in 2005, enabling major upgrades to the GFDL hurricane forecast system to be made. Most significant was a doubling of the finest resolution which has lead to a much better representation of the hurricane inner core. Overall, the upgraded hurricane model performed very well throughout the record 2005 hurricane season. A brief summary of the track and intensity forecasts in both basins will be presented. During the past year further upgrades to the model physics have been developed and are currently being tested. Coupling of the GFDL forecast model with the NCEP Wavewatch model has been successfully made, to more accurately predict the momentum fluxes at the surface. This has lead to much better prediction of the magnitude and distribution of the surface winds. A new version of the model's moist physics utilizing the NCEP Ferrier micro-physics is currently being evaluated on cases during the 2005 hurricane season. Preliminary results continue to indicate that this physics improvement is leading to significantly better intensity forecasts in sheared situations. Examples of the effect of these two major physics improvements in GFDL forecasts from the 2005 season will be shown as well as a summary of the improved track and intensity forecasts for the cases tested. Some of the other additional minor changes to the model planned for 2006 will also be discussed. The Hurricane WRF (HWRF): Addressing our Nation's next generation hurricane forecast problems Naomi Surgi, Environmental Modeling Center/NCEP, Camp Springs, MD; and S. Gopalkrishnan, Q. Liu, R. E. Tuleya, and W. O'Connor The Hurricane Weather and Research Forecast system (HWRF)is scheduled for operational implementation at NCEP in 2007 and will replace the current GFDL hurricane model. Under development at EMC, the HWRF is being designed to address the intensity, structure and rainfall forecast problem in addition to advancing wave and storm surge forecasts. Continued advancements in track prediction will remain an important focus of this prediction system. The HWRF is a coupled air-sea-land prediction system with a movable nested grid and physics suitable for high resolution. For initialization of the hurricane core circulation, an advanced data assimilation is being development at EMC that will make use of real time airborne Doppler radar data from NOAA's aircraft to initialize the three dimensional storm scale structure. To address the full scope of the operational hurricane forecast problems noted above, the HWRF will also include coupling to an advanced version of the operational hurricane wave model WAVEWATCH, that will feature a multiscale grid structure over the hurricane environment with a moving nest around the hurricane. This system will eventually be coupled to a dynamic storm surge model. Additionally, the land surface component will also serve as input to hydrology and inundation models to address to hurricane related inland flooding problem. The HWRF was run four times a day during the 2005 hurricane season testing various aspects of the HWRF system. Progress at EMC on HWRF development for the initial 2007 implementation will be addressed in this presentation. Future development plans for HWRF advancement will also be discussed. High-resolution vertical profiling of ocean velocity and water properties under Hurricane Frances in September 2004 Thomas B. Sanford, University of Washington, Seattle, WA; and E. A. D'Asaro, J. B. Girton, J. F. Price, and D. C. Webb In ONR's CBLAST Hurricane research program observations were made of the upper ocean's response to Hurricane Frances. Three EM-APEX floats (velocity sensing versions of Webb Research APEX floats) and two Lagrangian floats were deployed north of Hispaniola from a C-130 aircraft ahead of Hurricane Frances in September 2004. The EM-APEX floats measured T, S and V over the upper 500 m starting about a day before the storm's arrival. The Lagrangian floats measured temperature and salinity while following the three-dimensional boundary layer turbulence in the upper 40 m. One EM-APEX float was directly under the track of the storm's eye, another EM-APEX and two Lagrangian floats went in about 50 km to the right of the track (where the surface winds are strongest) and the third float was about 100 km to the right. The EM-APEX floats profiled for 10 hours from the surface to 200 m, then continued profiling between 35 and 200 m with excursions to 500 m every half inertial period. After 5 days, the EM-APEX floats surfaced and transmitted the accumulated processed observations, then the floats profiled to 500 m every half inertial period until recovered early in October aided by GPS and Iridium. The float array sampled in unprecedented detail the upper-ocean turbulence, momentum, and salt and heat changes in response to the hurricane. The buildup of surface gravity waves in advance of the storm was also observed in the velocity profiles, with significant wave heights of up to 11 m. Rapid acceleration of inertial currents in the surface mixing layer (SML) to over 1 m/s stimulated vertical mixing by shear instability at the SML base, as indicated by low Richardson numbers and SML deepening from about 40 m to 120 m under the strongest wind forcing. Surface cooling of about 2.5 C was primarily due to the SML deepening and entrainment of colder water, with a small contribution from surface heat flux. Intense inertial pumping was observed under the eye, with vertical excursions of 50 m or more. Comparison with a 3-D numerical model of the ocean response to Frances' winds reveals encouraging similarities in SML deepening and surface cooling as well as significant differences in maximum currents and heat content changes. These differences highlight the sensitivity of the ocean's response to both the specification of the wind field and the parameterization of stress under high wind speeds. 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