27th Conference abstracts

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27th Conference abstracts

The Intensity Forecasting Experiment (IFEX): A NOAA multi-year field program for improving tropical cyclone intensity forecasting

Robert Rogers, NOAA/AOML/HRD, Miami, FL; and M. Black, R. E. Hood, J. B. Halverson, E. J. Zipser, and G. M. Heymsfield
NOAA's Hurricane Research Division began in 2005 a multi-year experiment with the NOAA Aircraft Operations Center (AOC) called the Intensity Forecasting Experiment (IFEX). Developed in partnership with NOAA's Environmental Modeling Center (EMC) and National Hurricane Center (NHC), IFEX is intended to improve the prediction of hurricane intensity change by 1) providing observations of current tropical cyclone intensity and structure; 2) providing data to improve the operational numerical modeling system (i.e., HWRF); and 3) improving our understanding of the physics of intensity change and rainfall. Observations are collected in a variety of hurricanes at different stages in their lifecycle, from formation and early organization to peak intensity and subsequent landfall or decay over open water. In July 2005, IFEX partnered with NASA during their Tropical Cloud Systems and Processes (TCSP) experiment, based in San Jose, Costa Rica. A variety of systems were flown with the NOAA P-3's and NASA ER-2 in coordination for a sizable portion of the systems' lifecycle, including Hurricane Dennis from tropical storm to landfall, Tropical Storm Gert from tropical disturbance to tropical storm strength, and a null case in the Eastern Pacific. A summary of these flights, including how they will satisfy the IFEX objectives, will be presented.
Development of a coupled hurricane-wave-ocean model toward improving air-sea flux parameterization in high wind conditions
Isaac Ginis, University of Rhode Island, Narragansett, RI; and I.-J. Moon, B. Thomas, T. Hara, H. L. Tolman, and M. A. Bender
This study aims to improve hurricane forecasts of the operational GFDL/URI model by introducing a new coupled hurricane-ocean-wave system. The coupled system consists of the 2005 high-resolution GFDL hurricane model, the Princeton Ocean Model (POM), the WAVEWATCH III model, the URI wave boundary layer (WBL) model, and the URI equilibrium spectrum model.
The key component of the coupled system is a newly-developed air-sea momentum flux parameterization based on the wave fields. In the coupled system, the complete wave spectrum is constructed by merging the WAVEWATCH III spectrum in the vicinity of the spectral peak with the spectral tail parameterization. The result is incorporated into the WBL model to explicitly calculate the wave induced stress, the mean wind profile, and the roughness length (z0). In the coupled system, the estimated wave-field dependent roughness length is transferred into the GFDL model, replacing z0 of the current GFDL hurricane model based on the Charnock relation. For computational efficiency, we introduce a movable grid mesh configuration for the wave model as well as the MPI parallel computing system for the coupled model.
We have tested and evaluated the new coupled system for hurricanes in the 2004 and 2004 season by comparing the storm intensity forecasts and the spatial distributions of the surface wind with and without the wave coupling. The wind structure with the wave coupling is evidently in a better agreement with the HRD wind analysis and its intensity forecast is improved, in some cases significantly. This is accomplished by the use of more realistic wave-dependent surface momentum fluxes and their spatial distribution.
The new GFDL coupled system is planned to be implemented operationally at NCEP in 2006 and some elements to be transitioned to the Hurricane WRF.

The Effect of Roll Vortices on Turbulent Fluxes in the Hurricane Boundary Layer

Jun Zhang, Univ. of Miami/RSMAS, Key Bisayne, FL; and W. M. Drennan, S. Lehner, K. B. Katsaros, and P. G. Black

The patterns observed in surface wind fields derived from synthetic aperture radar (SAR) images inside and around tropical cyclones (TCs) were investigated with data from RADARSAT-1 Satellite. Supporting field measurements obtained on research flights of the NOAA/Aircraft Operations Center (AOC) WP-3D aircraft provide a database for the interpretation of the unique features of the hurricane structure. The aircraft data include flight level winds and turbulence measurements of momentum and water vapor fluxes, dropsonde information, temperature, and surface winds obtained remotely by a stepped-frequency microwave radiometer (SFMR). The hypothesis that linear streaks observed in the SAR wind fields between rainbands were due to secondary flows, roll vortices, in the atmospheric boundary layer is verified. Our data analyses show that their contribution to the net fluxes and their distribution azimuthally around the storm could play an important role in boundary layer air-sea fluxes and hurricane dynamics. Many cases of roll-vortex signatures in the SAR wind fields in hurricanes are also documented. This work may play a role in developing parameterization of these features for future use in operational coupled numerical hurricane forecast models.
Air-sea fluxes in Hurricane Frances (2004) from dropsonde data and a coupled model
Mélicie Desflots, Univ. of Miami/RSMAS, Miami, FL; and S. S. Chen and W. Zhao
The importance of surface fluxes for tropical cyclone (TC) intensity is widely accepted by the scientific community. The determination of the surface fluxes under high-wind conditions is difficult due to the lack of accurate observations in high winds. The physical processes controlling the exchange coefficients of heat, moisture, and momentum fluxes are not well understood. Recent observations from the Coupled Boundary Layer Air-Sea Transfer (CBLAST) field program provided an excellent opportunity to evaluate coupled model simulations of air-sea fluxes in hurricanes. We calculated the surface heat fluxes using two different flux parameterizations using the Global Positioning System (GPS) dropsondes data from CBLAST and the sea surface temperature (SST) from the SSM/I and TMI Satellite data. The methods are based on budget analysis and the Monin-Obukhov stability theory Furthermore, the momentum and exchange coefficient of momentum flux are computed using these two methods and a third one which assumes that the mean wind profile is logarithmic. The fluxes from a fully coupled atmosphere-wave-ocean simulation of Hurricane Frances (2004) are compared with the air-sea fluxes based on the dropsonde data obtained during CBLAST 2004 field program from 30 August – 2 September 2004. The model used for this study is the coupled atmosphere-wave-ocean model developed at the University of Miami (Chen et al. 2005). The different dropsonde analysis show that the momentum exchange coefficient levels off above hurricane force winds, similar to that of the results of Powell et al. (2003) and Donelan et al. (2004), but are slightly greater than the ones found in both studies. The coupled model also shows that the drag coefficient is higher in the left-rear quadrant of the storm were the waves are younger and roughest. There is a strong asymmetry in the air-sea fluxes associated not only with the variability in the surface waves, but also ocean cooling in the wake of Hurricane Frances. More analysis is currently underway to include more dropsondes in this analysis and make a quadrant analysis to compare with the coupled model.

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