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Robert Rogers and Sundararaman Gopalakrishnan NOAA/AOML Hurricane Research Division

The impact of horizontal resolution on the structure and intensity of Hurricane Dennis in HWRF TM simulations. Robert Rogers and Sundararaman Gopalakrishnan NOAA/AOML Hurricane Research Division Miami, FL 33149. Motivation. 45% reduction in 15 yr. 17% reduction in 15 yr.

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Robert Rogers and Sundararaman Gopalakrishnan NOAA/AOML Hurricane Research Division

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  1. The impact of horizontal resolution on the structure and intensity of Hurricane Dennis in HWRFTM simulations Robert Rogers and Sundararaman Gopalakrishnan NOAA/AOML Hurricane Research Division Miami, FL 33149

  2. Motivation 45% reduction in 15 yr 17% reduction in 15 yr • Improvements in intensity forecasts have lagged improvements in track forecasts Annually-averaged NHC 48-h forecast errors from 1990 to 2005 Track Intensity • Numerical model guidance can be key contributor to intensity forecasts, but it faces challenges • resolution • initial TC vortex • physical parameterizations

  3. Motivation Courtesy NRL Monterey • Rapid intensification (RI) – defined as 30-kt increase of peak winds in a 24-h time period convective bursts • Enhanced IR valid 0315 UTC October 17 2005 • 30-kt Tropical Depression 24 • RI began 14 h later, becoming Hurricane Wilma • Multiscale process • environment – O(1000 km) – troughs, anticyclones • vortex – O(1-100 km) – VRWs, eyewall, rainbands • convection – O(1 km) – convective cores, VHTs • turbulence – O(10-100 m) – PBL, detrainment • microscale – O(1 mm) – hydrometeor production, latent heat

  4. Questions to consider • To get improved predictions of RI, how important is it to adequately represent (resolve) the features mentioned above? • Is it sufficient to parameterize them? • Are lower-resolution ensemble approaches preferable?

  5. Approach • simulate with HWRFTM a case of observed RI • Hurricane Dennis (2005) • period of RI beginning at 18 UTC July 6 • run two cases • operational grid length of 27:9 km • higher-resolution run at 9:3 km • two-way interactive movable mesh • GFDL initial conditions, GFS forecast boundary conditions, GFDL/GFS physics • no ocean coupling, no GSI • no convective parameterization on 3 km grid • models initialized at 00 UTC July 6

  6. 7/9 7/8 7/7 7/6 RI period 7/5 Dennis Observed Track and Intensity Track Intensity

  7. Results 27-h animation of 850 hPa model-derived reflectivity TM TM 27-9 km run 9-3 km run

  8. 9-3 km 27-9 km Best track 7/7 7/7 7/7 7/6 Results Intensity Track

  9. Results TM TM dBZ dBZ NOAA P-3 radar 0045-0144 UTC 7 July 27-9 km run 9-3 km run kt

  10. Results dBZ dBZ kt kt 27-9 km run 9-3 km run TM TM Reflectivity and MSLP TM TM Winds

  11. Results dBZ dBZ X 10-4 s-1 X 10-4 s-1 27-9 km run 9-3 km run TM TM Reflectivity and MSLP TM TM Vorticity

  12. Summary • 9-3 km run better able to produce vortex structures • distribution of convection • wind distribution and structure • vorticity • not sure about convective structure yet • Despite this better representation of vortex structure, intensity forecast not significantly improved • track problems • vortex initialization • physical parameterizations • still insufficient resolution

  13. Future work • evaluate differences in convective structures between two runs • vertical motion, hydrometeor, reflectivity profiles and distributions • expand tests to more Dennis forecast cycles, more cases • perform direct and statistical comparisons of vortex and convective structures with observations • ensemble runs at 9 km vs. deterministic runs at 3 km • initial condition variations • physics diversity • try runs at 1 km

  14. Time-height mean profiles of 1.67-km MM5 simulation of Dennis level of peak upward motion stratiform convective vertical motion bursts bursts vorticity bursts bursts

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