High-Resolution Numerical Atmospheric and Ocean Simulations of Typhoon Maemi (September 2003)

1. High-Resolution Numerical Atmospheric and Ocean Simulations of Typhoon Maemi (September 2003) Travis A. Smith Tim Campbell Richard Allard James Dykes Justin Small Shelley Riedlinger Naval Research Laboratory January 13, 2009

2. AIMS • To provide model validation to a region unaccustomed to intense tropical cyclones • To further improve tropical cyclone modeling in terms of structure, intensity, and ocean response • To prepare a stand alone model test case for comparison to future coupled atmospheric, oceanic, and wave model investigations

3. INTRODUCTION • Super Typhoon Maemi (5 SEP – 13 SEP 2003) • Most intense typhoon to make landfall in South Korea in 50 years • Traversal of typhoon over several warm core eddies in the South China Sea allowed for rapid intensification. • Exceptionally warm SSTs in the South China Sea may have contributed to reduced weakening of the typhoon before landfall.

4. MODELS • Three models are utilized for atmospheric, ocean, and wave computations of Typhoon Maemi. • COAMPS (Coupled Ocean/Atmosphere Mesoscale Prediction System) • Surface forcing provided by the atmospheric component • Triply nested (27, 9, 3 km resolution) • Boundary conditions provided by NOGAPS • Data assimilation included (every 12 hr) • NCOM (Navy Coastal Ocean Model) • Two nests (6 and 2 km resolution) • Boundary conditions provided by global NCOM • Tidal and monthly river discharge data included • SWAN (Simulating Waves Nearshore) • Forced by COAMPS wind output

5. COAMPS • VALIDATION RESULTS: • Positive: • Excellent track validation • Cyclone structure • East Sea intensity • Negative: • NOGAPS MSLP fields before landfall • Weaker wind field near core at landfall

6. NCOM 10 m depth 50 m depth • Expected right-bias of SST cooling near the typhoon track • Upper-ocean mixing induces cooling near the surface • Mixed-layer depth increases which warms sea temperatures below the surface

7. NCOM Vertical Profiles • Mixed-layer depth increases • Thermocline thickness decreases • Warming of sub-surface waters

8. SWAN Buoy Observations Significant Wave Height (SWAN) Maximum: 4.19 m • Significant wave height results agree • well with buoy observations • Buoy (ESROB) location (37.5N, 129.5E) : • offshore South Korean east coast

9. RESULTS AND FUTURE WORK • Although validation data is sparse, models produce respectable results in a region unaccustomed to intense typhoons. • Inclusion of data assimilation in COAMPS further increased accuracy of results. • Further studies of shallow-water air-sea interactions with tropical cyclones are necessary to provide increased clarification of shallow- water dynamics (i.e, scaling, parameterizations, etc.) • ESMF (Earth System Modeling Framework) coupled modeling will become primary focus in FY09 and will include validation of different meteorological and oceanic phenomena. (Maemi included)

10. ESMF COUPLED MODELING • Model data is interpolated onto • exchange grids for interaction at a • specified coupling interval. • Data assimilation will soon be included. • Increased coupling of air/sea interactions • between atmospheric and ocean properties • should increase accuracy.