Air-Sea Interaction during Super-Typhoon Jangmi (2008)

Super-typhoon Jangmi was a category-5 storm of 2008 over West Pacific. During its lifetime from 24 September to 2 October, Jangmi formed over the deep warm ocean northeast of Yap, then moved northwestward crossing over warm eddies and then cold eddies, and made landfall over northern Taiwan on 28 September. Dropsonde and AXBT data were collected for this case during THORPEX Pacific Asian Regional Campaign/ Tropical Cyclone Structure 2008 Experiment (T-PARC/TCS08), which took place in W. Pacific during August – September. The objective of this study is to examine the impact of the evolving ocean on Jangmi intensity change through comparisons of high-resolution coupled and uncoupled simulations.

The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®), a fully coupled atmosphere-ocean modeling system using the Earth System Modeling Framework (ESMF), is used for this study. The ocean model employed is Navy Coastal Ocean Model (NCOM) with one domain at 15-km resolution and 36 vertical levels from the ocean surface to ~4 km depth. First guess and boundary conditions are from U. S. Navy's Operational Global Atmospheric Prediction System Model for the atmospheric model and global NCOM Forecasts for the ocean model for the 5-day forecasts initialized at 0000 UTC 25 September 2008 SST. The same initial SST is used for the coupled and uncoupled forecasts, but the SST is unchanged during the uncoupled run and SST is predicted by the ocean model during the coupled run. We demonstrate that the air-sea interaction in the coupled simulation improves the intensity forecasts while the both the coupled and uncoupled simulations produce very good track forecast over the first 4 days of the simulations. A maximum of 4oC SST cooling occurs as Jangmi passes over the cold eddies. Vertical ocean temperature profiles from the coupled forecasts are in good agreement with AXBT observations. The inner core structure and outer rainbands are being verified with radar reflectivity observations as the storm approached Taiwan. We also touch upon briefly the storm dynamics at landfall. More detailed analysis of the forecasts and comparisons with the observations in both the atmosphere and ocean will be presented at the workshop.