Sub-Kilometer Simulation of Landfall of Typhoon Rammasun (2014)

Typhoon Rammasun (2014), one of only three Category 5 super typhoons on record in the South China Sea, had destructive impacts across the Philippines, South China, and Vietnam. It experienced rapid intensification and reached its peak intensity just before it made landfall near Wenchang City on the island of Hainan on July 18, bringing extreme precipitation up to 572 mm in 24 hours. Our study performed 4-day simulation of Rammasun from 16 to 20 July 2014 with a resolution of 667 m by using the YSU BL parameterization (YSU run). Simulation results are verified in terms of track, intensity, size and precipitation using high-resolution observations of automatic station data, doppler radar data and satellite data. The YSU run captures the rapid intensification process and the simulated rainbands are very similar to the observation. The inner core size of the YSU run was slightly bigger, while the outer peripheral wind scale was smaller in comparing to the results of Multiplatform Tropical Cyclone Surface Wind Analysis (MTCSWA). In addition, a large eddy simulation (LES) without PBL scheme (LES run) was conducted. There are no significant differences in track and intensity between the two runs. However, the eye size in the LES run is smaller than that in YSU run, close to the observation. From the axisymmetric perspective, the simulated TC in the LES run has stronger vertical motion in the upper level above 10 km. There is no significant change in the strong vertical motion in the LES run during early landfalling stage, while the upward motion > 6 m/s in YSU run is significantly reduced. From the asymmetric perspective, the eyewall structure in the LES run is stronger than that in YSU run, while the outer rainband is relatively weaker, especially after landfall. Although the horizontal resolution of ≤ 100 m was considered adequate in the LES, this study suggests that the structure of the simulated typhoon during landfall is different between the two experiments.