The Study of Inland Eyewall Reformation of Typhoon Fanapi (2010) Using Numerical Experiments and Vorticity Budget Analysis

Abstract

Numerical simulations of Typhoon Fanapi (2010) interacting with the terrain of Taiwan are conducted using the Advanced Research Weather Research and Forecasting model (ARW, version 3.3.1) on a triply nested grid (with the finest grid size of 1 km and 55 vertical levels). Fanapi made landfall on eastern Taiwan at 0000 UTC 19 September and left Taiwan at 1200 UTC 19 September 2010, producing heavy rainfall and severe floods. After landfall, the Fanapi eyewall weakened and broke down over the Central Mountain Range. Vortical hot towers (VHTs) occurred along the Fanapi rainband, and the VHTs in land have weaker maximum updrafts (7.0–8.0 m/s), narrower diameter (7.0–11.5 km), and shallower depth (6.5–9.0 km), compared with oceanic VHTs over the Taiwan Strait. The VHTs over the Taiwan Strait remained organized along the rainband and propagated toward the southeast quadrant of the Fanapi circulation over land by the tangential flow. These organized VHTs in the southeast quadrant help transport cyclonic vorticity from lower into middle levels and then cooperate with the rich vorticity within the rainband by horizontal vorticity advection to rebuild the Fanapi eyewall upward from the bottom. The vorticity balance within the entire Fanapi circulation is largely dominated by its southeast quadrant with organized VHTs over Taiwan Island. In the simulation with no latent heat release, the VHTs quickly decay and radiate outward from the eyewall as gravity‐wave perturbations.

An observational study of the inner core structure of Typhoon Meranti (2016) near landfall

“…Meranti's northward defection, as well as the cold cloud shield evolution, was the evidence of terrain impact. Moreover, CMR will also affect the distribution of deep convection and vortical hot towers along the rain band and eyewall (Yang et al ., ), thus affecting the inner core structure.…”

“…Meranti's northward defection, as well as the cold cloud shield evolution, was the evidence of terrain impact. Moreover, CMR will also affect the distribution of deep convection and vortical hot towers along the rain band and eyewall (Yang et al, 2018), thus affecting the inner core structure. (Figure 1f), the main body of Meranti is evident as solitary and continuous regions, however, finer structures, such as distinct rain bands originating from the eyewall, are undistinguishable.…”

“…For instance, when passing Luzon, Typhoon Zeb (1998) experienced original eyewall breakdown and a much larger new eyewall reformation; slightly different from Zeb, when passing Taiwan, the eyewall of Typhoon Fanapi (2010) disappeared on the eastern side of Central Mountain Range (CMR) and reemerged on the other side. Both observational and numerical studies (Wu et al, 2009;Liou et al, 2016;Yang et al, 2018) found underlying topography and moist processes were crucial during this process, and for Fanapi, hot towers over terrain were observed. Because of the complicated and nonlinear physical processes, TC at different intensity may involve differently when encountering terrain of different type in different ways.…”

Examining Terrain Effects on the Evolution of Precipitation and Vorticity of Typhoon Fanapi (2010) after Departing the Central Mountain Range on Taiwan

“…Typhoon Fanapi ( 2010) is a unique typhoon case in which dual-Doppler radar observations from two Doppler radars (one ground-based operational radar and one mobile research radar) were available to document the kinematic and precipitation structure within Fanapi's inner core, and vortical hot towers (VHTs) over land were documented for the first time in the literature. Yang et al (2018) conducted a high-resolution WRF Model simulation (with finest horizontal grid size of 1 km) to compare the VHTs over the open ocean and over land. The VHTs over land had weaker maximum updrafts (7-8 m s 21 ), narrower diameters (7-11.5 km), and shallower depths (6.5-9 km) than those over the ocean.…”

A study of the rainfall and structural changes of Typhoon Koppu (2015) over northern Philippines

“…Wu and Kuo (1999) summarized decades of studies on the understanding of the characteristics of TCs making landfall at Taiwan. The development of numerical forecasting systems (Hong et al, 2015;Hsaio et al, 2020), the application of new observing equipment, such as meteorological satellites and radars (Lee et al, 2000;Liu et al, 2001;Huang et al, 2005), and the observations and research programs (e.g., Lee et al, 2000;Liu et al, 2001;Huang et al, 2005;Lin et al, 2005;Wu et al, 2007;Lee et al, 2008;Chien and Kuo, 2011;Wang et al, 2013;Chen et al, 2017;Yang et al, 2018) have contributed to the improvement of the understanding and forecast of the movement and structural changes of TCs in Taiwan.…”