Water Budget and Precipitation Efficiency of Typhoon Morakot (2009)

Abstract

In this study, the Weather Research and Forecasting model, version 3.2, with the finest grid size of 1 km is used to explicitly simulate Typhoon Morakot (2009), which dumped rainfall of more than 2600 mm in 3 days on Taiwan. The model reasonably reproduced the track, the organization, the sizes of the eye and eyewall, and the characteristics of major convective cells in outer rainbands. The horizontal rainfall distribution and local rainfall maximum in the southwestern portion of the Central Mountain Range (CMR) are captured. The simulated rain rate and precipitation efficiency (PE) over the CMR are highly correlated. In the absence of terrain forcing, the simulated TC's track is farther north and rainfall distribution is mainly determined by rainbands. The calculated rain rate and PE over the CMR during landfall are about 50% and 15%-20% less than those of the full-terrain control run, respectively. By following major convective cells that propagate eastward from the Taiwan Strait to the CMR, it is found that the PE and the processes of vapor condensation and raindrop evaporation are strongly influenced by orographic lifting; the PEs are 60%-75% over ocean and more than 95% over the CMR, respectively. The secondary increase of PE results from the increase of icephase deposition ratio when the liquid-phase condensation becomes small as the air on the lee side subsides and moves downstream. This nearly perfect PE over the CMR causes tremendous rainfall in southwestern Taiwan, triggering enormous landslides and severe flooding.

Influence of southwest monsoon flow and typhoon track on Taiwan rainfall during the exit phase: modelling study of typhoon Morakot (2009)

“…The daily rainfall distribution over Taiwan on 8 August shows the highest accumulation along the southern CMR and in southwestern Taiwan (Figure (c)). The precipitation efficiency of Morakot over the CMR was enhanced to more than 95% due to strong orographic lifting (Huang and Yang, ).…”

Torrential rainfall processes associated with a landfall of Typhoon Fitow (2013): A three‐dimensional WRF modeling study

“…Huang et al . [] analyzed water budget and precipitation efficiency of Typhoon Morakot (2009) and showed that condensation and ice deposition caused the high precipitation efficiency over the Central Mountain Ranges, producing tremendous rainfall in southwestern Taiwan. Fritz and Wang [] investigated the evolution of water budgets from tropical wave stage to tropical cyclone stage using a high‐resolution model.…”

“…Yang et al [2011] analyzed water budget of Typhoon Nari (2001) with Weather Researching and Forecasting (WRF) Model and revealed that Taiwan's steep terrain enhanced precipitation efficiency and surface rain rate by significantly strengthening secondary circulations and producing stronger vapor import at low levels. Huang et al [2014] analyzed water budget and precipitation efficiency of Typhoon Morakot (2009) and showed that condensation and ice deposition caused the high precipitation efficiency over the Central Mountain Ranges, producing tremendous rainfall in southwestern Taiwan. Fritz and Wang [2014] investigated the evolution of water budgets from tropical wave stage to tropical cyclone stage using a high-resolution model.…”

A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima

“…One was aligned north-south (N-S) near 120.7 • E along the windward slopes of the southern Central Mountain Range (Figs. 2a-d and 3a, Wang et al, 2012), produced through forced uplift of moisture-laden air by the steep topography at high precipitation efficiency (Yu and Cheng, 2013;Huang et al, 2014). On the other hand, the second type of rainbands was nearly E-W oriented and parallel to the flow.…”