Water Budget of Typhoon Nari (2001)

Although there have been many observational and modeling studies of tropical cyclones (TCs), the understanding of TCs' budgets of vapor and condensate and the changes of budgets after TCs' landfall is still quite limited. In this study, high-resolution (2-km horizontal grid size and 2-min data interval) model output from a cloud-resolving simulation of Typhoon Nari (2001) is used to examine the vapor and condensate budgets and the respective changes of the budgets after Nari's landfall on Taiwan. All budget terms are directly derived from the model except for a small residual term. For the vapor budget, while Nari is over the ocean, evaporation from the ocean surface is 11% of the inward horizontal vapor transport within 150 km of the storm center, and the net horizontal vapor convergence into the storm is 88% of the net condensation. The ocean source of water vapor in the inner core is a small portion (5.5%) of horizontal vapor import, consistent with previous studies. After landfall, Taiwan's steep terrain enhances Nari's secondary circulation significantly and produces stronger horizontal vapor import at low levels, resulting in a 22% increase in storm-total condensation. Precipitation efficiency, defined from either the large-scale or microphysics perspective, is increased 10%-20% over the outer-rainband region after landfall, in agreement with the enhanced surface rainfall over the complex terrain.