Wook Jang

Characteristics of Binary Tropical Cyclones Observed in the Western North Pacific for 62 Years (1951–2012)

AbstractThe statistical and dynamical characteristics of binary tropical cyclones (TCs) observed in the western North Pacific (WNP) for 62 years (1951–2012) are investigated by using best track and reanalysis data. A total of 98 binary TCs occurred with an annual average of 1.58. The occurrence frequency of binary TCs shows significant year-to-year variations and there are two peaks in the mid-1960s and early 1990s. Three-fourths (76.3%) of the binary TCs occurred between July and September, which is consistent with the high activity season of TCs in general. A relatively higher track density for binary TCs is present to the east of the maximum track density for total TCs. This result is likely due to the differences in the locations of genesis and environmental steering flow between binary and total TCs. The poleward steering flow, weaker vertical wind shear, and warmer sea surface temperature are pronounced for binary TCs, and these result in a longer lifetime of TCs, which can increase the chances that...

The Effects of Topography on the Evolution of Typhoon Saomai (2006) under the Influence of Tropical Storm Bopha (2006)

AbstractThe effects of topography on the evolution of Typhoon Saomai (2006) are investigated by conducting a series of numerical simulations with the Weather Research and Forecasting (WRF) Model using 100%, 75%, 50%, and 25% of terrain heights of the Central Mountain Range (CMR) in Taiwan. Differences in the track and intensity of Typhoon Saomai between the experiments are strongly related to those of Tropical Storm Bopha, which passed Taiwan earlier than the typhoon. In the sensitivity experiments, the higher CMR drifts Bopha more southward, which results in the weakening of Bopha by prohibiting the interaction between the CMR and Bopha, and the flows induced by Bopha force Saomai to propagate along a more southerly track. The higher CMR weakens the easterly flow in the lower troposphere and suppresses the northerly flow in the upper troposphere to the west of Saomai. The resultant weak vertical wind shear keeps warm air near the typhoon center in the upper troposphere, which promotes the intensification...

Effects of thermodynamic profiles on the interaction of binary tropical cyclones

The interactions between idealized binary tropical cyclones (TCs) on f and β planes with different separation distance and thermodynamic soundings obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data averaged over the western North Pacific are investigated through ensemble three-dimensional numerical simulations with a horizontal resolution of 10 km in a single domain. In the simulations on the f plane, two TCs show mutual cyclonic rotations with symmetric structures. Two TCs with thermodynamic profiles of larger convective available potential energy (CAPE) and maximum potential intensity (MPI) show greater interaction than those with a smaller CAPE and MPI due to the stronger tangential velocity near the TC center. In the simulations on the β plane, the two TCs do not merge, because the beta effect prevents the attraction of the two TCs by generating asymmetric motions of the TC with northwestward forcing. The relative strengths of the two TCs change with time and depend on the low-level inflow influenced by the Coriolis parameter. Similar to the results on the f plane, the two TCs only merge with the thermodynamic soundings of large CAPE and MPI.