Mechanism analysis and numerical simulation of strong marine typhoon duct caused by super typhoon "Lupit" (2009)

Based on the high-resolution global positioning system (GPS) dropsonde data from Dropwindsonde Observations for Typhoon Surveillance near Taiwan Region (DOTSTAR), ducts induced by tropical cyclones (TC ducts) over the ocean near Taiwan from September 2003 to August 2012 are analyzed. A typical case of strong ducts induced by super typhoon "Lupit" (2009) is selected for further research. The mechanism for these strong ducts is diagnosed first based on the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (horizontal resolution of 0.125°×0.125°). Using the WRF model, two initialization schemes are compared in terms of their abilities in simulating the TC intensity, inner-core size and TC ducts. These strong TC ducts are largely formed in the weak subsidence area on the northwestern periphery of the typhoon. Their formation is mainly caused by the sharp decrease of moisture with altitude, which is resulted from the strong southward dry advection near 850 hPa. The TC dynamical initialization (DI) scheme used in WRF model improves the simulation of TC intensity, track and inner-core size, which subsequently leads to better simulation of TC ducts especially their heights. Moreover, ducts formed outside the TC are mainly elevated ducts. Their simulations are mainly associated with the simulation of the TC spiral rainband and inner-core size, whereas the simulation of TC intensity and eye wall structure have little impact. Finally, the WRF model is capable of simulating TC ducts and producing high-resolution data. Thereby, it is a robust tool for the study of TC ducts.