Numerical investigation on detailed structure of Typhoon"Meranti"(2016) and extreme heavy rainfall event induced by it before and after landfall in Fujian

Based on the intensive observations at automatic weather stations over Fujian province, NCEP/NCAR reanalysis with 0.5°×0.5° resolution and simulations from WRF mesoscale numerical model, we have performed an analysis of the features of surface rainfall in the extreme heavy rainfall event induced by Typhoon"Meranti"(1614) in Fujian and the detailed three dimensional structures of airflow, temperature and moisture, energy, dynamic and thermodynamic fields, and conducted a preliminary investigation of the reason why the extreme heavy rainfall of the typhoon spiral rain band locates in the northeast quadrant after the typhoon landfall. The main results are as follows. (1) Before typhoon' s landing, it showed warm core, moist core and positive vorticity column features in the lower to mid-high levels of the typhoon circulation and the funnel-shaped structure of pseudo-equivalent potential temperature (θ_se) in the mid-high level. The radial inflow obviously persists in the boundary level. The asymmetry of typhoon spiral rain band is weak. Only in the southwest quadrant of the typhoon, the intensity and area of spiral rain band are not as strong and wide as in other quadrants. (2) After typhoon' s landing, its warm and moist core disappears fast and the horizontal range of positive vorticity column decreases gradually. The funnel-shaped structure of θ_se in the mid- and upper-level touches down to the ground. The deep radial outflow begins to prevail in the southwest quadrant and the radial inflow start to weaken in the northwest quadrant. However, the deep radial inflow persists in the east and northeast quadrants, which leads to a spiral rain band mainly locating in the northeast quadrant. (3) The severe precipitation in the spiral rain band mainly locates in the northeast quadrant after typhoon' s landing, which is related to the decentration of tangential waves with wave numbers 0-3 in the typhoon circulation. (4) The extreme heavy rain in Xiamen and Quanzhou is mainly caused by typhoon inner core rain band, and that in Ningde and Fuzhou predominantly results from typhoon spiral rain band. It is also found that the environments and physical mechanisms are different for the formation of extreme heavy rainfall in the typhoon inner core and spiral rain band.