Interaction and Influence of Binary Typhoons

The non-static mesoscale numerical model WRF V3.3 is used to study the influence of the interaction between binary typhoons on their moving path, intensity and precipitation. Data of NCEP FNL are used as initial field and side boundary conditions, and satellite data of ATOVS such as AMSUA, AMSUB, HIRS (3/4) are assimilated. Simulation results of binary typhoons in control runs, which are based on hybrid ensemble three-dimensional variational data assimilation (Ens-3DVar) system, are very close to the real intensity, moving path and precipitation. Beyond that, 6 sensitive experiments based on control runs are designed. The 96-hour simulations are conducted after one of the binary typhoons (Fitows/Danas/Goni/Morakot) is removed from the initial field which adopts the first step of vortex reconstruction technology in WRF ARW in the sensitive experiments (C1-RMF/C1-RMD/C2-RMG/C2-RMM). Experiment C2-WEM (C2-STM) is conducted by weakening or enhancing one of the binary typhoons in order to study effects of typhoon Morakot on typhoon Goni, but the typhoon radius is unchanged. Results of sensitive experiments and control runs are further compared and analyzed.In Case 1, the role of typhoon Danas leads typhoon Fitow to move southward and slower. The role of typhoon Fitow causes typhoon Danas to move northward but has little effects on the shifting speed. The strength of binary typhoons Fitow and Danas have been changed by the interaction between them. Specifically, the interaction of binary typhoons makes the intensity of typhoon Fitow and typhoon Danas stronger in the strong stage and weaker in the dying stage of typhoon Fitow. From 6 October to 9 October in 2013, the heavy precipitation in East China is mainly affected by typhoon Fitow. Affected by typhoon Danas, the precipitation intensity brought by typhoon Fitow is enhanced, and the heavy precipitation center moves southward.In Case 2, the interaction of binary typhoons makes typhoon Goni move southward and faster, but typhoon Goni has little influence on the movement and speed of typhoon Morakot. The winding path and direction change of typhoon Goni are all associated with typhoon Morakot. The bending extent of typhoon Goni is positively correlated with the strength of typhoon Morakot. Main causes are the interaction and transportation mechanism of vorticity, water vapor flux between binary typhoons.