Taiwan (TW) terrain is studied by inserting a TC at a location so that landfall occurs at the central part of TW in the no terrain (control) case. By subtracting the asymmetric wind field in the control case from that in with terrain case, a pair of terrain-induced gyre is found. This gyre pair then rotates around the TC center and leads to the northward track deflection of TC track. Diabatic heating cannot be ignored prior to and during landfall which tends to retard the fast displacement caused by the gyre advection.
TW terrain is regarded as a remote topography in the second part of the research that TCs cross the region north and south of TW without making landfall on TW. Results show that the northward deflection is largely mitigated for a TC moving further north of TW while TCs moving south of TW have sharp northward deflection and the reductions on the speed prior to the deflection are more significant. Both these effects are gradually eased off for the southern TC. Moreover, the northward deflection occurs more westward. In addition to TW terrain, China terrain, which is regarded as local topography, is present in the additional experiments. China terrain induces another weaker gyre pair and leads to a westward drift of the TC prior to landfall on China. Due to its strength, vertical advection in the PVT equation cannot be neglected. Diagnostics of these results and the possible mechanisms will be discussed at the conference.
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