The effect of tropical cyclone size on its movement as TC approach the coastline

In this study, numerical experiments with different initial radius of maximum wind (RMW) are performed to study the effects of tropical cyclone (TC) size combined with land-sea contrast on TC motion and low-level wind structure before landfall. By idealized numerical simulations, we found that when TCs approach the coastline, the translation speed of them will accelerate. The larger TC arrived coastline earlier than smaller TC, when they started moving from the same position. This is because that the larger TCs not only accelerate earlier but also have greater movement speed than smaller TCs when they approach the coastline. The mechanism responsible for this is that the edge of large TCs reach coastline earlier, thus their movement speed accelerated earlier than small TCs, due to the asymmetries in diabatic heating and radial flow generated by the land-sea contrast. Moreover, when TCs in three experiments all affected by the land-sea contrast, the stronger asymmetries generated in larger TC, thus resulting in faster movement in larger TC. The stronger inflow in western quadrant and weaker inflow (even outflow) in eastern quadrant of larger TC deduced apparently difference in vertical motion and diabatic heating between western and eastern quadrant of TC before landfall. An analysis of potential vorticity tendency proved that the diabatic heating terms were important and considered in determining the TC landward drift because asymmetries in vertical motion and relative vorticity developed due to asymmetric flow. This achievement can deepen the understanding of the evolution of TC structures in coastal areas and provide certain reference value for the accurate prediction of TC landing time over land.