Impacts of an Upper Tropospheric Cold Low on Tropical Cyclone Intensity

Abstract

Abstract Following a previous study examining the influence of an upper tropospheric cold low (CL) on the track of a nearby tropical cyclone (TC), this study investigates the impacts of a CL on TC intensity. The results suggest that the relative position and separation distance between the CL and TC are the key factors affecting TC intensity. When located outside the CL’s radius of maximum wind (RMW) but within its circulation, TCs initially in the northwest quadrant of the CL intensify faster than those in the other quadrants. The β effect causes the CL to move northwestward toward the TC and enhances eddy momentum flux convergence. Meanwhile, the upper-level TC outflow erodes the CL and reduces the associated vertical wind shear, promoting TC intensification. In contrast, for TCs initially located southeast of the CL, the attraction of Fujiwhara effect between the two entities counteracts the CL’s β drift and helps to maintain their separation distance. Moreover, Rossby wave energy dispersion induces an anticyclone southeast of the CL, which transports lower-θe air toward the TC and hinders the TC development. Furthermore, TCs within the CL’s RMW reach a similar intensity due to their PV superposition, irrespective of their relative positions to the CL. For TCs located outside the CL circulation, the CL’s impacts are largely negligible for TCs located northwest of CL, but TCs located southeast of the CL may still be affected by the CL-induced anticyclone.