1 Looping Tracks Associated with Tropical Cyclones Approaching an Isolated 2 Mountain. Part I: Essential Parameters 3 4 5 Yi-Chih Huang1,@ and Yuh-Lang Lin2,3 6 7 8 1 Research Center for Environmental Changes, Academia Sinica, 9 Taipei, Taiwan 10 2Department of Physics 11 3Department of Energy & Environmental Systems 12 North Carolina A&T State University 13 Greensboro, North Carolina 14 15 16 17 18 19 May 7, 2017 20 Submitted for publication 21 22 23 24 25 26 27 28 29 30 @Corresponding author address: Dr. Yi-Chih Huang, Research Center for Environmental 31 Changes, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 115, 32 Taiwan. 33 Email:
[email protected] 1 34 Abstract 35 Essential parameters for making a looping track when a westward-moving tropical 36 cyclone (TC) approaches a mesoscale mountain are investigated by examining several key 37 nondimensional control parameters with a series of systematic, idealized numerical 38 experiments, such as U/Nh, Vmax/Nh, U/fLx, Vmax/fR, h/Lx, and R/Ly. Here U is the 39 uniform zonal wind velocity, N the Brunt-Vaisala frequency, h the mountain height, f the 40 Coriolis parameter, the maximum tangential velocity at a radius of from the 41 cyclone center and Lx is the halfwidth of the mountain in the east-west direction. It is 42 found that looping tracks (a) tend to occur under small U/Nh and U/fLx, moderate h/Lx, 43 and large Vmax/Nh, which correspond to slow movement (leading to subgeostrophic flow 44 associated with strong orographic blocking), moderate steepness, and strong tangential 45 wind associated with TC vortex; (b) are often accompanied by an area of perturbation high 46 pressure to the northeast of the mountain, which lasts for only a short period; and (c) do 47 not require the existence of a northerly jet.