Description of cloud-rain bands in a tropical cyclone by a hyperbolic-logarithmic spiral

Based on the law of inflow angle change in a tropical cyclone (TC) as a function of radius, an analytical expression as a combination of hyperbolic and logarithmic spirals (HLS) for the description of TC spiral cloud-rain bands is retrieved. Parameters of the HLS are deterlnlned by the physical parameters of a TC. The advantage of the proposed approximation over the empirical logarithmic approximation is shown with several examples of satellite and radar images of a TC.