American Meteorological Society Demo

as radially symmetric motion in a storm-centered or the National Hurricane Center (Fig. 2). This frame of reference. This motion is also observed function has three principal elements. First, the in conventional surface-based radar animations at eyewall region does not have a rotational composmaller scales (~20 km) as individual precipitation nent, recognizing that the observed trends in the features advect with the vortex f low. An example can be found in the movie for Hu r r ica ne Kat r i na (2005) in the following section. The second trend i s t he de velopment of larger organized convective events, which are usually driven by forces that are not directly foretold in the microwave imagery— diabatic heating, localized convergence, shear, etc. An example is the formation of an eyewall. As opposed to the first trend (advection), the organized convection trend can appear to be quasi stationary and/or not dictated by the rotational winds. In order to address both trends, the algorithm employs what we call a “rotating fade” within a cyclone-centered frame of reference.1 This process is demonstrated in Figs. 1 and 1a. The rotation component of the algorithm is a radial wind loosely based on a tropical cyclone wind profile (Holland 1980) for FIG. 1. The steps of the MIMIC-TC algorithm. The morphing process is shown an average well-organized for a 5-h time interval between three satellite overpasses (a) of Hurricane storm (with a major modKatrina. The dashed boxes in (a) indicate the detail that is shown in the subseif ication for t he radia l quent steps. (b) Intermediate images are created at each hour from a simple winds in the vicinity of time-weighted average of the nearest storm-centered images before and after t he eyewa l l) sca led by the hour. (c) The algorithm uses each intermediate image in an overlapping the estimated maximum 2-h period. (d) Within the span of an hour, the earlier intermediate image is sustained surface winds rotated forward from its original time and blended into the later image, which is rotated forward toward its original time. Arrows indicate the direction of the reported by the Joint Tyadvection function. (e) These two components are weighted linearly such that phoon Warning Center 1 When the algorithm runs in real time, we employ an automated center-fixing scheme that will be described in a subsequent paper. the earlier image rotates and fades into the later image in the final product. Note the following changes over time in the final product: more convection emerges on the southwestern side of the image, convective cells on the eastern side of the “4:00” image move cyclonically and are replenished by cells from the “5:00” image, and the inner spiral band on the western side weakens. The full-length animation of the MIMIC-TC product created from these three original microwave images can be seen in Fig. 1a. AUGUST 2007 AMERICAN METEOROLOGICAL SOCIETY | 1191

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