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Figure 12. Horizontal cross-sections of the radial wind component at (a, b) 2 km, (c, d) 6 km, (e, f) 10 km altitudes. The left panels (a, c, e) refer to EVTD-derived values, the right panels (b, d, f) to PDD-derived values. (From Roux and Marks, 1996.)

pressure distribution from R = 20 km to R = 60 km (Fig. 14; note that there is no surface pressure measurement within 20 km of the TC center). This agreement suggests good internal consistency of the GBVTD-retrieved axisym-metric circulation and the retrieved pressure deficit, which is likely accurate to ~2-3hPa if there is no significant aliasing from the unresolved cross-beam mean wind and wave number 2 asymmetric radial wind. Lee and Bell (2007) showed that the rapid intensification process of Hurricane Charley (2004) could be captured by GBVTD-retrieved pressure deficit in real time. The result is very encouraging, and it is feasible to estimate the central pressure of landfalling

TCs from coastal Doppler radar data. This could be a valuable tool for diagnosing the intensity of landfalling TCs.

5.2. Structure of mesoscale vortices in MCS

Zhao et al. (2007) presented the first GBVTD-derived 3D kinematic structure of a mesovortex embedded within a quasi-linear convective system (QLCS) over the northern Taiwan Strait. A hook-echo-like structure [Fig. 15(a)] developed at the southern end of a convective line segment and possessed a pronounced velocity dipole signature. The asymmetric structure of the mesovortex at 4 km [Fig. 15(a)] indicates that the maximum wind of 25 m s-1 was located in the rear of the mesovortex (upper left corner). The asymmetric component of the tangential wind was retrieved to wave number 2 and most of the amplitude was contained in the wave number 1 component. At a 2 km height, the kinematic structure of the vortex [Fig. 15(b)] was quite different. In the rear of the mesoscale vortex, there was a secondary maximum of tangential wind consistent with the wind distribution at 4 km. However, the most intense tangential wind of 25 ms-1 was located at the front quadrant of the mesoscale vortex (upper right). Through examining the sequence of the Doppler radial velocity, it is evident a strong rear-to-front flow developed during the formation period of the mesoscale vortex. The downward penetration of this rear-to-front jet enhanced the low-level cyclonic vorticity. At the leading edge of this rear-to-front jet there was a pronounced flow convergence triggering a line of convection evident in the reflectivity field at the 2 km height.

The MATW [Fig. 15(c)] at the lowest retrieved level (1km height) is 18ms-1. It is consistent with the location of the maximum mean reflectivity field. The axis of the MATW is tilted inward to the center of the vortex with

Typhoon Alex

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