A Multiscale Numerical Study of Hurricane Andrew (1992). Part III: Dynamically-Induced Vertical Motion

Zhang, D.-L., Y. Liu and M.K. Yau

ABSTRACT

Figure 1. . Radius-height cross sections of the hourly and azimuthally averaged (a) perturbation pressure p2 at intervals of 5 hPa; and (b) perturbation pressure p1 (see the text for definition) that are obtained from 12 model outputs at 5-minute intervals during the 1-h budget period ending at 2100 UTC 23 August 1992. Solid (dashed) lines are positive (negative) values. Axes of downdrafts (DN), updrafts (UP) and the RMW, determined from Fig. 2, are also given; Similarly for the rest of figures.

Figure 2. As in Fig. 1 but for (a) vertical velocity (W) at intervals of 0.2 m s-1; (b) tangential winds (V) at intervals of 5 m s-1, and (c) absolute angular momentum (AAM) at intervals of 5 x 105 m2 s-1, superimposed with in-plane wind vectors and equivalent potential temperature [i.e., dashed lines in (c), every 4 K].

Figure 3. As in Fig. 1 but for the vertical momentum budget: (a) the perturbation PGF (WP); (b) the buoyancy force (WB) with its positive thermal component shaded at 0 and 10 m s-1 h-1; (c) WBP = WB + WP (solid lines) and radar reflectivity (shaded at 5, 15, 25, 35 and 45 dbz); (d) WBPL = WB + WP + WL; (e) the Coriolis contribution plus numerical diffusion (WCD); and (f) the net vertical acceleration (dW/dt).

Figure 4. Azimuth-height cross sections of (a) the vertical acceleration (dW/dt) at intervals of 5 m s-1 h-1 with the downdrafts shaded; (b) the q e deviations at intervals of 1 K with the inflows shaded; and (c) the system-relative radial flow at intervals of 3 m s-1 with the inflows shaded, that are taken, after the temporal average, along a slanting surface in the eyewall (i.e., from R = 30 km at the surface to R = 70 km at z = 17 km). The q e deviations are obtained by subtracting the azimuthally-averaged values at individual heights. Thick dashed lines denote the axes of incoming (I) and outgoing (O) air. Thin solid (dashed) lines are for positive (negative) values. In-plane wind vectors are superposed.

Figure 5. As in Fig. 1 but for (a) total advection (WADV); and (b) local tendency (Wt) in the vertical momentum equation.

Figure 6. (a) A vertical sounding taken at a radius of 42 km; (b) a slantwise sounding taken along an absolute angular momentum surface of 2.5 x 106 m2 s-1; and (c) the horizontal distribution of hourly-averaged CAPE with air parcels initiated at 500 m above the surface. They are obtained by averaging 12 model outputs at 5-minute intervals during the 1-h budget period ending at 2100 UTC 23 August 1992 (see text). Dashed lines in (c) denote the RMW at 900 hPa.

Figure 7. As in Fig. 1 but for (a) the buoyancy-induced pressure perturbation (Pb) at intervals of 5 hPa; (b) the dynamically-induced pressure perturbation (Pd) at intervals of 2.5 hPa; (c) the difference field between the perturbation pressure p2 shown in Fig. 1a and the azimuthally-averaged inverted P (= Pd + Pb); (d) the buoyancy source (Fb) for Pb; (e) the dynamic source (Fd) for Pd ; and (f) the approximated dynamic source, which is the first term on the RHS of Eq. (9b)].

Figure 8. As in Fig. 1 but for (a) the dynamically-induced PGFd ; (b) the buoyancy-induced PGFb; (c) the buoyancy force (i.e., b), and (d) the net buoyancy force (i.e., WNB = PGFb + b).

Figure 9. Horizontal distributions of the net buoyancy force (i.e., WNB = PGFb and the net dynamic force (i.e., WND = PGFd + WCD) at intervals of 10 m s-1 h-1 at the given heights (a) and (d) z = 14 km; (b) and (e) z = 8 km; and z = 2 km over a subdomain of the 6-km resolution mesh. They are obtained by averaging 12 model outputs at 5-minute intervals during the 1-h budget period ending at 2100 UTC 23 August 1992 (see text). Shadings denote the system-relative radial inflow at these levels.

Figure 10. As in Fig. 1 but for the decomposed components of PGF associated with the term (a) The Laplace of V*V/2; (b) the divergence of V x third coponent of vorticity; and (c) the residual [see Eq. (7) for definitions].