A Comparison of Inner and Outer Spiral Rainbands in a Numerically

A Comparison of Inner and Outer Spiral Rainbands in a Numerically Simulated Tropical Cyclone Qingqing Li Shanghai Typhoon Institute of CMA Yuqing Wang International Pacific Research Center, and Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa Haikou 7 Nov. 2012
Outline Ø Motivation Ø Model configuration Ø Dynamical features of the inner and outer rainband regions Ø Movements of inner and outer rainbands Ø Structure of inner rainbands and convective cells in outer rainbands Ø Conclusions
Outer rainbands existing outside the inner core of a TC: inertiagravity waves (Kurihara 1976; Willoughby 1978; Chow et al. 2002) Lowlevel PPI scan of radar reflectivity (dBZ) of Typhoon Longwang (2005) at 1953 UTC 1 Oct (Yu and Tsai 2010).
Oct (Yu and Tsai 2010). Inner rainbands occurring in the innercore region (inside a radius of about three times the radius of maximum wind): outwardpropagating vortex Rossby waves (Montgomery and Kallenbach 1997; Wang 2002b) Motivation • Since inner and outer rainbands of a TC are predominant in different local environments, we examine the similarity and dissimilarity of dynamic and thermodynamic features of the bands using a highresolution cloudresolving model.
Model configuration Model Horizontal resolution TCM4 Mesh 1：67.5 km × 67.5 km (201 × 181 × 26 grid points) Mesh 2：22.5 km × 22.5 km（109 × 109 × 26 grid points）
Mesh 3：7.5 km × 7.5 km（127 × 127 × 26 grid points） Mesh 4：2.5 km × 2.5 km（163 × 163 × 26 grid points） Subgrid scale vertical turbulent mixing Eε turbulence closure scheme Precipitation scheme Mixedphase cloud microphysics Convective parameterization surface flux calculation None Modified MoninObukhov scheme Initiation Initialized in a resting environment over the ocean with a constant sea surface temperature of 29°C Integration 96 hours
Time evolution of intensity
Outline Ø Motivation Ø Model configuration Ø Dynamical features of the inner and outer rainband regions Ø Movements of inner and outer rainbands Ø Structure of inner rainbands and convective cells in outer rainbands Ø Conclusions
Dynamical features of the inner and outer rainband regions Outerrainband region (80160km radii) Innerrainband region (3060km radii) 3kmheight modeled reflectivity at 64 h
Rapid filamentation zone Filamentation timescale (min) Effective beta (10 9 m 1 s 1 ) Beta skirt
Vertical profiles of upward (positive), downward (negative), and net vertical mass transport (VMT), averaged between 55 and 66 h
Vertical profiles of the horizontal divergence in the innerrainband convective region, averaged between 55 and 66 h
Outline Ø Motivation Ø Model configuration Ø Dynamical features of the inner and outer rainband regions Ø Movements of inner and outer rainbands Ø Structure of inner rainbands and convective cells in outer rainbands Ø Conclusions
Azimuthally and temporally averaged streamlines superposed with PV anomalies (contours) and cloud water (shaded) at 3 km height
Movements of inner and outer rainbands 1 R = 40 km ~38 m s Azimuthal phase speed:
w n R = 35 m s 1 Radial phase speed:
w k
= 9.4 m s 1
7.7 m s 1 Wavenumber2 PV (shading) and vertical motion (contours) Vertically integrated liquid and solid water substance (kg kg 1 , shading) coincident with azimuthally and temporally averaged streamlines at 300 m Vertically integrated liquid–solid water substance
500 m 100 m 50 m
Outline Ø Motivation Ø Model configuration Ø Dynamical features of the inner and outer rainband regions Ø Movements of inner and outer rainbands Ø Structure of inner rainbands and convective cells in outer rainbands Ø Conclusions
Structure of inner rainbands and convective cells in outer rainbands
Vertical profiles of upward (positive), downward (negative), and net VMT
Conclusions l Movement of inner rainbands is closely connected with vortex Rossby waves. l Movement of outer rainbands follows the vector winds associated with the lowlevel flow and the radially outward cross band flow caused by the downdraftinduced cold pool in the boundary layer. lThe innerrainband region is generally coincident with a rapid filamentation zone, and a beta skirt exists in the innerrainband region and extends radially up to 90km radius in the lower troposphere. lBoth the upward and downward VMTs in the innerrainband region peak at the height of about 3.5 km. The maximum downward VMT in the outerrainband region occurs at around 2 km height.
Conclusions (Cont.) l In the innerrainband region, net convergence appears in a shallow layer below 2kmheight. In the outerrainband region, net convergence is found in a deep layer below 7.5km height and net divergence is found aloft. l Two types of downdrafts associated with the mature convective cells in the outer rainbands: one originating at the upper levels and one originating at the midlevels. Because of the radially inward slope of the simulated high reflectivity core, the midlevel subsidence is mainly due to precipitation evaporation, and the upperlevel downdraft likely results from sublimation heating due to dry air intrusion.
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