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Asymmetric Structures and Tropical Cyclone Intensity Bo Yang August 24, 2010

Asymmetric Structures and Tropical Cyclone Intensity Bo Yang August 24, 2010. Introduction. Asymmetric structures are generally characterized by Quasi-stationary or moving (Willoughby et al.,1984) spiral rainbands

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Asymmetric Structures and Tropical Cyclone Intensity Bo Yang August 24, 2010

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  1. Asymmetric Structures and Tropical Cyclone IntensityBo Yang August 24, 2010

  2. Introduction Asymmetric structures are generally characterized by Quasi-stationary or moving (Willoughby et al.,1984) spiral rainbands Vortex Rossby waves (MacDonald 1968; Guinn and Schubert 1993; Montgomery and Kallenbach 1997; Chen and Yau 2001; Wang 2001; Wang 2002a, b) Polygonal eyewalls (Lewis and Hawkins 1982; Kuo et al. 1999) Asymmetric structures can be generated by External forcing beta effect (Adem 1956, Fiorino and Elsberry 1989 a, b; Li and Wang 1994; Wang and Holland 1996 a, b) Large-scale environmental flow( Shapiro 1983; Li and Wang 1996, Wang and Holland 1996c; Bender 1997; Frank and Ritchie 1999) Internal dynamics (Schubert et al. 1999) How do inner-core asymmetries affect TC intensity?

  3. Outline I Internally generated inner-core asymmetric structures and tropical cyclone intensity II Environmentally generated inner-core asymmetric structures and tropical cyclone intensity III Future work

  4. How do internally generated inner-core asymmetries affect TC intensity? Model: • TCM3 (Wang 1999) Hydrostatic primitive equations Second-order conservative differencing and time integration scheme Triply-nested moveable mesh configuration Explicit cloud microphysics scheme Modified Monin-Obukhov surface layer E-epsilon turbulence closure scheme 5-Km finest resolution with 25 vertical levels Initialized using inverse balance equation • An axisymmetric version of TCM3 Numerical Experiment Design: • CTL: f-plane 3-D run • SYM: f-plane axisymmetric run CTL and SYM have identical model structures and model parameters and use the same initial bogus vortex. rm=100km, vm=20m/s,SST=302.15k, f-plane at 18N. The initial water vapor mixing ratio and environmental sounding have the vertical profile of climatological mean over the western Pacific (Gray 1975).

  5. 120-240hr Composite symmetric structures of Vt, W and Vr Intensity: SYM > CTL Eyewall slope in SYM is greater than that in CTL Below 6km SYM has strong downdrafts under the tilted eyewall. Vt & W Vr Unit : m/s

  6. PV mixing reduces eyewall tilt Evaporational cooling & mesoscale subsidence under the eyewall decrease PBL relative humidity increases Entropy deficit decreases Reduced final intensity Internally generated-inner core asymmetries reduce the TC final intensity by limiting the air-sea entropy flux under the eyewall. SYM CTL Mechanism PV CH RH PV and EPT budget has been performed to validate the mechanism Yang et al. 2005

  7. NW (6) NE (8) SW (14) SE (22) How do environmentally generated inner-core asymmetries affect TC intensification? La Nina NW (9) NE (12) Remarkable contrast in the number of TC RI over the SE quadrant of the WNP between strong El Niño and strong La Niña years (Wang and Zhou 2008). They speculated that it is primarily due to the meridional shear of zonal environmental flows. Large-scale Zonal flow with low-level cyclonic and upper-level anticyclonic shear could be an important factor that contribute to TC RI in an weak vertical shear environment. SW (11) SE (2) El Nino

  8. Meridional and vertical shear of zonal flows Numerical experiment E0: No environmental flow E1: Idealized environmental zonal flow with low level cyclonic shear and upper level anticyclonic shear Observation: In addition to weak vertical shear, zonal environmental flow with strong (and deep) cyclonic shear in the lower troposphere and strong anticyclonic shear in the upper level Is more conducive to TC RI.

  9. TC responses to the environmental shear flow: continuous excitation of propagating asymmetries at the TC inner core Inner core asymmetric eddy and its axisymmetrization Coupled with moist and boundary layer process Early contraction of RMW and convection organization Inner core convection dominates over outer convection Rapid intensification

  10. Effect of Meridional Shear-Induced Inner Core Asymmetries The axisymmetrization of asymmetries inside the initial radius of maximum wind accelerates the contraction of the radius of maximum wind and better organize inner-core convection, leading to early and rapid intensification. Meridional Shear-Induced Inner core Asymmetries & their axisymmetrization Contraction of Radius of Maximum wind &TC RI Low-level (0-4km) average

  11. Future work Satellite Observational studies More realistic simulations Other research activities Intra-seasonal Oscillations modeling studies satellite observations Model physics improvements MIT convection and AER radiation in CAM model

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