References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-10-3163-2010

A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

Riemer

¹ Montgomery

M. T.

¹ ² Nicholls

M. E.

Department of Meteorology, Naval Postgraduate School, Monterey, CA, USA

NOAA's Hurricane Research Division, Miami, FL, USA

University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, USA

01 04 2010

10 7 3163 3188

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An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the canonical problem of a TC in vertical wind shear on an f-plane. A suite of numerical experiments is performed with intense TCs in moderate to strong vertical shear. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θe) air – "anti-fuel" for the TC power machine – can enter the core region of the TC. Strong and persistent, shear-induced downdrafts flux low θe air into the boundary layer from above, significantly depressing the θe values in the storm's inflow layer. Air with lower θe values enters the eyewall updrafts, considerably reducing eyewall θe values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a close association of the downward transport of low θe into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the boundary layer with low θe air are tied to a quasi-stationary, azimuthal wave number 1 convective asymmetry outside of the eyewall. This convective asymmetry and the associated downdraft pattern extends outwards to approximately 150 km. Downdrafts occur on the vortex scale and form when precipitation falls out from sloping updrafts and evaporates in the unsaturated air below. It is argued that, to zero order, the formation of the convective asymmetry is forced by frictional convergence associated with the azimuthal wave number 1 vortex Rossby wave structure of the outer-vortex tilt. This work points to an important connection between the thermodynamic impact in the near-core boundary layer and the asymmetric balanced dynamics governing the TC vortex evolution.

References 1

Bender, M A.: The effect of relative flow on the asymmetric structure in the interior of hurricanes, J. Atmos. Sci., 54, 703–724, 1997.

Black, M L., Gamache, J F., Marks, F D., Samsury, C E., and Willoughby, H E.: Eastern Pacific Hurricanes Jimena of 1991 and Olivia of 1994: The effect of vertical shear on structure and intensity, Mon. Wea. Rev., 130, 2291–2312, 2002.

Black, P G., D'Asaro, E A., Drennan, W M., French, J R., Niiler, P P., Sanford, T B., Terrill, E J., Walsh, E J., and Zhang, J A.: Air-sea exchange in hurricanes: Synthesis of observations from the Coupled Boundary Layer Air-Sea Transfer experiment, Bull. Am. Meteorol. Soc., 88, 357–374, 2007.

Braun, S A. and Wu, L.: A numerical study of Hurricane Erin (2001). Part II: Shear and the organization of eyewall vertical motion, Mon. Wea. Rev., 135, 1179–1194, 2007.

Braun, S A., Montgomery, M T., and Pu, Z.: High-resolution simulation of Hurricane Bonnie (1998). Part I: The organization of eyewall vertical motion, J. Atmos. Sci., 63, 19–42, 2006.

Carr, L E. and Williams, R T.: Barotropic vortex stability to perturbations from axisymmetry, J. Atmos. Sci., 46, 3177–3191, 1989.

Chen, Y. and Yau, M K.: Spiral bands in a simulated hurricane. Part I: Vortex Rossby wave verification, J. Atmos. Sci., 58, 2128–2145, 2001.

Chen, Y., Brunet, G., and Yau, M K.: Spiral Bands in a Simulated Hurricane. Part II: Wave Activity Diagnostics, J. Atmos. Sci., 60, 1239–1256, 2003.

Clark, T L. and Farley, R D.: Severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting: A possible mechanism for gustiness, J. Atmos. Sci., 41, 329–350, 1984.

Corbosiero, K L. and Molinari, J.: The relationship between storm motion, vertical wind shear, and convective asymmetries in tropical cyclones, J. Atmos. Sci., 60, 366–376, 2003.

Cotton, W R. and Coauthors: RAMS 2001: Current status and future directions, Meteor. Atmos. Phys., 82, 5–29, 2003.

Cram, T A., Persing, J., Montgomery, M T., and Braun, S A.: A Lagrangian trajectory view on transport and mixing processes between the eye, eyewall, and environment using a high-resolution simulation of Hurricane Bonnie (1998), J. Atmos. Sci., 64, 1835–1856, 2007.

Davis, C A., Jones, S C., and Riemer, M.: Hurricane vortex dynamics during Atlantic extratropical transition, J. Atmos. Sci., 65, 714–736, 2008.

DeMaria, M.: The effect of vertical shear on tropical cyclone intensity change, J. Atmos. Sci., 53, 2076–2088, 1996.

Emanuel, K A.: An air-sea interaction theory for tropical cyclones. Part I: Steady-state maintenance, J. Atmos. Sci., 43, 585–605, 1986.

Emanuel, K A.: The theory of hurricanes, Annu. Rev. Fluid Mech., 23, 179–196, 1991.

Frank, W M. and Ritchie, E A.: Effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes, Mon. Wea. Rev., 129, 2249–2269, 2001.

Halverson, J B., Simpson, J., Heymsfield, G., Pierce, H., Hock, T., and Ritchie, L.: Warm core structure of Hurricane Erin diagnosed from high altitude dropsondes during CAMEX-4, J. Atmos. Sci., 63, 309–324, 2006.

Hill, G E.: Factors controlling the size and spacing of cumulus clouds as revealed by numerical experiments, J. Atmos. Sci., 31, 646–673, 1974.

Jones, S C.: The evolution of vortices in vertical shear. I: Initially barotropic vortices, Q. J. R. Meteorol. Soc., 121, 821–851, 1995.

Jones, S C.: The evolution of vortices in vertical shear. III: Baroclinic vortices, Q. J. R. Meteorol. Soc., 126, 3161–3185, 2000.

Jordan, C L.: Mean sounding for the West Indies area, J. Atmos. Sci., 15, 91–97, 1958.

Kepert, J.: The dynamics of boundary layer jets within the tropical cyclone core. Part I: Linear theory, J. Atmos. Sci., 58, 2469–2484, 2001.

Kepert, J. and Wang, Y.: The dynamics of boundary layer jets within the tropical cyclone core. Part II: Nonlinear enhancement, J. Atmos. Sci., 58, 2485–2501, 2001.

Kessler, E.: On the distribution and continuity of water substance in atmospheric circulations, Meteor. Mon. 32, Amer. Meteor. Soc., 1969.

Klemp, J B. and Wilhelmson, R B.: The simulation of three-dimensional convective storm dynamics, J. Atmos. Sci., 35, 1070–1096, 1978.

Lilly, D K.: On the numerical simulation of buoyant convection, Tellus, 14, 148–172, 1962.

Makarieva, A M., Gorshkov, V G., Li, B.-L., and Nobre, A D.: A critique of some modern applications of the Carnot heat engine concept: the dissipative heat engine cannot exist, Proc. Roy. Soc. A, in print, 2010.

Melander, M V., McWilliams, J C., and Zabusky, N J.: Axisymmetrization and vorticity-gradient intensification of an isolated two-dimensional vortex through filamentation, J. Fluid Mech., 178, 137–159, 1987.

Montgomery, M T. and Kallenbach, R J.: A theory for vortex Rossby-waves and its application to spiral bands and intensity changes in hurricanes, Q. J. R. Meteorol. Soc., 123, 435–465, 1997.

Montgomery, M T., Nguyen, V S., Persing, J., and Smith, R K.: Do tropical cyclones intensify by WISHE?, Q. J. R. Meteorol. Soc., 135, 1697–1714, 2009.

Nguyen, S V., Smith, R K., and Montgomery, M T.: Tropical-cyclone intensification and predictability in three dimensions, Q. J. R. Meteorol. Soc., 134, 563–582, 2008.

Ooyama, K V.: A spectral prediction model on nested domains and its application to asymmetric flow in the hurricane boundary layer, in: International Symposium on Short and Medium Range Numerical Weather Prediction, WMO/IUGG, Tokyo, Japan, 1986.

Pielke, R A. and Coauthors: A comprehensive meteorological modeling system – RAMS, Meteor. Atmos. Phys., 49, 69–91, 1992.

Powell, M D.: Boundary layer structure and dynamics in outer hurricane rainbands. Part II: Downdraft modification and mixed layer recovery, Mon. Wea. Rev., 118, 918–938, 1990.

Reasor, P D. and Montgomery, M T.: Three-dimensional alignment and corotation of weak, TC-like vortices via linear vortex Rossby waves, J. Atmos. Sci., 58, 2306–2330, 2001.

Reasor, P D., Montgomery, M T., and Grasso, L D.: A new look at the problem of tropical cyclones in vertical shear flow: Vortex resiliency, J. Atmos. Sci., 61, 3–22, 2004.

Rogers, R., Chen, S., Tenerelli, J., and Willoughby, H.: A numerical study of the impact of vertical shear on the distribution of rainfall in Hurricane Bonnie (1998), Mon. Wea. Rev., 131, 1577–1599, 2003.

Schecter, D A. and Montgomery, M T.: On the symmetrization rate of an intense geophysical vortex, Dyn. Atmos. Oceans, 37, 55–88, 2003.

Schecter, D A. and Montgomery, M T.: Waves in a cloudy vortex, J. Atmos. Sci., 64, 314–337, 2007.

Schubert, W H., Montgomery, M T., Taft, R K., Guinn, T A., Fulton, S R., Kossin, J P., and Edwards, J P.: Polygonal eyewalls, asymmetric eye contraction, and potential vorticity mixing in hurricanes, J. Atmos. Sci., 56, 1197–1223, 1999.

Shapiro, L J.: The asymmetric boundary layer flow under a translating hurricane, J. Atmos. Sci., 40, 1984–1998, 1983.

Shapiro, L J. and Montgomery, M T.: A three-dimensional balance theory for rapidly rotating vortices, J. Atmos. Sci., 50, 3322–3335, 1993.

Simpson, R H. and Riehl, H.: Mid-tropospheric ventilation as a constraint on hurricane development and maintenance, in: Proc. Tech. Conf. on Hurricanes, pp. D4.1–-D4.10, Amer. Meteor. Soc., Miami, FL, 1958.

Smagorinsky, J.: General circulation experiments with the primitive equations, Mon. Wea. Rev., 91, 99–164, 1963.

Smith, R K., Ulrich, W., and Sneddon, G.: On the dynamics of hurricane-like vortices in vertical-shear flows, Q. J. R. Meteorol. Soc., 126, 2653–2670, 2000.

Smith, R K. and Montgomery, M T.: Balanced boundary layers used in hurricane models, Q. J. R. Meteorol. Soc., 134, 1385–1395, 2008.

Smith, R K., Montgomery, M T., and Vogl, S.: A critique of Emanuel's hurricane model and potential intensity theory, Q. J. R. Meteorol. Soc., 134, 551–561, 2008.

Tripoli, G J. and Cotton, W R.: The use of ice-liquid water potential temperature as a thermodynamic variable in deep atmospheric models, Mon. Wea. Rev., 109, 1094–1102, 1981.

Vecchi, G A. and Soden, B J.: Increased tropical Atlantic wind shear in model projections of global warming, Geophys. Res. Lett., 34, 2007.

Wang, Y.: Vortex Rossby Waves in a Numerically Simulated Tropical Cyclone. Part I: Overall Structure, Potential Vorticity, and Kinetic Energy Budgets, J. Atmos. Sci., 59, 1213–1238, 2002.

Wang, Y., Montgomery, M., and Wang, B.: How much vertical shear can a well-developed tropical cyclone resist?, in: Preprints of the 26th Conference on Hurricanes and Tropical Meteorology, pp. 100–101, Amer. Meteor. Soc., Miami, FL, 2004.

Willoughby, H E., Marks, F D., and Feinberg, R J.: Stationary and moving convective bands in hurricanes, J. Atmos. Sci., 41, 3189–3211, 1984.

Wong, M. L M. and Chan, J. C L.: Tropical cyclone intensity in vertical wind shear, J. Atmos. Sci., 61, 1859–1876, 2004.

Wu, C.-C. and Emanuel, K A.: Interaction of a baroclinic vortex with background shear: Application to hurricane movement, J. Atmos. Sci., 50, 62–76, 1993.

Wu, L. and Braun, S A.: Effects of environmentally induced asymmetries on hurricane intensity: A numerical study, J. Atmos. Sci., 61, 3065–3081, 2004.

Zhang, J A., Black, P G., French, J R., and Drennan, W M.: First direct measurements of enthalpy flux in the hurricane boundary layer: The CBLAST results, Geophys. Res. Lett., 35, 2008.