HELICAL SCENARIO OF TROPICAL CYCLONE GENESIS AND INTENSIFICATION

1. European Turbulence Conference Warsaw 2011 HELICAL SCENARIO OF TROPICAL CYCLONE GENESIS AND INTENSIFICATION GalinaLevina1,2 and Michael T. Montgomery3,4 1Institute of Continuous Media Mechanics UB RAS, Perm, Russia 2Space Research Institute RAS, Moscow, Russia 3Naval Postgraduate School, Monterey, CA, USA 4 NOAA/Hurricane Research Division, Miami, FL, USA Financial support: Russian Foundation for Basic Research N 10-05-00100 U.S. National Science Foundation ATM-0733380 International Science and Technology Center N 3726 THE AIM OF THE INVESTIGATION: Theoretical investigations and numerical simulation are intended to study the tropical cyclogenesis and further evolution of intense vortex for diagnosis and forecasting catastrophic atmosphere states

2. HELICAL SCENARIO OF TROPICAL CYCLONE GENESIS AND INTENSIFICATION OUTLINE: 1.Motivation. •Helicity of velocity field •Hypothesis on the turbulent vortex dynamo 2. New scenario of tropical cyclone (TC) genesis and intensification based on self-organization of convective processes •Vortical Hot Towers (VHT) – main coherent structures 3.RAMS (Regional Atmospheric Modeling System) near-cloud- resolving numerical simulation •Vortical Hot Tower route to tropical cyclogenesis •Investigation of the role of helicity in tropical cyclogenesis and vortex intensification SUMMARY

3. HELICITY OF VELOCITY FIELD ’ From Moffatt and Tsinober, 1992 • ·characterizes a structure of the vector velocity field, • topological invariant measuring the degree of linkage of the vortex lines; • ·inviscid constant of motion in barotropic fluids, • existence of the second quadratic constant of motion (in addition to the • energy) makes helical flows relatively more stable, helical cells resist • dissipation and survive longer; • sign of helicity determines a predominance of the left-handed or the right-handed spiral motions in a fluid flow, • favors the energy transfer from small to large scales, found in 3D rotating helical turbulence – Pouquet et al., 2010.

4. HYPOTHESIS ON THE TURBULENT VORTEX DYNAMO H≠ 0 no mirror symmetry, large-scale instability is possible ! Volume integrated helicity Mechanism for intensification of large-scale vortex disturbances in the atmosphere – Moiseev, Rutkevich, Sagdeev, Tur, Khomenko, and Yanovsky (1983-1988) The first sign of the hypothesized large-scale instability – generation of the linkage of horizontal and vertical circulation on the system scale and the resulting positive feedback An attempt to mimic the large-scale instability by using a special helical forcing L06 :Levina G.V., and Burylov I.A., 2006, Nonlin. Processes Geophys., v. 13, pp. 205-222 Non-zero helicity is generated, and after exceeding its threshold value the large-scale vortex instability appears and is progressing by merging of helical vortex cells

5. A VORTICAL HOT TOWER (VHT) ROUTE 200 km new scenario of hurricane formation based on self-organization of convective processes TO TROPICAL CYCLOGENESIStropical depression (TD) formation MO6 :Montgomery, M. T. et al., 2006, J. Atmos. Sci., v. 63, pp. 355-386 absolute vorticity—mergers at 925hPa • A nonhydrostatic cloud model was used to examine • the thermomechanics of tropical cyclogenesis. • The focus was on the problem of how an initial mesoscale • midtropospheric cyclonic vortex may be transformed into • a surface-concentrated tropical depression (TD). Δx= Δy=1 km • Self-organization of vortical (!) convection was observed as: • an enlargement of vortex structures from the size of • individual rotating cumulus clouds in the model; • their induced concentration of absolute angular • momentum on the system scale circulation; • their merging with each other to yield newly forming larger • vortices and intensifying circulation on the system scale. AND FURTHER VORTEX INTENSIFICATIONup to hurricane (H) strength MS11 :Montgomery, M. T. and Smith, R. K., 2011, Q.J.R. Meteor Soc., accepted The new paradigm for intensification recognizes the importance of rotating deep convection. The spin up of the inner-core winds occurs within the boundary layer due to the convergenceofabsolute angular momentum and is coupledwith that of the winds above the boundary layer through boundary-layer dynamics.

6. NEW SCENARIO FOR TC FORMATION: THE MAIN ACTORS Vortical Hot Towers (VHTs) Riehl and Malkus (1958) implicated the role of HOT TOWERSin the vertical heat transport and mass flux in the tropical atmosphere. Later their rotation was identified. VHTs - rotating convective cloud structures of10-30 km in horizontal size and lifetime of ~ 1 hour, the most intense of which extend throughout the whole troposphere height up to 14-16 km. Dunkerton, Montgomery, Wang. Atmos. Chem. Phys. 2009, N 9, 5587-5646; Glossary, p.5640: Vortical hot towers: Deep moist convective clouds that rotate as an entity and/or contain updrafts that rotate in helical fashion (as in rotating Rayleigh-Benard convection). Although early observations suggested that VHTs are neither necessary nor sufficient for tropical cyclogenesis, it is becoming increasingly clear from cloud-representing numerical simulations that moist vortical updrafts arethe essential building blocks of the tropical storm within the rotating proto-vortex. These hot vortical plume structures amplifypre-existing cyclonic vorticity and equivalently induce concentrations of vorticity substance much larger than that of the aggregative vortex. Tropical Storm Gustav (2002) From Hendricks et al., 2004, JAS, 61.

7. HELICAL NATURE OF VHTs AND THEIR ROLE AS GENERATORS OF HELICITY AND NATURAL CONNECTERS OF CIRCULATIONS M06

8. FIELD EXPERIMENTNSF-PREDICT 2010 Saint Croix, U.S. Virgin Islands, August 15 – September 30, 2010 With participation of theEarth Observing Laboratory, NCAR Lead Principal Investigator – Dr.M.T. Montgomery1,2 1Naval Postgraduate School, Monterey, CA, USA 2 NOAA/Hurricane Research Division, Miami, FL, USA 65 participants GOALS of the EXPERIMENT : ▪ Testing the “Marsupial Paradigm”- a series of hypotheses on tropical cyclogenesis in a critical layer of tropical easterly waves (Dunkerton, Montgomery, Wang, 2009, Atmos. Chem. Phys.) ▪ Testing the “Marsupial PouchTracking” high accuracy predicting of genesis location – up to 3 days with an error < 200 km (Wang,Montgomery, Dunkerton,2009,Geophys. Res. Lett.) ▪ Investigations of deep convection - VHTs

9. EXAMINATION OF THE HELICAL NATURE OF TROPICAL CYCLOGENESIS [LM10] Collaborative Studies with Montgomery Research Group, Naval Postgraduate School, Monterey, CA, USA: • concept of vortical hot tower (VHT) route to tropical cyclogenesis through an upscale • vorticity growing proposed by Montgomery et al.[M06] represents the most appropriate • basis to take into account helical features of moist convective atmospheric turbulence; • theoretical ground and numerical approach developed by Levina et al. [L06] • for diagnosis of large-scale helical-vortex instability in tropical cyclogenesis; • numerical realization: • - non-hydrostatic version of mesoscale models– RAMS, MM5, WRF; • - near-cloud-resolving simulation, nested grids, 1-3 km horizontal grid spacing; • - meteorological database on TC observation and investigation. In this work we use the velocity fields obtained in [M06] to calculate and analyze helical characteristics of the cyclogenesis and intensification process for the problem as posed by [M06]. LM10:G.V.Levina, and M.T. Montgomery. A first examination of the helical nature of tropical cyclogenesis. Doklady Earth Sciences. 2010. Vol. 434, Part 1, pp. 1285-1289.

10. RAMS SIMULATIONS in [M06]: DNS, NO ANY HELICAL FORCING! RAMS - REGIONAL ATMOSPHERIC MODELING SYSTEM List of Model Parameters Cape Verde Islands

11. RAMS SIMULATIONS in [M06] Genesis experiments analyzed in our current work (initial conditions) * Tropical Depression (TD) Vmax ≤17 m s-1 Tropical Storm (TS) 17 m s-1<Vmax ≤33 m s-1 Hurricane/Typhoon (H) Vmax >33 m s-1 No significant differences between A1 and A2. Experiments A1, A2, B3, and E1 resulted in TDs after ~ 24-48 h . A1 and A2 - intensification to hurricanes during 72 h. In B3 and C3 development notable slower than A1. In E1 no intensification (of TD vortex) after 24 h. C1: no intense VHTs and no surface spinup.

12. VELOCITY FIELD CHARACTERISTICS CALCULATED OF RAMS SIMULATION OUTPUT TO ANALYZE A TROPICAL CYCLONE EVOLUTION Post processing:Cartesian co-ordinates - x, y, z ; i, j - 92x92 – horizontal directions, increment = 3 km; k - 40 vertical levels, increment = 0.5 km; Time of process evolution – 72 hours, increment = 10 min. 1. Vertical components of velocity, vorticity and helicity - to identify VHTs 2. 3D kinetic energy, enstrophy and helicity densities • integral kinetic energy, enstrophy and helicity • normalized by number of grid points 3. A number of other characteristics: -3D kinetic energy, enstrophy and helicity moments (mean, variance, skewness, kurtosis, standard deviation); - MAX and MIN values over the computational domain and their locations; - helicity integrated over the 0-6 km layer.

13. INTEGRATED KINETIC ENERGY,ENSTROPHY AND HELICITY DURING TROPICAL CYCLONE FORMATION Break of the mirror symmetry ! t > 18, Integrated over 3D domain and normalized by number of grid points

14. HELICITY EVOLUTION DURING 72 HOURS OF TC FORMATION (increment = 10 min) 3D HELICITY DENSITY Local helicity values Intensity of the forming TC Mean near-surface tangential wind t = 16 h : 9 m s-1TD formation, t= 45 h : 17.2 m s-1TS formation, t= 56 h : 33.4 m s-1 H formation, t= 60-63 h : 42 m s-1H Maximal wind

15. HELICAL NATURE OF VHTs AND THEIR ROLE AS GENERATORS OF HELICITY AND NATURAL CONNECTERS OF CIRCULATIONS

16. POSITIVE “HELICAL” FEEDBACK BETWEEN PRIMARY (HORIZONTAL) AND SECONDARY (VERTICAL) CIRCULATION t=0-10 : a population of VHTs develops and becomes strong enough, t=10-12 : VHTs collectively result in formation of the system scale secondary circulation and its linkage with the primary circulation, The positive feedback starts working - both circulations intensify, the forming vortex becomes self-sustaining, t=16 : TD forms;soon after, <H> becomes persistently positive and increasing, t>16 : in intensifying TD near surface wind increases and generates vertical shear which represents an additional and powerful source of vorticity/helicity generation and allows the TD vortex reaching TS and H strength. <ES> <EP> Kinetic energy <EP> and <ES> evolution

17. HELICAL SCENARIO OF TROPICAL CYCLONE GENESIS AND INTENSIFICATION SUMMARY 1.Non-zero mean helicity generation was found in a natural system – the tropical atmosphere of the Earth 2. Special role of VHTs as helicity generators and connecters of the primary and secondary circulation in a forming TC was emphasized 3. Two quantitative helical and two energetic characteristics were used to pinpoint the tropical cyclogenesis (when the vortex becomes self-sustaining) and trace its subsequent intensification 4. Z-component of helicity is closely linked with rotating deep convection and can be useful in pre-depression investigations of cloud systems in the Tropics. We are going to combine the above analysis with the Marsupial Pouch Tracking to predict tropical cyclogenesis by using global operational weather models

18. VHTs in forming Atlantic Hurricane Karl (2010) From the space From 14.5 km From sea level THANK YOU FOR YOUR ATTENTION !

19. Computer facilities used for RAMS simulation and post-processing • in Montgomery Research Group, NPS, Monterey, CA, USA • Dual processor Linux workstation has • two AMD Opteron CPUs At 2.00GHz each • 4 GB of RAM • 1 TB of hard drive space • It runs CentOS 4.7 Linux