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Tropical Cyclone Intensification

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Page 1: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Tropical Cyclone Intensification

Page 2: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

CISK (Charney and Eliassen 1964)

Cooperative Intensification Theory (Ooyama 1969).

WISHE (Emanuel 1986 … , Holton and Hakim, 2012)

Vortical deep convection paradigm whose mean field view provides an extended Cooperative Intensification Theory

Theories for tropical cyclone intensification and structure

To appear in The Bruce Morton Memorial Volume of the Australian Meteorological and Oceanographical Society Journal

http://www.meteo.physik.uni-muenchen.de/~roger/Publications/M8.pdf

Page 3: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Schematic cross-section through a hurricane

CirrusCirrus

Eye

Spiral bandsEyewall

Page 4: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

r

v

Lowest pressure in the centre

Rotation axis

Pressure gradient force

Centrifugal forceand

Coriolis force2v 1 pfv

r r

Gradient wind balance

Primary (tangential)circulation

Force balance in a vortex

Page 5: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Are the eyewall clouds buoyant?

Eye is the warmest place in the storm

See Smith, Montgomery and Zhu (2005) Dyn. Atmos & Oceans

Page 6: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Have to consider generalized buoyancy!

g

ge

2v fvr

p = constant

pref ref

refe

( )

g

2

ev fv, gr

gz

r

g

ge

2v fvr

p = constant

pref ref

refe

( )

g

2

ev fv, gr

gz

r

Page 7: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

A simple example: steady two-dimensional boundary layer on a flat plate at normal incidence to an almost parallel stream U(x).

z

x

U(x) boundary layer

Boundary layers in nonrotating fluids

U(x)

u(x,z) < U(x)

Page 8: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

V

Pressuregradient

force

Centrifugal force and Coriolis force reduced by friction

v

Secondary circulation

Frictionally-induced secondary circulation

Boundary layer

V(r)

r

21 p v fvr r

Page 9: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,
Page 10: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Basic principle: conservation of absolute angular momentum:

r

v

If r decreases, v increases!

Spin up requires radial convergence

Tropical cyclone intensification

212M rv fr

12

Mv frr

M

M

Page 11: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

wz

0

wz

0

Boundary layer Level of non-divergence

V

Vertical cross section

Dynamics of vortex spin down

Vt

Page 12: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

V

C

A

The secondary, or in-up-out, circulation

Vds dAC A

ds

secondarycirculation

secondarycirculation

Page 13: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,
Page 14: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

15

10

5

0 50 100r km

M conserved

M not conserved, inflow feeds the clouds with moisture

M 1v frr 2

z k

mThermally-forced secondary circulation leads to spin up

Conventional view of intensification: axisymmetric

Is that it?

Page 15: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

The basic thought experiment for TC intensification

sea

rV(r,z)

Initial condition

p(z)T(z)q(z)

Axisymmetric vortex

Mean sounding

27oC

Nguyen, Smith and Montgomery calculation, QJRMS, 2008: Idealized numerical model simulations, simple physics, MM5 5 km (1.67 km) resolution in the finest nest, 24 -levels

Page 16: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,
Page 17: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Vertical velocity\vorticity pattern at 24 h

850 mb ~ 1.5 km 850 mb

Vertical velocity Relative vorticityFrom Nguyen, Smith and Montgomery, QJ, 2008

Page 18: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Movie

Page 19: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

From Montgomery, Nguyen & Smith (2009): QJRMS

Page 20: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

From Montgomery, Nguyen & Smith (2009): QJRMS

Page 21: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

From Montgomery, Nguyen & Smith (2009): QJRMS

Page 22: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Movie Time-height sequence of Absolute Angular Momentum

21M rv fr2

M 1v frr 2

Page 23: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Movie

Page 24: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

15

10

5

0 50 100r km

z k

mRevised view : two spin-up mechanisms

M conserved

M 1v frr 2

M reduced by friction, butstrong convergence small r large v

Page 25: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

A surprise

The maximum wind speed in the boundary layer canexceed that above the boundary layer.

• An unusual in feature boundary layers in general.

• A special feature of the termination boundary layerof intense vortices.

Anthes (1972):

• Inward increase of V due to large radialdisplacements in the boundary layer with partialconservation of AAM opposes the fictional loss ofAAM to the surface.

Page 26: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Emanuel (JAS 1986) : An air-sea interaction theory for tropical cyclones. Part I: Steady state maintenance.

Wirth & Dunkerton (JAS 2006): A unified perspective on the dynamics of axisymmetric hurricanes and monsoons.

Hakim (JAS 2011): The mean state of axisymmetric hurricanes in statistical equilibrium.

Some steady theories/models

Questions

What would be the requirements for a (globally) steady-state hurricane to exist?

Do the foregoing theories/formulations satisfy such conditions?

Page 27: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones.

For a tropical cyclone to achieve a steady state, there would have to be an input of cyclonic relative angular momentum to replenish that lost by friction to the sea surface.

Carrier et al. (JFM 1971): A model of the mature hurricane.

A hurricane could last about 30 days before it used up its angular momentum.

Angular momentum considerations

Page 28: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

M satisfies

Absolute angular momentum

Steady flow, no diffusion or eddies:

Page 29: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Continuity

Flux form

Page 30: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Integrate the flux form for the steady state:

Advective flux through r = R

Diffusion at z = 0

Eddy and diffusive flux flux through r = R

0 R0

H

Page 31: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

The basic thought experiment for intensification

sea

rV(r,z)

Initial condition

p(z)T(z)q(z)

Axisymmetric vortex

Mean sounding

26oC

Persing, Montgomery, McWilliams, Smith, Atm. Chem. Phys. 2013: Idealized numerical model simulations, simple physics, CM1 3 km horizontal grid spacing, 24 -levels

Page 32: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Evolution in intensity

Page 33: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Azimuthal mean tangential wind component

Page 34: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

The overturning circulation

Page 35: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Radius-time plots of v and M at 1.5 km

v M

Page 36: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Radius-time plots of v and M at 12 km

v M

Page 37: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Evolution in intensity at 12 km

cyclone

anticyclone

Page 38: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

M surfaces

Page 39: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

RAM surfaces

Page 40: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

RAM surfaces

Page 41: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

M tendencies

Page 42: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

M tendencies

Page 43: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Integrated RAM / Integrated RAM(t = 0)

cyclonic

anticyclonic

Page 44: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Integrated KE / Integrated KE(t = 0)

cyclonic

anticyclonic

Page 45: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

The Emanuel (1986) steady model

Page 46: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Summary 1: thermodynamic requirements for a steady state

Moisture fluxes

rain

Subsidence, radiative cooling, dry

u

e conserved

Page 47: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Summary 2: dynamic requirements for a steady state

Loss of cyclonic AM Gain of cyclonic AM?

Eddy flux of cyclonic AM

Page 48: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,

Thank you

See: http://www.meteo.physik.uni-muenchen.de/~roger/Publications/M16.pdf

Page 49: Tropical Cyclone Intensificationroger/TCLecs/...Anthes (Rev. Geophys. 1974): The dynamics and energetics of mature tropical cyclones. For a tropical cyclone to achieve a steady state,