![Page 1: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/1.jpg)
Tropical cyclone intensification
Roger Smith Ludwig-Maximilians University of Munich Collaborators: Michael Montgomery, Naval Postgraduate
School, Monterey, California Ph. D. students: Sang Nguyen, Seoleun Shin (LMU) Postdoc: Hai Hoang, Vietnam National University
![Page 2: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/2.jpg)
A quote and questions
“ … . This is not to say that using simple models is folly. Indeed the aim of any scientific modelling is to separate crucial from incidental mechanisms. Comprehensive complexity is no virtue in modelling, but rather an admission of failure.”
I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou model for the Hadley circulation:
What is the analogue of the Eady Problem for hurricanes?
What are the basic dynamics of hurricane intensification?
![Page 3: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/3.jpg)
Topics
1. How do tropical cyclones intensify?
• The basic thought experiment for intensification
• Important physical principles
3. Paradigms for intensification
4. Recent discoveries using idealized model simulations with simple physics
• Dynamics of vortex spin up
• Is WISHE relevant?
• Axisymmetric view of spin up – comparison with the other paradigms
5. New frontiers
![Page 4: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/4.jpg)
The basic thought experiment for intensification
sea
r V(r,z)
Initial condition
T(z) q(z)
p
Axisymmetric vortex
Mean sounding
28oC
![Page 5: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/5.jpg)
r v
Pressure gradient force
Centrifugal force and Coriolis force
The primary circulation
LO
sea
![Page 6: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/6.jpg)
Friction layer r v
Pressure gradient force
Centrifugal force and Coriolis force are reduced by friction
v
Secondary circulation
Frictionally-induced secondary circulation
primary circulation
![Page 7: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/7.jpg)
“Tea cup” Experiment
![Page 8: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/8.jpg)
Basic principle
r
v
v = M/r - rf/2 If r decreases, v increases!
Spin up requires radial convergence
- Conservation of absolute angular momentum: M = rv + r2f/2
Hurricane intensification
f = Coriolis parameter = 2Ωsin(latitude)
![Page 9: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/9.jpg)
Paradigms for intensification
1. Conventional view articulated by Ooyama (1969, 1982), Willoughby (AMM 1998, WMO, 1995) involving convectively-induced convergence together with absolute angular momentum conservation above the boundary layer.
2. Thermodynamic view (E-theory) articulated by Emanuel (1989, 1994, 1995, 1997) involving the WISHE mechanism.
3. Asymmetric view (M-theory) invoking “Vortical Hot Towers” or VHTs (Hendricks et al. 2004, Montgomery et al. 2006, Nguyen et al. 2008, Shin and Smith 2008, Montgomery et al. 2009, Smith et al. 2009, Hoang et al. 2009).
![Page 10: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/10.jpg)
15
10
5
0 50 100 r km
z
km
Conventional view
M conserved
M not conserved,
![Page 11: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/11.jpg)
Thermodynamic view: A steady hurricane model
Journal of the Atmospheric Sciences 1986
![Page 12: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/12.jpg)
Region I Region II Region III (RH = 80%)
rmax re r
z
h
Emanuel’s 1986 steady hurricane model
Boundary layer controls dθe/dM
E86 ignores BL dynamics here!
Μ = Μ(θe) ⇒ θe = θe(p)
![Page 13: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/13.jpg)
2008
Available on my website
Thermodynamic view has problems!
![Page 14: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/14.jpg)
Revised Cannot ignore unbalanced BL dynamics!
![Page 15: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/15.jpg)
WISHE = Wind induced surface heat exchange
Basic air-sea interaction feedback loop: Increase in surface wind speed => Increase in surface moisture transfer from the sea surface => Increase in “fuel supply” to the storm => Increasing wind speed …
Accepted subject to minor revision
![Page 16: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/16.jpg)
Idealized numerical model simulations with simple physics (MM5)
5 km (1.67 km) resolution in the finest nest, 24 σ-levels
Available: http://www.meteo.physik.uni-muenchen.de/~roger
Asymmetric view
![Page 17: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/17.jpg)
Evolution of Intensity
![Page 18: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/18.jpg)
Vertical velocity\vorticity pattern at 24 h
850 mb ~ 1.5 km 850 mb
Vertical velocity Relative vorticity
![Page 19: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/19.jpg)
Vertical vorticity evolution at 850 mb
10 h 12 h
![Page 20: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/20.jpg)
Vertical vorticity pattern at 850 mb
18 h 24 h
300 km 300 km
300
km
![Page 21: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/21.jpg)
Vertical vorticity pattern at 850 mb
36 h 48 h
![Page 22: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/22.jpg)
Movie 1
![Page 23: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/23.jpg)
Interim conclusions
The flow evolution is intrinsically asymmetric.
The asymmetries are associated with rotating convective structures that are essentially stochastic in nature.
We call these structures vortical hot towers (VHTs).
Their convective nature suggests that the structures may be sensitive to the low-level moisture distribution, which is known to possess significant variability on small space scales.
Suggests a need for ensemble experiments with random moisture perturbations.
![Page 24: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/24.jpg)
Evolution of local intensity: 10 ensembles
control
From Nguyen et al. 2008 VTmax
![Page 25: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/25.jpg)
Vertical velocity pattern at 850 mb at 24 h
control Ensemble 1
Ensemble 3 Ensemble 2
From Nguyen et al. 2008
![Page 26: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/26.jpg)
Is WISHE relevant?
Capped flux experiments
![Page 27: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/27.jpg)
In press
![Page 28: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/28.jpg)
Azimuthal average of the Nguyen et al. control calculation
Tangential wind speed
![Page 29: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/29.jpg)
Radial wind speed vertical velocity
![Page 30: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/30.jpg)
Movie 2
Time-height sequence of Absolute Angular Momentum
![Page 31: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/31.jpg)
15
10
5
0 50 100 r km
z k
m
Revised view of intensification: two mechanisms
M conserved
M reduced by friction, but strong convergence small r
![Page 32: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/32.jpg)
Exciting times!
There is much work to do to pursue all the consequences of our recent findings and the new paradigm for intensification.
We need to determine the limits of predictability for intensity and especially for rapid intensification.
We need to much better understand the flow in the inner core, beneath and inside the eyewall, and to determine the utility of conventional (boundary layer) representations of this region in models.
We need to develop a new theory for the potential intensity of tropical cyclones for climate assessments.
![Page 33: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/33.jpg)
Thank you
![Page 34: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/34.jpg)
What is WISHE?
WISHE = Wind Induced Surface Heat Exchange
Acronym used to link source of fluctuations in sub-cloud layer entropy or θe arising from fluctuations in wind speed (Yano & Emanuel 1991).
Q: What is the WISHE mechanism of TC intensification?
A: Positive feedback between near-surface mean θe and near-surface mean wind speed.
It has become the accepted paradigm for explaining TC development in Univ. Textbooks and Review Articles (Holton 2004; Asnani 2005; Lighthill 1998)
Q: But how does it work?
![Page 35: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/35.jpg)
Thermal wind balance Answer:
start
![Page 36: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/36.jpg)
Balanced versus unbalanced dynamics
![Page 37: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/37.jpg)
Balanced versus unbalanced dynamics
![Page 38: Tropical cyclone intensificationkestrel.nmt.edu/~zeljka/downloadfiles/swap/smithp.pdf · I. N. James, Introduction to Circulating Atmospheres, p93, when referring to the Held-Hou](https://reader034.vdocuments.us/reader034/viewer/2022050503/5f94e982fa1cbb509b15f512/html5/thumbnails/38.jpg)
Effects of different boundary layer schemes