Work presented in collaboration with: Roger Smith and Jun Zhang

New insights from GRIP/HS3

HS3

Overarching NASA-HS3 Science Questions:

How do hurricanes form?

What causes rapid intensity change?

What is the role of deep convection in intensification?

What is the role of Saharan Air Layer (SAL) on intensity change?

S. Braun and R. Kakar

Highlights of our work relevant to addressing the first three questions

Thermodynamic environment of developing and non-developing disturbances during PREDICT and GRIP (Smith and Montgomery 2012, QJRMS)

How important is the isothermal expansion effect in elevating theta_e in the hurricane inner-core? (Smith and Montgomery 2013, QJRMS)

** Analysis of dynamical and thermodynamical structure during the evolution of Earl (2010) (Montgomery, Zhang and Smith 2013, QJRMS, in review) **

Developed new model of secondary eyewall formation that can be tested with HS3 data (Abarca and Montgomery 2013, JAS, in press; see posters)

Obtained new insight on the dynamics and predictability of the tropical cyclogenesis of Hurricane Sandy (2013). These findings can be applied to other Atlantic and Caribbean tropical disturbances (Lussier, Rutherford, Montgomery, Dunkerton and Boothe, 2013;see poster)

Developing new insight into processes supporting the longevity of Tropical storm/Hurricane Nadie (Rutherford, Dunkerton and Montgomery; see poster)

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10

5

0 50 100r km

z k

mRevised view of intensification: two mechanisms

M conserved

M 1v fr

r 2

M reduced by friction, but strong convergence small r (for details, see review paper by Montgomery and Smith (2013 AMOJ))

Absolute angular momentum

in review

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Lower fuselage radar coverage straddling periods 1 & 2 (22 Z 28 Aug – 12 Z 30 Aug; rapid spin up)

dropsonde data spatial coverage during four 12 h analysis periods (1-4)

durin

Blue, P-3Red, DC-8 Green, C-130 Black, G-IV

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Observed evolution of absolute angular momentum:

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Vertical profiles of Vt and Vr for Period 2

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Vertical profiles of Vt and Vr for Period 3

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Gradient wind Vg at height of max Vt for periods 1 and 2 (Aug. 28 and 29)

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Gradient wind at height of max Vt for periods 3 and 4 (Sept. 1 and 2)

Lessons learned Re low-level intensification of Earl (2010)

• Maximum mean Vt is within the frictional boundary layer during the spin up phase

• Supergradient mean Vt was found in the eyewall region at the height of maximum Vt during both spin up and maturity

• These findings support in part the new intensification paradigm in which HBL plays an active role in dynamics

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Emanuel 1986

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(r) at z = 100 m and 1500 m

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New dynamical and thermodynamical insights from GRIP/HS3

1. Revised intensification model helps synthesize multi-scale observations and predicts new aspects of the intensification process. Observational data and analyses support the revised model, which predicts that the maximum tangential velocity occurs persistently within the frictional BL and the generation of significant supergradient winds within but near the top of the BL.

2. In the azimuthally-averaged view, the revised model comprises the cooperative intensification mechanism (Ooyama) + BL spin up mechanism in conjunction with moderately enhanced surface moisture fluxes to maintain convective instability in the developing core of the storm.

3. Observations suggest that radial inflow is maximum near the surface, and consistent with that of Bodewat boundary layer flow (Schlichting 1968, Ch. 11). [Is `Log layer’ universal? No!]

[This work is complementary to that of Neil Sanger et al. 2013 (MWR, accepted with minor revision).]

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End of Presentation

Thank you!