Work summarized in collaboration with: Roger Smith, Jun Zhang, S. Braun, Jason Dunion

On the dynamics of secondary eyewall formation in Hurricane Edouard (2014)

HS3 NOAA

Mike Montgomery, Sergio Abarca

Overarching NASA-HS3 Science Questions:

How do hurricanes form?

What causes intensity change?

[secondary eyewall formation of H. Eduoard (2014)]

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 (2013)

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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

Absolute angular momentum

Montgomery and Smith (2014 AMOJ)

Radial convergence of M:•Above the BL (M~conserved)

•Radial gradient of diabatic heating•Convective structures•Presence of surface moisture fluxes•Described in terms of balanced dynamics

Montgomery and Smith (2014)

•Within the BL (M~ not conserved)•Friction is important•A coupled system of equations!•Presence of supergradient winds

1st M

ech

an

ism

2n

d M

ech

an

ism

=0

=0The 2nd mechanism is coupled

to the 1st

5

Vertical profiles of Vt and Vr for Period 2 (Aug 29)

H. Earl (2010)

Gradient wind Vg at height of max Vt for periods 1 and 2 (Aug. 28 and 29)H. Earl (2010)

Lessons learned from H. 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

The Secondary Eyewall tangential wind maximum:

a) Emerges within the BL?

b) In the presence of supergradient flow?

Is this relevant to Secondary Eyewall Formation?

Observations?

Didlake and Houze (2011)Bell et al. (2012)

Rita (2005)

Tangential wind

WRF•Three domains 45, 15 and 5 km (with two-way movable nests)•WSM6 microphysics•YSU PBL•Grell-Devenyi (2 coarsest domains)•NCEP Analysis for initial and boundary conditions•Observations integrated and assimilated into the model

• High-spatial/temporal-resolution and model/observation- consistent dataset

Hsuan, Montgomery and Wu (2012)

Typhoon Sinlaku (2008)

Hsuan et al. (2012)

Time

SE

SEF regionRadially outside of the

SEF region

Composite Structure At Peak Intensity

Hurricane Edouard on September 16-17

Relative Humidity at 700 hPa

Tangential Velocity

Radial Velocity

Temperature Perturbation

Relative Humidity

Equiv. Pot. Temp.

Valid for reference time of 00Z Sept. 17

Valid 0520Z Sept. 17

courtesy, Scott Braun

Observations of Hurricane Eduoard during HS3-IFEX 2014

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H. Edouard (2014)Sep 15: ~14-19 UTC

New dynamical insights from HS3-2014

1. Revised intensification model helps synthesizes multi-scale observations and predicts new aspects of the intensification and structure change process.

2. In azimuthally-averaged view discussed mainly here, the revised intensification model suggests a new pathway to secondary eyewall formation in which the BL exerts a progressive control on the location and organization of convective instability as vortex matures and broadens with time.

3. Data collected during Hurricane Eduoard (2014) reveal for the first time a clear obs. signature of supergradient winds, enhanced convergence in BL outside the primary eyewall, well before the formation of secondary eyewall. The 2014 HS3 observations strongly support the new theory of secondary eyewall formation proposed first by Huang et al. (2012) based on Typhoon Sinlaku (2008) case.

Stand by for Sergio’s Part II presentation …

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End of Presentation

Thank you!