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

1. On the dynamics of secondary eyewall formation in Hurricane Edouard (2014) Mike Montgomery, Sergio Abarca NOAA HS3 Work summarized in collaboration with: Roger Smith, Jun Zhang, S. Braun, Jason Dunion

2. 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)

3. Revised view of intensification: two mechanisms Absolute angular momentum 15 10 z km 5 M conserved 0 50 r km 100 Mreduced by friction, but strong convergence  small r Montgomery and Smith (2014 AMOJ)

4. =0 Montgomery and Smith (2014) • 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 1st Mechanism • Within the BL (M~ not conserved) • Friction is important • A coupled system of equations! • Presence of supergradient winds 2nd Mechanism =0 The 2nd mechanism is coupled to the 1st

5. Vertical profiles of Vt and Vr for Period 2 (Aug 29) H. Earl (2010)

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

7. 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

8. Is this relevant to Secondary Eyewall Formation? The Secondary Eyewalltangential wind maximum: a) Emerges within the BL?b) In the presence of supergradient flow? Observations?

9. Rita (2005) Tangential wind Bell et al. (2012) Didlake and Houze (2011)

10. Typhoon Sinlaku (2008) • 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)

11. Radially outside of the SEF region SEF region Time SE Hsuan et al. (2012)

12. Composite Structure At Peak Intensity Tangential Velocity Hurricane Edouard on September 16-17 Valid 0520Z Sept. 17 Relative Humidity at 700 hPa Radial Velocity Temperature Perturbation Equiv. Pot. Temp. Valid for reference time of 00Z Sept. 17 Relative Humidity courtesy, Scott Braun

13. Observations of Hurricane Eduoard during HS3-IFEX 2014

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

15. 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 …

16. End of PresentationThank you! 16