Tropical Cyclone Formation, Structure, and Longevity during HS3 Mike Montgomery and Mark Boothe Naval Postgraduate School Tim Dunkerton and Blake Rutherford NorthWest Research Associates Sponsored by NSF

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? What determines storm resilience and longevity, such as Nadine (2012)?

Understanding Nadine Scientific Questions Formation How did it form? (Is there a pouch?) Structure How does the wind field evolve? Longevity Why so resilient? (Was Nadine always in a favorable environment OR was it able to protect itself from an occasionally hostile environment?)

Understanding Nadine Approach Conduct Lagrangian analyses within the marsupial framework 1.Review genesis sequence 2.Examine dropsonde data to study change in circulation 3.Examine dividing streamlines to document structure change with the ECMWF model analyses 4.Examine ECMWF theta-e tracer field for possible interaction with environmental dry air

Animations of Nadine

Formation of Nadine Comoving Phase speed: -7.3 m/s Earth-relative Phase speed: 0 m/s 0000 UTC 4 September Initial time of pouch designation ~ 13N, 4W 700 hPa ECMWF Streamlines and Okubo-Weiss

Formation of Nadine 700 hPa ECMWF Streamlines and Okubo-Weiss P25L frame of reference P25L P23L P24L P23L P24L P25L P23L P24L P25L P23L P24L P25L 0000 UTC 4 September UTC 5 September UTC 6 September UTC 6 September 2012 P25L initially arrests P24L/pre-Nadine westward motion, but growing P24L/pre-Nadine then absorbs P25L on 7 September

Formation of Nadine P23L P24L P23L P24L 0000 UTC 8 September UTC 8 September UTC 10 September hPa ECMWF Streamlines and Okubo-Weiss (P24L/pre-Nadine frame of reference) 700 hPa ECMWF Ozone Tracer (P24L/pre-Nadine frame of reference) Stretched P23L is then absorbed into the outer portion of P24L/pre-Nadine P23L tracks along blue manifold around P24L

Track of Nadine kt 50 kt ~30-35 kt

-10.3 RF2 RF3 RF4 50 kt kt kt NHC HURDAT2 Intensities Circulation Average tangential cyclonic wind C / perimeter

RF4RF5 50 kt RF6 50 kt

ECMWF Dividing Streamline Analysis Drops: 1701Z Sept 14 – 0808Z Sept 15 (-6:59…+8:08) Small, vertically aligned ( hPa) pouch High TPW Saddle point to the southwest Understanding Nadine: Dividing Streamlines RF03 Courtesy Michael Riemer, NRC postdoc

ECMWF Dividing Streamline Analysis Drops: 0107Z – 1235Z Sept 20 (-10:53…+00:35) Larger, with a saddle point to the northeast TPW decreased Vertically aligned Understanding Nadine: Dividing Streamlines RF04

ECMWF Dividing Streamline Analysis Drops: 1638Z Sept 26 – 0428Z Sept 27 (-7:22…+4:28) Has shrunk TPW had continued to decrease, now increasing again Still vertically aligned Understanding Nadine: Dividing Streamlines RF06

Simple Kinematic Model of Point Vortex in Uniform Flow with Mass Sink

Understanding Nadine: Theta-e tracer field

Understanding Nadine Scientific Questions Answered Formation How did it form? (Is there a pouch?) Yes. Merged with P25L (east) and P23L (west). Structure How does the wind field evolve? Grows in extent, then declines (presumably grew again when it reintensified to a hurricane on 28 September) Longevity Why so resilient? (Was Nadine always in a favorable environment OR was it able to protect itself from an occasionally hostile environment?) Size growth contributes to extensive pouch and shear sheltering from hostile intrusions in lower troposphere