Two Distinct Regimes in the Kinematic and Thermodynamic ...

Two Distinct Regimes in the Kinematic and Thermodynamic Structure of the Hurricane Eye and Eyewall
James P. Kossin and Matthew D. Eastin, 2001
Erin DoughertyATM 741: Special Problems in Tropical Cyclone ResearchFeb. 8 2015
Changes in hurricane eye thermodynamic structure:
Documented by Jordan (1961), Franklin et al. (1988), and Willoughby (1998)Intensifying: inversion level descends in eye, eye is warm and dryWeakening: inversion ascends, eye moistensGoal: Understand changes in hurricane regimes between the eye and eyewall using flight-level dataRegime 1: intensifyingRegime 2: weakening
Data & Methods
Presentation of Results
2casesstudies:HurricaneDiana (1984)Intensified from Cat.1-Cat.4 hurricane Sept. 10-12Located in the AtlanticObserved at 850mb
Hurricane Olivia (1994)Intensified from TS- Cat.4 hurricane Sept.23-25Located in the PacificObserved at 600mb
Presentation of Results
Numericalstudy: used to explain regime changes2-D nondivergent barotropic model comparedtoSchubert et. al (1999)Schubert et. al (1999) examined potential vorticity redistributionbetween eye andeyewall
Initial vorticity profile supportive of barotropic instability, leading to turbulent exchange between eye and eyewall
From Schubert et al. (1999)
THIS IS KEY TO KOSSIN & EASTIN’S STUDY!
Case Study Results from Hurricane Diana and Hurricane Olivia
Angular velocity in different regimes
Hurricane Diana
Hurricane Olivia
Fig.1
Fig.3
RMW
T, Td, andΘe
Hurricane Diana
Hurricane Olivia
Fig.4
Fig.5
ζand v
Hurricane Diana
Hurricane Olivia
Fig.6
Fig.8
Another perspective ofζand V
HurricaneDiana
Hurricane Olivia
Fig.9
Fig.7
Numerical Modeling Results
Vorticity evolution
t=0.0 hHigh vorticity ringLow vorticity center
x 10-4s-1
t=3.0 hWaves phase-lock and grow
t=5.5 hMesovortices form and migrate inwards
t=6.0 hMesovortex rotates cyclonically around eyeEyewall vorticity collapses inward
Fig.10
Vorticity evolution
x 10-4s-1
t=12.0 hOne strong vorticity structure orbits around center
t=24.0 hAxisymmetrization occursVorticity maximum in center
Schubert et al.’s (1999) Result
Numerical Model ofΘe(approximated using passive tracers)
T=0
T=24
Initial location: eye
Initial location: eyewall
Initial location: outside the eyewall
Not entirely consistent with observations, sinceΘein eyewall does not decrease
Fig.11
Model vs. Observations
Model
Hurricane Diana
Similar results, but transition between regimes occurs quicker in Diana, possibly due to lack of axisymmetrization in real hurricane
Fig.9
Comparison of Results with Other Studies
Willoughby (1998):Eye is composed of two distinct air masses above and below inversionInward mixing from eyewall not reasonable- this would reduce localΘeminimum
Θe
w
P-Psat
Saturated from surface- 740hPa
Unsaturated above inversion & lowΘe
Air not saturated after transition to regime 2
If transition was just vertical displacement of an inversion &air above inversion was horizontally homogeneous, then this cannot explain for Olivia’s transition given thehigherΘeair in the eyeAFTERthetransitionThus mixing with eyewall
Comparison of Results with Other Studies
Increase inΘein eye
Summary
Transition in hurricane regimes in eye and eyewall thermodynamic and kinematic variables associated with horizontal mixing:
Regime 1
Regime 2
ζ
v
ω
Θe
T
Td
Questions and Observations
How/why did they select only Hurricane Diana and Olivia? Why didn’t they include results from the other 44 hurricanes or provided more statistics on these cases?Are there any other processes responsible for these transitions aside from horizontal mixing?Thoughts on using flight-level data to make observations and theories on the hurricane eye?Feelings on the layout of the paper?