Eric D Rappin Michael C Morgan and Gregory J Tripoli J Atmos Sci Volume 68 February 2011 ATM 527 Paper Discussion Patrick Duran 332014 Thoughts Motivation TC environment is known to have an influence on TC structure and intensification ID: 616247
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Slide1
The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure
Eric D.
Rappin
, Michael C. Morgan, and Gregory J. Tripoli
J. Atmos. Sci., Volume 68, February 2011
ATM 527 Paper Discussion
Patrick Duran
3/3/2014Slide2
Thoughts?Slide3
Motivation
TC environment is known to have an influence on TC structure and intensification
If the environment is less resistant to outflow…
TC needs to do less work to expand its outflow
More energy available to overcome inflow friction
TC may intensify more rapidlySlide4
Objective
A
ssess the effect of varying environmental inertial stability on storm structure and intensification.Slide5
Model Setup
University of Wisconsin
Nonhydrostatic
Modeling System (UW-NMS).
Three nested grids of 48-, 12-, and 3-km horizontal grid spacing; 42 vertical levels
Innermost grid turned on after 10 hours
Outermost grid: Emanuel (1991) cumulus parameterization with radiative lateral BCs
Jordan (1958) sounding base state
Vortex initialization:
Rotunno
and Emanuel (1987) symmetric vortex
Fixed SSTs of 28°CSlide6
Symmetric Environment
For no environmental flow, inertial stability reduces to
f
2
Uniformly change environmental inertial stability by changing the latitude
10°N (f10) and 30°N (f30) on an f planeSlide7
Symmetric Environment Results
Lower inertial stability leads to RI more quicklySlide8Slide9
f10
f30Slide10
Much more work must be done by the TC to expand the outflow for the
f30
simulation due to higher inertial stability.Slide11
Symmetric Environment Summary
Lower environmental inertial stability leads to more rapid intensification to a TC’s MPI
.
Lower inertial stability leads to a stronger secondary circulation.
Symmetric expansion of outflow requires much more energy for higher environmental
intertial stability.Slide12
Asymmetric Environment
How do horizontal variations of inertial stability affect TC evolution?
Create variable inertial stability on an
f
plane by introducing a zonally uniform jet N of the TCZonally uniform
No initial secondary circulations
Potential issues:
Separation distance of jet and TC
Too far No interaction
Too close Jet shears TC
Separation distance of 900 km chosenSlide13
Decreased low-level inertial stability and resultant more compact low-level circulation in Exp. 1 could have driven timing of RI.
Vertical wind shear associated with jet leads to asymmetries in the core, which delay intensification.
Intensity evolution of both cases nearly identical
Contrasts sharply with 1
st
experimentSlide14
NO JET
Strong, symmetric outflow jet forms and expands symmetrically.
Reaches Rossby radius of deformation and expansion slows.
Further expansion eats up energy.Slide15
JET
Outflow immediately accesses low inertial stability north of storm.
Even after expanding to Rossby radius of deformation, TC continues to intensify, as outflow jet can continue to expand with little resistance.Slide16
Least work required to expand outflow to the NE of TC center.
After RI, outflow requires less energy to expand in NE quadrant, but more energy in all other parts of the storm. Slide17
Beta Plane Simulation
In addition to JET and NOJET simulations, perform a simulation on a Beta plane.
Idential
to
f
10, except no f-plane approximationSlide18Slide19
Shaded Left:
Logarithm of divergent to rotational flow.
Shaded Right:
Precip
.Slide20
“Regions with the most persistent convective activity, be it in the storm core or
rainband
activity, are located radially inward from regions where the strongest rotation feeds most directly into the paths that expand outward toward environments dominated by divergence and low inertial stability (the darker colors).”Slide21
Concluding Point
“Convective elements within the storm core and
rainbands
organize in a manner such that the outflow has direct access to regions of weak inertial stability in the environment.”Slide22
Summary
Lower environmental inertial stability leads to more rapid intensification to a TC’s MPI.
Asymmetries in environmental inertial instability will lead to asymmetric outflow, which is favorable for intensification.
If TC is able to “tap into” low inertial stability, it might RI.
Convection organizes radially inward of low environmental inertial stability regions.