Rappin et al. (2011) Paper Discussion Patrick Duran 1 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

The Impact of Outflow Environment on Tropical Cyclone Intensification

and Structure

Eric D. Rappin, Michael C. Morgan, and Gregory J. TripoliJ. Atmos. Sci., Volume 68, February 2011

ATM 527 Paper DiscussionPatrick Duran

3/3/2014

Rappin et al. (2011) Paper Discussion Patrick Duran 2 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Thoughts?

Rappin et al. (2011) Paper Discussion Patrick Duran 3 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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 rapidly

Rappin et al. (2011) Paper Discussion Patrick Duran 4 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Objective

Assess the effect of varying environmental inertial stability on

storm structure and intensification.

Rappin et al. (2011) Paper Discussion Patrick Duran 5 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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°C

Rappin et al. (2011) Paper Discussion Patrick Duran 6 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Symmetric Environment

• For no environmental flow, inertial stability reduces to f2

– Uniformly change environmental inertial stability by changing the latitude• 10°N (f10) and 30°N (f30) on an f plane

Rappin et al. (2011) Paper Discussion Patrick Duran 7 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Symmetric Environment Results

Lower inertial stability leads to RI more quickly

Rappin et al. (2011) Paper Discussion Patrick Duran 8 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Rappin et al. (2011) Paper Discussion Patrick Duran 9 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

f10 f30

Rappin et al. (2011) Paper Discussion Patrick Duran 10 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Much more work must be done by the TC to expand the outflow for the f30 simulation due to higher inertial stability.

Rappin et al. (2011) Paper Discussion Patrick Duran 11 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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.

Rappin et al. (2011) Paper Discussion Patrick Duran 12 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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 TC– Zonally 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 chosen

Rappin et al. (2011) Paper Discussion Patrick Duran 13 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

• 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 1st experiment

Rappin et al. (2011) Paper Discussion Patrick Duran 14 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

NO JET• Strong, symmetric

outflow jet forms and expands symmetrically.• Reaches Rossby

radius of deformation and expansion slows.

• Further expansion eats up energy.

Rappin et al. (2011) Paper Discussion Patrick Duran 15 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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.

Rappin et al. (2011) Paper Discussion Patrick Duran 16 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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.

Rappin et al. (2011) Paper Discussion Patrick Duran 17 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Beta Plane Simulation

• In addition to JET and NOJET simulations, perform a simulation on a Beta plane.– Idential to f10, except no f-plane approximation

Rappin et al. (2011) Paper Discussion Patrick Duran 18 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Rappin et al. (2011) Paper Discussion Patrick Duran 19 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

Shaded Left: Logarithm of divergent to rotational flow.Shaded Right: Precip.

Rappin et al. (2011) Paper Discussion Patrick Duran 20 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

“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).”

Rappin et al. (2011) Paper Discussion Patrick Duran 21 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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.”

Rappin et al. (2011) Paper Discussion Patrick Duran 22 of 22

Introduction Asymmetric Env. Conclusions QuestionsSymmetric Env.

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.