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The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure

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 3/3/2014. Thoughts?. Motivation.

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The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure

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  1. 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 3/3/2014

  2. Thoughts?

  3. 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

  4. Objective Assess the effect of varying environmental inertial stability on storm structure and intensification.

  5. 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

  6. 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

  7. Symmetric Environment Results Lower inertial stability leads to RI more quickly

  8. f10 f30

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

  10. 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.

  11. Asymmetric Environment • How do horizontal variations of inertial stability affect TC evolution? • Create variable inertial stability on an fplane 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

  12. Intensity evolution of both cases nearly identical • Contrasts sharply with 1st experiment • 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.

  13. NO JET • Strong, symmetric outflow jet forms and expands symmetrically. • Reaches Rossby radius of deformation and expansion slows. • Further expansion eats up energy.

  14. 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.

  15. 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.

  16. 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

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

  18. “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).”

  19. 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.”

  20. 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.

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