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On the Rapid Intensification of Hurricane Wilma (2005). Hua Chen Committee members: Dr. Da-Lin Zhang (Advisor) Dr. James Carton

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on the rapid intensification of hurricane wilma 2005

On the Rapid Intensification of Hurricane Wilma (2005)

Hua Chen

Committee members: Dr. Da-Lin Zhang (Advisor)

Dr. James Carton

Dr. Chuan Liu (Dean’s Representative)

Dr. Xin-Zhong Liang

Dr. Kayo Ide

Dr. Takemasa Miyoshi

slide3

Overview of Hurricane Wilma (2005)

  • Record intensity in the Atlantic basin – 882 hPa
  • Record intensification rate: 54 hPa/6 h, 83 hPa/12h,
  • and 97 hPa/24 h (RIDef: > 1.5 hPa/hr)
  • Record small eye size: 5 kilometer in diameter
  • Huge storm surge: 12 - 14 feet surge
  • Torrential rainfall: 1600 mm rainfall/24h at Yucatan peninsula
  • Above the mean fcst errors: track - 160 km/48 h, 250 km/72 h, and
  • large intensity underforecast (GFDL: 924 hPa and 50 m s-1).
slide4

Outline

  • Numerical prediciton
    • Model description
    • Model Verification
  • Diagnostic analysis
    • The upper level warm core
    • Small symmetric eyewall
slide5

Model Description (WRF-ARW)

  • Two-way, movable, quadruply nested (27/9/3/1 km),55 levels in the vertical;
  • Thompson et al. (2004) 3-ice cloud microphysics scheme;
  • The Betts-Miller-Janjic cumulus scheme for 27 and 9 km;
  • The YSU PBL scheme;
  • NOAH surface-layer physics;
  • Cloud-radiation interaction scheme;
  • Initial and boundary conditions: The GFDL’s then operational data, except for the specified daily SST;
  • Integration period: 0000 UTC 18 ~ 0000 UTC 21 October 2005 (72 h) for all the four meshes.
slide7

The best track (dashed) vs the 72-h predicted track (solid),SST (shaded), SST (00 Z 19 – 00 Z 18; contoured)

Predicted

Observed

NASA/GSFC, 26 March 2012

slide9

Predicted reflectivity at 1-km altitude

Visible Satellite picture

A

B

C

D

1900 UTC 18 OCT

1800 UTC 18 OCT

slide11

Verification against the flight-level observations

RMW = 15 km

RMW = 7 km

Observed

Predicted

slide12

Hypothesis – upper level warm core

  • An upper level warm core is important for RI;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
slide13

Hypothesis – upper level warm core

  • An upper level warm core is important for RI;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
slide14

a)

Shadings:

Temperature perturbation with respect to t = 0;

Contours:

Potentialtemperature

Wind barbs

all taken at the eye center.

b)

Total warming

Warming above 380 K

Warming below 380 K

slide15

t = 36 h

380 K

340 K

slide16

Efficiency of upper level warming

Pt

T1+∆T

T1

T2

T2+∆T

Pb

Pa

slide17

Hypothesis – upper level warm core

  • An upper level warm core is important for RI;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
slide18

RI

Post-RI

Pre-RI

slide19

t = 30 h,

t = 30.08h

The cloud field at z = 17.5 km and CBs. The red circle is the RMW at z = 1 km

slide20

Vertical cross section of cloud hydrometeors (shaded,g kg-1), storm-relative flow vectors, and vertical motion (downward/dashed every 1 m s-1 and upward/solid every 3 m s-1).

NASA/GSFC, 26 March 2012

slide21

Hypothesis – upper level warm core

  • An upper level warm core is important for RI;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from being ventilated;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
slide22

b

a

Differences:

t = 30 h

  • Higher altitude of warm core
  • at t =30 h;
  • Higher outflow layer at t=30 h;
  • Higher inflow layer at t=30 h;

Common feature:

  • Warm core is located at the
  • same altitude as the outflow
  • layer

t = 54 h

slide23

RI onset

Z = 14 km

Shading: θ

Red contour:

Upward motion

Blue contour:

Downward motion

Black circle:

RMW at Z = 1 km

“W”:

warm anomaly

slide24

Pre-RI

Z = 14 km

Shading: θ

Red contour:

Upward motion

Blue contour:

Downward motion

Black circle:

RMW at Z = 1 km

“W”:

warm anomaly

slide26

Hypothesis – upper level warm core

  • An upper level warm core is important for RI;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
slide27

The 18/6/2 km control

simulation

The SST-1 sensitivity

simulation

CTL: 3.5 hPh/hr

SST-1: 1.9 hPa/hr

NASA/GSFC, 26 March 2012

slide29

Hypothesis – small symmetric eyewall

  • The small eye is important;
  • The symmetric patter is important
slide30

Hypothesis – small symmetric eyewall

  • The small eye is important;
  • The symmetric patter is important
slide31

Onset of RI

Adapted from Schubert and Hack (1982)

slide32

AAM conservation

  • Gradient wind balance
  • solid body rotation
slide33

Hypothesis – small symmetric eyewall

  • The small eye is important;
  • The symmetric patter is important
slide36

How does the eye size contract fast in pre-RI stage?

Shading:

radar reflectivity

contour:

Vorticity

“A”, “B” denote the rainbands.

conclusion
Conclusion
  • WRF model reproduces reasonable well the track, intensity and storm structure given the reasonable configuration;
  • An upper level warm core is important for the storm to undergo RI because of its efficiency;
  • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts
  • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation;
  • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.
conclusion continued
Conclusion -continued
  • The small eye size is important in determining RI;
  • The asymmetric pattern is hostile to RI because it induces tilting and the asymmetric divergent outflow advects warming away from the center;
  • The change of vertical wind shear with time is a key factor for the trigger of RI since it prevents the formation of a large symmetric eyewall at early stage.
future work
Future work
  • Perform more clear SST sensitivity tests to identify its impact on convective bursts and associated warm core;
  • Microphysics sensitivity test.