An Overview on Eyewall Replacement Cycles

1
An Overview on Eyewall Replacement Cycles
2
Introduction

• Modulate intensity in powerful hurricanes
• Only studied since 1982
• Kinematics/Dynamics not well understood

3
Formation

• Nong and Emanuel (2003) show that environment
  perturbations are necessary for the formation of
  the secondary eyewall

4
Formation

• Kossin et al. (2000) do not form concentric
  eyewalls, but instead what they term a tripole

5
Formation

• Kuo et al. (2004) show that Kossin et al. used an
  outer vorticity ring that was too strong.
• With a weaker vorticity ring, a concentric
  eyewall can form

Idealized
Typhoon Lekima
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Formation

• Molinari and Vollaro (1990) suggest eddy angular
  momentum flux
• is responsible for the perturbation, with a 30h
  lag

7
Evolution

• Willoughby et al. (1982) show the classic
  structure of eyewall replacement cycles

8
Evolution

• Willoughby (1990) looked at radial profile of
  tangential wind to identify classic pre- and
  post-eyewall replacement cycle wind fields

9
Evolution

• Samsury and Zipser (1995) identified collapsing
  rain bands (recall Nong and Emanuel) as a cause
  of the secondary eyewall and the collapse of the
  primary eyewall

Primary
Secondary
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Conclusions

• Dynamics of secondary eyewall formation not well
  understood
• An eyewall replacement cycle signals the
  (relative) end of intensification
• Extremely difficult to forecast one of the
  reasons it is difficult to forecast intensity