Relationships Between Eye Size and Intensity Changes of a N. Atlantic Hurricane

1
Relationships Between Eye Size and Intensity
Changes of a N. Atlantic Hurricane

• Author Stephen A. Kearney
• Mentor Dr. Matthew Eastin,
• Central College

2
Introduction

• Two primary components to hurricane forecasting
• - Track
• - Intensity
• Current research on structure and intensity
• Knowledge gained about storm structure with
  flight level data (e.g., Jorgensen, 1984)
• Do relationships exist between eye size and
  intensity?
• Previous studies (e.g., Weatherford and Gray
  1988) show weak correlation between eye size and
  minimum sea level pressure (MSLP)

3
Introduction/Hypothesis

• Temporal changes associated with eye wall
  replacement cycles also noted (Willoughby et al.
  1990 Willoughby et al. 1982 Black et al. 1992)
• Generally, smaller eye sizes coincident with
  greater intensity
• Project investigates impact of eye diameter
  asymmetries on intensity changes
• Hypothesis Eye sizes are characterized by
  changes in storm intensity

4
Overview

• Procedures
• Investigations
• - Direct relationship
• - Intensity change with eye size change
• Effect of eye symmetry on storm intensity

5
Procedure

• 88 total flights analyzed, only at hurricane
  strength
• Flights analyzed at 850 mb and 700 mb levels
• 14 various N. Atlantic hurricanes from 1979
  through 1995
• Included some notable storms
• Gilbert, 1988 Andrew, 1992

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Procedure

• Flights composed of several legs, or passes
  through eye
• RMW Radius of Maximum Wind (Shea et al. 1973)
• - Value of eye size
• Two values for mean RMW
• RMW1 Average of RMW from first four legs
• RMW2 Average of RMW from last four legs
• Only flights with at least eight legs used

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Procedure

• Mean times found in same way as mean RMW.
• Labeled t1 and t2 , respectively
• Change in Mean RMW per second

Mean RMW RMW2 RMW1
Change t2 t1
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Procedure

• Calculated change in Maximum Wind (m/s) and
  change in MSLP (mb)
• Change values covered separate six-hour periods
  during and after each flight
• - Immediate or future impact?
• RMW Standard Deviation (RMW SD) found separately
  for RMW-1 and RMW-2

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Investigations of RMW

• Direct relationship
• Initial Max Wind to RMW1
• Final Max Wind to RMW2
• Initial MSLP to RMW1
• Final MSLP to RMW2

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RMW vs Max Wind

• Any direct relationship between RMW and Max Wind?

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RMW vs MSLP

• Any direct relationship between RMW and MSLP?
• Very low pressures with small RMW values
  (Gilbert, 888 mb)

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Investigations of RMW Change

• Intensity change relationship with eye change
• Max Wind Change during flight
• Max Wind Change after flight
• MSLP Change during flight
• MSLP Change after flight

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RMW Change vs Max Wind Change During Flight

• Any immediate effect on Max Wind?
• Little to no correlation found
• Statistics
• y 2.496 - 1.095 x
• R0.039804

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RMW Change vs Post Flight Max Wind Change

• Any future effect on Max Wind?
• Little to no correlation found
• Statistics
• y 1.888 - 0.298 x
• R 0.003811

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RMW Change vs MSLP Change During Flight

• Any immediate effect on MSLP?
• Little to no correlation found
• Statistics
• y 2.722 0.602 x
• R 0.034097

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RMW Change vs Post Flight MSLP Change

• Any future effect on MSLP Change?
• Little to no correlation found
• Statistics
• y 1.534 0.392 x
• R0.01604

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Results

• Direct Relationship
• Very little correlation present
• Relationship to RMW Change
• Not much correlation
• Agrees with findings of Weatherford and Gray
  (1988)

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RMW Std Dev

• Approximate measure of eye structure symmetry
• Larger RMW SD RMW values dissimilar
• Indicated more asymmetric eye structure
• Smaller RMW SD RMW values similar
• Indicated more symmetric eye structure

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MSLP vs RMW SD

• MSLP and RMW SD had noticeable correlation
• Found ranges of RMW SD to get different levels
  of eye symmetry (i.e., lt 3, 3 to 6, 6 to 9)
• Calculated Mean and Std Dev of MSLP Change within
  each RMW SD range

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MSLP Change vs RMW1 SD During Flight

• Std Dev bars on left - Variability of MSLP Change
• Diagonal lines indicate mean MSLP in each level
• MSLP change values plotted on right against RMW1
  SD

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MSLP Change vs RMW2 SD During Flight

• Std Dev bars on left - Variability of MSLP Change
• Diagonal lines indicate mean MSLP in each level
• MSLP change values plotted on right against RMW2
  SD

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Post Flight MSLP Change vs RMW1 SD

• Std Dev bars on left - Variability of MSLP Change
• Diagonal lines indicate mean MSLP in each level
• MSLP change values plotted on right against RMW1
  SD

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Post Flight MSLP Change vs RMW2 SD

• Std Dev bars on left - Variability of MSLP Change
• Diagonal lines indicate mean MSLP in each level
• MSLP change values plotted on right against RMW2
  SD

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Summary and Conclusion

• Very little relationship between eye diameter and
  intensity change, current or future
• Symmetric structure indicated by RMW SD
• Lower MSLP Std Dev trended with higher RMW SD
• MSLP changed the most with more symmetric
  structure

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Summary and Conclusion

• More asymmetric structure negative impact on
  storm
• More time for vertical shear
• More time for colder SSTs to inhibit
  strengthening
• More symmetric structure positive impact on
  storm
• Allows winds to increase quicker
• Other studies (e.g. Shapiro and Willoughby 1982)
  show more symmetric structure has better
  spin-up effect

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Summary and Conclusion

• Eye symmetry important to forecasting
• Case study by Willoughby et al. 1990
• - Outer eye wall observed to contract before
  becoming asymmetric
• - Retained intensity on one side, then weakened
  on the other
• - Can create different effects on a local area,
  depending on landfall time and location

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Points to Consider

• Only flights from 1979 to 1995 were used
• Tropical cyclones stronger and more frequent in
  past ten years
• Further studies, especially on 2005 record
  breaking season, can be done
• More frequent flights into storms today
• Higher resolution data may indicate further
  relationships

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Acknowledgements

• Author would like to thank the following
• Dr. Matthew Eastin - mentorship, guidance, and
  data
• Dr. Takle - advice
• NOAAs Hurricane Research Division - data
• Classmates and Professors - moral support

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Any Questions?