Relationships Between Eye Size and Intensity Changes of a N. Atlantic Hurricane Author: Stephen A. Kearney Mentor: Dr. Matthew Eastin, Central College

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

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

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

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

Procedure Flights composed of several legs, or passes through eye Flights composed of several legs, or passes through eye RMW = Radius of Maximum Wind (Shea et al. 1973) RMW = Radius of Maximum Wind (Shea et al. 1973) - Value of eye size Two values for mean RMW Two values for mean RMW RMW 1 = Average of RMW from first four legs RMW 1 = Average of RMW from first four legs RMW 2 = Average of RMW from last four legs RMW 2 = Average of RMW from last four legs Only flights with at least eight legs used Only flights with at least eight legs used

Procedure Mean times found in same way as mean RMW. Mean times found in same way as mean RMW. Labeled and t 2, respectively Labeled t 1 and t 2, respectively Change in Mean RMW per second Change in Mean RMW per second Mean RMW = RMW 2 – RMW 1 Change t 2 – t 1

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

Investigations of RMW Direct relationship Initial Max Wind to RMW 1 Initial Max Wind to RMW 1 Final Max Wind to RMW 2 Final Max Wind to RMW 2 Initial MSLP to RMW 1 Initial MSLP to RMW 1 Final MSLP to RMW 2 Final MSLP to RMW 2

RMW vs Max Wind Any direct relationship between RMW and Max Wind? Any direct relationship between RMW and Max Wind?

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

Investigations of RMW Change Intensity change relationship with eye change Max Wind Change during flight Max Wind Change during flight Max Wind Change after flight Max Wind Change after flight MSLP Change during flight MSLP Change during flight MSLP Change after flight MSLP Change after flight

RMW Change vs Max Wind Change During Flight Any immediate effect on Max Wind? Little to no correlation found Statistics: y = x R=

RMW Change vs Post Flight Max Wind Change Any future effect on Max Wind? Little to no correlation found Statistics: y = x R=

RMW Change vs MSLP Change During Flight Any immediate effect on MSLP? Little to no correlation found Statistics: y = x R=

RMW Change vs Post Flight MSLP Change Any future effect on MSLP Change? Little to no correlation found Statistics: y = x R=

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

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

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

MSLP Change vs RMW 1 SD During Flight Std Dev bars on left - Variability of MSLP Change Std Dev bars on left - Variability of MSLP Change Diagonal lines indicate mean MSLP in each “level” Diagonal lines indicate mean MSLP in each “level” MSLP change values plotted on right against RMW 1 SD MSLP change values plotted on right against RMW 1 SD

MSLP Change vs RMW 2 SD During Flight Std Dev bars on left - Variability of MSLP Change Std Dev bars on left - Variability of MSLP Change Diagonal lines indicate mean MSLP in each “level” Diagonal lines indicate mean MSLP in each “level” MSLP change values plotted on right against RMW 2 SD MSLP change values plotted on right against RMW 2 SD

Post Flight MSLP Change vs RMW 1 SD Std Dev bars on left - Variability of MSLP Change Std Dev bars on left - Variability of MSLP Change Diagonal lines indicate mean MSLP in each “level” Diagonal lines indicate mean MSLP in each “level” MSLP change values plotted on right against RMW 1 SD MSLP change values plotted on right against RMW 1 SD

Post Flight MSLP Change vs RMW 2 SD Std Dev bars on left - Variability of MSLP Change Std Dev bars on left - Variability of MSLP Change Diagonal lines indicate mean MSLP in each “level” Diagonal lines indicate mean MSLP in each “level” MSLP change values plotted on right against RMW 2 SD MSLP change values plotted on right against RMW 2 SD

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

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

Summary and Conclusion Eye symmetry important to forecasting Eye symmetry important to forecasting Case study by Willoughby et al Case study by Willoughby et al 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

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

Acknowledgements Author would like to thank the following: Author would like to thank the following: Dr. Matthew Eastin - mentorship, guidance, and data Dr. Matthew Eastin - mentorship, guidance, and data Dr. Takle - advice Dr. Takle - advice NOAA’s Hurricane Research Division - data NOAA’s Hurricane Research Division - data Classmates and Professors - moral support Classmates and Professors - moral support

Any Questions?