The School of Environmental Systems

1. Global influences of the 18.61 year lunar nodal cycle and 8.85 year cycle of lunar perigee on coastal flooding Ivan Haigh, Matt Eliot and Chari Pattiaratchi The School of Environmental Systems Engineering and the UWA Oceans Institute The University of Western Australia School of Environmental Systems Engineering

2. 1. Introduction New Orleans, Hurricane Katrina Source: http://newsmediainsider.blogspot.com/2010/08/katrina-survivor-talks-about-escaping.html

3. 1. Introduction Observed Tide = Mean Sea Level + Astronomical Tide + Surge

4. 1. Introduction FREMATLE 4.4 years BROOME 18.6 years

5. 1. Introduction • The aim of this study is to examine the contribution of the 18.61 year lunar nodal cycle and 8.85 year cycle of lunar perigee to high tidal levels (coastal flooding) on a global scale; • A global assessment of when these tidal modulations occur allows for prediction of periods when enhanced risk of coastal flooding/inundation is likely in different coastal regions.

6. 23.5° + 5° = 28.5° 5° 2. Background: A. 18.61 year lunar nodal cycle Cross-section view: 23.5° - 5° = 18.5° 5° 23.5° 23.5°

7. 2. Background B. 8.85 year cycle of lunar perigee View from above: Quasi-4.4 years cycle (of perigean influence)

8. 2. Background • Tidal analysis (Matlab t-tide) performed on a year or two of tide gauge observations; • Inter-annual modulations can not be independently determined from a single year of data; • Handled using small adjustment factors: • f (amplitude); • u (angle);

9. TPXO 7.2 Global Ocean Tidal Model 3. Methodology • Best fits the Laplace Tidal Equations and T/P and Jason altimetry data using OTIS (Oregon State University Tidal Inversion Software); • 8 primary and 2 long period const. on ¼ deg resolution global grid; • Tidal Model Driver (TMD) Matlab toolbox • Infers 16 minor const; • Modulation corrections based on equilibrium tide expectations. Egbert and Erofeeva (2002)

10. 3. Methodology Fremantle Broome 4 cm 8 cm 26 cm 2 cm

11. 4. Results: Range 18.6 lunar nodal year 0 – 80 cm

12. 4. Results: Range 4.4 year cycle of lunar perigee 0 – 50 cm

13. 4. Results: Range Form Factor 18.6 year Tidal Range 4.4 year

14. 4. Results: Range as % of tidal range 18.6 lunar nodal year 18.6 lunar nodal year 4.4 year cycle of lunar perigee

15. 4. Results: Dominant 4.4 year cycle dominates 18.6 year cycle dominates FF >~ 0.6 (mixed, diurnal) FF <~ 0.6 (semi-diurnal)

16. Broome 4. Results: Phase Fremantle 1997 2006 2006 2008 23.5° + 5° 23.5° - 5° maximise semi-diurnal at expense of diurnal maximise diurnal at expense of semi-diurnal

17. 4. Results: Phase 18.6 year cycle 1987, 2006, 2024 1978, 1997, 2015 FF <~ 0.6 (semi-diurnal) FF >~ 0.6 (mixed, diurnal)

18. 5. Conclusions • Paper in press: Haigh, I.D., Eliot, M., Pattiaratchi, C., in press. Global influences of the 18.61 year nodal cycle and 8.85 year cycle of lunar perigee on high tidal levels. Journal of Geophysical Research. • Future work compare with measured data – GESLA (Hunter, Woodworth) data set:

19. 6. Future Work Model Measured Brest, France Fremantle, Australia San Francisco, USA Balboa, Panama Honolulu, Hawaii

20. Ivan Haigh, Matt Eliot and Chari Pattiaratchi Any Questions