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

1. Introduction

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

1. Introduction

Observed Tide = Mean Sea Level + Astronomical Tide + Surge

1. Introduction

FREMATLE 18.6 years BROOME 4.4 years

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.

2. Background: A. 18.61 year lunar nodal cycle Cross-section view: 23.5

°

= 18.5

°

5

°

5

°

23.5

°

+ 5

°

= 28.5

°

23.5

°

5

°

23.5

°

2. Background

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

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);

Constituent

M 2, N 2 K 2 Q 1 , O 1 K 1

f (factor)

3.7% 28.6% 18.7% 11.5%

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.

TPXO 7.2 Global Ocean Tidal Model Egbert and Erofeeva (2002)

3. Methodology

Fremantle Broome 8 cm 2 cm 4 cm 26 cm

4. Results: Range

18.6 lunar nodal year 0 – 80 cm

4. Results: Range

4.4 year cycle of lunar perigee 0 – 50 cm

4. Results: Range

18.6 year Form Factor 4.4 year Tidal Range

4. Results: Range as % of tidal range

4.4 year cycle of lunar perigee

4. Results: Dominant

18.6 year cycle dominates FF >~ 0.6 (mixed, diurnal) 4.4 year cycle dominates FF <~ 0.6 (semi-diurnal)

4. Results: Phase

Fremantle Broome 2006 2008 1997 2006 23.5

°

5

°

+ maximise diurnal at expense of semi-diurnal 23.5

°

5

°

maximise semi-diurnal at expense of diurnal

4. Results: Phase 18.6 year cycle

1987, 2006, 2024 FF >~ 0.6 (mixed, diurnal) 1978, 1997, 2015 FF <~ 0.6 (semi-diurnal)

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:

6. Future Work

Measured Model Brest, France Fremantle, Australia San Francisco, USA Balboa, Panama Honolulu, Hawaii

Ivan Haigh, Matt Eliot and Chari Pattiaratchi

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