Oceanography off Western Australia – what have we learnt in ......Oceanography off Western...

Oceanography off Western Australia –what have we learnt in the first decade of

IMOS? Charitha Pattiaratchi

School of Civil, Environmental and Mining EngineeringThe UWA Oceans Institute

The University of Western Australia

Indeed, I think that as we go on piling measurements upon measurements, making one instrument after another more perfect to extend our knowledge, the sea will always continue to escape us

Belloc, The cruise of the Nona (in Pugh, 1987)

A scholar’s positive contribution is measured by the sum of the original data that they contribute. Hypotheses come and go but data remain.

Santiago Ramon y Cajal, 1897

Ningaloo Nino

Passive Acoustics: Perth Canyon

AATAMS: Ningaloo

Personnel: Ming Feng, Rob McCauley, Patrick Sears, Gary Kendrick, Julian Partridge, Lynnath Beckley, Steve Buchan, Nick D’Adamo, Nick Caputi, Sasha Gavrilov, David Antoine, Peter Thompson, Craig Steinberg, Richard Brinkman, Mark Meekan, Simone Cosoli

+ support staff, students + others

Emeritus: Jamie Oliver, Peter Rogers, Agi Gedeon, Merv Lynch, Anya Waite, Steve Blake, Alan Pearce

AUV–habitats

SRFME

WAMSI

Step Change ?

FranklinSouthern Surveyor

ozROMS (2000-2014)Australian Boundary Currents

Australian Boundary Currents

Holloway Current

Leeuwin Current

SICC

Results indicate that at least during the low wind conditions of the Southern Hemisphere autumn, a reasonably well-defined, south-westward coastal flow occurs along the shelf and shelf break. We propose to formalise the name of this autumn current over the North West Shelf as the Holloway Current, in honour of the pioneering work by the late Dr Peter Holloway.

Holloway Current

D’Adamo et al.:

Holloway Current

Seasonal winds/Sea level

Seasonal winds

Kronborg (2004)

Holloway Current

Geostrophic current anomaly- from Altimeter for April

Kimberley and Pilbara transects funded through WA State Govt co-investment in IMOS

Holloway Current: annual mean

Holloway Current inflow

~4 Sv

~2 Sv~2 Sv

Pilbara Transect: seasonal

Kimberley Transect : seasonal

WA Mean Sea level/LC Transport

Geostrophic Velocity fromAltimeter

Ocean Glider deployments

Dense shelf water cascade

Dense Shelf Water Cascade

Critical latitude and Resonance

An oscillation can be driven by an oscillating driving force; the frequency of the driving force may or may not be the same as the natural frequency of the system.

If the frequency is the same as the natural frequency, the amplitude can become quite large. This is called resonance.

In the ocean we have to take Earth’s rotation into account.

A parcel of water will rotate, time taken to complete a circle is the inertial period. At 30o N & S the inertial period is 24 hours.

24 hours is also the same period as the sea breeze !!

Simpson et al. 2002

Critical latitude and Resonance

Sea Breeze Cycle

Critical latitude

Critical latitude

Coffs Harbour

HF Radar surface currents

Ocean GlidersMoorings

ADCP, thermistorsShipborne Measurements

SatelliteOcean colour, SST

Multi-platform

Tea Leaf Paradox = Peddies ?

When you stir a cup of tea with tea leaves, where do the tea leaves usually end up?

Solved by Einstein in 1926.

When stirring, rotation is usually slower at the bottom. This creates a secondary flow where fluid rises in the center and falls at the edges. Tea leaves participate in this flow, but are too heavy to become lifted by the flow at the bottom, and so stay at the bottom center.

HF Radar coverage

Peddies: 16 August –Glider track

Density

Peddies: 16 August –Glider track

Locations of Peddies

Cyclonic 768 Anti-cyclonic 816

36 months of data

Eddies – strong currents

Eddies (>2 days)

12041359

Billow clouds

Shear mixing

Kelvin-Helmhotz Billows

Kelvin-Helmhotz Billows

Kelvin-Helmhotz Billows

West Australian Coast

Capes Current

Leeuwin/Capes interaction23 December 2013

Leeuwin/Capes interaction

Leeuwin/Capes interaction

Leeuwin/Capes interaction

Leeuwin/Capes interaction

Leeuwin/Capes interaction

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Leeuwin/Capes interaction

Leeuwin/Capes interaction

2013

Leeuwin/Capes interaction

Leeuwin/Capes interaction

Continental Shelf Waves

Tropical low

Narelle5-15 January 2013

Olwyn8-14 March 2015

Remote forcing from tropical cyclones generate sub-mesoscale eddies

Rottnest Swim

http://coastaloceanography.org/

Port to Pub swim

Acknowledgements

Sarath Wijeratne, Yasha Hetzel, Ivica Janekovic, Simone Casoli, Hrvoje Mihanovic

Mohammad Hadi Bahmanpour, Tanziha Mahjabin, Miaoju Chen, Jennifer Penton

Pawsey Supercomputing Centre