Extreme oceanic events

David Griffin

CSIRO Marine and Atmospheric Research

Special thanks to

• Madeleine Cahill• George Cresswell and Jason Middleton• John Wilkin and Alan Pearce• Peter Campbell, Jason Waring, • Kim Badcock (and the whole remote sensing group)• Jim Mansbridge• The Bluelink and IMOS communities (many great people)• Peter Thompson, referees and the panel

1995 Mass Mortality of Pilchard –due to an extreme ocean event?

?

• Event was extreme but not unprecedented• Shift focus to the virus• Exposed ill-preparedness for addressing urgent questions• Assembling data took too long• Available data were too few• Too hard to know ‘how anomalous’ various observations were• Nevertheless, I think we got it right• BTW, the next comparable upwelling was not til 2010:

2010 upwelling event, similar to 1995:

The cause: occasional summer wind pattern

Sea Surface Temperature

Sea level anomaly

High

wind

Next, two Qld events. Ocean impact unnoticed?

beautiful one day….(9 Feb 1997)

Sea level anomaly Sea Surface Temperature

TC Andrew (25 March 1997) the next.

Sea level anomaly Sea Surface Temperature

Month later: cold along NGBR

Sea level anomaly

16 March 2010: TC ULUI

Sea level anomaly

L

25 May (TC ULUI + 40d)

30 June 2010 (TC ULUI + 110d)

Fast current,Possibleupwelling

Tropical cyclones on NWS: hazard to oil and gas.TC Phil 31 Dec 1996, cat 3 but slow moving

More recently (15 March 2012)

TC Lua

20 March 2012 (TC Lua + 5d)

Chlor-a for same day(new on IMOS OceanCurrent):

100km.100km.30m=60t chl-a

Highest-ever sea level at Fremantle, 2pm WST:

3h period seiche (Molloy, 2001)

MSL

surge

tide

Leeuwin

Two weeks before storm:

Cold core eddy

Leeuwin

0.4m

ROAM sea level, 10-12 June 2012.

Sea level anomaly

N

E

Rottnest Is

Cockburn SoundLeeuwin

180km

CSIRO Bluelink Relocatable Ocean Atmosphere Model sea level, 10 June 2012

200m1000m

2pm WST 10 June 2012

Cockburn Sound.Highest sea level: 2pm WST 10 June 2012:

Photo Credit: Steve Brooks, PerthWeatherLivePhoto: Steve Brooks, Perth Weather Live

A few days later

Photo: Steve Brooks, Perth Weather Live

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Median energy flux of ocean currents

0 Median non-tidal current speed 0.8 (m/s)

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Median energy flux of ocean currents

0 Median non-tidal current speed 0.8 (m/s)

Cyclonic Eddy(Low sealevel)

Is it real? Yes, see drifter.

Is it extraordinary?Lets look at some history

Maximum (in 1994-2011) gridded altimetric (+ filtered tidegauge) sea level anomaly:

+1m

SLA

-1m

wide range:

0.3m

to

1.1m

99th percentile anomaly (exceeded 1% of time) - the max is 30% higher than this

+1m

SLA

-1m

0.2m

0.7m

1st percentile anomaly (exceeded 99% of time)

+1m

SLA

-1m

-0.7m

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Lowest sea level is 30% lower than 1st %-ile

-1m

Maximum anomaly map again.highest highs are south of the lowest lows

+1m

SLA

-1m

Lowest low was here

Highest highIs here

Median elevation (50th percentile)near zero – i.e. distribution is fairly symmetric

+1m

SSHA

-1m

Cyclonic Eddy(Low sealevel)

Is it real? Yes, see drifter.

Is it extraordinary?Lets use that history

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16 Jan 2011: Many extreme highs and lows

1.5m/s

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Back 4 days (to 12 Jan)

flood

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Back 4 days (to 8 Jan)

Pre flood:Sea level extreme

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Back 4 days (to 4 Jan)

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Back 4 days (to 31 Dec)

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Back 4 days (to 27 Dec)

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Back 4 days (to 23 Dec)

That high sea level all along the Qld-NSW coast was not a ‘storm surge’

• Coastal sea level was very high. Anomaly of nearshore current was zero. Odd situation – still needs investigation.

• Lets now go back to 16 Jan then step forward.

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vanishing

growing

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Discussion

• Marine science has tended to focus on the ‘normal’ behaviour of the ocean

• But observing systems are now adequate for us to also focus on the rare occasions when something extreme happens

• Some events have obvious societal impacts, e.g. beach erosion, coastal flooding, coral bleaching, fish kills, oil rig failures

• Many do not – but may – e.g. chlor-a blooms and deserts• Extreme events pose a challenge to observing system

design, quality control of data, and data interpretation• I think the effort is warranted

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Thank you