3rd Jan – Floating in currents


SST Anomalies for Australia – RAMSSA


SST Anomalies for VIC/TAS – RAMSSA

The Tasman Sea and Bass Strait have warmed rapidly against the climatological monthly average (1961-1990). The pattern has spooky similarities to the Tasman Sea marine heatwave of November 2017- January 2018 that was described in a Special Climate Statement. However, it is not quite as extreme as that … yet.

Percentile maps show that northeastern Bass Strait temperatures are above the 95th percentile but not above the 99th percentile. Only a small area on the east coast of New Zealand is above that threshold.

95th percentile exceedance for 3rd Jan 2019 – OceanMAPS
99th percentile exceedance for 3rd Jan 2019 – OceanMAPS

Compare this to the same time last year.

Much of the Tasman Sea was above the 95th percentile, with a broad area also above the 99th percentile. Extreme temperatures were more widespread.

95th percentile exceedance for 7th Jan 2018 – OceanMAPS
99th percentile exceedance for 7th Jan 2018 – OceanMAPS

It didn’t stop there – the marine heatwave of last year continued to warm surface temperatures further into February before the heat mixed down into lower levels by March.

Perhaps we won’t see the record broken again this year, but we still could see anomalously high temperatures continue and increase. Especially if extended periods of light winds and high insolation occur in the next two months.

These past two years are not isolated cases. The recent State of the Climate 2018 report by BOM shows that the ocean surface around Australia has warmed in recent decades. A particular hot spot is in the southeast.

Trends in sea surface temperatures in the Australian region from 1950 to 2017 (Source: BOM)

The summer positive SST anomalies in the southeast may be a recurring pattern. It is even more likely when a SST product uses an old climatological baseline, such as 1961-1990.

TC Penny

Tropical Cyclone Penny is a copycat of TC Owen: with a yo-yo track and ‘Never Say Die’ attitude.

TC Penny formed from a low pressure system embedded in the monsoon trough. The low crossed the York Peninsula from east to west and then intensified into a tropical cyclone in the Gulf of Carpentaria where the SSTs are 30 to 31 deg C. TC Penny changed direction shortly after New Years Eve and travelled eastward to hit the Gulf coast near Weipa as a Category 1 system and dump 110 mm of rain.

The system decayed while travelling over the Peninsula and was downgraded to a Tropical Low. But 24 hours later ex-TC Penny had re-intensified over the 30 deg C water of the Coral Sea and was upgraded again. TC Penny is expected to intensify further to a Category 2 system by the 4th of January. It is predicted to track back towards QLD tomorrow but coastal impacts are still uncertain.

Tropical Cyclone Penny’s track – BOM

The OceanMAPS model is representing the ocean-atmosphere interaction with TC Penny, and showing the following impacts:

  • SSTs are cooler in the wake of the TC
  • Momentum flux into the ocean is large
  • Latent heat flux out of the ocean is large
SST 6-hour average for 2nd Jan 2019 at 1800 UTC, arrow showing cooler SSTs along TC Penny’s track – OceanMAPS
Latent Heat Flux 6-hour average for 2nd Jan 2019 at 1800 UTC – OceanMAPS
Momentum Flux 6-hour average for 3rd Jan 2019 at 1800 UTC – OceanMAPS

Ocean Currents


Last month the ARGO program celebrated the milestone of two million ocean measurements.  ARGO floats use ocean currents to move around.

Approximately every 10 days, an Argo float dives about 2,000 meters (1.2 miles) deep, drifts with the ocean currents, and then surfaces to transmit data in real-time via satellite. Argo floats cycle through these dives, or “profiles” for five years or longer on battery power. – Scripps Institution of Oceanography

How Argo Floats work (Source: Argo)

floating objects

Two other floating objects have made the news recently. This includes a yacht called Wild Eyes that was dismasted and abandoned eight years ago by the then 16-year-old sailor Abby Sunderland. She was attempting to set the record for the youngest person to sail around the world, but her boat was badly damaged in a storm halfway across the Indian Ocean. Abby was rescued on 21st June 2010 by a French commercial shipping vessel.

This week Wild Eyes has been found floating upside down to the west of Kangaroo Island, South Australia.

The yacht Wild Eyes, found near Kangaroo Island (Source: ABC)

The Antarctic Circumpolar Current would have played a major part in delivering her overturned yacht from the Indian Ocean to Kangaroo Island.

Abby’s rescue position in June 2010 was at 40°48′S 74°58′E, approximately 2033 nm west-southwest of Perth. Kangaroo Island is at 35°55′S 136°15′E.

Rhumb line from rescue point to Kangaroo Island – Google Earth
  • Floating distance along the great circle route: 2856 nm.
  • Floating time: 8.5 years = 3102 days = 74460 hours.
  • Speed: 0.04 knots.

This seems slow. Typical speeds of the ACC are 0.2 m/s or 0.4 knots. The boat may also have been helped by the Leeuwin Current extension along the Great Australian Bight. It should have arrived earlier!

But the calculations do assume that the boat travelled in a straight (rhumb) line. Who knows what journey it has actually taken along the way…

In another recent story, a Frenchman will be hoping he gets currents that move a lot faster than the ACC. Jean-Jacques Savin is attempting to cross the North Atlantic Ocean in a barrel. He set off from the Canary Islands on the 28th of December and intends to reach the Caribbean by March.

Frenchman sets out to sea in a barrel (Source: ABC)

Along the way, Mr Savin will drop markers to help oceanographers from the JCOMMOPS international marine observatory study currents in the Atlantic. (Ed: you would think that the barrel itself is a big marker).

Jean-Jacques believes that ocean currents will carry him 4500 km across the Atlantic in less than 3 months. That would be an average speed of 0.5 m/s or 1.1 knots.

Following the Canary Current and then the North Equatorial Current – Google Earth

This seems fast. To be carried by currents alone, Jean-Jacques will have to first catch the Canary Current down the West African coast from 32 N to 20 N. This current has typical speeds of 0.1 m/s but can be up to 0.7 m/s through the Canary Islands. He would then turn west and catch the North Equatorial Current from 20 W to 65 W. This current has typical speeds of 0.1 m/s.

He will be travelling a similar distance to Wild Eyes in similar strength currents but let’s hope it doesn’t take 8.5 years.

One thing that differentiates the barrel from the capsized boat Wild Eyes is that it floats high in the water and will have significant windage. It will probably be the effective ‘sail’ of the huge barrel that will push him across the ocean, rather than the currents.

Do you think Jean-Jacques will make it to the Caribbean before his foie-gras runs out?



3 thoughts on “3rd Jan – Floating in currents”

  1. Great Stuff Jess! Am enjoy reading it.

    Two comments
    – Can we see the warm SST anomaly in the southeast for the past decade from Reynolds’ SST products. I hope NOAA use different SST climatology for their SST anomaly products. If that is the case, we should get the climatology updated soon in our analysis systems
    – For this TC event, would that be interesting to see SST and surface fluxes from ACCESS-S system comparing those with OceanMAPS. It woudl be interesting to see the importance of coupling feedback betweem the atmosphere and ocean for the TC event

  2. Hi Jessica,

    Enjoyable read.
    The pattern of anomalies from last year to this year is different. However the pattern is very similar. I expect this is in part a reflection of the pattern in the reference percentile map. Probably worth looking at.

    Another crazy frenchman…
    not alot of keel? https://www.france24.com/en/20181226-frenchman-sets-sail-across-atlantic-barrel

    How much shorter did it take to get from 1 to 2 million than from 0 to 1 million?

    A comparison of the bulk formulae heat fluxes and the operational system would be worth looking at. The comparison between ACCESS-S and ACCESS-G may be more challenging with the change in resolution.
    APS2 and APS3 ACCESS-G might also be interesting to compare.

  3. It took 13 years (from 1999 to 2012) to reach the 1 million ocean measurements mark.

    Then only 6 years to observe the second million measurements.

    – in answer to Gary’s question.

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