17 May – Downwelling everywhere *

* Almost everywhere.


Temperatures are cooling down on the North West Shelf, now only 28 to 29 C. The stronger E’ly trade winds are encouraging mixing of the heat downwards. It is still holding a lot of warmth at 50 m depth.

SSTA North West Shelf

Cool water has developed along the coast. The surface water is cooling in the shallow depths. It related to the large tides in the region: when the tide comes ashore it cools due to longwave radiation, then is drawn back out to sea and mixed. This draws down the summer SSTs in the coastal regions, cooling the surface temperatures, while offshore water remains more stratified.

Similar effects are being seen in the Northern Territory and Gulf of Carpentaria.

SSTA Northern Territory

This is a seasonal feature of the winter months (slightly early here, which is why it is being picked up in the anomalies). Typically, the features will remain in the shallow water and form a temperature front with sharp discontinuity to the water offshore waters.

Sea level anomaly

There is downwelling everywhere!

The persistent high pressure around the country is keeping the winds going round and round in an anti-clockwise fasion. Ekman transport means that wind forcing pushes the water to the left in the Southern Hemisphere. So when wind blows parallel to the coast, the water is pushed onshore and the sea level rises.

Blocking high pressure dominants the country

If we look at an animation of SLA we can see this. (Ignore the active region off NSW where the anomalies are due to warm and cold core eddies, a completely different phenomenon). The red, positive SLAs in QLD and WA are due to downwelling. It is extensive and persistent over the next week as the blocking atmospheric high pressure continues.

A negative SLA can be seen in the Gulf is due to the E’lies pushing the water out of the shallow basin.

Sea level anomaly around Australia- Click for animation

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