West Antarctic Warming Triggered by Warmer Sea Surface in Tropical Pacific

New University of Washington research shows that rising sea surface temperatures in the area of the Pacific Ocean along the equator and near the International Date Line drive atmospheric circulation that has caused some of the largest shifts in Antarctic climate in recent decades.

The warmer water generates rising air that creates a large wave structure in the atmosphere called a Rossby wave train, which brings warmer temperatures to West Antarctica during winter and spring.

Antarctica is somewhat isolated by the vast Southern Ocean, but the new results "show that it is still affected by climate changes elsewhere on the planet," said Eric Steig, a UW professor of Earth and space sciences and director of the UW Quaternary Research Center.

Steig is the corresponding author of a paper documenting the findings that is being published April 10 in the journal Nature Geoscience. The lead author is Qinghua Ding, a postdoctoral researcher in the UW Quaternary Research Center. Co-authors are David Battisti, a UW atmospheric sciences professor, and Marcel Küttel, a former UW postdoctoral researcher now working in Switzerland.

The scientists used surface and satellite temperature observations to show a strong statistical connection between warmer temperatures in Antarctica, largely brought by westerly winds associated with high pressure over the Amundsen Sea adjacent to West Antarctica, and sea surface temperatures in the central tropical Pacific Ocean.

They found a strong relationship between central Pacific sea-surface readings and Antarctic temperatures during winter months, June through August. Though not as pronounced, the effect also appeared in the spring months of September through November.

The observed circulation changes are in the form of a series of high- and low-pressure cells that follow an arcing path from the tropical Pacific to West Antarctica. That is characteristic of a textbook Rossby wave train pattern, Ding said, and the same pattern is consistently produced in climate models, at least during winter.

Using observed changes in tropical sea surface temperatures, the researchers found they could account for half to all of the observed winter temperature changes in West Antarctica, depending on which observations are used for comparison.
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2011 Floods in Brisbane, Australia: How Much Water?

Brisbane, the third-largest city in Australia and the capital of Queensland, has been seriously flooded, a natural disaster not seen here since 1974. As I write this post, thousands of volunteers are helping affected people and businesses to clean up and get back on their feet.

The media has been providing extensive coverage of the disaster and its aftermath for weeks now, providing opportunities for math teachers to investigate with their students some of the statistics being quoted. This article explores one statistic in particular, the amount of water released from the Wivenhoe Dam in one day. There are many similar opportunities for the math teacher who wishes to incorporate some "real math" with relevant, interesting connections with these current events.

Brisbane Flood, 1893

Over 100 years ago, in 1893, Brisbane suffered serious flooding of the inner city and low-lying suburbs, when the Brisbane River broke its banks in February 1893 after a tropical cyclone: The 1893 flood was just one of several floods around that time, there being other floods in 1887, 1890 and two others in 1893 a fortnight after the major flood.

Brisbane Flood, 1974

In January 1974, after weeks of heavy rain, Cyclone "Wanda" developed off the Queensland coast, which then turned into a rain depression and dumped huge amounts of water onto the city and the catchment of the Brisbane River. The result was flooding of many riverside and low-lying suburbs of the city, and over 6,700 houses being flooded.

Wivenhoe Dam

After the water had gone and city planners had a chance to analyze what caused the flood and how they might prevent a repeat of the devastating inundation of so many homes and businesses, it was decided to build a large dam upstream from Brisbane, as a flood mitigation measure. That dam is the Wivenhoe Dam: This dam, which is presently spilling huge quantities of water over the above spillway, is an impressive structure with some impressive statistics:

    * Height: 50 meters
    * Length: 2.3 kilometers
    * Capacity: 2,640,000,000 cubic meters
    * Surface Area: 109.4 square meters
    * Length of Shoreline: 462 kilometers
    * Catchment Area: 7.020 square kilometers
    * Average Annual Rainfall: 904 millimeters
    * Maximum Capacity: 225%

The 2011 Flood, Brisbane, Queensland, Australia

At the time of this article, Brisbane is slowly recovering from yet another serious flood, the peak of which was on 13 January 2011. Even though the peak of the flood was around 1 meter below the 1974 peak, this time 20,000 houses have been inundated, and the economic cost is much higher. In the media coverage of this natural disaster, Wivenhoe Dam has attracted an understandable amount of attention. Specifically, the management of the water kept behind the dam and the water released over the spillway is of great interest to the people of Brisbane. At the peak of water release, over 645,000 megaliters of water were released in one day. This is around half of the flood abatement part of the storage at Wivenhoe, which is 1,450,000 megaliters on top of the water stored for drinking and supply to Brisbane.

How Much Water is That?

Six hundred and forty-five thousand megaliters sounds like a lot - it is. But this quantity of water is very difficult to visualize. How can a teacher help students understand this quantity?

Step 1: How big is a liter?

One liter is a familiar quantity to students who buy milk in liters. It may be converted into 1,000 milliliters, or 1,000 cubic centimeters. This is the same volume of a place value thousands block, which is a 10 centimeter cube.

Ask students what would have the same volume as one liter - one liter of milk, obviously, a medium bottle of soft drink, less than one old-style house brick.......
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