Australasian Science: Australia's authority on science since 1938

Exclusive news for subscribers

By Stephen Luntz

Subscribe for complete access to all news articles, columns and features each month.

GPS Signal Bending Improves Weather Forecasts
A new way of measuring atmospheric conditions is proving particularly valuable in Australia, increasing the accuracy of weather forecasts and climate modelling.

The world has become accustomed to the use of satellites for weather forecasting, but the infrared measurements used over the past few decades only provide part of the picture needed for accurate predictions.

However, NASA and NOAA scientists in the United States found that a different part of the picture could be gained by examining how GPS signals bend as satellites rise or set relative to each other. “The refractive index of air is temperature-related,” says Prof John Le Marshall of RMIT. “So when the temperature changes, the signal bends like light going into water.”

Satellite positions are known with such accuracy that the extent of this bending can be calculated when the signal appears to suggest that one of the satellites is transmitting from a slightly incorrect location.

The GPS constellation of satellites, along with a handful of others, is large enough to supply sufficient data on atmospheric temperatures in different parts of the world, although Le Marshall says the addition of several to be launched soon will be useful.

Le Marshall was Inaugural Director of the Joint Centre for Satellite Data Assimilation in Washington, but recently returned home to Australia, where he has engaged RMIT and the Bureau of Meteorology in a project to analyse the data gained over and near Australia. “It’s particularly useful in the Southern Hemisphere, where ground and aerosonde data is so much more sparse,” Le Marshall says. Without satellites here we could only make accurate forecasts a day in advance, whereas this can be extended to 4 days by combining signal bending and information from space sensors.

“Other satellite instruments provide better vertical resolution, whereas this has better horizontal resolution, so they are quite complementary and every 6 hours we cross-calibrate,” Le Marshall says. “Since the research was completed and began being used in forecasts this year, we estimate the Bureau is now delivering forecasts of the same accuracy 10 hours earlier.”

Le Marshall adds that GPS bending also provides bias-free data over the oceans, increasing the accuracy of climate change measurements.

Sea Star Breeding Hotspots
The northern Pacific sea star is proving a devastating pest in Tasmanian estuaries. It appears that its affinity for port environments is an important part of the sea star’s success, but this offers hope for slowing the species’ advance.

Sea stars reproduce by releasing sperm and eggs into the water column rather than by direct copulation. “The sea star must release eggs in close proximity to sperm sources because chances of fertilisation decline drastically with increasing distance between spawning sea stars,” says Dr Scott Ling of the University of Tasmania’s Institute of Marine and Antarctic Studies.

Consequently, fertilisation is far more likely where sea star concentrations are high, and this is particularly the case around ports. Moreover, Ling found that northern Pacific sea stars congregating in these locations are unusually large and produce exceptional quantities of sperm and eggs. “Beneath wharves a super-abundant supply of food leads to a veritable orgy of highly aggregated and fecund sea stars that achieve great fertilisation success,” Ling says.

These wharf areas make up less than 0.1% of the Tasmanian estuarine territory, and hold less than 10% of the sea star population. Yet they are the source of 90% of larval invasive sea stars, which are then carried on currents to the rest of the estuary.

Strangely, most native species are not attracted to the rich food resources around the wharves, leaving the northern Pacific sea stars to flourish without competition. However, at one site Ling has recently seen increases in spider crab abundance, and he says that these crabs not only compete with sea stars for food but may eat the sea stars.

Ling says that attempts to control the sea star have appeared fruitless. “There were trials in the early 2000s where 30,000 were collected in one day, but the government said this was just a drop in the ocean.”

However, Ling ponders: “If we could knock down the numbers around the wharves just before the winter spawning season we might be able to reduce larvae enough to allow other species to compete, but it would be expensive to do each year.”

Alternatively he suggests making the wharves a less rich source of food, or creating an engineering solution to deter either sea stars or their prey.

Don’t Eat the (Bright) Red Ones
The colour schemes of ladybirds signal their toxicity to potential predators, with brighter colours associated with bad-tasting chemicals.

Dr John Endler of Deakin University’s Centre for Integrative Ecology used a well-established model of avian eyesight to take a bird’s-eye view of ladybirds. “We know birds have four classes of colour vision receptors: ultraviolet, blue, green and red, plus a double cone that detects luminosity,” Endler says. “We can model how bright an object will appear to birds, and other studies have confirmed this is predictive of their response.”

The finding was part of a study, led by Dr Jon Blount of the University of Exeter and published in Functional Ecology, demonstrating that the beetles that look bright to birds contain more toxins. These chemicals may be produced by the beetles or consumed in their food.

While every ladybird may aspire to look as unsavoury as possible, Endler says: “We found access to a good diet influenced this potency in colour and toxicity”.

It takes energy to produce bright red colours and the foul-tasting chemicals if these are not directly consumed in food. Consequently, only the better-fed ladybirds could afford to look the brightest, although Endler adds: “Some have the genetics to produce brighter colours with the same food source”.

The finding was also complicated by the fact that the colour intensity of females correlated with both major toxins, while in males one poison had a negative correlation with colour.

Among butterflies and moths it is common for tasty species to mimic the colouring of their less palatable relatives. Endler says it is puzzling that this Batesian mimicry does not appear to exist among ladybirds.

He points out that, beside the cost of producing the colours, the bright “don’t eat me” signals also make an individual highly conspicuous, so if the claim to bad taste is not convincing a mimic species can be particularly vulnerable. “This makes it quite hard to work out how the red signal first emerged.”

Endler says ladybirds’ famous spots exist to provide contrast, making the red stand out more brightly.

Pilots Need to Beware of Gravity Waves
Thunderstorms can produce turbulence more than 100 km away from the storm cell, prompting a call for a rewrite of aircraft turbulence guidelines.

Disruptions to the atmosphere by mountains, weather fronts or thunderstorms can produce what are called gravity waves. While very different to the gravitational waves produced by black holes and neutron stars, University of Melbourne climate researcher Dr Todd Lane explains that “these are buoyancy waves, and without gravity we would not have buoyancy. The atmosphere’s structure makes it stratified by temperature and you get waves similar to those on the ocean.”

While it has long been recognised that thunderstorms create turbulence around them, Lane says that when the safety guidelines used by commercial airlines were created it was not realised how far the gravity waves could spread. As with ocean waves, these atmospheric gravity waves can become too steep for the conditions and collapse into turbulence, dumping objects caught up in them.

“Previously it was thought turbulence outside of clouds was mostly caused by jet streams and changes in wind speed at differing altitudes, known as wind shear,” Lane says. However, over the past decade it has been recognised how important storms can be, even at great distances.

Commercial aircraft try to divert around thunderstorms, but Lane says such procedures would be more effective if we knew more about the turbulence involved. “We don’t know what sorts of thunderstorms produce the most turbulence,” he says. “We know that cloud anvils produce lots of turbulence, but we don’t know why.

“Now we can answer some crucial questions, but there are only a few groups working on this problem. We need more researchers to become engaged to improve the guidelines and passenger safety.”

Deep and Slow Tremors Beneath Alpine Fault
New Zealand’s Alpine Fault is experiencing small, slow earthquakes that last up to 30 minutes, research at Victoria University of Wellington has found. The discovery may eventually shed light on why one stretch of the Alpine Fault is not experiencing large earthquakes along with the rest.

“We’ve been aware since seismology started in New Zealand that one section of the Alpine Fault has few earthquakes,” says Prof Tim Stern. This is particularly puzzling since the relevant stretch, from Fox Glacier to Whatoroa Valley is, in Stern’s words, “where the fault is at its most dramatic”.

Stern led a team from the Geophysics Department to install an array of sensors along this stretch. To increase their sensitivity the seismometers were placed 5 km apart rather than the usual 50 km, and buried in boreholes 2–100 metres deep to protect them from the weather and surface activity.

The result, published in Geophysical Research Letters, was the detection of long-lasting tremors at depths of 20–45 km. Most quakes occur at depths of less than 10 km.

Stern says the tremors are only around 1 on the Richter scale, but they prove that “faults can move in ways other than the conventional picture, on a range from very fast to very slow”.

Similar slow earthquakes have been detected beneath the San Andreas Fault, as well as under fault lines that are very different from the Alpine Fault’s “strike-slip” nature. “It’s still an important question whether they occur in other places, but we need to look harder,” Stern says. It is thought these sorts of quakes are associated with fluids under high pressure.

“It’s not yet clear what this means for future earthquakes – it could be that constant tremor builds up stress and may trigger a major fault movement or, alternatively, the activity may decrease the likelihood of a major quake by acting as a release valve for stress,” says team member Dr Aaron Wech.

Universe’s Dark Age Exposed
We may know little about the universe’s Dark Ages, a period prior to 13 billion years ago, but now a little more is known as a result of a study of star clusters in surrounding galaxies.

The traditional way to explore the early life of the universe is to look outwards, observing objects so far away that we see them as they were soon after the universe formed. However, this is difficult for what is known as the Dark Ages, when large clouds of hydrogen gas absorbed light before it could travel far.

“During the Dark Ages, the hydrogen fog condensed in certain places, which allowed the formation of stars, black holes and the first galaxies,” says Swinburne University astrophysicist Dr Lee Spitler. Eventually the stars ionised the hydrogen, “much as the Sun burns off a morning fog on Earth,” allowing us to see them. However, what happened before this is harder to detect.

Spitler instead tried to map the way in which the hydrogen was ionised by looking at the age of nearby clusters and seeing which emerged from the fog first.

“We can see regions around galaxies where reionisation has just finished, and use that information to understand important questions about the dark ages: what were the first stars like; how were the first galaxies formed; and were there many supermassive black holes?” says Spitler’s colleague, Prof Duncan Forbes.

Denser areas had more stars to emit ionising radiation, but also more hydrogen to absorb what was produced. Spitler and Forbes reveal in the Monthly Notices of the Royal Astronomical Society the outcome of this arm wrestle.

It turns out that the hydrogen became ionised in isolated low-density regions a few hundred million years before the process took place in more crowded areas, despite the shortage of stars in thinner pockets to disperse the fog.

Spitler says the conclusion is based on the evolution of computer models fed with data from observations of the modern concentrations of clusters within galaxies. “We didn’t really expect information to carry through all that time, but we found that it did,” says Spitler. “It’s critical to understand the initial conditions if we want to make sense of the modern universe.”

Marsupials Running Cold
Small marsupials can evade predators while in a state of torpor, according to new research.

Many mammals drastically reduce their body temperatures to save energy, but this normally means they are unable to escape danger or take advantage of opportunities.

“Lack of movement has been used, in fact, to define the state of torpor,” says Ms Daniella Rojas of the University of New England. “Then a few years ago it was discovered that small marsupials move out of their burrows to bask in the sun while still in a state of torpor.”

The kalutas, dunnarts and planigales that Rojas is studying have resting body temperatures around 33°C when active but around 15°C while in torpor. Rojas and colleagues have revealed in Biology Letters how they induced torpor in these marsupials by putting them in a cold cabinet without food overnight and then filmed their movements on a running track.

At low body temperatures the marsupials were unable to move fast even when Rojas encouraged them, travelling at less than 0.5 m/s compared with 2–3 m/s when in an active state. However, Rojas says this may still be enough to escape predators. “They never move far from their burrows, just basking in or near crevices, so even at low speeds they may be able to escape.” She also notes that they were alert enough to notice her every time.

Planigales are mouse-like marsupials growing to just 7 cm long. They were the champion cool runners, still managing to move with body temperatures of only 14.8°C. Dunnarts needed slightly higher temperatures and kalutas did not run below 17.9°C.

All of the small dasyurids in the study are arid zone species, including one from the tropics, but Rojas says a combination of limited food supply and cooler temperatures makes energy conservation essential. Using solar energy to warm themselves up is a further efficiency, since crawling outside the burrow is less demanding than raising their body temperature through internal heat production.

Rojas says it is possible that the capacity to escape while in a state of torpor may exist in placental mammals as well. For example, introduced house mice and small native bats may also do this.

Hendra Hits Hungry Horses
Horses infected by the Hendra virus are often suffering from a shortage of feed, according to a collaboration by the University of Queensland and Bahrinna Thoroughbred Services.

“Hendra virus infections in 2011 coincided with the very low pasture growth season, which was also affected by extended periods of frost and rain, and so horses were likely to have been hungry at the time of infection,” says Prof Bryden of UQ’s School of Agriculture and Food Sciences.

Bryden used models of the growth pattern for unimproved subtropical pastures and the rain and frost data from the Bureau of Meteorology to create a map of pasture quality through 2011, and overlaid this with incidences of Hendra infection.

Bryden says that Hendra research so far has concentrated on the virus and the bats that carry it. However, he notes that the virus does not transmit directly to humans – it can only be a problem if it first infects horses. Yet the conditions under which horses become infected have been largely ignored.

Bryden proposes two theories for why the virus is transmitted during seasons with poor pasture growth. “A hungry horse is more likely to consume bat-related material found on pastures,” he reasons, “and because a horse’s nutrient intake is significantly reduced due to poor pasture quality and availability, its immune system is possibly also compromised, thereby setting the scene for an infection”.

It is possible that the conditions that limit pasture growth also induce a change in bat behaviour, but Bryden says the bats are so transient and range over such large distances that this seems a less likely explanation.

Bryden adds that the virus has such low infectivity, and degrades so quickly outside a host, that “the real question no one has got hold of is how the horses pick up the virus. We don’t know if it is from bat urine or by eating fruit partly chewed by bats.”

Fears of the virus have stoked calls for bat culls, but Bryden says: “If we know the peculiarities of how infection takes place we could think about strategies to minimise exposure. You have to be extremely unlucky to be infected, so there must be ways and means to reduce this risk even further.”

Bright Future for Solar
A CSIRO report has suggested that solar power can provide a larger proportion of Australia’s electricity than previously suspected without needing storage for cloudy days.

As the prices of wind and solar have become competitive with fossil fuels, debate has turned to the problem of intermittency. Electricity grids are designed to cope with a certain amount of fluctuation, both from varying demand and when power plants experience shut-downs. However, the intermittent nature of solar and wind produces far more frequent variations than plants being taken offline for maintenance. Debate, much of it largely unsupported by evidence, rages over how much grids can depend on renewable energy before they need to include storage, whether it be in batteries, molten salts or hydroelectric dams.

Lead author Dr Saad Sayeef says that different grids have very different levels of flexibility, so estimates based on international studies are misguided. “In a rural network with a long skinny structure, grid impedance is quite high. A small injection of power can raise the voltage and affect power quality,” Sayeef says.

On the other hand, a system with multiple sources of power can be quite robust – a passing cloud might reduce solar output at one site by 60% in a matter of seconds, but dispersed generators will not all be plunged into darkness at once.

Solar and wind penetration into Australia’s eastern grid is small enough that there is plenty of room to expand, although Sayeef says that some small networks in isolated areas may be reaching their solar capacity. The figure of 20% of energy production from intermittent sources is often bandied around as a ceiling, but Sayeef says: “There is not a lot of evidence to back this figure up”.

The report, Solar Intermittency: Australia’s Clean Energy Challenge, stresses that intermittency can be managed. In particular, solar forecasting is crucial so that grid managers have time to bring back-ups online or send signals to users who can adjust the timing of their demand to minimise prices.

“Fast-acting storage, ancillary services such as hydro power and peaking gas, and curtailing of demand will all be important,” Sayeef says. “We need to plan for intermittency at different time scales.”

The research was funded by the Australian Solar Institute, and conducted in conjunction with the Australian Energy Market Operator and the Energy Networks Association.

Climate Models Need to Catch the Waves
Incorporating the effect of waves from tropical storms could make climate models more accurate, argues Dr Alessandro Toffoli of the Swinburne Centre for Ocean Engineering, Science and Technology. The mixing effects produced by these waves are currently ignored.

“Climate models are dominated by the exchange of energy between the atmosphere and ocean,” Toffoli says. “Wind blows on the surface transferring energy, and the cooling or heating has an effect on the atmosphere. This is related to the mixing of the ocean’s surface. Warm water normally lies on top, but can be shifted into a deeper layer if something is mixing the water.”

Since the top 3 metres of the ocean have the same heat capacity as the entire atmosphere, the effects are enormous.

Turbulence generated by ocean currents is a major source of mixing, and has been modelled in detail. However, Toffoli says that mixing caused by the motion of storm waves has not been taken into account.

“Large waves that occur in tropical storms and cyclones can contribute in mixing a wider layer of the upper ocean with the cooler deeper parts, exchanging heat and carbon dioxide with the atmosphere, which affects weather and climate.”

Data from the Rankin A gas platform on the North-West Shelf during 2006 reveals that wave heights greater than 3 metres and produced by winds stronger than 10 m/s generated considerable mixing. The well-mixed surface layer during tropical storms was twice as deep as other times at the same location.

Toffoli says that inclusion of the effect of large waves will not alter climate models in many parts of the world. “The mixed layer is normally only 20–40 metres deep at Rankin A. If you were to look at places where the mixed layer is already 100 metres deep, waves would not make a difference,” he says.

However, much of the Southern Ocean has a shallow mixed layer, making the effects of large storms potentially significant. “We should concentrate research where the mixed layer is normally shallow,” Toffoli says.

Besides mixing heat, waves can drive oxygen and carbon dioxide to greater depths, potentially affecting plankton and other marine life. The storage of heat in the upper layers of the ocean can also be important for more short-term weather forecasting.

Aussie Technology Reaches Depths
When filmmaker James Cameron reached the deepest point in the ocean, the event attracted worldwide publicity yet few realised that his capacity to send back images of the event depended on Australian technology.

Cameron, conducting a joint scientific expedition with National Geographic and Rolex, was at the bottom of the Mariana Trench, which is deeper than the height flown by commercial airlines. “Neither visible light nor radio waves penetrate water well,” says Paul Roberts of L-3 Communications, making it difficult to transmit messages between the surface and the submarine.

The first voyage to these depths was in 1960, but the research potential of that expedition was limited by the inability to communicate with the surface. Cameron was able to study the life forms existing more than 10 km down in greater detail.

The solution was provided by the Australian arm of L-3, using technology originally developed as an independent company. Long before humans were considering the problem, whales had demonstrated the capacity of sound to travel enormous distances under the ocean. L-3 have taken this up and combined it with spread spectrum technology, which Roberts calls an acoustic version of CDMA.

L-3 use frequencies higher than whales’ and dolphins’ sonar, and Robinson says they have added “some tweaks I can’t talk about” since Collins Class submarines are part of their more usual customer base.

Despite the enormous depth to which Cameron’s craft sunk, the obstacles to communication were actually smaller than for naval submarines, since his location was known and relatively constant.

Cameron transmitted messages from a sphere located above the main portion of the submarine. While everything in the craft needed to be designed to survive pressures of 17,000 PSI, Robinson notes: “In terms of acoustics there is not much difference between transmitting 11 km vertically and 11 km horizontally. In fact, the pressure actually makes sound travel a little better.”

On the other hand, it is not possible for roaming submarines to transmit substantial messages thousands of kilometres back to base while at depth, so aircraft need to drop buoys above them for communication to occur.

Nevertheless, L-3’s Australian work has been recognised by the US Department of Defense as the winner of a foreign provider trial, offering potential to supply to a far more lucrative market than film-makers on exploratory scientific missions.