Archive for the ‘Rapid Article’ Category

The 2011 World Solar Challenge has been run and won

October 20, 2011

They started under clear skies and blazing heat and finished in steady rain, but the winner of the 2011 World Solar Challenge has been decided. After 4 days of travelling, Tokai University (Japan) crossed the finishing line north of Adelaide today in the lead.

Tokai University's car crossing the line surrounded by team members

In the closest finish in the history of the WSC, mere minutes separated Tokai and second placed Nuon Solar Team from the Netherlands. Third placegetters University of Michigan (USA) were themselves only a short distance behind. The close finish is remarkable given the distance travelled and time spent on the road. Ashiya University, of Japan, and Team Twente, also of the Netherlands, are further behind vying for fourth place and expected to finish Friday, as is Team Aurora of Australia, not far behind Ashiya and Twente.

The World Solar Challenge is an epic 3000km solar car challenge, running down the length of Australia from Darwin to Adelaide. With unlimited regulations it is likely all the cars would be able to exceed the road speed limit and run for extended periods of time. Instead, the regulations deliberately limit battery sizes and solar collection area to prevent the ability for the cars to run at maximum speed for hours on end and hence to help promote the development of more efficient solar collector units and motors.

The main differentiator between the cars is the ability of the solar cells to collect energy from the sun and convert it into electricity. With limited battery sizes, the energy which can be held on board the car isn’t enough to allow unrestricted running. Instead, the speed of the car is dictated by the combination of the amount of energy being collected from the solar panels, and the efficiency of the motor using that energy. The faster a car runs, the more energy it uses and hence the more energy it needs to collect to replace that used. Quite simply, if a car’s solar panels aren’t efficient in collecting energy to replace that being used, the car will run out of electricity. So a balance needs to be found between energy collection and expenditure, with cars more efficient at collecting and using energy able to run at higher speeds.

Further adding to the challenge, running of the cars is restricted to certain hours of the day, with cars required to hold at positions overnight. To ensure that the cars do maintain these hold positions, and stay within the legal speed limits, a sophisticated tracking system is employed to monitor the progress of each team. This ‘Mission Control’ was this year based in the Science Exchange in Adelaide.

This year’s race was never going to break any records with the challenge suspended for several hours due to bushfires close to the race route. There was also another dramatic development on day 4 when a car from Team Philippines, having been parked for repairs to its battery system, suffered an explosion in its battery packs. Thankfully, no one was injured.

Another challenge faced by the teams competing in the World Solar Challenge are the outsized road trains which Australian highways are famous for. These extremely long and wide trucks normally require traffic coming the other way to pull off the highway to allow the truck to pass. However, according to Bruno Moorthamers from Nuon in an interview with The Register, a solar car’s steering doesn’t allow this manoeuvre. Instead, Bruno said he has to drive “a little under” the overhanging loads of the trucks.

Despite crossing the official finishing line Thursday afternoon, a late developing fault meant that Nuon would not enter Adelaide city until the following day, meaning that celebrations in the Victoria Square ceremonial finishing line were reserved for Tokai. Dutch supporter groups hoping to cheer home Nuon and Twente were left instead to congratulate the victorious team and wait for their teams to arrive on the Friday. Tokai certainly celebrated in the rain, and definitely showed their excitement at having won such a hard-fought challenge.

Tokai team members celebrating at the finish

Celebrating with sake

Zoz Brooks from the Discovery Channel meets the driver who brought the Tokai car across the line.

The winning Tokai University team

The team celebrates by jumping into the Victoria Square fountain.

The Tokai team congratulate each other

Team Twente supporters at the finishing line

Supporters of Nuon Solar Team at the finishing line

Tokai celebrate in the Victoria Square fountain

Breaking News: Cyclones

February 1, 2011

Given the approach of Tropical Cyclone Yasi towards the Queensland coast, I have delayed publishing Part 2 of the UV and skin series in order to present this rapid article on cyclones.

Information specific to TC Yasi is accurate at time of publishing but should not be used to plan evacuation from affected areas.

Cyclones mainly form along a belt near the equator where the temperature of the water is warmer. The minimum water temperature needed for a cyclone to form is 26.5 degrees Celsius, however already formed cyclones can travel over areas of cooler water temperatures, but will lose intensity.

Map of cyclone areas worldwide. Orange areas are regions where conditions are suitable for cyclone formation. Image courtesy of NASA

The warm moist air above this warm water rises, resulting in a local low air-pressure area near the ocean surface. Surrounding air is literally sucked into this low-pressure area, which then too become warm and moist and rises. As this process repeats, fed by the warmth from the ocean and water evaporation, the air begins to swirl around the low-pressure area (the same effect as water swirling as it drains into a plug hole), and as the warm moist air cools away from the ocean surface it forms clouds. The combination of the swirling winds caused by the low-pressure area and cloud formation forms the characteristic spinning cloud.

Cyclone formation. Air swirls the area of low-pressure before rising upwards from the ocean surface. Image courtesy of Geoscience Australia

The swirling of air around a low-pressure area is caused by the Coriolis Effect, a result of the earth’s rotation. The direction of the Coriolis Effect depends on the hemisphere, in the southern hemisphere a cyclone will always spin clockwise.

The category of tropical cyclone is determined by wind strength. In Australia the minimum category of a tropical cyclone is reached when sustained wind speeds exceed 63km/h.

Australian Region – Tropical Cyclone Intensity Scale
Category Sustained winds Gusts Expected damage
Tropical Low <34 kts
<63 km/h
<49 kts
<91 km/h
 

 

One 34-47 kts
63-88 km/h
49-67 kts
91-125 km/h
Negligible house damage. Damage to some crops, trees and caravans. Craft may drag moorings 

 

Two 48-63 kts
89-117 km/h
68-89 kts
125-164 km/h
Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small craft may break moorings. A Category 2 cyclone’s strongest winds are DESTRUCTIVE winds
Three 64-85 kts
118-159 km/h
90-121 kts
165-224 km/h
Some roof and structural damage. Some caravans destroyed. Power failures likely. A Category 3 cyclone’s strongest winds are VERY DESTRUCTIVE winds 

 

Four 86-107 kts
160-200 km/h
122-151 kts
225-279 km/h
Significant roofing loss and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures. A Category 4 cyclone’s strongest winds are VERY DESTRUCTIVE winds
Five >107 kts
>200km/h
>151 kts
>279 km/h
Extremely dangerous with widespread destruction. A Category 5 cyclone’s strongest winds are VERY DESTRUCTIVE winds 

 

Table adapted from BoM


Cyclone Intensity

There are two main factors which affect cyclone intensity – the warmth of the water and wind conditions. Warm water is required for cyclone formation, and cooler waters will degrade the intensity. In the case of Yasi it is encountering warm north Queensland waters caused by the La Nina climate.

High winds surrounding the cyclone can also reduce the cyclone’s intensity. The cyclone requires the swirling winds caused by the Coriolis Effect, high incidental winds can disrupt this swirling pattern, literally tearing the cyclone apart. Yasi is encountering only mild winds which have very little affect on the cyclone formation.

The shape of Yasi is also described as being very efficient, with good ventilation at both the top and bottom, allowing a very efficient formation of the low-pressure system which cyclones form around, and high wind velocities.

Storm Surge

As the air surrounding the low-pressure area swirls it pushes water towards the centre of the storm, literally forming a mound of water. This mound is the “storm surge”, which when reaching landfall effectively acts like a tsunami and causes significant flooding of the coastal areas. A storm surge will be greater in areas where the ocean floor slopes gradually towards the coastline, such as the areas around north Queensland.

Storm surge. The top imageis normal conditions. The lower image is the rise in sea levels caused by a storm surge at high-tide. Image courtesy of BoM

Storm surges typically measure around 60-80 kilometres across, meaning areas more than 30 km from the crossing point of the cyclone can become flooded. A category 4 cyclone will produce a storm surge approximately 4-6 metres higher than normal tidal levels.

The actual height of the storm surge depends on the tides. If the storm surge hits the coast during low tide, destruction will be minimal. However if it hits during high tide, the effective height and reach of the surge will be greater.

Cyclones and climate effects

Cyclones are more common in Australia during La Nina climate periods than during El Nino periods. La Nina is characterised by a large scale cooling of water temperatures across the Pacific, except near the north Australian coasts where there is a gathering of warm ocean waters. This area of warm water and changes in wind patterns during La Nina periods together contribute to the increased numbers of cyclones during these periods.

The La Nina period being experienced by Australia at the moment is one of the strongest on record and was also a cause of the Queensland floods.

Cyclone paths

Not all cyclones are unpredictable; their path is determined by the environment around it. Yasi is situated in a well characterised belt of easterly winds which are carrying it towards the Queensland coast. While it can be said with some certainty Yasi will strike the Queensland coast because of these winds, there is still some variability in exactly where on the coast it will hit. Latest BoM predictions are that it will reach landfall at Cairns.

The spread of Yasi has been estimated by the Bureau of Meteorology to be around 800km, stretching along the coast from Cooktown to Sarina.

Predicted path of Tropical Cyclone Yasi. Orange areas are regions of high impact. Image courtesy of BoM

Inland reach

Cyclones require warm water to maintain intensity, so once the cyclone makes landfall it will begin to lose intensity. However given its size and high intensity, Yasi may take a long time to degrade. This means it may reach as far inland as Mt Isa, however it will have likely degraded into a tropical storm by this time and not a categorised cyclone.

Floods

The wetness of the catchment areas affects the amount of runoff from rains and storm surges. Simply, the wetter the ground, the less water that can soak in, increasing runoff and the potential for flooding. Townsville and Cairns have had slightly above normal rains this season, but it is hard to tell if it will cause abnormal flooding.

Yasi no longer appears to be headed for areas affected by the January Queensland floods, so it is less likely serious weather events will affect those areas.

Cyclones and Climate Change

At the moment the BoM and World Meteorological Organisation cannot draw certain conclusions about the effect of climate change on cyclones. There is no clear evidence of long-term trends in the numbers of cyclones, and limitations in knowledge and technical limitations limit the ability to predict changes in cyclone frequency. However, they expect little or no change in global frequency of cyclones, nor significant changes in the regions affected by cyclones.

Increases in the economic damage and disruption by tropical cyclones have been caused mainly by increased population centres in coastal areas.

However, rising sea levels may increase the effects of storm surges. This is particularly of concern as historically the primary cause of death during cyclones has been due to flooding.

Satellite Images of Yasi:

NASA Earth Observatory

http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=49043

University of Wisconsin Cooperative Institute for Meteorological Satellite Studies

http://cimss.ssec.wisc.edu/tropic2/real-time/imagemain.php?&basin=austeast&prod=wvbbm&sat=gms

(links at the top change image type)

 

Thanks to Jim Davidson, Regional Director Queensland at the Bureau of Meteorology and Andrew Western from the University of Melbourne for providing their expertise.


References and further information

Geosciences Australia, http://www.ga.gov.au/hazards/cyclone.html

Magdalena Roze, Weather Channel, http://magdalena-roze.blogspot.com/

Dick Whitaker, Weather Channel, http://passingparade-2009.blogspot.com/

Bureau of Meteorology, http://www.bom.gov.au/cyclone/about/

Statement on tropical cyclones and climate change, Bureau of Meteorology, http://www.bom.gov.au/info/CAS-statement.pdf