Ep 115 (Enhanced): Dust storms in Sydney

The dust is finally starting to clear from Sydney, leaving a ruddy orange layer of muck all over the city. This podcast goes with our previous article Red Sydney, and as well as being a description of the science involved, is a video slide show of photos of the dust-storm. All the photos in this enhanced podcast come from flickr and are available to use under Creative Commons licences.

Watch the following youtube video, or download the wmv or mp4 versions - mp4 will play on your ipod, wmv is slightly higher quality:



The photos come from the following flickr users (click to see the original photo):

• tolomea (here, here and here);
• _gemma_;
• spudmurphy (here and here);
• psychopyko (here and here);
• blentley (here and here);
• halans;
• colinwynterseton; 
• jamckay (here and here);
• q15928;
• jujuly;
• muffytyrone;
• sillypucci;
• planetchopstick;
• halans;
• kaptainkobold;
• t_lawrie;
• iansand (here and here);
• mezuni;
• avlxyz;
• chanc;
• 33868550@N07;
• photosydney;
• emmettanderson (here and here);
• sketchesbymez.

And after you've checked out the above podcast and photo links, have a look at this - this is a video of a couple driving into a dust storm in Broken Hill, NSW. Amazing!

Red Sydney

Waking this morning was a very eerie experience. Blood-red light peaked through the sides of my blinds, and given I was half asleep at the time, I thought the four horsemen of the apocalypse had come to Earth.

When I shook the haziness from my head and peaked outside, the view was astonishing. Not surprisingly, Twitter had loads of comments and on-the-fly photos, and the TV and radio news broadcasts were full of dust-storm stories.

Dust storms are not uncommon in Australia - indeed, central and eastern Australia are a major global source of atmospheric dust, and this particular storm, estimated to be 600 km long and dumping 75000 tonnes of dust into the Tasman Sea every hour, could be headed to the New Zealand ski-slopes (that'll teach you to beat us at rugby). Dust can travel a very long way in the atmosphere, with dust from Chinese storms found in the French Alps.

The storm has its origins in the Indian and Southern Oceans, where low pressure storms create severe cold fronts. Low pressure air sinks to the ground, forcing hotter, higher pressure air upwards. This can cause thunderstorms, and on Monday, winds of more than 100 km per hour formed in South Australia. As inland Australia is in drought, the winds picked up dust not fixed to the ground by vegetation. The dust likely came from the Lake Ayre Basin, according to ABC Science Online, and has caused the worst pollution ever seen in NSW.

The reddish colour of the sky is an interesting phenomenon. Normally during the day, the sky is blue. This is because of Rayleigh scattering. Shorter wavelength light from the Sun (blue) is scattered by the air in all directions to a greater degree than longer wavelength light (red). The amount of scattering is related to the fourth power of the wavelength - blue light with a wavelength of ~400 nm is scattered about 10 times more efficiently than red light (~ 700 nm). The scattering in this case is mainly due to oxygen and nitrogen molecules smaller than the wavelength of the light.

Due to the scattering of blue, when you look directly at the Sun, you see more of the longer wavelength light, which is why it appears yellow. The rest of the sky is lit by the diffuse scattered blue light. At dawn and dusk, the Sun's light has to travel through more of the atmosphere to get to your eyes as it comes in at a tangent to the Earth (go on, draw it...). This means even more blue is scattered and a larger piece of the sky looks a even deeper red.

Dust particles are quite large compared with oxygen and nitrogen, and so do not scatter light in the same way. Some dust absorbs light more effectively at blue wavelengths than at red wavelengths, meaning that light shone through it will appear more red. Dust also scatters sunlight, but as the particles are large, this scattering is independent of wavelength. This means that the dust particles act something like tiny mirrors, diffusing the light throughout the sky. This is why the red colour was so intense at dawn - as the light that hit the dust was already red due to Rayleigh scattering, it was then scattered throughout the whole sky. Normally at sunrise, the red colour is confined to only a small part of the sky. The presence of dust (and pollution for that matter) can cause beautiful effects. As the sun climbed higher in the sky today, the red colour softened. Eventually the sky just looked a dirty orange - the colour of the iron-rich dirt.

Here are some of my favourite pics from today - the above zombie was found through @ozdj. I received the following Godzilla pic in an email and found it on flickr, but I don't know who the originator is. It is brilliant. None of these images have been manipulated - yes, it was back to the 60s with sepia Sydney today!

From MarchingAnts on flickr:

From TomHide on flickr:

Also see the Red Dust Collection and The Red Sydney Project. More dust storms are predicted for this week, so stay tuned.

Science survival guide for The Ashes

Ashes backyard cricket
Originally uploaded by westius.

The sporting highlight of 2009 is only hours away. The Ashes cricket series between Australia and England will mean little sleep for cricket-obsessed Aussies, and little work done by the English.

Here is our science survival guide to the Ashes:

• Ashes success and El Nino

Is the winner of The Ashes already pre-determined? Manoj Joshi has shown that the El Nino Southern Oscillation (ENSO) phenomenon has a significant effect on the results of The Ashes cricket series when the series is held in Australia. The Australian Cricket team is more likely to succeed after El Nino years, while the English cricket team does better following La Nina years (the opposite phase). Their study, Could El Niño Southern Oscillation affect the results of the Ashes series in Australia? was published in the journal Weather.


• How to rank cricketers
  
Cricket is one of the world's most statistical sports, and mathematicians in cricket-loving nations love nothing more than delving into the minutiae of the numbers and diving into averages, strike-rates and custom-made measures of batting and bowling effectiveness.

For many people, including me, cricket isn't just a sport, it is a way of life.

These words could easily have come from me, but are actually the words of Rob Eastaway, a cricket-loving mathematician from the UK, and originator of the official International Cricket Council cricket-ratings which rank not only teams, but players within each team. In this podcast, I chat to Rob about how you mathematically rank cricketers.


• Science, Psychology and Cricket

Every cricket season, the TV coverage of cricket becomes more spectacular and technological, with the introduction of microphones to detect the finest of edges through to the keeper, improved abilities to determine the trajectory of a ball once it has left the bowler’s hand, and now even heat sensors to see how the batsman sweats.

But the scientific aspects of cricket are not limited to TV companies, with science playing an increasing role in shaping the performance of players, from their general fitness to specific training techniques for both their physical, and possibly more importantly mental, well-being. It is with science that countries are aiming to find the competitive edge.


• The curse of the duck

The recent news of the great Indian batsman Sachin Tendulkar surpassing West Indian Brian Lara's record number of test runs has given maths-loving cricket geeks another opportunity to pull out their calculators and Excel spreadsheets. At the time of writing, Tendulkar had scored 12,027 runs across 247 innings, to overtake Lara's 11,953 from 232 innings. After a little investigation, I found that despite his outstanding average of over 54 runs per innings, Tendulkar's most common score in test cricket is ... zero! Even the great Don Bradman scored a duck more times than any other score. And their next most common? One! We look at how are cricket scores are distributed.

• Science, Cricket, Fitness and Psychology

Do you need to be fit to play cricket? Do the best batsmen in the world really have the ability to predict the type of ball they will receive before it even arrives? And is cricket really more of a mental game than a physical one?

In this podcast episode, we talk to Dr Rob Duffield from the School of Human Movement at Charles Sturt University who has found that indeed you really do not need to be as physically fit to play cricket as you do other sports such as football. We also chat to Dr Allistair McRobert from Liverpool John Moores University whose work has shown that the best batsmen can predict to some extent where a bowler will bowl. This work encompasses a look into the subconscious mental game of cricket and how the most successful players are more mentally prepared for the top level than lesser players. More on this topic can also be found in our article The Science of Cricket.


• Sex before Sport?

It is the virile sports-person's eternal question - should one abstain from a little bit of nookie before a big sporting event? If I was Michael Clarke and engaged to Lara Bingle, I wouldn't be...


• Economists, oil, cricket and correlation

Can we predict cricket results using the price of oil? Or is this just bad stats. Also see our article Poor correlations, or why it's not the fault of Aussie cricketers.

Good luck to all and come on you Aussies!

Correlation of the Week: Ashes success and El Nino

As we have shown on this blog a number of times (see here, here and here for starters), cricket fans love their maths. So it should come as no surprise that another cricket/maths story has recently come out, this time from the University of Reading linking cricket success with the weather! I only blog my maths/cricket geekiness, these guys have research funding!

Manoj Joshi has shown that the El Nino Southern Oscillation (ENSO) phenomenon has a significant effect on the results of The Ashes cricket series between Australia and England when the series is held in Australia. The Australian Cricket team is more likely to succeed after El Nino years, while the English cricket team does better following La Nina years (the opposite phase). Their study, Could El Niño Southern Oscillation affect the results of the Ashes series in Australia? was published in the journal Weather.

I didn't quite believe this at first, so I took their data, redid the maths, and it turns out that they are correct! However, the media interpretations of these results are not surprisingly a little over the top. Whilst there is a significant correlation between the state of El Nino in the year before the Ashes series and the result, the correlation itself is weak. This is an important point to keep in mind with any correlation - strength and significance are two different things - even sciencedaily got this wrong in its reporting on the topic. There is a nice explanation of these ideas here.

Strength refers to how well the data sets move with each other, significance refers to how likely it is the correlation occurred by chance. For example, you can easily get a strong correlation between two data sets if you have only a small amount of data. But as you lack data, it is unlikely that the relationship will actually be significant. In our case however, the correlation is quite weak, but the relationship is significant. The conclusion to this study should be that ENSO plays a very small role in determining the results of Ashes series in Australia, but that other factors are likely to be more important, and that simple noise and randomness will probably have more of an effect than the phase of ENSO. It is only over time that this correlation can be teased out. The study does admit this, with Joshi saying:

"There are of course many different factors governing the outcome of any given sporting contest, which would act as noise in this analysis."

But I think his statement that "the study could even influence whether the England touring team should include more fast bowlers or more 'swing' bowlers" is probably a little bold (and to his credit he does admit this)!

So, how does this all work?

There are two phases of ENSO - during El Nino, the eastern equatorial Pacific Ocean warms by about 1 degree. For Australia this means low rainfall and high temperatures. La Nina is a reverse, with more rain and a drop in temperature. The study analysed the results of all Ashes matches held in Australia from 1882-2007 and found that during El Nino years, the Australian team won 13 out of 17 series (76%), but only five out of the 13 played in La Nina years (38%). England has only won one Ashes series in the last 100 years following an El Nino event - the Bodyline series in 1932/33. The author speculates that cricket pitch conditions can affect the outcome of a match with the drier pitches of El Nino favouring fast Australian bowlers with the English slower swing bowlers enjoying La Nina.

Now to the maths. I have reproduced the results from the paper in our chart as you can see here. On the y-axis is the series result (English wins minus Australian wins). On the x-axis is the Nino 3 index, which is the mean monthly temperature anomaly in the eastern tropical Pacific: 5S-5N; 150W-90W. Of course, all the dots should be on integer values of y - some were shifted in the original paper for ease of viewing. The correlation is still correct.



What we can see here is a very weak correlation - the R² value is only 0.1. R² is the coefficient of determination and gives some information about goodness of fit. A value this low is generally accepted as suggesting no correlation at all. One interpretation is to say that about 10% of the correlation can be explained by the Nino 3 index. The paper itself quotes R (=-0.31) as opposed to R², but to determine whether a relationship is strong or not, you need R².

To test for significance, Joshi generated 10000 sets of randomly generated numbers to represent the Nino 3 index - each set had 32 members (the same number as the number of Ashes series) and a normal distribution with a mean of zero and a standard deviation of 0.8, similar to ENSO observations. They found that the chance of R being more negative than -0.31 was 5%, which is the level generally accepted as being significant.

There is, however, an easier way to do this - you can use t-tests (as we used in our earlier Correlation of the Week on vampire and zombie movies). To generate your t-statistic, you use the formula:

where N is the number of sample points (32). When you do this, you get a t value of -1.78. This means that if our null-hypothesis is r=0 (that is, there is no correlation), when you look this t-value up in a t-distribution table, you find that it is more negative than the critical value of -1.70 in a one-tailed test, which means it is significant. What all this means is that there is a very weak significant correlation very close to zero. I wouldn't put any money on either team based on this result! In any case, Australia is going to win....

Tanneries and water - meandering through Morocco

Morocco is a hot, dry place. We were lucky enough to visit the town of Marrakech last week, and apart from being stunning to look at, it was 40 degrees and chaotic! This latest post is not meant to be a travel blog - there are plenty of them out there - but instead we are going to take a look at some of the science from this most recent trip abroad.

Tanneries

To work in a tannery in Marrakech is to work under some of the harshest working conditions there are. Not only are you exposed to the blazing sun, but you are are soaked in blood, animal bodily fluids and parts, pigeon poo, and get paid appallingly.

But there is some science to the ancient Moroccan tannery tradition.

Legend has it that the tanners are descended from demons who lived under a black king. As they didn't obey his rules, they were condemned to work in the tanneries. They use hundreds of concrete vats to process animal skins which are bought locally in the souks. The skins (mainly sheep and goat although cow and camel are sometimes used - lions are no longer used as they were hunted to extinction in the region around 1900) are treated far differently to the way leather is treated in other parts of the world as the process clings to its ancient traditions. Hair and flesh are removed by soaking the skins in quicklime (Calcium Oxide formed when limestone - calcium carbonate - decomposes) and water. After this, the skins are placed in a vat of water and blood, then separated and rung out, before being coloured using a few natural products:

• Pomegranate for yellow;
• Olive oil for shininess;
• Bark for various colours, presumably brown;
  
• Saffron for golden yellow;
  
• Henna for red/orange;
  
• Poppy for many other colours including white, pink, yellow, orange, red and blue.

The skins are stretched out and left to dry for over 20 days in little piles that look rancid. Pigeon poo is used to soften the leather, and if anyone knows why, I would love to know. Presumably the poo is slightly acidic. Pigeon poo has actually been reported to be quite dangerous, with people almost dying after ingesting it. The poo adds to the smell of the place, with there being large pigeon coups near the top in which you could wade knee deep in the brown-smelly stuff.

Our guide, apart from ripping us off ridiculously, did give us some mint to hold under our noses to mask the smell.

If you want to be a tanner, you need to be born into it, and only men are allowed. Many suffer from arthritis and are forced into an early retirement. And it has been reported that in Bangladesh, half a million people are at risk of serious health issues due to their tanneries emitting toxic chemicals such as sulphuric acid. Not a place I would like to work.

Water

Morocco has a massive water problem. It rains about a third of that in Canberra, Australia, which is considered in severe drought. The average rainfall in a summer month is 3 mm, and there are increasing demands on the scare water-supply by a massive push to increase tourism and reduced rain-fall, presumably due to global warming. The period in which crops woudl grow in the 1960s was about 180 days per year. Now it is 110, and most of the country still live off the land. Add to this food shortages and there will be a problem in the years to come.

It has not always been this way. When Marrakesh was originally settled by the Almoravids, who had lived in the desert all their history, water management was done well. The Almoravids built massive underground piping systems called khettaras which brought water from melted snow from the Atlas Mountains, a few hundred kilometers from Marrakech. It was quite an engineering project, but unfortunately western irrigation techniques, developed in places where there is lots of water, are now being used and water is running out. There are still magnificent oases in Marrakech, such as the Palmeraie and the Majorelle Gardens, but these are irrigated using modern methods.

I took my recording gear to Marrakech, so listen up to the podcast here. You will also here some commentary from the local lads on Australia, east and west coast America, and north and south England, and some of the sounds of Marrakech.

Listen here:

More of my Marrakech photos can be found on my flickr site.

Turbulent Townsville

Sometimes, the weather just doesn't work in your favour. Whether its raining out weekend sport or a BBQ, bringing an early end to the snow season, or simply melting the polar caps, raising sea levels and displacing millions of people, it can often be a minor inconvenience.

But on other occassions, it can be truly annoying.

I am currently sitting in the airport lounge in Townsville, North Queensland, awaiting my extremely delayed flight and hoping beyond hope that I don't have to stay here any longer. Townsville is a town that is built around James Cook University, the Army and the North Queensland Cowboys Rugby League team. However, univerisity hasn't gone back, much of the Australian Army is deployed overseas, and its not rugby league season yet, so suffice to say, there is not alot to do. Although, I'm not sure whether I would be tempted by that combination of attractions in any case...

No, to be fair, Townsville has its fair sure of beautiful attractions and lovely people. I'm just grumpy - that grumpiness that only airports can bring out of you!

Northern Australia is currently in the grip of cyclonic weather conditions. Cyclone Nelson has cut off much of the north by road, and caused massive flooding. This is a very strange thing to see coming from Sydney, which like much of the rest of the country, is drought-striken and in a water crisis.

So for my flight to be delayed is not surprising. However, for my flight to be delayed because the plane is late from Sydney because of Sydney storms, whilst it is perfectly clear outside here in Townsville, is rather infuriating! (Marc - I'm adding this 6 hours after we were supposed to leave, and we're still here. Each hour they delay the departure time by an hour.)

OK, time to stop complaining, and make something sciencey out of all this. One of the "features" of the trip up, and considering the weather conditions probably the trip back, was turbulence. Turbulence is air movement that cannot normally be seen and whilst many people enjoy this aspect of flying, I struggle with it!

There are a number of ways that turbulence can come about:

Thermals - Air rises when it is heated by the sun, and cold air sinks. So if one mass of air heats up, this can cause air flow causing turbulence.

Jet streams - At high altitudes, there are fast air currents. These can shift, causing a disturbance in the nearby air.

Mountains - Air passes over mountains and causes turbulence as it flows above the air on the other side.

Wake turbulence - If you are flying near the ground, a passing plane or helicopter can set up small, chaotic air currents.

Microbursts - A storm can cause a strong downdraft close to the ground.

The danger with turbulence is that it cannot always be predicted. The cockpit suffers least from turbulence, whilst the rear of the plane cops most of the disturbance. You don't need clouds for turbulence, however I usually notice it most when flying through them. On the way up, the pilot tried to stay below the clouds that were causing the turbulence. However, after a period of time, the clouds got lower and lower, and the plane couldn't continue to stay below them. However, the pilot said we were too heavy to fly above them - so we flew in the clouds for the best part of the flight, and it was a bumpy ride!

Aircraft radars can't detect turbulence. Turbulence is the leading cause of in-flight injuries, so remember to keep those seat-belts done up! It can range from very mild, to the extremely dangerous (but rather unlikely) case of the plane being totally out of control with massive changes in altitude. Between 1981 and 1997, there were 342 reports of turbulence affecting major air carriers. Three passengers died, two of which were because they were not wearing seat belts. 80 suffered serious injuries, 73 of these were also not wearing their seat belts.

One example of turbulence was a flight from Singapore to Sydney with 236 passengers on board, as well as and 16 crew. The airplane encountered turbulence over central Australia when it hit an air pocket and dropped 100 m. Nine passengers, including one pregnant woman, and three crew members suffered neck, back and hip injuries, with one of the passengers requiring surgery. They were all not wearing seat belts.

I'll get this out on the podcast soon, assuming I get back..... (mp3 here)

For more info and some examples of turbulence incidents, see: Civil Aviation Safety Authority

For a fluid dynamics explanation, see here.