The Accu Weather Report for Manchester at 0700 hours on the 8th August 2014, the second day of the 4th Test Match between England and India, is 15 degrees C, 91% humidity and wind speed 0 mph. The leaves on the trees outside the window that Third Man is looking through are still. No doubt the flags around the Old Trafford Ground are motionless.
Throughout the first day of the Test the ball swung yet it did so even as humidity fell from 88% at 12 noon to 55% at 1600 hours.
Today the old swing bowler Andy Caddick was on Five Live explaining the effects of “humidity” on the propensity of the cricket ball to swing. Then towards the end of the interview he also mentioned structural changes to cricket grounds, using as a prime example the effects of the construction of the new stand at Trent Bridge. “Once it didn’t swing there, now it does.” No inference was then drawn to the effect on ground level atmospheric turbulence resulting from these changes to the physical environment.
Yet still old cricketers hang on to the lore that the cricket ball swings when OVERHEAD conditions are humid. Caddick even said that humidity helped cricketers to keep the shine on the ball.
Yet scientists helping cricketers understand the dynamics of cricket ball motion have long been able to provide them with information on why the ball swings and how best to maximize that swing. Nearly 25 years ago in 1991, Brian Wilkins, published The Bowlers Art.
In a chapter on ’Swing and the Atmosphere’ he is scathing, “No great knowledge of science is required to appreciate that there is no way in which a change in the moisture content in the air can affect swing.”
“It is too much to hope that the ‘flat earthers’ in the commentary box and elsewhere will finally erase humidity from the book of cricket terminology?”
It is atmospheric turbulence, not lack of humidity, that interferes with the helpful airflows around a cricket ball and especially when encountering the seam and reduces the propensity for the ball to swing.
So, conditions that minimize atmospheric turbulence at and below the height from which the ball is delivered are what really matter – it’s UNDERHEAD conditions that count.
Nor is the ECB in ignorance of this, as Jasoon Palmer reported for the BBC science pages here. They have been reading the work of Dr David James and his colleagues John Hart at Sheffield and Danielle MacDonald at AUT University in New Zealand.
“When the ground heats, it makes convection currents which make the air rise off the cricket pitch – that creates turbulence in the air on a sunny day.”
“On a cloudy day you get stiller air, because you don’t get these convection currents coming off the ground.”
They too concluded that it is the stiller air through which a ball passes that is the key factor; doing less to affect the imbalance of smooth and chaotic flow on either side of the ball that leads to swing. Sunshine can create turbulence, but not always.
Ian Botham at the Lord’s Test suggested that Bob Massie took his wickets in bright sunshine. This video suggest otherwise. And TM was there and can confirm the evidence of the video – no shadows.
http://www.youtube.com/watch?v=g_mAF2-PKew
But sunshine and lack of cloud does not preclude swing, if the hot conditions are such that there is minimal atmospheric turbulance. It swings in Pakinstan, no?
Note also that Boycott ‘fans’ will be delighted to see how the ‘great man’s’ bat comes down from the direction of FOURTH slip, across the line of the ball.
Down At Third Man 
Yes indeed, TM. It seems hard for the non-scientific mind to grasp the idea that it can be the absence of some condition that explains a phenomenon. In this case, as Jason Palmer reports, swing is explained by the absence of convection currents that would disrupt the laminar flow around the smooth side of the ball, preventing the required asymmetry. How much easier to posit that swing is explained by the presence of something (such as humidity)!
I recently heard Boycott (who played in the match) also saying that Massie took his wickets on a sunny day, so perhaps Botham picked it up from him. I knew that this was wrong as I’ve seen film of the game many times and I’m pretty sure the entire match was played under slate grey skies.
There would, of course, be no point in telling Boycott that, as, as far as he’s concerned, he’s never wrong about anything.
Pleased you can confirm this, Brian.
I know that Ray Illingworth always says that it was cloudy when Massie bowled and sunny when England bowled but I am not sure I believe this. For one thing, it took an innings of exceptional quality from Greg Chappell to get Australia in the driving seat – and John Snow took 5 for 57 in 32 overs, which kind of suggests he was making the ball talk as well. I also recall that my Saturday cricket match got rained off (in South London) and that our Monday sports period was held indoors because of rain. There was a distinct absence of sunshine in London that particular weekend. I recall Boycott getting out bowled Lillee – he let a ball that rose abruptly from not too short of a length hit him, and then it looped over his shoulder and trickled onto the stumps. I only mention it because it must be one of the oddest ways of getting out.
I had a word with the guardians of the Met Office archives (with whom I share an office) and they confirmed that there was virtually no sunshine on any day of the match, with very small amounts of rain on Thursday and Friday evening and early on Saturday morning. Daily maximum temperatures ranged from 16.6 celsius to 20.3.
Sunny it was not.