Meteorology in legal cases

The forensic meteorologist carries out an investigation into the weather over a few hours, days, or even, on occasions, months or years.

So, why do the courts need an expert in meteorology?

Although meteorology is an everyday science, in that almost everyone understands the terms fog, snow, rain, hail, and so forth, the forensic meteorologist is required to examine weather records and offer an opinion based on the minutiae of the science. This almost always involves preparing the equivalent of a weather forecast or backcast. The meteorologist is required to explain to the court why, when, and where the weather occurred and how it affected the incident.

The meteorologist's part is to describe to
the court, by means of a written report and,
if required, verbally in the witness box, the evolution of a weather event, and from the records, witness statements, and other sources give an opinion on any matter concerning the weather that affects the case. For example, it may be a question of how much rain fell, how strong the wind was, or what time ice formed. On some occasions, a forensic entomologist needs to know the weather over a number of days, in particular temperature and humidity, to assess the effect
of the weather on the development of fly larvae
in a body.

The role of the meteorological expert witness
is the same as any other: to give an honest and unbiased opinion, based on sound scientific principles, with supporting data and references
to published work.

The weather is a matter of record and is well documented, not only in the weather records
but, in the case of severe weather events and often road traffic accidents, in newspapers, on television, in witness statements, and so on. Although there is a time element involved, the changes of the various weather parameters in terms of time are fixed. It is therefore a problem
of spatial separation of the weather events at the nearest weather stations and the weather at the site of the incident that the expert has to consider. The opinion is based on weather data from a variety of sources: the internet, the Met Office, witness statements, the media, and on some occasions CCTV from the site of the incident.

'Dreamspace': A meteorological investigation

Although meteorological evidence is not vital in many cases, occasionally it is very important. Such a case was R v Agis (24 February 2009, Newcastle Crown Court).

Agis was the designer of 'Dreamspace', an inflatable artwork that was erected in a park
in Chester-le-Street in July 2006. It was a large plastic structure measuring about 50 metres by
50 metres, and comprising five-metre-by-five-metre 'rooms', each of a different colour, through which the public could walk while listening to music. The structure was tied down by ropes pegged into the ground.

Agis was charged with manslaughter and breaking health and safety laws after the structure broke free from its moorings and lifted off the ground, injuring 20 or so people and killing two. He pleaded guilty to the latter charge and not guilty to the former.

I was instructed by the defendant's solicitors to prepare a weather report.

There were many witness statements and CCTV footage available for examination. Data was also available from three weather stations: Durham, Newcastle Airport, and Albemarle (upper air sounding station).

The meteorological expert for the prosecution gave as his opinion that the cause of the accident was a strong gust of wind, which should have been anticipated.

The day of the incident, 23 July 2006, was bright and sunny. Air temperatures were around 23 to 25 degrees Celsius at the three nearest weather stations at about 3.30pm.

Weather station data suggested a rather windy day. Mean wind speeds were around seven to 11 knots at ten metres above the ground (force three to four on the Beaufort wind force scale - a gentle to moderate breeze). At times gusts were almost - or even more than - double the mean speed.

However, an examination of the upper air sounding from Albemarle showed the wind at the surface at 1pm from the ascent was only three knots from the west.

Further, almost all of the witnesses described the wind as being light, and only two referred to winds stronger than light - one witness said there was a light to moderate breeze (two to four on the Beaufort scale) and another said that at around 3.30pm 'a very moderate breeze was blowing across the park'.

There was, therefore, a disparity between the wind conditions at two of the stations and the evidence of many of the witnesses, the CCTV coverage, and the data from the upper air ascent, all of which indicated there was very little wind. An examination of the topography of the area showed that the park was sheltered by high ground to the west, with the town being on
high ground.

The defence theory was that a strong convection current formed on the top of the structure during a period of bright sun, causing
it to be sucked into the air.

Convection occurs when differential heating is caused by the proximity of hot and cooler areas. In this case, the top of the structure would have been much hotter than the surrounding grass in the park from early in the morning. At about 3.30pm, the cloud was well broken with a long period of bright sunshine. It is possible that the temperature of the upper surface of the structure exceeded 35 degrees Celsius. Some of the witnesses also said that it became very hot
inside 'Dreamspace'.

CCTV showed that just prior to its lifting, at about 3.30pm, the sides of the structure were sucked in and then out for a matter of minutes, rather like a wobbly jelly but with an up-and-down motion too. At the same time, trees just to the west were quite vigorously blown about, where before they were almost still. This indicated quite a strong wind towards the structure. Where there is a strong vertical motion, air is sucked in to replace the rising air (sea breezes and tornados are good examples).

In the event, it appeared that the CCTV evidence was conclusive in destroying the wind theory.

The jury could not agree on a verdict on the charges of gross negligence manslaughter and the Crown Prosecution Service decided not to ask for a retrial. Agis was found guilty of failing to ensure the safety of members of the public under section 3 of the Health and Safety at Work Act 1974.

Road traffic accident

In Goodes v East Sussex County Council [2000] UKHL 34, the weather was again important.
The claimant was driving along a road when he skidded on ice while overtaking and crashed into the wall of a bridge, suffering severe injuries. He claimed damages on the basis that the Highway Authority had failed in its duty to 'maintain the road' by not putting down salt or grit in time to prevent ice forming.

A weather report showed the high probability of the presence of ice on road surfaces, which would have been obvious to drivers due to hoar frost appearing on grass and trees.

The claimant was initially successful but lost after the local authority appealed to the House of Lords.

Miners' strike

My first court appearance was in 1984, one month after joining the legal enquiries section of the Met Office, with no formal training in the legal sense. The case was one of murder. During the miners' strike of 1984, two strikers threw a rock from a bridge on to a taxi taking a non-striking miner to work. The taxi driver was killed.

A policeman had given evidence that he saw the accused by bright moonlight. I testified that weather reports showed this was a cloudy night with light drizzle. The police evidence was later withdrawn. SJ

John Coates-Greetham is a consultant forensic meteorologist and former head of legal enquiries at the Met Office

www.coates-greetham.co.uk