D-Day and the Met Office

If I were being glib (and I often am) then I might have titled this post 'How the Weather Won the War'. However, I find it hard to be glib about war, particularly World War II. Perhaps it's memories of my grandfather, who fought a role in the war that went far beyond the stories he told me as a child. More likely it is simply the staggering loss of life that I am now better able to comprehend. Certainly, I am sobered by the realisation that the work I now do may once have contributed to one of the most important battles ever fought.

If ever there was an example of high-pressure meteorology then it must have been the weather forecasts made by the chief meteorological officer for Operation Overlord, Group Captain James Stagg on and around June 4th 1944. Though, to see a picture of the guy, he looks like he could probably handle it. That steely glare was presumably captured at some other time than the 4th of June though when he wrote in his diary 'I am now getting rather stunned - it is all a nightmare'.

Stagg was responsible for advising Eisenhower when D-Day (variously referred to as the largest seaborne, the largest amphibious and the largest just plain old invasion of human history) would go ahead. The requirements placed upon Stagg were that the day be close to a full moon and that low tide be at or around dawn. So far, so good, a reasonable almanac and/or calendar would be able to supply that information. However, it was also necessary that winds be light, that conditions be no worse than slightly cloudy (30% coverage below 8,000 feet) and that visibility be more than three miles. These conditions are considerably harder to predict and forecasting them, particularly 70 years ago, is an error-prone business.

Sian Lloyd has written a great piece at the Huffington Post which lays out the order of events which came from James Stagg's predictions, including his advice that the operation not go ahead on the 5th, as planned. Instead, on the night of the 4th, Stagg told Eisenhower that there should be a break in the otherwise unsettled weather on the morning of the 6th. This break in the weather was not predicted by the Germans and so German intelligence had decided that a landing would be unlikely on that day.

It is likely that James Stagg would have known that the Germans failed to predict the break in the weather as he had access to observations coming from the Germans themselves. Weather reports originating from German U-boats were encoded by the Enigma machine and, thanks to the deciphering done by Bletchley Park these reports were now readable by Allied forces. An intriguing sidenote, given the meteorological theme here, is the vital role that weather reports played in the Allied capture and decoding of the Enigma code. It was Harry Hinsley, working at Bletchley Park, who reportedly realised that German weather trawlers must be able to decode Enigma messages and so must have code books aboard. This realisation led directly to the attack of one of these trawlers and the capture of a code book.

The fact that Group Captain Stagg had access to German weather reports may well have led directly to the success of the Normandy landings. However, it was weather coming from the west that was most crucial to the D-Day landing decision and so it certainly helped that an observation network was in place providing data from reconnaissance aircraft as well as ships at sea. While ships were supposedly restricted by a radio silence order, it has been speculated that weather reports were sent in via messenger pigeon. All of these observations contributed to the hand-drawn charts used at the time for forecasting. The chart from the day itself is available (upon request) at the Met Office library and is a remarkable piece of scientific history. Seeing the chart, which admittedly looks like almost any other synoptic chart, makes one feel the weight that history placed on that single sheet of paper. Not only that but the responsibility that those scientists that drew the chart bore for being absolutely correct in their determinations. Quite frankly, I think I would prefer the astronomical observations I'm more familiar with, I am unable to think of a single situation in which anyone's life has been placed at risk due to my mis-calibration of GBT data!

Weather charts from both the Allied and Axis forces for June 6th, 1944 are shown below. Note how the Allied chart contains observations covering Germany while the German chart contains none of Britain. The entire outcome of World War II may well have come down to the simple superiority of our knowledge about the weather.

Allied weather chart for 6th of June, 1944

Axis weather chart for 6th of June, 1944

There is a webpage hosted by the Met Office itself with some embedded videos which go into detail regarding the interpretation of the weather charts and what the contributing factors were at the time. If you are interested in some of the finer details of the meterology involved here then I advise you to go here.

I think it is worth pointing out the role that women meteorologists played in these predictions. Although there were no women forecasters until 1947 Wren meteorologists were stationed with the other navy staff at Portsmouth collectively responsible for drawing the D-Day planning charts and other work. It was often roles such as these chart-drawers and the 'Harvard Computers' that were 'allowed' to be filled by women and lay the groundwork for a future which includes female Lego scientists(!) While I have mainly focussed on James Stagg in my post, it should be remembered that there were other contributors to the forecasts that decided that the Normandy invasion should go ahead. They too, must have surely felt the gripping tension James Stagg did when he wrote 'Fair interval confirmed, invasion put on "Final and Irrevocable Decision". Whatever the outcome the decision is taken.'

The next possible window for the planned invasion was to be two weeks later, at the next suitable tides. Stagg later wrote to Eisenhower that, had the landing been delayed until that day, the troops would have met the worst weather in the region for 20 years. Eisenhower wrote back - 'Thanks, and thank the Gods of war we went when we did'.

Something in the Air

A lot happens at the Met Office that goes largely unreported upon. For example, planting transmitters on seals to measure sea temperature might not be the first thing to cross your mind if you were asked what the Met Office actually does. As I listened to a talk this week about tracking the spread of atmospheric particles I realised that this was something else that would fall under this umbrella. Time for a blog post!

The talk was by the Atmospheric Dispersion and Quality (ADAQ) group who are responsible for some very interesting aspects of the MO services like supporting the emergency services in the event of civil contingencies like chemical fires, radioactive accidents, volcanic ash and animal and plant health. This is achieved through the use of NAME - the Nuclear Accident ModEl, one of the more outrageous examples of acronym abuse I've come across.

NAME was developed by the MO following the Chernobyl disaster in 1986 when weather conditions conspired to spread the released radioactive particles across Europe, including the Welsh hills. How exactly this happened can be seen in the model image below.

Since then, NAME has been through multiple iterations, capable of predicting the transport, dispersion and chemistry of atmospheric particles. If you're interested in the gritty (haha) details then I can tell you that it does this through the modelling of core atmospheric processes such as turbulence, deep convection, deposition & sedimentation^* and chemistry. If you want to know exactly how it does that then here would be a good place to start.

^*material removed from atmosphere by transport to, and uptake by the ground. Gravitational settling, rain 'washout' (material is brought down to ground by rain), rain absorption (precipitation forms around particles directly).

The latest generation of NAME is NAME III and this has been used extensively in recent times to track the effects of the Fukushima Daiichi nuclear disaster, the second event ever to reach the highest rating of 7 on the International Nuclear and Radiological Event Scale. Research into the health effects of the Fukushima disaster is ongoing, incorporating the results of NAME's model analysis.

NAME is supported by many tools which work over different scales, interesting in various ways. In order of increasing scale over which they function:

• PACRAM (Procedures And Communications in the event of a release of Radioactive Material) gives little information generally but the main priority is to be fast so as to advise emergency services, etc. on possible hazardous directions or areas to avoid in the event of a UK nuclear power plant event.

• RIMNET (not sure if this is a really convoluted acronym or just a name...) a Met Office-managed project in partnership with DECC and DEFRA. A country-wide network of gamma radiation detectors (isn't this a plot device from the Avengers?!) which allow the UK to monitor background radiation levels. All measurement and reference data is stored in the UK National Nuclear Database.
• Regional Specialized Meteorological Centers and the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) give the international radiological response. The CTBTO (actually a preparatory commission as the treaty is not yet law) are tasked with establishing and developing a worldwide network which monitors the planet for nuclear explosions. This network is reportedly 85 percent complete at the time of writing.

One of the more useful aspects of atmospheric modelling is that it can be run backwards to establish the source of an atmospheric feature. For example, if a non-reported nuclear event were to occur, this can be traced back to its source through inputting current observations into the NAME model.

This feature has proved particularly useful in disease control such as in the outbreak of  Legionnaires Disease in Edinburgh in 2012. Not only can the model predict the spread of airborne bacteria and so inform the public and authorities if certain areas are at particularly high risk but, once an infection has been found, the model can be run backwards to see where the bacteria might have originated from in the first place. Useful again in the case of animal and plant health. The Met Office has been researching the spread of Foot and Mouth Disease since the 1960s, again through the dispersion in the atmosphere of airborne particles originating from infected pigs.

There is more use to this than might be immediately obvious, vaccines are often limited in amount, especially in the case of a sudden outbreak. By identifying the likely spread of diseases, the vaccines can be distributed in a targeted way.

There are yet more applications of this technology and, to be honest, I wasn't particularly familiar with them before the talk. I'd heard of 'Ash dieback', apparently spread on the small scale (up to 10s of miles) by windborne spores but what has apparently been called the 'polio of wheat', UG99, is also the subject of Met Office research.