Our memory of the weather.
When you think of memorable weather events, what comes to mind? It will be different for all of us, but some of you will share my memory of the ‘great storm’ that hit southern England and northern France in October 1987 (pictured). Strictly speaking, I missed the actual storm by sleeping through it, but I well remember the strong winds and fallen trees of the following morning.
Our memory of the weather is a vital component in the process of understanding and predicting it, but human memory is not enough – we need records that cover more than one human lifetime, and the whole planet – so we have to build an international, institutional record containing as much information as possible about the weather and its changes. We are particularly concerned about high-impact weather: storms, floods, heat waves, severe cold spells – these are the kinds of events that kill people and do expensive damage. A key aim of meteorologists today is to improve our ability to predict such events. Will your home town have more or fewer severe weather events in the future – when will the next storm strike? To answer these questions we need to test and improve our predictive tools by asking how well they would have done for known, historical events.
Fortunately, really damaging weather events are fairly rare. Until October 1987, for example, , the UK had not seen a storm of such magnitude since 1703. This makes them difficult to study, and means that improving and lengthening our international record of the weather is particularly important, as we need to have records of as many weather events as possible on which to base our understanding and test our predictive skills. We know a great deal about the 1987 storm – it hit a time and place where there were many weather observers, and so it can be very precisely characterised; but severe weather events from longer ago, and from places with fewer observers, are not so well fixed in our institutional memory, and are much less well understood.
Unless you are a sailor, your memories will be of weather over the land – that’s where we notice weather impacts; but storms and other weather events often have their beginnings over the sea, and if we are to understand the events we need records of their entire life cycles, so we need the naval records – they are a vital component in our records of weather history. In the early years of the twentieth century we have very few weather observations from much of the ocean, and that’s why those rescued by OldWeather can make such a difference. Who knows what storms, droughts, and heatwaves we’ll restore to memory, and make available for testing and improving predictions of future events?
(The illustration shows a visualisation of sea-level pressure (colours – blue low, red high) and wind speed (black arrows) on October 16th, 1987. The points mark observations, from ships and land stations, and the lines show the fields synthesised from those observations by the 20th Century Reanalysis. The visualisation was made using Google Earth.)