You may not have heard the term ‘autumn gales’ before, but you’ll have certainly experienced them.
These are the bouts of strong wind we get fairly often during the autumn months that help to rip the leaves from the trees, and occasionally the whole tree out of the ground.
But what causes these stronger winds at this time of year, and why do we associate autumn with wind and storms? Well, it’s all down to nature’s fine balancing act, where it tries to prevent the pole from getting too cold and equally the equator too warm.
The sun sets over the North Pole at the end of September and doesn’t rise again until the end of March. The darkness in the Arctic means it rapidly turns colder and the equator remains fairly consistent. This widening temperature contrast strengthens the jet stream travelling across the Atlantic and this can create more storms.
The jet stream is a narrow tube of fast moving air around 25,000-30,000ft which circles the globe and drives low pressure (areas of wind and rain) from west to east. When this strengthens in the autumn and winter, it affectively spins low pressure systems quicker, which then become deeper, and the winds at the surface get stronger – giving us the famous autumn gales. The jet will usually travel at speeds between 100-200mph, but can reach in excess of 250mph in more volatile spells.
There is a bonus to a stronger jet stream for those flying from the US or Canada to Europe. This can cut travel time, and also means that less fuel is required. The opposite is true to a certain extent going west across the Atlantic, although pilots will often fly around the jet to avoid fighting against the flow (headwinds).
The other reason that storms and strong winds are associated with the autumn is down to the Atlantic Hurricane Season. As the jet stream ramps up, this will occasionally catch the remnants of a storm drifting up the eastern seaboard of Canada or the US and drag it towards the UK.
Of course, we’ve started naming our own storms here, but when the remnants of a hurricane drift towards us, we still generally refer to is as ‘ex-hurricane’ rather than give it a new name. The same is also true if the Portuguese or French weather organisations name a storm, we will also not re-name it with one from our own list.
So the next time you’re standing at the bus stop or train station in the horizontal rain, you can look up to the sky and blame it all on the jet stream, but take comfort from the knowledge that those flying back from New York will be home quicker – lovely!