Last weekend marked the beginning of British Summer Time, as we put the clocks forward one hour, giving us an extra hour’s light to enjoy of an evening.
The hours of daylight are increasing quickly, with an extra five minutes of sunshine possible from one day to the next. Associated with this, is the height to which the sun climbs in the sky each day. A ‘higher’ sun means a smaller amount of atmosphere the radiation from it has to pass through before reaching the ground.
Since the atmosphere scatters, reflects and absorbs much of the sun’s radiation, the result is an increase in the ‘strength of the sun.’
So whilst, up until last weekend, it still felt quite chilly outside, the sun’s rays now have the same intensity as they do in early September. Indeed the ‘UV index’, a measure of the amount of the sun’s radiation emitted in the UV (ultra-violet) wavelengths reaching the ground, can now climb to a value of fouron a clear day across Bucks, high enough to give a welcome boost to our vitamin D levels.
In the UK, maximum possible UV levels continue rising until the Summer Solstice on June 21, by which time values of over seven can be attained in Bucks in clear weather. Whilst sufficiently high to burn unprotected skin in less than half an hour, this is still much lower than found elsewhere across the world. In the Mediterranean, values peak at around 10 in the June midday sunshine.
Closer to the Equator, values are higher still, making it potentially dangerous to be outside, unless in the shade or with adequate protection, such as sun cream on exposed skin, a hat and sunglasses.
Whilst time of day, day of the year, latitude and cloud amounts are key drivers in determining the UV index, other factors also contribute, including altitude and snow, which reflects the UV radiation.
Back in Aylesbury Vale and how long is the current warmth going to last? Well, for a while at least, with the rest of the week staying unseasonably warm with plenty of sunshine, although there’ll be the threat of a few thundery showers too. Unfortunately, thicker cloud is likely to bring more widespread rain over the weekend.