Sunshine
The sunniest parts of the United Kingdom are along the south coast of England. Many places along this coast achieve annual average figures of around 1,750 hours of sunshine. Coastal areas in the south-west have average annual sunshine totals above 1600 hours, the English Channel coast being more favoured than the Bristol Channel coast. Tourist resorts used to vie with each other for sunshine records and there were even national prizes for the sunniest places each year. The prizes were usually won by south coast resorts but Bristol Channel resorts won occasionally and Ilfracombe won several times. Much depended upon whether the local council was prepared to invest in a weather station and its manning and many recordings ceased with local government reorganisation in 1974.
The maximum recorded duration of sunshine in a month is 383.9 hours at Eastbourne in July 1911with the record for Pendennis Point in Cornwall not far behind. There are several records of less than 20 hours for December, with the minimum duration recorded in a month was 0.0 hours in central London in December 1890. Presumably this was in the days of smogs. Most sunshine records are old ones. We do not have the smogs nowadays but we do not have such clear skies either. Summers are becoming warmer but often more overcast at the same time. Some of this is due to the 'pollution haze' caused by the particles released from the burning of fuels.
The number of hours of bright sunshine is controlled by the length of day and by cloudiness. The day is shortest in December and longest in June, and so in general December is the dullest month and June the sunniest. The south-west of England has a favoured location with respect to the Azores high pressure when it extends its influence north-eastwards towards the UK, particularly in summer. Subsidence associated with high pressure reduces cloud cover, and in spring and summer when the sea is cool relative to the air there is little convective cloud over the sea. Coastal areas are then favoured by high sunshine amounts. Convective cloud often forms inland, especially near hills, and acts to reduce sunshine amounts. Inland in the West Country the annual sunshine totals are mainly between 1400 and 1600 hours.
The Met.Office publishes sunshine maps for which the data has been extrapolated for Exmoor. From this it is clear that the south of Britain has much more sunshine than the north and the whole of Exmoor comes within the top half of the scale for sunshine. However, the Chains stands out as being possibly the least sunny part of England south of the Pennines, with an average of between 1311 and 1380 hours of sunshine per year. The coast of Exmoor is in the highest part of the scale for average annual sunshine, along with the English Channel coast, with an average of between 1511 and 1842 hours. However, in winter months, December in particular, there is no difference between the Chains and the Exmoor coast. Taking this from the annual average means that the Exmoor coast is particularly sunny in summer. Conversely, the Chains are particularly cloudy in August and September compared with other uplands in the south of England. The annual average for most of Exmoor is between 1381 and 1450 hours of sunshine per year.