Explained: What is UV index and why is it different around the world? 

UV index is an important aspect of environment, which is not taught in detail during the school days. However, it is important for students to know about it for more reasons than one. Here is all about this element of the weather. 

UV Index: What does it mean? 
The UV index provides us with the information that on a given day, how much ultraviolet radiation of the sun is surrounding us at the ground level and has the potential to harm human eyes and skin. The term UV index was coined way back in 2002 by the World Health Organisation to raise awareness about the harmful effects of UV radiation, such as cataracts, skin cancer, and sunburn. A UV index has different kinds of scores such as: 1 to 2, meaning low, 3 to 5 meaning moderate, 6 to 7 meaning high, 8 to 10 meaning very high and above 10, meaning extreme.  

How is UV index calculated? 
The UV index takes into consideration how much UV radiation having different wavelengths is around us, and how more the number of wavelengths, the more it affects human health. For this, governments and weather agencies lay out a network of UV sensors that measure sunlight at different wavelengths to determine the UV index. This data is then combined with other data such as location, cloud cover, and atmospheric conditions to create weather forecasts. 

Why is the UV index different around the world? 
The UV index that is reported in a weather forecast is usually the daily maximum, i.e., the highest it can reach all day. However, how much high it will reach depends on a lot of factors like location, time of the year, the rate of cloud cover, ozone and pollution levels.  

If the location is closer to the equator or at high altitudes, the UV index is usually higher as the sun’s radiation has to pass through less amounts of air before reaching the ground level. This is why during Australian summers, the UV index ranges from 10 to 14, while during British summers it is usually between 6 and 8. Moreover, during summer in the southern hemisphere, the earth is closer to the sun compared to summer in the northern hemisphere. For this reason, the UV radiation is automatically higher in the southern hemisphere. Moreover, if the pollution content is high in a location, it is able to absorb or block the UV radiation, in turn lowering the UV index.