Specify the location by giving the callsign or IATA code of a nearby airport. 2000 USA airports and the biggest 300 world airports are in the database, which is extracted from the FlightGear database. Alternatively, leave the airport blank and give the latitude, longitude and elevation of the target point.
The Ultraviolet Index is 40 times the erythemal irradiance (sunburn power) in watts/M2. Here is a qualitative translation:
|UV Index||Adjective||Fry time (mins)||Protection|
|3-4||Low||15-90||Clothes and sunscreen|
|5-6||Moderate||10-60||Stay in shade|
|7-9||High||7-40||Avoid noon sun|
|10 and up||Very high||3-30||Stay inside|
One Dobson Unit is 1e-5 meters equivalent thickness of ozone at standard temperature and pressure. In Los Angeles between 1979 and 1994 the ozone layer thickness declined from 368 to 330 Dobson Units. It is expected to reach a minimum in 1996 and then slowly increase, due to the Montreal Protocol on Fluorocarbons.
The fudge factor multiplies the ultraviolet intensity. On snow or sand it may be as high as 2 due to reflection off the snow; under smog or clouds it would be less than 1.
You may specify the Sun's elevation above the horizon (in degrees) directly; if you enter a number in that box, it will be used instead of the ultraviolet index, ozone level and fudge factor.