TEMIS -- UV index & UV dose based on GOME -- archive

UV index & UV dose based on GOME	UV radiation monitoring
Overview of the data product archive

Monthly averages versus 10-day averages
It is common practice to produce monthly averages of quantities that fluctuate from day to day, such as the UV index and the UV dose, in order to better understand the yearly variation. But there can be large differences between two consecutive monthly averages. The following graph shows as an example the relative difference of two monthly averages.

Relative difference between the monthly average erythemal UV index fields for February and March 2002 where the UV index exceeds 0.25 (in the polar regions the UV index is lower than that). For clarity only relative differences larger than 10% are plotted. The largest relative difference in the plot is about 276%.

There are large areas where the relative differences exceeds 50% (white areas in the plot), going up to 276%. For such comparisons it may be more useful to have a look at differences between 10-day averages. The following graphs show some examples of the same period as in the above graph. The areas with differences above 50% are now clearly much smaller.

Relative difference between the 10-day average erythemal UV index fields during February and March 2002 where the UV index exceeds 0.25 (in the polar regions the UV index is lower than that). For clarity only relative differences larger than 10% are plotted.

Largest relative difference: 77%. Largest relative difference: 69%.

Largest relative difference: 77%. Largest relative difference: 96%.

Relative difference between the 10-day average erythemal UV index fields during February and March 2002 where the UV index exceeds 0.25 (in the polar regions the UV index is lower than that). For clarity only relative differences larger than 10% are plotted.
Largest relative difference: 77%.	Largest relative difference: 69%.
Largest relative difference: 77%.	Largest relative difference: 96%.