The graph shows the average daily amount of INcoming SOLar radiATION (insolation) for Decorah. The units are watts per meter squared. This is the amount, on average, of energy incident at the top of the atmosphere for the given day. About 30% is reflected back to space without being absorbed by air, clouds or the surface of the earth.

The maximum value is 486.7 on June 21 (Julian day number 172 in a non-leap year).

The minimum value is 133.3 on December 21 (Julian day number 355).