UVB highest at noon?

Question

Is it true uvb is highest at noon? How could that be for the continguous 48 states- thanks

Answer 1

Place a one foot square of material in a darkened room.  Hold a flashlight about 6 feet from it and shine the light on the square from about floor level (sunrise), directly overhead (high noon) and floor level on the other side (sunset).  Because of the low or high angle of the flashlight, the light intensity will pass from minimum to maximum to minimum.  At minimum the square will look like a small rectangle (one foot wide) receiving very little light (per square inch).  For the actual sunlight, length of path through the atmosphere (filled with particles?) will be greater at sunrise and sunset).  This also explains why the poles never receive direct (overhead) sunlight and the sun intensity (on a square foot) varies from summer to winter everywhere but near the equator.

Answer 2

Yes it is true. All solar radiation is most powerful at noon because the light has less atmosphere to penetrate. The greater the angle (the earlier in the day) the longer the distance the light has to travel, through the atmosphere, before it reaches the surface. The atmosphere is our main protection against harmful solarradiation as it absorbs and reflects many wavelenghts of EM radiation.

Answer 3

On a cloudless day this is true for local solar noon wherever you are.  However, this will almost certainly not fall at noon as measured on the clock.  First, there is the matter of daylight saving time, which will push the maximum back an hour.  Second, it will depend on how far east or west you are in your particular time zone.

Answer 4

Peak hours are 10-4 with noontime being when the sun is directly overhead.