- #1
simonbour
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Hi all,
I am interested in estimating the amount of UVA and UVB from the UVI index for parctical purposes.
I have found 2 research papers that shed some light on the matter (see [1][2]).
Let us define first UVB as the solar irradiance integral in the range 280-315mm
and UVA as the solar irradiance integral in the range 315-400mm
From [1] it is established that for zenith angles < 70deg the following relationship hold with an accuracy > 90%:
UVB[W/m2] = 18.9 UVI
From [2] it is established, for a specific region (Kuwait), that the relationship between UVA and UVB for zenith angles < 50deg is:
UVA = 41 UVB
Here comes the part where I hit the wall. Doing a simple google search on weather condition today in Kuwait, I get and UVI = 6, this would imply (for zenith angle < 50deg):
UVB = 113 W/m2
UVA = 4649 W/m2
This is way to much radiation in the UV band. Even at the Atacama Desert, full-spectrum irradiance values only go as high as ~1300W/m2
So I am left with 3 options (not mutually exclusive):
1. Paper [1] is wrong
2. Paper [2] is wrong
3. I am wrong
Any thoughs?
Thanx in advance!
Simon.
References:
[1] McKenzie et al. Relationship between UVB and erythemally weighted radiation
[2] Kollias et al. The value of the ratio of UVA to UVB in sunlight
I am interested in estimating the amount of UVA and UVB from the UVI index for parctical purposes.
I have found 2 research papers that shed some light on the matter (see [1][2]).
Let us define first UVB as the solar irradiance integral in the range 280-315mm
and UVA as the solar irradiance integral in the range 315-400mm
From [1] it is established that for zenith angles < 70deg the following relationship hold with an accuracy > 90%:
UVB[W/m2] = 18.9 UVI
From [2] it is established, for a specific region (Kuwait), that the relationship between UVA and UVB for zenith angles < 50deg is:
UVA = 41 UVB
Here comes the part where I hit the wall. Doing a simple google search on weather condition today in Kuwait, I get and UVI = 6, this would imply (for zenith angle < 50deg):
UVB = 113 W/m2
UVA = 4649 W/m2
This is way to much radiation in the UV band. Even at the Atacama Desert, full-spectrum irradiance values only go as high as ~1300W/m2
So I am left with 3 options (not mutually exclusive):
1. Paper [1] is wrong
2. Paper [2] is wrong
3. I am wrong
Any thoughs?
Thanx in advance!
Simon.
References:
[1] McKenzie et al. Relationship between UVB and erythemally weighted radiation
[2] Kollias et al. The value of the ratio of UVA to UVB in sunlight