For some time now I have been looking for a correct definition on how
to compute global radiation. I have a number of parameters, which
could be used such as downward and upward short & long flux. However I
have not been able to find any helpful information. Would anybody be
able to help me with either a mathematical equation and or some other
definition in order to calculate global radiation derived from other
parameters??

Thanks a million

Rob wrote:

For some time now I have been looking for a correct definition on how
to compute global radiation. I have a number of parameters, which
could be used such as downward and upward short & long flux. However I
have not been able to find any helpful information. Would anybody be
able to help me with either a mathematical equation and or some other
definition in order to calculate global radiation derived from other
parameters??

Thanks a million

Which other parameters ? This can be an easy or very difficult problem
depending on the accuracy desired and which part of the spectrum considered.
The clear sky problem is generally rather accurate, but clouds greatly
complicate the matter. Obstructions to the horizon also may be a
consideration.

Joseph Bartlo wrote in message ...
Rob wrote:

For some time now I have been looking for a correct definition on how
to compute global radiation. I have a number of parameters, which
could be used such as downward and upward short & long flux. However I
have not been able to find any helpful information. Would anybody be
able to help me with either a mathematical equation and or some other
definition in order to calculate global radiation derived from other
parameters??

Thanks a million

Which other parameters ? This can be an easy or very difficult problem
depending on the accuracy desired and which part of the spectrum considered.
The clear sky problem is generally rather accurate, but clouds greatly
complicate the matter. Obstructions to the horizon also may be a
consideration.

Joseph,

Thanks for your reply!!

I have access to all GFS (AVN) parameters provided in the GRIB files.

Rob wrote:

Joseph,

Thanks for your reply!!

You're welcome.

I have access to all GFS (AVN) parameters provided in the GRIB files.

I'll have to look to see all the radiation parameters included here, but I
seem to recall it includes just about all of them - i.e., global solar, in
& outgoing IR - I'm not sure about UV. What do you want ? Net radiation
on the horizontal plane ?

If you are looking for very accurate calculations, the GFS probably isn't
the way to go - but if you want something automated, it may be the best you
can do (past the 84 hour period - prior the ETA would probably be better).

Again, what is it you are trying to accomplish/calculate that the GRIB files
don't include ?

I'll have to look to see all the radiation parameters included here, but I
seem to recall it includes just about all of them - i.e., global solar, in
& outgoing IR - I'm not sure about UV. What do you want ? Net radiation
on the horizontal plane ?

All parameters included in GFS can be found he
http://strc.comet.ucar.edu/software/.../AVN_WO10I.htm

If you are looking for very accurate calculations, the GFS probably isn't
the way to go - but if you want something automated, it may be the best you
can do (past the 84 hour period - prior the ETA would probably be better).

ETA doesn't cover Europe, so for now we'll have to work with GFS.
Unlike NCEP models, European models are very $$$$$$$$$$$. :-(

Again, what is it you are trying to accomplish/calculate that the GRIB files
don't include ?

I would like to compute/calculate global radiation in J/cms. According
to what I know and read on the web, global radiation in the sum of
"direct radiation" and "diffuse radiation".

I heard that Net radiation flux can be derived from the up & downward
short and long flux.

Thanks for your time and help!!

Rob wrote:

I would like to compute/calculate global radiation in J/cms.

Of course, then the problem is simply converting from W/m^2 to J/cm^2
(W = J/sec). So if you want J/cm^2, you actually seek a total for a
period of time.

Rob wrote:

According to what I know and read on the web, global radiation in the sum of
"direct radiation" and "diffuse radiation".

That's true, though this terminology is only relevant for solar radiation,
because there is a direct component (from the sun) and a diffuse (scattered)
component.

Though the term is rarely used, I suppose there is a "global terrestrial
radiation" also, which would refer to the downward terrestrial (longwave)
amount incident to horizontal. But for the idea of direct and diffuse
components is obviously meaningless.

Thus the term "global radiation" could refer to both solar and terrestrial -
essentially the sum of ALL wavelengths, downward and incident to horizontal.
Yet again, that's probably not what you want. Above, you speak of the sum of
a direct and diffuse component, which as I said is only relevant for solar.
This is why I asked what you are trying to calculate - i.e., ultimately what
are you using this for ? That'd clarify which "global radiation" you really
want.

Though the basic ideas are simple, see how confusing the terminology can
become ?