Angstrom, Hargreaves and extended Hargreaves coefficients for various
countries are available at: http://www.iwan-supit.cistron.nl/radiation
The website describes the Crop Growth Monitoring System (CGMS) and the crop
growth simulation module WOFOST 6.0 description at:
http://www.iwan-supit.cistron.nl/~iwan-supit/contents/start.htm.
Within CGMS, the WOFOST output is used as a basis for monitoring the quality
of the agricultural season over the whole EU territory and for yield
forecasting per administrative region. The WOFOST/CGMS documentation is
based on the WOFOST 6.0 documentation prepared by I. Supit, A.A. Hooijer and
C.A. van Diepen which on its turn was based on published papers, research
reports and source code of earlier WOFOST versions
Regards
Michele Bernardi
Environment and Natural Resources Service (SDRN)
Food and Agriculture Organization of the United Nations (FAO)
-----Original Message-----
From: Maurits Van den Berg
[mailto:[log in to unmask]]
Sent: 21 April 2002 21:19
To: [log in to unmask]
Subject: Re: How to convert bright sunshine hours to solar radiation
As Ayman Suleiman suggests, it is obviously impossible to explain 100% of
variation in solar radiation by any equation based on bright sunshine hours.
Nevertheless, pretty good estimates can be obtained. The best way to find
out is to check for a nearby climate station with sufficient data.
I just compared records of 6 years (1995-2001) of measured daily solar
radiation (Rg) with bright sunshine hours (n) and calculated
extraterrestrial radiation (Ra) and daylength (N) for a weather station in
São Paulo State Brazil, using the equation
Rg = Ra*(a + b*(n / N))
N and Ra were calculated using equations of the ASTRO subroutine of the
SUCROS model (which at first glance are the very same ones as those in the
FAO publication mentioned by Michele Bernardi).
Parameters a and b were calculated by simple regression for the equation
Rg/Ra = a + b*(n / N)
I found a=0.23 , b=0.45 and an R^2 of 0.82
Obviously, different values may apply for different regions.
The same parameter values were found when using data of either January
(rainy summer season) or June (dry winter season), suggesting that the
relation is stable over the seasons. However, slightly (but significantly)
different values for "a" were found when using the regression analysis for
1995 and 2001 separately. I haven't had time to find out if this difference
is something "real" or a small systematic error in one of the measuring
devices which might have been corrected (or introduced) between 1995 and
2001.
Regards,
Maurits van den Berg
- - - - - - - - - - - - - - Original Message - - - - - - - - - - - - - -
From: "Bernardi, Michele (SDRN)" <[log in to unmask]>
Subject: Re: How to convert bright sunshine hours to solar radiation
Date: 04/20/02 09:14
You can find detail reference on various methods to calculate solar
radiation in Chapter 3 of the FAO book "Crop evapotranspiration - Guidelines
for computing crop water requirements - FAO Irrigation and drainage paper
56".
It is avilable on-line here:
http://www.fao.org/docrep/X0490E/x0490e00.htm#Contents
Regards,
Michele Bernardi
Agrometeorology Group, Room B-650
Environment and Natural Resources Service (SDRN)
Research, Extension and Training Division
Sustainable Development Department
Food and Agriculture Organization of the United Nations (FAO)
Viale delle Terme di Caracalla 00100 Rome (Italy)
Tel: +39-06-57052442; Fax: +39-06-57055731
E-mail: [log in to unmask] Web site: www.fao.org
Environmental information: www.fao.org/sd/ENdef_en.htm
-----Original Message-----
From: Ayman Suleiman [mailto:[log in to unmask]]
Sent: 19 April 2002 19:34
To: [log in to unmask]
Subject: Re: How to convert bright sunshine hours to solar radiation
Dear Dr. Dharam and Roger:
I have a thought about Roger's comments. Any relationship of the form: Rg =
Ra*(a + b*(n / N)) , where Rg is global solar radiation, Ra is
extraterrestrial solar radiation , and a, b are numerical parameters, has
an assumption about the ratio of clear day global solar radiation and the
extraterrestrial solar radiation (Ra). For instance, FAO relationship Rg =
Ra*(0.25 + 0.50*(n / N)) assumes that Rg/Ra for a clear day is 0.75. From
my experience, I know that Rg/Ra for a clear day varies from one day to
another and from on location to another. That leads me to belive that using
clear day global solar radiation instead of extraterrestrial solar
radiation in the above equation would give more accurate estimates of
global solar radiation using n / N. More than two years ago, I and Joe
Ritchie developed a procedure to find clear day global solar radiation at
any place in the world. I have not heard from Joe about it for so long, but
as far as I know, this work has not been published yet but I think it is
obtainable!
Regards,
Ayman
Ayman Suleiman, PhD
Research Associate
Civil and Environmental Engineering Dept.
7B DANA Engineering Building
Bucknell University
Lewisburg, PA 17837
Voice: (570) 577-1692
Fax : (570) 577-3415
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