Dear all:

I completely agree with Ralph and Gerritt about watt meaning J/s. I add to
this a commentary about my knowledge of the existence of energy units (J is
energy and watt is power) such as kilowatt - hour, but I've never heard of
an energy unit named as watt-s (even if we could easily define it). I wonder
if in the original request of our colleague Camerino the second letter "s"
in Wattss means Watts - s or is simply an additional pluralization of Watts?

And I have one or two additional uncertainties of my own:

If I had my solar radiation reported in watt/m2 (per day!) should I multiply
it by 86 400 seconds in a day and divide by one million to obtain MJ/m2, or
should I multiply by the number of seconds between sunrise and sunset?

And besides:

If I had my solar radiation reported hourly in watt/m2 (That's what I have
in practice in my specialized solar radiation stations) then I should use
some numerical aproximation (let's say Simpson's rule) to the integral of
solar power between sunrise and sunset to obtain global solar radiation in
MJ/m2? I can't just simply multiply by the number of seconds in an hour or
day!

I would advice Camerino to ask his weather station or met service what and
how are they really measuring as global solar radiation which in some cases
is even reported separatedly as direct and diffuse solar radiation.

Sorry for taking some of your time,

Roger



----- Original Message -----
From: "Sommer, Rolf (ICARDA)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 24, 2007 1:56 AM
Subject: Re: I NEED HELP CONVERT DATA CLIMATIC


> Dear all,
>
> though a bit nitpicking, but:
>
> Watts are of course _not_ expressed in W/s!
>
> 1 Watt per definition is 1 J/s.
>
> So solar radiation expressed in W/m2 is equal solar radiation expressed in
> J/(sec * m2)
>
> Everything else is playing around and converting from seconds to day and
> to Mega-Joule. (Should be straight forward)
>
> Regards,
> Rolf
>
> ==============================================
> Dr. Rolf Sommer
> International Center for Agricultural Research
> in the Dry Areas (ICARDA)
> P.O. Box 5466, Aleppo, Syria
> Tel 00963 21 2213433
> and
> ZEF, Center for Development Research
> Department of Ecology and Resource Management
> University of Bonn
> Walter-Flex-Str. 3
> 53113 Bonn Germany
>  Help save paper - do you really need to print this email?
> ==============================================
>
>
>
>> -----Original Message-----
>> From: DSSAT - Crop Models and Applications
>> [mailto:[log in to unmask]] On Behalf Of Gerrit Hoogenboom
>> Sent: Thursday, May 24, 2007 05:24
>> To: [log in to unmask]
>> Subject: Re: I NEED HELP CONVERT DATA CLIMATIC
>>
>> Camerino Rojas Montes,
>>
>> 1 Ws/2 = 1 J/m2
>>
>> Watts is normally expressed as W/s, which is the
>> equivalent of radiation intensity. You,
>> therefore, need to integrate the intensity over
>> the day in order to calculate total energy  = MJ/m2/day.
>>
>> Regards,
>>
>> Gerrit
>>
>>
>>
>> At 09:31 PM 05/23/2007, you wrote:
>>
>> >I UNDERSTAND WHICH DSSAT OPERATE WITH CLIMATIC
>> >DATA OF SOLAR RADIATION IN Megajoules/m2 BUT MY
>> >WEATHER STATION TO CAST OUT DATA SOLAR RADIATION
>> >IN Watss/m2.<?xml:namespace prefix = o ns =
>> >"urn:schemas-microsoft-com:office:office" />
>> >
>> >
>> >
>> >I NEED HELP FOR CONVERT Watss/m2 TO Joules/m2.
>> >
>> >
>> >
>> >THANKS.
>> >
>> >
>> >
>> >CAMERINO ROJAS MONTES.
>> >
>> >UNIVERSIDAD AUTONOMA AGRARIA ANTONIO NARRO.
>> >
>> >SALTILLO, COAHUILA, MEXICO.
>> >
>> >
>> >----------
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>
>