## Simple question about conversion factor

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susonic
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### Simple question about conversion factor

Hi,

I'm trying to use ERA40 forcing. The solar radiation unit is w/m^2/s.

I need to convert this to w/m^2 which is unit for ROMS.

What should I do?

-JH

susonic
Posts: 160
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Location: Jeju National University
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### Re: Simple question about conversion factor

turuncu
Posts: 128
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### Re: Simple question about conversion factor

Hi,

I think that you should do following,

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``W/m^2/s --> 1/(60*60*dt) W/m^2``
In this case dt (in hour) should be the time interval of the input data. For example for 6 hourly data the conversion factor will be,

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``1.0/(60.0*60.0*6.0) = 1.0/21600.0 = 4.62963e-5``
So, you can also check the results after conversion. I also plan to use the ERA40 and i think that variable ssr can be used for net shortwave radiation but i am not sure. If you have any information about it, please let me know. For example, is it includes the cloud effect?

susonic
Posts: 160
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### Re: Simple question about conversion factor

Hi back,

I tried to search in google and got an answer like below.
http://stommel.tamu.edu/~baum/ecmwf.html
2. The "Surface solar radiation" in "W m**-2 s" needs to be converted into a "shortwave radiation flux" in "W m**-2".
shortwave radiation flux (W/m^2) = surface solar radiation (W/m^2/s) * 3600*3 s
They suggest 10800 as a conversion factor. Is it because ERA-interim data is 3 hourly data?

When I compare the value between monthly ERA 40 and NCEP, I saw that the conversion factor supposed to be 21600 even though the input data interval is monthly time scale. Would you clarify why is this, please?

i think that variable ssr can be used for net shortwave radiation but i am not sure.
As far as I know, ssr is net shortwave radiation.

is it includes the cloud effect?
Yes I believe that the cloud effect is included in net shortwave radiation.

-JH

turuncu
Posts: 128
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### Re: Simple question about conversion factor

Yes. The ERA Interim is 3 hourly. So the conversion factor will be different in that case. I am using 4.62963e-5 for 6 hourly ERA40 data.

susonic
Posts: 160
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### Re: Simple question about conversion factor

Then the monthly ERA-40 data is probably averaged value from 6 hourly data.

Thank you very much for your replies.

-JH

mashinde
Posts: 135
Joined: Mon Jun 22, 2009 3:46 pm
Location: Indian Institute of Tropical Meteorology, Pune, INDIA

### Re: Simple question about conversion factor

Hi

I am using ERA40 from 00hrs, 06hrs, 12hrs and 18hrs. so in that case what should be the multiplication factor for ssr ?

any suggestions ?

thanks