Hi everyone,
I have downloaded the Surface thermal radiation downwards data from ERA5-Land hourly data:
https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-land?tab=overview
The unit is J/m2 and I want to change to W/m2/s. So The Surface solar radiation downwards data (J m-2) is divided by 86400 seconds (24 hours) to convert to the commonly used units of W m-2 according to the ERA5 documentation:
https://confluence.ecmwf.int/display/CKB/ERA5%3A+data+documentation
I found the value is very strange. The left panel (a)(c) is extracted from the Surface solar radiation downwards data in ERA5 Land. The right panel (b)(d) are observations from FLUXNET2015 dataset (They are in same periods year 2010). I don't know why they have such large differences (the data outside red dashed line represent the values outside observations). Does anyone have some ideas? Thanks a lot!
Wenli
I think that should be divided of the Surface solar radiation on number of hours’ sunrise only.
Basim Freegah Hi Basim, Thanks a lot for your suggestion. But according to the ERA5 documentation, it should be divided by 86400 seconds (24 hours). https://confluence.ecmwf.int/display/CKB/ERA5%3A+data+documentation
Anyway, I would send an email to them. Thanks.
Hi
In the documentation you provided the link for:
Under the sub-section: Mean rates/fluxes and accumulations
"reanalysis: accumulations are over the hour [...]"
I think you should divide by 3600.
By now I think you got the answer, it would be nice if you could share it here. Because I am getting very large values of shortwave and longwave from ERA5 when I divide J/m2 by 3600.
To the future researchers having questions on the conversion of J/m2 into W/m2 for ERA5-land hourly data:
please look at the conversion table provided in the following link,
https://confluence.ecmwf.int/pages/viewpage.action?pageId=197702790
The critical note: "Accumulations are from 00 UTC to the hour ending at the forecast step"
So in order to have the W/m2 for 05UTC, you need to subtract J/m2 of 04 from 05 and divide the number by 3600. Only for 01UTC you do not need to subtract from the previous time step.
Hope it helps and make sure you check the url.
----- App
if you look at J/m2 values of shortwave radiation for instance for 24 hrs, its like this (scaled by 1e-4, and from 00 to 23UTC):
473.072511449194, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.05968637480363, 35.0146683716601, 112.767829020493, 216.360691462317, 323.604816114019, 424.342204263501, 502.610286506035, 552.791736364885, 571.750213223872, 572.124701655654, 572.124701655654
location: 45 lat, -73 long
The reason why 00UTC is not "zero", its because it is accumulated from previous day, as the "critical note" notes.
Alireza Amani Thank you for the clear explaination! I just have the same question and found your answer here. It provides me a great solution!
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