I suspect that it is Joules per day. The heat will transfer into the soil during the day mainly through solar radiation, and leave during the night as long-wave terrestrial radiation. The figure you are being given is the net radiation averaged over 24 hours.

I could be wrong, but if some values are negative depending on the season then it is likely I am correct.

Dear Alastair Bain McDonald,

I am confused with this data. If you find time, please have a look at the data.  Thank you.

http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/

Hi Kishore,

I opened the web page you cited the title says that it is daily data.

I then downloaded a netcdf file with the following parameters:

================================

Request abstract:

Atmospheric model, Surface, 1, interim_daily, 3 to 12 by 3, 0.75°, Surface sensible heat flux, 00 UTC 12 UTC, 1979-12-01...1979-12-31, Forecast, ERA Interim

The status of the request is: complete

Download (54.8MB)

==============================

Note that the file is fairly large and if you dump it as a text file, few editors will handle it efficiently, if at all. So I only dumped the header using ncdump, a program freely available on the web with NetCDF, but which I had compiled from the source to run with my operating system (Windows XP :-)

==============================

units = "J m**-2" ;

long_name = "Surface sensible heat flux" ;

standard_name = "surface_upward_sensible_heat_flux" ;

=============================

So that confirms that the units are in J m-2, but the long_name and standard_name seem to be reversed. The standard name is longer than the long name.

Moreover, it seems to suggest that what is being measured is not the net radiation, which I proposed in my first reply, but rather the heat lost by conduction/convection across the surface-air boundary, although I cannot imagine how it is measured. (In fact there is another question open in ResearchGate asking that very question.)

My advice is to contact ECMWF directly. Although they are a European group, they are based in England and English is their working language.  I think you will find them friendly and supportive.

HTH, Alastair.