Counting days with Temp < 0 (frost days) using cdo eca_fd
Added by Malcolm Mistry over 9 years ago
Hello All,
I need to count the number of days below 0 deg C (over each grid point) from a daily global gridded temperature (in deg Kelvin) .nc file. The file is a model daily mean temperature for a particular year (e.g. 1971), at 0.5 x 0.5 deg resolution, in deg Kelvin
I used 'cdo eca_fd input_file output_file' and have the count created as 'frost days index' variable in output file without any errors. Since it is annual gridded file, I would need to read/count temp over each day and verify the results.
My question is whether this eca_fd' operator can be applied to a file of 'daily mean temp'? The CDO user guide says that the input variable should be 'daily min temp'. It does not elaborate more as to how the CDO operator would distinguish between the variable (temp), whether it is 'daily mean' or 'daily min' (I am assuming from the attributes).
So basically, do I need to find the data of 'daily min temp' in order to apply this operator correctly.
CDO version: 1.6.3
Rgds
Malcolm
Replies (3)
RE: Counting days with Temp < 0 (frost days) using cdo eca_fd - Added by Jaison-Thomas Ambadan over 9 years ago
I need to count the number of days below 0 deg C (over each grid point) from a daily
global gridded temperature (in deg Kelvin) .nc file. The file is a model daily mean
temperature for a particular year (e.g. 1971), at 0.5 x 0.5 deg resolution, in deg Kelvin
I guess you could use the comparison operators for the same purpose. For example,
cdo -timsum -lec,0 daily_temp_1971.nc no_of_days.nc
should give the number of days below 0 at each grid-point.
Cheers,
J
RE: Counting days with Temp < 0 (frost days) using cdo eca_fd - Added by Malcolm Mistry over 9 years ago
Thank you Jaison,
However, the -timsum is meant to sum up the values over all timesteps (and give a total value of temp in my case). I am not sure what -lec,0 is suppose to do. But when I tried, it gives me '0' in the output file (over all those gridpoints where I actually have a count of certain number of days below < 0 deg).
The eca_fd is operator is actually meant to do this count. However, the user guide says that the variable should be 'daily min temp'. In my case, the variable is 'daily mean temp'. My doubt is whether it really matters cause the end operation is suppose to count days < 0 deg out of a file (whether it is a 'min' file, 'mean' file or 'max' file).
Rgds
MNM
RE: Counting days with Temp < 0 (frost days) using cdo eca_fd - Added by Malcolm Mistry over 9 years ago
Hello Jason,
I understand what -lec means now (found it in the user manual). However, I am not sure if it is of relevance on this operation that I am doing.
In fact, I have another thread which I opened for a similar operation ("histcount"). May be it is more applicable there..am checking on that..
Thanks
MNM