I have ERA5 files that I am trying to concatenate into monthly files. It appears the files have been packed to reduce size making the data type within the file a short. When I try **ncrcat**, it will warn about encountering a packing attribute **"add\_offset"**, then concatenate all the files together. However the values of the data become messed up. I tried using **ncpdq -U** to unpack the files, then **ncrcat** to concatenate which works. But the resulting files are too large to be useful and when I try **ncpdq** to repack the resulting file I receive a **malloc() failure** which seems related to a memory/RAM issue.

I've also tried **cdo merge** which strangely works perfectly for most of the concatenations, but a few of the files fail and output this error **"Error (cdf\_put\_vara\_double): NetCDF: Numeric conversion not representable"**

So is there anyway to concatenate these files while they are still packed, or at least a way to repack the large files once they are concatenated