The net temperature tendency from the parametrised processes (accumulated from the beginning of the forecast) is available on model levels from the twice daily forecasts at forecast steps 3, 6, 9, 12 hours, see Table 15 of the ERA-Interim archive document:
To download this data, please follow the instructions on How to download ERA-Interim data from the ECMWF data archive.
In ERA5, this quantity, the Mean temperature tendency due to parametrisations, is archived as a mean (since previous post processing), see Table 13, paramId=235005, in the ERA5 data documentation.
To download this data, please follow the instructions on How to download ERA5.
References of interest:
Robin Hogan, Radiation Quantities in the ECMWF model and MARS
Jian Ling and Chidong Zhang: Diabatic Heating Profiles in Recent Global Reanalyses. JCLI 3307-3325, 2013, DOI: http://dx.doi.org/10.1175/JCLI-D-12-00384.1
J. S. Wright1 and S. Fueglistaler2: Large differences in reanalyses of diabatic heating in the tropical upper troposphere and lower stratosphere. Atmos. Chem. Phys., 13, 9565–9576, 2013