ERA5 solar radiation at surface variables: direct, net, downwards

I am using ERA5 database to analyze solar radiation parameters at the surface. Here I encounter the problem that I don’t understand very clear the meaning/definition of each variable. What is the difference between total sky direct radiation at surface, surface net solar radiation and surface solar radiation downwards? I couldn’t find the answer in ERA documentation. At first, I thought that net solar radiation comprises direct and scattered radiation, hence total sky direct radiation at surface should be always less than surface net solar radiation. However, after loading the data it turns out that it is not always the case. That fact made me curious: how total sky direct radiation at surface may be higher than surface net solar? I have uploaded the graph to illustrate my question. Thank you!

Try this document:

Robin Hogan, Radiation Quantities in the ECMWF model and MARS

Thank you very much , Anabelle!