Okay good one but but you do realise that the graph is from 2017. 

Anyway that cycle shown in the graph doesn't seem to be following in the reality. I mean it just look like the cyclic patterns made with the copy paste job and shown on the higher scale thats all.

However if we see the numbers then we do have similar kind of pattern in reality where prices has always dumped in the Q1-Q2 and then again rise back before the year end. This is continuing since many years and will follow ahead to rebounding the prices to higher one in the side to end year.