Here is my time series plot of some data. There appears to be a constant variance, but I don't believe that the mean is constant (e.g., big dip around time $t=17$ and big increase around time $t = 57$). Is it correct for me to say that this time series does not have a constant mean, but it does have a constant variance? I am a beginner to time series analysis.
If you are a beginner to the time Sseries topic: I would advise you to someone, who has the same charm as Josh Starmer:
He is known under the channel ritvikmath: https://www.youtube.com/watch?v=oY-j2Wof51c&t=6s
You should check if your series is stationary by applying visual, global/local tests of rolling windows (e.g. mean,variance) but the better would be a statistical test. Thus, I would advise you to check this video, and the video on
If you then still dont know how to deal with your time series, we are pleased to help you. But I would advise to first look into a few of his incredible vids.