I couldn’t help but notice that there was an equally cold spike at the bottom.

Can you please define "equal"? (and exactly which pic you're referring to?)

-3.5 sigma in the middle of the year in the only graph the article has.

It's one year, from left to right. The termination of the red line is in the middle because it's the middle of the year.

The range is provided in the title. Presumably it's just regularly sampled over that range.

It is labelled "Day of Year".