Mathematically characterise 3-series, and their interaction

#1
Dear smart people,

Can you give me some guidance on a characterization problem. I want to characterize behaviour of these 3 lines, they cross each other and then diverge eventually.

Where should I start?

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hlsmith

Not a robit
#2
I haven't worked much with time series, so I will see what vague help I can provide. How often were data collected in these series, it seems like perhaps weekly.