Up/down bars in excel graph - how to interpret?

Dear Excel Experts,

I need to explain the meaning of the up/down bars in the Excel graph, which I attach here.

The graph shows the variable, its linear trend, and the 95% confidence intervals. Also I want it to demonstrate the error bars (which it does) ad the up/down bars (which it does). 
And eventually, in the caption to the figure I need to provide the proper explanation of the graph (which I did) and the professional explanation of the up/down bars - which I seek from you.
Thank you in advance,