overlay multiple time series on one plot

Hello,

I have four different time series from the same time period within a 
year (February through August) but they are from different years. I can 
not figure out how to plot them all  (so they will be overlayed instead 
of plotted on after another) on the same graph with the x-axis 
corresponding to the month/day instead of  year/month/day.

Thank you.

Max