|Number of stations at each reporting interval|
|Proportion of stations at each reporting interval|
The first plot shows the number of stations at each reporting interval. I've included the option of 6 hourly as well. Firstly, there is a drop in the number of active station after around 1990. This plot shows the reporting intervals for the ~4200 "accepted" stations, i.e. those which are thought to be suitable for climatological studies. The second plot shows how the proportion of the different reporting intervals changes. The number of three hourly stations falls off with time, and the number of hourly stations increases.
If your application could depend on the reporting interval (or changes in it) then this may be of use.