Plotting the number of active weather stations

Not all weather stations are active over the entire history of the data set, so another way to look at the data is in terms of how many weather stations are active for any given year. In order to be considered active a weather station must have made at least one temperature measurement during a particular year.

For example:

    tempgraph --ghcn v2.mean --countrycodes v2.country.codes --start 1900 --activestations graph_active_stations.png

Produces a graph showing the number of active ground weather stations worldwide since 1900.

You can also narrow down the search for particular countries:

    tempgraph --ghcn v2.mean --countrycodes v2.country.codes --start 1900 --activestations graph_active_stations.png --countries "france,germany"

The number of active stations per year for the entire GHCN data set looks like this: