System-defined monhly time series
As the roots of the Climate Explorer are in ENSO teleconnections, the following monthly time series are always available to correlate when the time scale is monthly. For other time scales only time is available at the moment. You can also correlate with a user-defined time serie, which is generated by selecting it. If it is of type "index" it will atomatically be added to the list, otherwise add it to the list explicitly.