How many observations were used to produce the grids?
The number of stations used as input to the gridding varies with time, partly due to changes in the size of the observing network and partly due to the availability of digitised data. A typical starting year for daily and monthly data is 1961, although some monthly data have been digitised further back (see Q4). During the period 1961 to 2000, the average number of stations used is shown in the following table. Climate variable Average no. of stations Air temperature 540 Rainfall 4400 Sunshine duration 290 Pressure, cloud, wind speed 70 The variation in the numbers of rainfall and temperature stations used from 1960 to 2006 is shown in the following graph.
