Climate Variables are time dependent variables: Each value has a time when this value took place. Simple way to look at climate time dependence is to plot the climate variable versus time (Figures 1 and 2)

Figure 1. Time Series Plot of Maximum Daily Temperature (degree F) at Bismarck, North Dakota

The temperature time series (Figure 1) displays a pattern that resembles a sin/cosin function because of the annual cycle. There is also variability within each individual year and between years.

Figure 2. Time Series Plot of Daily Precipitation (inches) at station Roosevelt, Arizona

The precipitation time series (Figure 2) displays discrete character: Precipitation episodes interrupted by periods of dryness. In this example the annual cycle is less obvious. Precipitation amount vary within a year and between years.