Timing differences between variables that exhibit large diurnal magnitudes can be difficult to discern in time series plots. However, when plotted against each other systematic deviations can be seen directly. This is illustrated for solar radiation Rsd and two variables Y1 and Y2 in Fig. 1 as a time series plot in Fig. 1a and hysteresis loop plot in Fig. 1b. The example shows a variable Y1 that has a different magnitude than Rsd but is perfectly in phase with Rsd. This results in a linear relationship as illustrated in Fig. 1b. In contrast, variable Y2 has a time lag with respect to Rsd. This time lag results in a counterclockwise hysteresis loop when plotted against Rsd, see Fig. 1b. Such a time lag is difficult to identify from a time series plot.