Timeseries: correlation - Hysteresis (image 1)

A scatter plot of water temperature versus air temperature on April 27, 2019, for the Paine Run stream in Shenandoah National Park. Points are plotted for each 30-minute interval. Daytime points are hollow, while nighttime points are solid. The points form a figure eight shape, illustrating the concept of hysteresis – a phenomenon in which the value of a physical property lags behind changes in the effect causing it. For example, stream temperature changes in response to air temperature, but the stream warms more slowly than air in the mornings, and cools more slowly than air in the evenings. If water temperature tracked stream temperature exactly, the points would fall on a straight line, rather than in a figure eight.