The featured graph is a preview of some exciting upcoming changes to the ISU Soil Moisture Network. The presented data is one minute interval solar radiation from one of the sites just north of Ames at the Horticulture Farm. The chart overlays the data from Thursday and Wednesday. Can you tell which day had clouds and which barely had any? Once you figure that out, you may wonder how the radiation data is sometimes higher on the partly cloudy than the clear one. The sensor is not tracking the sun attempting to directly measure what comes from the sun, but is sensing total global radiation arriving at the sensor. As such, during convective and partly cloudy days, those bright white clouds you see are scattering solar energy to the sensor and thus increasing the amount of radiation received. There is one other obvious quirk shown in the plot, happening about 5 PM. Can you guess what it is?

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Tags:   radiation