Hukseflux are a company that make a range of environmental sensors for laboratories and for outside. For a while now they have made a cool little thing that means you can use the camera of your iphone, with their app to measure the intensity (energy flux density in Wm-2) of the sunshine (shortwave solar radiation).
I’ve used it in some teaching exercises before, but its mostly very cool for outreach activities and letting people see and understand the energetic differences between diffuse and direct sunlight, how the angle of the sunbeam alters the energy received, and the role of reflected sunshine from the surroundings.
Here is the presentation about their app, and if you’re interested then you can download the manual and have a go yourself.
In recent decades central Europe has experienced higher rates of solar radiation because air quality regulations have meant the air in the lowlands and valleys of central Europe now contains fewer small particles (aerosols) from pollution. Such aerosols can block some of the sunlight reaching the ground, so as they reduce the measured intensity of the sunshine increases. A Swiss study (Philipona and others, 2013) nicely shows that the effects of changing aerosols on the solar radiation and temperature trends can only be seen at lower elevations as the mountain tops were generally not affected by the aerosols of earlier decades as much as the lowlands were.
Philipona, R. (2013), Greenhouse warming and solar brightening in and around the Alps. Int. J. Climatol., 33: 1530–1537. doi:10.1002/joc.3531