You might have noticed that the days are getting shorter up here underneath the 49th Parallel (aka Canada’s Waistband). It’s not your imagination, it’s true! Insolation is a climatological term for Incoming Solar Radiation, or the total amount of the sun’s energy that strikes the Earth during a day. This number varies quite a lot depending on latitude and time of year.
For example, in Minnesota we’re at about 45º North, halfway between the red and green lines here. The point is that the number of hours of sunlight combined with the sun’s angle means our total amount of solar energy declines a lot, down to about 200 watts per square meter (WM-2) at the moment. That’s less than half our June peak, and a lot less than even a month ago. The total insolation drives our climate, so bring a warm jacket.