Chart of the Day: Daily Incoming Solar Radiation (By Latitude)

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.


arrow = now in Minnesota

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.

6 thoughts on “Chart of the Day: Daily Incoming Solar Radiation (By Latitude)

  1. Rebecca AirmetRebecca Airmet

    It also influences the amount of UV and thus the amount of Vitamin D you’re able to naturally make. I believe that amount is zero when the sun is below 50 deg above the horizon, i.e., from early/mid-sept till next March.

      1. Rebecca AirmetRebecca Airmet

        Sorry I missed your reply, Bill. Here is a brief response, and perhaps a more thorough investigation is in order, although it hardly qualifies as “land use”.

        Harvard Health notes that most people living north of the line connection San Fran to Philly don’t get enough Vitamin D. Lack of Vitamin D has been linked to a host of health problems, from “osteoporosis, heart disease, some cancers, and multiple sclerosis, as well as infectious diseases, such as tuberculosis and even the seasonal flu.”

        More recent studies have also shown Vit D to have a strong link to immune function in general, and diabetes.

        Also significantly, Vit D has a strong influence on those with seasonal affective disorder. And NIH study shows significant improvement in SAD symptoms with Vitamin D treatment. Vitamin D has also been shown effective in treating symptoms of depression.

        Interestingly, it may also be important in both developing muscle strength, and of all things, preventing cavities.

        Personal experience tells me that I’m much better off, physically and mentally, if I start supplementing with Vitamin D in early September and continue through April or so.

  2. Walker AngellWalker Angell

    We are in the design phase for a passive haus. It’s really amazing how well you can heat a house during a MN winter. With proper insulation, airtightness, and lack of thermal bridging it’s almost possible to do it completely with solar energy through high gain windows on the southern side of the building. Of course this comes with the opposite problem during spring, summer, and fall when you need to shield windows. Fortunately trees were designed well for this in providing shade when needed and loosing their leaves at just the right time.

Comments are closed.