I got this question while walking in the bright sunshine today. To be honest, I felt exactly what the person asking the question felt. The sun did feel very strong. But wait, it’s the latter part of September and isn’t the sun lower in the sky and less effective because of that? Yes. It would be if everything would be identical. Because of the change in sun angle, at it’s highest point in the sky, the sun is about 20% less effective at heating the surface today as it was on the summer solstice.
So given all this, why does it feel so strong? Well some of that has to with the amount of moisture in the air. Water vapor scatters the energy more than pure dry air. This is why the sky can seem so milky white during real humid weather patterns. The air mass that was over our region today was very dry for this time of the year. With less moisture, the sun was a little more intense than it would be on this date.