I stopped at the grocery store on the way home and got that 5 lb bag of carrots. It was 10 degrees F on the way home at about 11 am. By then the warmer upper atmosphere layers mixed in with the cool ground layer. Winds were 7 mph from the west.
Wednesday, January 28, 2009
Jan 28 ride
Today I went to yoga, so left an hour later than usual. This is what I want to see at 6:50 am, nice bright sunshine (view from my driveway)! Oh well, it will happen sometime in February I hope. It was cold again, -3 degrees F, at 7:50 am. But perfectly calm winds. I think we probably had a temperature inversion. When the winds are calm, the ground radiates heat away, and snow is an even stronger radiator (it has a high infrared emissivity), so it emits away whatever heat it has at infrared wavelengths, and gets really cold and cools the air above it. So the lower layers of the atmosphere (where we bike) are cooler than the upper. This is called a temperature inversion because normally the temperature goes in the other direction, decreasing higher in the atmosphere. Anyway, I think we had strong radiation cooling last night and that's why it was so cold this morning. But it was very calm and peaceful and I was plenty warm. Here's the start of the bike path at 8 am: