“What causes the temperature to drop as much as 5 degrees at sunrise? I start my morning walks before the ‘crack of dawn’ noting the temperature at that time and when I finish (approx. 45 minutes later), it has dropped as much as 5 degrees. I live in the south end of the Carson Valley in Gardnerville and I see this temp variation on a regular basis.”
Many wonder if they are just imagining that post-sunrise cool down, but it does occur often… especially on a clear calm morning. Here’s how it works. Because of radiational cooling, on clear nights the ground gets much colder than the air just a few feet above it. Since thermometers are placed about five feet above the ground, it will show a warmer temperature than the air touching the ground. Once the sun comes up, the sunlight excites the cold air in the first foot or so above the ground (which can be 10 or more degrees colder), which causes it to move around and mix into the next several feet of air. That “mixing upward” drops the temperature of the air at thermometer level.
Jeff Roseborough said:
I was taught it science it was because it takes time for warmth from the sun to reach the earth. There is a delay in warming and cooling. This also occurs with seasons. The hottest months are July/August, even though the longest, sunniest day is in June. Same with the wintertime. The coldest months are January/February not the shortest day of the year in December.
Mike Alger said:
Actually there is almost no delay for the energy from the sun to get to the earth since it is electromagnetic energy and travels at the speed of light, but I think what you are referring to is the “lag time” which is represented by the seasonal example you gave. But while there is a slight lag for the energy balance to reset after sunrise, if that were the case, the temperature drop after sunrise would be at the same rate (or slowing down) as before sunrise. In fact in the hour before sunrise, the temperature drop has almost leveled out and is very slow. But if you look at a time/temperature graph, there is a very rapid drop just after sunrise, which doesn’t fit the bell curve of simple energy lost vs energy gained. That quick and often noticeable drop in temperatures is caused by the effect described above.
Pingback: Weather: why does the temperature drop after sunrise? – Oracle Tutoring, Campbell River, BC