Sometimes nature does some truly beautiful things. One of them is the sight of steam rising from a surface on a Very Cold Day.
Yesterday, the air temperature was about 40 F on the back patio in the shade. ( I have a picture of that thermometer, but don’t feel the need to upload it, as for 3 MB of limited storage, it’s just not that impressive a picture. I just took it for photodocumentation purposes. But be comforted that I do in fact have that photo complete with time stamp.)
When I went to the front porch at about 11:30 am to let the cat in ( it was cold and wet out, and Mr. Cat wanted warmth, love, and food; in roughly reverse order…) I noticed one of my favorite phenomena. The “hot steam on a cold day” as sunshine warms a surface and evaporates the wet, but just millimeters above the surface it condenses again into steam.
I ran for the camera and the thermometer…
Here was a great chance to measure and document just how much variation there can be in surfaces over a very short period of time and space. The back and the front are about 50 feet apart.
So I put my ‘photo chemical’ thermometer on the fence. It’s a fairly fast reacting and very accurate thermometer (or your pictures come out wrong…) The sun had just come out after a fairly heavy cold rain. Everything HAD been roughly the same temperature 1/2 hour before… The question was: How fast and how far can surfaces warm in the sun on a cold wet day?
A bit under 20 F hotter.
So this is a very simple example of the highly variable nature of temperatures. To some extent, it illustrates the dependency of air temperatures over a surface on the very nature of that surface. As the surface of the planet is fractal in topology, that implies that temperatures over the surface of the planet are also fractal in nature.
When we measure “global average temperature” we are simply measuring the error band in our instruments. The size of a measurement of a fractal surface is directly controlled by the size of the ‘ruler’ used to measure it. As we are constantly changing the number and location of thermometers used to measure “global temperature” we will get constantly varying results, even if the state were constant.
What makes “1 meter over the surface” more or less ‘right’ than 2 meters? Or 1/2 meter? What makes ‘over grass’ more or less right than “near the runway”? As we keep changing those things, we simply get closer to that 40 F or that 60 F from the same small place on the very same day and time…
FWIW, note also that all that steam rising is taking one heck of a lot of heat with it into the air. The water evaporates at a constant temperature, so we have massive heat gain with no temperature change. Then that heat is given back into the air as the condensation happens. Here we see it happening in millimeters. With clouds and oceans we see it happening in miles. That picture also illustrates the stupidity of using temperature as a proxy for ‘heat flow’. The actual heat flows are much much higher than that temperature differential suggests. ( about 1/2 kW / m^2 on the fence top, about zero on the patio… yet a meter up in the air over the fence, it’s all ‘disappeared’… gone into vapor instead of temperatures…)