03 August 2011

A hot rock

The eastern North America has been under the influence of a heat wave that hasn't quite abated yet. For about 3 weeks now, the daytime temperatures have been hovering around at least 30ºC (what's that on the Fahrenheit scale?).

July 22nd was an exceptionally hot day. At 1545 a few centimeters above the soil in my backyard, I measured an air temperature of 39.3ºC. When I put the probe of the thermistor in contact with the surface of a rock that had been baking in the sun, it shot past 46ºC*.

It eventually went up to 46.7ºC and would have gone up even higher if I hadn't gotten too hot from squatting out there and escaped inside.

My underlying purpose was to figure out how the snails and slugs that normally inhabit the undersides of those rocks were faring with the heat. I could not find any Vertigo to run a test, though. Had they all retreated deep into the soil?

*Admittedly, this was not a good measurement. The thermometer probe, being unshielded, was probably exposed to radiation. On the other hand, it would have been difficult to shield it while measuring the temperature of the surface of a rock.


Fred Schueler said...

What you need is a few data loggers and a backyard with Cepaea - after a wet night before a heat wave, place data loggers beside Cepaea stuck to rocks or walls, and see which ones survive. I know this is an improbable concatenation of cirumstances, but I know of situations where Ceapea, Neohelix, and the Succinea putris-like thing that's taken over the Lake Ontario waterfront have crawled out into the open, and then died. I suppose this kind of mortality would be less frequent among xeric-adapted species.

John said...

Could the temperature be different under the rock than on top of the rock?

To shield the thermometer, could you hold something over the probe to shade it from direct sunlight, like a large book or a wide-brimmed hat? I imagine the surface temperature wouldn't change much from the shade if you were just doing a quick measurement.


The temperature under the rock was probably lower than at the top of it.
I was indeed shading the thermometer with my body. But the probe still need to be shielded from stray radiation. The best thing to do would be to drill a horizontal hole just below the top surface of a concrete block & then put the probe into the hole.