19 December 2009

Temperature under the snow — Part 2

The snow storm we have been having since last night has provided another opportunity to measure the temperature under the snow. In Part 1 of this series I had monitored the temperature at a fixed depth under the snow over several hours. Today I measured the temperature as a function of depth under the snow.

First, I had to construct an apparatus by taping a waterproof thermometer to a ruler.

USTMA1


Here is the apparatus in use.

USTMA2

During the afternoon measurements, when the snow had gotten deeper, I constructed a new, improved apparatus by taping the thermometer to a long, thin pole.

Here is a graph of the data.

TempUnderSnow2

The blue X signs are for the measurements taken around 10:45 in the morning, while the red dots are for the afternoon data from around 14:15. Both sets of data were collected at the same location. The deepest readings, -21 cm in the morning and -45 cm in the afternoon, were taken presumably right above the soil.

Once again, the data demonstrate the insulating effect of snow. What makes the temperature go up as one goes deeper in the snow is that because the soil temperature is almost always higher than the air temperature, when there is snow on the soil, the air temperature above the soil ends up being higher than the air temperature above the snow. See this post for soil temperature measurements in the winter.


Technical details: Temperatures were measured with a Cole-Parmer Waterproof Remote Probe Thermometer in fresh, unpacked snow while it was still snowing. Cole-Parmer told me that this unit uses a thermistor sensor. During the morning measurements, the probe was not shielded during the surface readings, but during the afternoon surface measurements, it was placed inside a narrow cardboard tube open at both ends and covered with aluminum foil. I don't know if radiation is significant under thick cloud cover. Surface temperatures were taken within ~1 cm of the snow surface; not being standard "air" temperatures, they are not likely to agree with the temperatures from meteorological stations.

Part 3

No comments: