Monday, March 23, 2009

Solar Energy, Small Farming, and Last Snow

Earlier today I went walking with my camera to capture some pictures that illustrate the relation of terrain and foliage to ambient and ground temperature. In one direction I discovered that I was a day late. I had missed the last snow before it melted. In the other direction I was going to lower ground, and I captured what I wanted.

In the first picture we see snow on the north-facing rise to the south of the tracks. No surprise there. A question that might be asked is why the snow has melted on the other north-facing slopes.

In the second picture we see that there is still a small area of ice adjacent to the stream. You can see the sunlight and shadows playing on the ice, so this spot has not been entirely shaded during the winter and spring. This suggests that the remaining ice is on very low ground, where the cold air falls.

The next picture is of the stream, which typically is covered with ice during the winter. You can see remaining snow to the left, where it is both on low ground (remember cold air is heavier than warm air, and therefore goes to the low ground), partly shaded by evergreens, and on the north-facing side.

Thus there are at least three factors in the temperatures for a particular location. When I was once looking for some land in New Hampshire for a house and field, the realtor showed me a plot with a pitch facing north and sloping down to the north. As would be predicted from solar energy calculations, this was cool during the summer, but was also a poor solar site -- the last area to be ready for planting. I rejected that plot. If I had only been concerned with a cool summer house, I might have made an offer. But I was concerned with raising food as well as warmth during the winter, so I rejected it.

These scenes may appear to be just what they are, but to a physicist there is more. When I get time, maybe I will write about the unseen things in these photos. These include various forms of electromagnetic radiation. Hmmm ... I did not see any birds either. I wonder why. I have seen birds such as geese migrating north, but maybe it is not yet time for the song birds.

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