. Effectiveness of orchard heaters . Feb. 14- 10 15, 1942 12:30 J / / f f / 30 35 40 40 Temperature °F Fig. 1. Temperature profiles in orchard and above bare, plowed ground before lighting heaters, for two nights with different inversions. (Taken in and near 28-acre orchard at West Covina.) which comes in contact with the foliage. Therefore, in an orchard, air cooling takes place throughout the entire height of the tree zone, and particularly at the tree tops. The foliage has a relatively low capacity for storing heat, and therefore cools rapidly by radiation, to a few de- grees bel
. Effectiveness of orchard heaters . Feb. 14- 10 15, 1942 12:30 J / / f f / 30 35 40 40 Temperature °F Fig. 1. Temperature profiles in orchard and above bare, plowed ground before lighting heaters, for two nights with different inversions. (Taken in and near 28-acre orchard at West Covina.) which comes in contact with the foliage. Therefore, in an orchard, air cooling takes place throughout the entire height of the tree zone, and particularly at the tree tops. The foliage has a relatively low capacity for storing heat, and therefore cools rapidly by radiation, to a few de- grees below air temperature. The soil, on the other hand, has a high heat capacity; heat stored in the lower levels of soil during the daytime is conducted to the surface during the night and in this way retards the chilling of the top layer of soil. The greater cooling of the foliage ac- counts for the lower air temperatures within the orchard as compared to those above bare ground. Within the orchard, the retarding effect of the subsoil heat causes the soil surface to be a little warmer than the air which has been cooled by the foliage. For example in the left-hand graph of figure 1, the average soil surface temperatures were probably between 29 [6]
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