Monthly Review of the California Climate and Crop Service, in Co-Operation with the State Agricultural Society Volume 9-10 by United States Weather Bureau
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt: ...the night of the freeze, but above that not a leaf appeared injured. This showed the height to which the cold air reached at that place. When the flood of cold air coming from the foothills reaches the orange groves and windbreaks, the flow is impeded and it must there accumulate until it rises high enough to flow over the groves and force its way through the windbreaks. Being heavier than the air at the same level over lower parts of the valley, it will find a way through, over, or around obstructions to obtain levels in accord with the differences in gravity. Take this illustration: In the town of Silverton, Colorado, the morning temperature is frequently 50 below what it is at the Aspen mine, 1,500 feet above; and the greater part of this difference is in the first 300 feet. Cold air flowing into a valley must fill it to some depth. Near Silverton I have myself noted an average difference of 28 in 300 feet on clear nights. Now, what is necessary to prevent a damaging fall of temperature is to free our groves of a portion of this cold air which flows down over the valley on cold nights, or warm it to above the danger point. With a sufficient number of small fires, both can be done without loss of heat, except by radiation, and this is not much when the fires are placed in a grove of large trees, as the foliage receives radiated heat which would otherwise escape into space direct from the fires. With the fires I use (coal burning in wire baskets) the radiation is mainly lateral, and warms up under the trees. If the ground and leaves are warmed by radiated heat from the fires, they give out heat to the air by contact, and thus the air is warmed. Small fires draw in air only from close to the ground--the cold air--warm it and cause it to rise. The column of ...
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