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peas and wild hay occupy the heads of subparallel valleys in the schist. Summer homes of Denver people and tourist cottages fill the "parks" and are concentrated on the southwest sides of granite mountains and ridges. North and northeast facing slopes are mostly timbered and lumber mills are numerous in the heads of the northwest facing valleys. The Structure of Summer Wind Over San Juan Island, Washington OAROL O. BEAMER University of Washington, Seattle, Washington This paper is the result of the first of a series of experiments being conducted at the University of Washington Océanographie Laboratories, Friday Harbor, San Juan Island, upon the problem of summer wind structure over San Juan Island, under the direction of Dr, Phil E. Church. Data for the experiment was obtained twice daily by pilot balloon observations . A reduction of the data taken gave a picture of the vertical structure of the air over San Juan Island to an altitude of four or five kilometers. The reduced data included wind velocity and direction. From a study of forty flights plotted on velocity -direction graphs of the Weather Bureau, a cross-sectional analysis of the winds present was made. Two general types of wind were found to exist. These were the gradient and the non-gradient winds. Of the non-gradient winds there are several sub-classifications : The Local Surface Sea Breeze, the outer edge of the Mainland Sea Breeze and other types which have not been classified as yet. In this analysis a gradient wind was considered to be one whose direction graph showed a turning of less than 90° in its entire vertical structure. There was a barometric gradient which determined the velocity and direction of the wind. The average direction of the gradient wind was found to be ill-defined, and its velocity was slow for the twenty days on which it was found to be blowing. The non-gradient wind was considered as one which showed a directional turning of more than 90° through the vertical. Therefore this general type of wind is the result of a thermal gradient set up between the warm land masses and the colder watiir surrounding them, which in turn cause local differences in pressure. Eighty per cent of the non-gradient winds occurred during the afternoon hours when thermal differences were at a premium. The Local Surface Sea' Breeze is a result of the difference in heating between San Juan Island itself and the surrounding water. Two excellent examples of this breeze were noted . One, on July 19, attained a thickness of five hundred feet and one on August S3 one thousand feet. The velocities of these winds were slow for both flights. The outer Edge of the Mainland Sea Breeze is the result of a difference in heating between the mainland of Washington State to the east some thirty miles, and the waters of Washington Sound, the Strait of Georgia and the Strait of Juan de Fuca. Due to the distance of San Juan Island from the mainland, this breeze was found at high elevations as a thin layer of air moving down the local barometric slope caused by heating of the mainland. There were some flights which showed winds of so complex a nature that as yet no attempt has been made to classify them. They may have been due to a combination of the other "causes. They will be taken up in a later paper when a more complete set of data, covering a longer period of investigation, have been accumulated. (31) ...

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