Observations of Atmospheric Structure During Summer in a Coastal Mountain Basin in Northwest Oregon

Abstract

During 53 days in the summer of 1966 continuous hygrothermograph records were obtained at 6 points along a north-south transect of the 11-km wide Valsetz Basin in the Oregon Coast Range. The 6 records sampled both north and south aspects and nearly the full range of elevations between 300 and 900 m above msl in the basin. Hourly values of temperature and relative humidity were tabulated from the charts, converted to values of potential temperature and mixing ratio, and put on punched cards. The period of record was divided into three relatively dissimilar types of day, and hourly mean cross-sections of potential temperature and mixing ratio were drawn for each type. Only comparatively minor variations superimposed on a basic nocturnal pattern and a basic daytime pattern of cross-section distinguish the three types of day. .Principal causes of the variations are nocturnal accumulation of cold air on the basin floor, nocturnal heating at ridge top levels associated with subsidence inversion, anti higher midday rates of evapotranspiration on south-facing slopes than on north-facing slopes.