Common Marginal Cold Pools

Abstract

his study examines marginal cold pools forming in a shallow valley. ?Marginal? refers to cold pools that are generally weak and intermittent. Nineteen stations were instrumented with sonic anemometers and accurate slow-response temperature measurements. The vertical structure of the cold pool is determined from a 20-m tower on the valley floor that includes eight levels of sonic anemometers and eight additional levels of slow-response temperature. On the basis of the data analysis, the traditional concept of a cold pool must be generalized to include cold-pool intermittency, complex variation of temperature related to some three-dimensional effects of terrain, and a diffuse cold-pool top. Different types of cold pools are classified in terms of the stratification and gradient of potential temperature along the slope. The strength of the cold pool is related to a forcing temperature scale that is proportional to the net radiative cooling divided by the wind speed above the valley. The scatter is large partly because of nonstationarity of the marginal cold pool in this shallow valley.