Spatiotemporal Evaluation of Nocturnal Cold Air Drainage Over a Simple Slope Using Thermal Infrared Imagery

Abstract

ABSTRACT:Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

Assessing the Cooling Potential of Tailing Piles for Urban Heat Mitigation in Germany’s Ruhr Metropolitan Area—A Case Study of the Rungenberg in Gelsenkrichen

“…In further studies, flow velocity, cold air production rates, and cold air volume should be measured or calculated with the aid of model simulations. A simple method for estimating mean wind velocity is provided in the [12]. They combined data from a digital elevation model with data from a meteorological station and TIR images.…”

“…According to [10], 5 K lower air temperatures or more can be measured in such cold air pools compared to the outside of the cold air pool. The generation and drainage of cold air on mountain slopes [11,12] and on low-roughness opened and greened spaces [13] and its benefits for surrounding urban areas has already been investigated by [14]. They demonstrated that with high-relief energy, there is cold air runoff, and the cold air can penetrate into urban structures and contribute to local cooling.…”