Anyone interested in weather can confirm the importance of wind since it is responsible for global and regional weather dynamics. Global wind systems are primarily responsible for large-scale weather, while small-scale wind systems influence local weather effects. For example, the corridor wind system is particularly relevant for urban areas, as it contributes to cooling and thus reduces the urban heat island effect. Especially for climate change and heat waves, these local systems are very important.
In a pilot project, meteoblue recorded and analysed the described small-scale wind systems using a high-resolution infrared camera in cooperation with Atmospheric Sciences, University of Basel. These visualisations and analyses provide a valuable contribution to understanding the systems.
In particular, the so-called corridor winds have been investigated. For example, thermally driven winds arise due to temperature differences between the city and its surrounding area. The temperature differences can be detected with our weather stations in Basel, Zurich and Tallinn. Urban areas generally warm up faster than the surrounding area due to the higher degree of sealed surfaces, denser buildings and other anthropogenic factors. Consequently, air pressure differs between the city and the surrounding area. Therefore, the urban pressure deficit is supplied with cooler air masses flowing in from the surrounding area to create a pressure balance - the so-called corridor winds. These contribute to cooling the city if not weakened or even stopped by flow obstacles such as buildings or topographical barriers.
14 locations in and around Basel were measured with the infrared camera. The recordings focused on areas temporarily affected by cold air currents (surface winds). The recordings are particularly interesting when they show both landscape and urban settlement areas because that is where the cooling effect of the cold air can be best detected.
Besides correctly selected cameras and flawless image processing, ideal weather conditions are also essential for taking good images. The most suitable nights are radiation nights - when terrestrial heat radiation is very strong due to low cloud cover. In addition, other meteorological factors, such as wind, humidity and temperature values, need to be considered, which can be found in our meteogram at one glance. Finally, it is important to identify suitable locations where the visible cold air flows. Experience has shown that slopes with only light vegetation are perfect for visualising cold air flows.
The video shows the local wind systems on the outskirts of Basel. We will use these results to extend our city climate offer further.
