ИСТИНА

Urban meteorology is still poorly studied for specific conditions of the so-called cold climate cities in high latitudes. Here, surface energy deficit in wintertime suppresses the turbulent mixing and supports the formation of long-lived stable boundary layers (BLs). Several recent studies based on in-situ observations and remote sensing data revealed intense urban heat islands (UHIs) even in small and medium-sized cold climate cities. This study extends urban climate research for cold climate cities towards the urban boundary layer (UBL). Canopy-layer UHI and vertical structure of urban and rural BLs were for the first time simultaneously observed in a sub-Arctic city (Nadym, West Siberia, Russia) in cold winter conditions. During five intensive observational periods distributed over 3 winters, we run simultaneous registration of urban and rural meteorological parameters using atmospheric sounding with unmanned quadcopters, microwave temperature profiler MTP-5 and ground-based temperature network. These observations revealed details of UHI development in the canopy layer and across the UBL. We found that pronounced UHI with intensity up to 6-8K appears when stable BL with strong ground-based temperature inversion develops outside the city. In such conditions, mixed layer typical persists in the city, yet it remains very thin with depth about 50 m. This is significantly less that UBL depth reported for temperate cities. Correlation analysis based on longer UHI observations and reanalysis data confirmed that presence of ground-based inversion is one of the strongest control factors for UHI in winter conditions. Other factors such as calm wind and radiative cooling are necessary, but not sufficient for UHI appearance. More details are available in our recent paper (Varentsov et al., 2023, https://doi.org/10.1016/j.uclim.2022.101351). Acknowledges: Observations were supported by Belmont Forum project SERUS (project no. 1729) and Russian Foundation for Basic Research, project no. 20-55-71004. Data processing was supported by Russian Science Foundation, project no. 21-17-00249.