Effects of Orography on the High-Temperature Event on 22 June 2023 in North China

• Published in: Atmosphere 2024-03, Vol.15 (3), p.324
• Main Authors: Wu, Haoyang, Xu, Xin, Wang, Yuan
• Format: Article
• Language: English
• Subjects: Adiabatic; Agricultural production; Air temperature; Atmospheric temperature; Daytime; Diabatic heating; Enthalpy; Environmental aspects; Experiments; Extreme high temperatures; Extreme weather; Foehn; Foothills; Forecasting models; General circulation models; Global warming; Heat; Heat flux; Heat transfer; Heating; High temperature; Influence; Long wave radiation; Mathematical models; Maximum temperatures; Mountains; North China; Numerical simulations; Orographic effects; Orography; Precipitation; Radiation; Sensible heat; Sensible heat flux; Sensible heat transfer; Short wave radiation; Simulation; Surface temperature; Temperature effects; Temperature preferences; Terrain; Weather; Weather forecasting
• ISSN: 2073-4433; 2073-4433
• DOI: 10.3390/atmos15030324

An extreme high-temperature event occurred in North China on 22 June 2023, with the maximum temperature reaching 41.8 °C. The high-temperature centers preferentially occurred at the foothills of the Taihang and Yanshan Mountains, indicating an important role of the underlying orography. In the present work, we study the orographic effects of this extreme high-temperature event according to high-resolution numerical simulations using the Weather Research and Forecasting model. The results show that the presence of the mountains in North China contributed notably to the high-temperature event, which can enhance the 2 m air temperature by up to 3 °C. In the daytime, the enhancement of temperature is primarily due to the diabatic heating of sensible heat flux at the terrain surface caused by solar shortwave radiation, whereas the well-known foehn effect has little contribution. Indeed, the dynamically forced downslope flow of foehn is totally suppressed by the upslope flow of the thermally driven mountain-plain circulation. In the nighttime, the sensible heat flux at the terrain surface changes to weakly negative, given the cooling of land surface longwave radiation. As a result, the enhancement of near-surface temperature at the terrain foothill is dominated by the adiabatic warming of downslope flow. Yet, the near-surface temperature far away from the mountain is enhanced by the subsidence warming of a synoptic anomalous anti-cyclone, which is induced by the diabatic heating over the mountains in the daytime. These findings help improve the understanding of the thermal and dynamical effects of orography on the occurrence of high-temperature events.