Abstract:

Air temperature observed at a national weather station in Shenyang increased by 6.5℃ in an hour at 01:00 on December 2, 2019.We accurately analyzed the causes of this abnormal temperature-increase process from the aspects of system configuration, thermodynamic diagnosis, and urban heat island effect, using regular and encrypted observation data, National Centers for Environment Prediction (NCEP) reanalysis data, and wind profiler radar data in Shenyang.The results indicated that a warm ridge between extremely low altitudes and near the surface passes by during the abnormal temperature-increase period, which is the major reason for the increase of air temperature at the midnight over most regions of Liaoning province.The national weather station is located in the southeastern region of Shenyang.In the presence of the northwesterly surface winds, air flows move from warm urban regions to cold suburb regions in Shenyang.This results in the increase in air temperature observed at all weather stations in the southern part of Shenyang, increasing by 3-4℃ in comparison with stations in northern suburbs.Therefore, the urban heat island center moving to the leeward is another reason for the abnormal temperature-increase event.Moreover, the base value of air temperature before temperature rise can affect the temperature-increase degree.The lower the basic temperature is, the greater the temperature-increase degree is.

Key words: Abnormal temperature rise, Sky condition, Warm ridge at extremely low altitudes, Urban heat island effect