The influence of atmospheric circulation on the intensity of urban heat island and urban cold island in Poznan, Poland

The study has analyzed influence of an atmospheric circulation on urban heat island (UHI) and urban cold island (UCI) in PoznaA". Analysis was conducted on the basis of temperature data from two measurement points situated in the city center and in the Aawica airport (reference station) and the data concerning the air circulation (NiedAwiedA's calendar of circulation types and reanalysis of National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR)). The cases with UHI constitute about 85 % of all data, and UCI phenomena appear with a frequency of 14 % a year. The intensity of UHI phenomenon is higher in the anticyclonic circulation types. During the year in anticyclonic circulation, intensity of UHI is 1.2 A degrees C on average while in cyclonic is only 0.8 A degrees C. The occurring of UHI phenomena is possible throughout all seasons of the year in all hours of the day usually in anticyclonic circulation types. The cases with highest UHI intensity are related mostly to nighttime. The cases of UCI phenomena occurred almost ever on the daytime and the most frequently in colder part of the year together with cyclonic circulation. Study based on reanalysis data indicates that days with large intensity of UHI (above 4, 5, and 6 A degrees C) are related to anticyclonic circulation. Anticyclonic circulation is also promoting the formation of the strongest UCI. Results based on both reanalysis and the atmospheric circulation data (NiedAwiedA's circulation type) confirm that cases with the strongest UHI and UCI during the same day occur in strong high-pressure system with the center situated above Poland or central Europe.