Abstract
The study has analyzed influence of an atmospheric circulation on urban heat island (UHI) and urban cold island (UCI) in Poznań. Analysis was conducted on the basis of temperature data from two measurement points situated in the city center and in the Ławica airport (reference station) and the data concerning the air circulation (Niedźwiedź’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 °C on average while in cyclonic is only 0.8 °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 °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 (Niedźwiedź’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.
Highlights
The process of urbanization has a significant impact on the properties of the surface of the earth and the atmosphere
Morris and Simmonds (2000) show that the intensity of urban heat island (UHI) depends on the position of the center of the high pressure and the dominant direction of the air advection, but they indicate that the lowest UHI intensity does not occur under cyclonic synoptic situations but under northwestern advection coming from anticyclonic circulation
The main objective of this paper is to characterize the UHI and urban cold island (UCI) phenomena under various synoptic conditions in the city of Poznań, based on the in situ measurement data from two measurement points located in the city center and the airport area in the period 2008–2013
Summary
The process of urbanization has a significant impact on the properties of the surface of the earth and the atmosphere. The intensity of UHI is calculated as a difference between urban and rural air temperatures and depends on many factors such as the following: the size of the city and its population, topography, climate zone, and meteorological conditions (Oke et al 1991). As can be seen from the previous papers considering this research problem, the maximal intensity of UHI occurs during anticyclonic synoptic situations (Yague et al 1991; Unger 1996). Morris and Simmonds (2000) show that the intensity of UHI depends on the position of the center of the high pressure and the dominant direction of the air advection, but they indicate that the lowest UHI intensity does not occur under cyclonic synoptic situations but under northwestern advection coming from anticyclonic circulation. An interesting approach to the problem was shown by Mihalakakou et al (2002) using the neural network model to the simulation of UHI under different synoptic types
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