Analysis of urban Heat Island intensity through air mass persistence: A case study of four United States cities

In conjunction with the ongoing rise in global air temperature, there is evidence to suggest that mid-latitude synoptic air masses have changed in frequency and persistence. The research pre-sented here focuses on an analysis of urban heat island (UHI) intensity through the period of synoptic-scale air mass stagnation for four UHI-prone United States cities. It is theorized that the thermal inertia associated with a stagnant air mass conducive to UHI development causes an intensification of the urban-rural temperature difference through time. Results indicate that UHI intensification is responsive to more than just the thermal characteristics of the respective air mass in place. While the magnitude of UHI was found to be smallest under a cool, dry air mass, it generally intensifies with persistence. Conversely, commonly associated with the greatest UHI intensity, a warm, moist air mass exhibits little change in UHI intensity or even a de -intensification with persistence. The warm, moist air masses that are conducive to a stronger UHI appear to be increasing in frequency, partly due to greater persistence. However, somewhat encouraging is that the results here do not show UHI intensification through the period of their persistence.