A tale of two cities: The influence of urban meteorological network design on the nocturnal surface versus canopy heat island relationship in Oklahoma City, OK, and Birmingham, UK

Interest in the investigation of the relationship between surface heat island intensity (sUHII) and canopy heat island intensity (aUHII) (sUHII-aUHII relationship) is growing mainly because of the global availability of satellite-sensed land surface temperature (T_s). It is hoped that if such a universal relationship can be found, it could compensate for the spatial discontinuity of air temperature (T_a) measurements that currently exist due to a paucity of weather stations in urban areas. In an attempt to investigate differences in the relationship in different urban environments, this study attempts to compare the linear sUHII-aUHII relationship between Oklahoma City, OK, and Birmingham, UK, based on the observations from Moderate Resolution Imaging Spectroradiometer and two dense urban meteorological networks (UMNs). Regression models and confidence ellipse, with two statistical tests, are applied in the comparison analysis under different climatic conditions with respect to specific ranges of wind speed (WS) and daily-accumulated solar radiation (DASR). Some general patterns of the linear sUHII-aUHII relationship are found across the two cities, such as the reduced rate of change of aUHII with respect to sUHII with increasing WS and the non-negligible advection effect in this relationship. Meanwhile, the differences of the linear sUHII-aUHII relationship across two cities are reduced under ideal conditions (clear skies, calm and large input of solar radiation from previous day into urban system). More importantly, the results emphasize the influence of the configuration of UMNs on the sUHII-aUHII relationship. By removing the climatic element in the relationship (i.e., WS and DASR), the impacts of the different local environments, source areas, and general configurations of the UMN become evident, indicating that a standardized protocol for the designs of UMN is the prerequisite for the generalization of the sUHII-aUHII relationship across cities.