Causal Interactions between Temperature and Geopotential Height in Cities of Contiguous United States

Excessive heat is becoming the source of many environmental challenges in urban areas. Finding causal interactions between urban ambient temperature and other meteorological variables will greatly facilitate our understanding of the underlying mechanisms of urban heat. Among all the atmospheric variables, detecting causality between temperature and geopotential height will help us understand this mechanism and improve the weather projections in the context of climate change. In this study, we use the data of 2-meter air temperature and 500 hPa geopotential height of 520 cities in the contiguous United States, from 2016 to 2022, to detect causations between them in urban areas using the convergent cross mapping method (the CCM method). The results unravel the distribution patterns of the causality strengths in the CONUS. For the local causal interactions, i.e., the causality between the temperature and geopotential height within the same location, the high-value areas of both directions site in the northern Appalachian Mountain and inland southwestern CONUS, and the low-value center is on the leeward side of the southern Rocky Mountains due to the baroclinic in this area. For the nonlocal interactions, i.e., the causality between the temperature and geopotential height of different locations, due to the regulation of the Rocky Mountains on the atmospheric circulations, both the average causal effect (ACE) and average causal susceptibility (ACS) of the two directions have relatively high values in two areas-the inland Rocky Mountains area and the eastern areas of the Mississippi River, and the lowest values are located in the areas between these two high-value centers aforementioned. The potential teleconnections identified in the causal interactions of every single city indicate the influence of the upstream and downstream westerly circulations on local atmospheric variables. The results can be informative to stakeholders in design sustainable countermeasures to mitigate excessive heat in urban areas.