A physical analysis of summertime North American heatwaves

Abstract This study examines the dominant heatwave variability over North America (NA), extracted from an empirical orthogonal function (EOF) analysis of summertime monthly warm extreme index anomalies 1959–2021. The principal mode features a dipole structure with large area anomaly northwestern NA and opposite sign southern U.S. corresponding component is associated large-scale atmospheric wave train extending Pacific to (NP-NA) northeastward injection moisture subtropical western towards NA, which are key factors in supporting variability. NP-NA can be systematically reinforced supported by synoptic-scale eddies, may also forced anomalous convection tropical-subtropical Pacific. Surface radiation heating directly contributes surface temperature dominated downwelling shortwave longwave radiations. In association positive phase variability, brings anticyclonic northern leading descent, reduced total cloud cover below-normal precipitation relative humidity NA. Over subsidence causes air through compression. Reduced results increased downward that contributor heating. addition, increase vertically integrated water vapour collocates tropospheric warming. atmosphere has more vapor holding capability acts as greenhouse gas absorb radiation, second major Processes circulation signs will likewise lead negative