Average synoptic meteorology for the four research periods of KORUS-AQ. Left panels coincide with dynamic conditions and right panels coincide with stagnant or blocking conditions. The polar jet stream is displayed as 250 hPa wind speed (shaded), vectors, and heights (black contours) averaged over each KORUS-AQ research period (NCEP–NCAR meteorological reanalysis). Brown arrows and dashed brown line indicate the mean position of the low-level mid-latitude storm track and the monsoon boundary (e.g., Meiyu, Baiu, Changma Front), respectively. DOI: https://doi.org/10.1525/elementa.395.f4