A Global Climatology of Large‐Scale Convergence Lines and Their Influence on Monsoon Variability in India, West Africa, and Australia

Abstract Low‐level (1,000–850 hPa), 6‐day time‐mean large‐scale convergence lines are identified objectively in the ERA5 reanalysis and are sorted into two classes according to whether the local specific humidity is high (high‐q) or low (low‐q). The high‐q convergence lines lie in the tropics, and in particular in the Intertropical Convergence Zone (ITCZ). The low‐q convergence lines are mostly heat troughs and mid‐high latitude convergence lines. High‐q convergence lines are a frequent feature of the Indian and Australian monsoons where they correlate closely with precipitation. Furthermore, high‐q convergence lines are more frequent during relatively wet monsoon years and during the active phases of the monsoon. Over India, high‐q convergence lines near the Tibetan Plateau shift southward during both wet years and active monsoon phases. Similarly, in Australia, the convergence lines shift southward from the Maritime Continent to continental Australia. In contrast, in the West African monsoon region, convergence lines are drier than in the Indian and Australian monsoon regions, with the frequency of the high‐q convergence lines increasing little in wet years or active monsoon phases. However, low‐q convergence lines, which do make up the west African ITCZ, shift northward during wet years and intraseasonal monsoon bursts.