摘要：The alternation of active and break phases in Indian summer monsoon(ISM) rainfall at intraseasonal timescales characterizes each ISM season.Both tropical and mid-latitude drivers influence this intraseasonal ISMvariability. The circumglobal teleconnection observed in boreal summerdrives intraseasonal variability across the mid-latitudes, and a two-wayinteraction between the ISM and the circumglobal teleconnection pattern hasbeen hypothesized. We use causal discovery algorithms to test theISM circumglobal teleconnection hypothesis in a causal framework. A robustcausal link from the circumglobal teleconnection pattern and the NorthAtlantic region to ISM rainfall is identified, and we estimate the normalizedcausal effect (CE) of this link to be about 0.2 (a 1 standard deviationshift in the circumglobal teleconnection causes a 0.2 standard deviationshift in the ISM rainfall 1 week later). The ISM rainfall feeds back onthe circumglobal teleconnection pattern, however weakly. Moreover, weidentify a negative feedback between strong updraft located over India andthe Bay of Bengal and the ISM rainfall acting at a biweekly timescale, withenhanced ISM rainfall following strong updraft by 1 week. This mechanismis possibly related to the boreal summer intraseasonal oscillation. Theupdraft has the strongest CE of 0.5, while the Madden–Julian oscillationvariability has a CE of 0.2–0.3. Our results show that most of the ISMvariability on weekly timescales comes from these tropical drivers, thoughthe mid-latitude teleconnection also exerts a substantial influence.Identifying these local and remote drivers paves the way for improvedsubseasonal forecasts.
