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. Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Nino–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extratropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not wellunderstood. Here, we assess how tropical convection interacts withmid-latitude summer circulation at different intra-seasonal timescales andhow ENSO affects these interactions. First, we apply maximum covarianceanalysis (MCA) between tropical convective activity and mid-latitudegeopotential height fields to identify the dominant modes of interaction.The first MCA mode connects the South Asian monsoon with the mid-latitudecircumglobal teleconnection pattern. The second MCA mode connects thewestern North Pacific summer monsoon in the tropics with a wave-5 patterncentred over the North Pacific High in the mid-latitudes. We show that theMCA patterns are fairly insensitive to the selected intra-seasonal timescalefrom weekly to 4-weekly data. To study the potential causal interdependencies between these modes and with other atmospheric fields, weapply the causal discovery method PCMCI at different timescales. PCMCIextends standard correlation analysis by removing the confounding effects of autocorrelation, indirect links and common drivers. In general, there is a two-way causal interaction between the tropics and mid-latitudes, but thestrength and sometimes sign of the causal link are timescale dependent. Weintroduce causal maps that show the regionally specific causal effect fromeach MCA mode. Those maps confirm the dominant patterns of interaction andin addition highlight specific mid-latitude regions that are most stronglyconnected to tropical convection. In general, the identified causalteleconnection patterns are only mildly affected by ENSO and thetropical mid-latitude linkages remain similar. Still, La Ninastrengthens the South Asian monsoon generating a stronger response in themid-latitudes, while during El Nino years the Pacific pattern isreinforced. This study paves the way for process-based validation of borealsummer teleconnections in (sub-)seasonal forecast models and climate modelsand therefore works towards improved sub-seasonal predictions and climateprojections.

Dominant patterns of interaction between the tropics and mid-latitudes in boreal summer: causal relationships and the role of timescales