A snow-jet bridging mechanism driving the Afro-Asian summer monsoon precipitation dipole

The Afro-Asian summer monsoon precipitation sustains billions of people across the two continents, and its variability strongly affects water supply, irrigation, and drought-flood risks. While this variability has been linked to air-sea interactions, its connection with land-surface signals remains unclear. Using large-ensemble snow perturbation experiments and information flow causal analysis, we show that reduced Tibetan Plateau snow cover (TPS) contributes to a dipole pattern in Afro-Asian summer monsoon precipitation: positive anomalies over tropical Africa and negative anomalies over South Asia. This relationship is modulated by an accelerated tropical easterly jet (TEJ). Reduced TPS enhances thermal heating, exciting an upper-level anticyclonic anomaly. The easterly flow along its southern flank intensifies the TEJ, enhancing moisture transport toward tropical Africa and reinforcing the low-level anticyclonic anomaly over South Asia, resulting in a dipole precipitation pattern. Since 2006, TPS extent has stayed below 9% (a transition after which the TPS-TEJ coupling substantially weakens), raising uncertainty in future projections of Afro-Asian monsoon under continued warming and TPS loss.