Strengthening Relationship Between Arctic Sea Ice Variability and Indian Ocean Warming after the Mid-1990s

Arctic sea ice has changed significantly in recent decades, with the East Siberian-Chukchi-Beaufort Seas (ECB) region exhibiting high interannual variability that plays a crucial role in the Arctic system. This study finds that the relationship between early autumn (August-September) ECB sea ice concentration (SIC) anomalies and tropical Indian Ocean (TIO) sea surface temperature anomalies has significantly strengthened since the mid-1990s. Post-1990s, a shift in the TIO spatial pattern accompanied by a warmer background triggers a wave activity flux (WAF) extending from the TIO to the southern ECB (Bering Sea). The altered North Pacific pressure pattern facilitates the establishment of a low-pressure system over the Bering Sea, intensifying southerly winds across the warm North Pacific and consequently accelerating SIC loss. The enhanced WAF mechanisms after the mid-1990s involve tropical divergent wind anomalies changing the Rossby wave source, regulating the location and intensity of the Rossby wave trains. Furthermore, both the conversion of local kinetic energy and available potential energy contribute to maintaining the stable propagation of the wave trains. Transient eddies strengthen East Asian circulation anomalies through positive feedback mechanisms, ultimately reinforcing the WAF. In contrast, before the mid-1990s, the lack of these synergistic mechanisms resulted in a weakened WAF that inhibited low-pressure system development over the Bering Sea. Instead, a high-pressure system with northerly wind anomalies hindered poleward warm air transport. Numerical experiments employing a linear baroclinic model further confirm the influence of the TIO warming after the mid-1990s on the atmospheric circulation response, validating the proposed mechanisms.