Influence of spring Bering-Okhotsk sea ice on boreal summer intraseasonal oscillation over equatorial central Pacific

This study investigates the influence of spring sea ice concentration (SIC) variability in the Bering-Okhotsk Seas (BOS) on the intensity of the Boreal Summer Intraseasonal Oscillation (BSISO) over the equatorial central Pacific (ECP) in June. Observational analyses reveal that a reduction in spring BOS SIC is significantly associated with enhanced BSISO activity. Sea ice retreat amplifies upward heat fluxes through positive air-ocean-ice feedback, which intensifies local warming and further accelerates ice melt. These thermal anomalies reduce lower-tropospheric geopotential height, inducing cyclonic circulation that enhances mid-tropospheric ascent. The upward motion transport compresses air in the upper troposphere, generating divergence and a Rossby wave source via vortex stretching. The resulting Rossby wave train propagates southward, facilitated by a weakened Pacific subtropical westerly jet that promotes latitudinal wave energy dispersion. Anomalous westerlies associated with the southern part of this pattern weaken the climatological easterly trades, thereby suppressing surface evaporation and elevating local sea surface temperatures (SSTs) through the wind-evaporation-SST (WES) feedback. This warming enhances ascending motion, convective available potential energy (CAPE), and low-level moisture convergence over the ECP, establishing a favorable thermodynamic and dynamic environment for BSISO intensification. Linear baroclinic model (LBM) experiments corroborate that thermal forcing over the BOS modulates ECP BSISO activity via this cross-latitudinal teleconnection. As a fundamental component of the high-latitude cryosphere, sea ice modulates global climate and serves as a key indicator of planetary warming. Recent decades have witnessed pronounced Arctic warming and sea ice loss, with repercussions extending from the polar to the tropical regions. In the tropics, the intraseasonal oscillation acts as a critical bridge between weather and climate systems. However, both how Arctic sea ice influences the BSISO and the underlying mechanisms connecting these systems remain unclear. This study aims to address these knowledge gaps, thereby advancing our mechanistic understanding of cross-spatiotemporal interactions between the Arctic and lower-latitude climate.