Wintertime Cross-correlational Structures between Sea Surface Temperature Anomaly and Atmospheric-and-Oceanic Fields in the East/Japan Sea Under Arctic Oscillation

The winter Arctic Oscillation (AO) modulates East Asian climate and the East/Japan Sea (EJS), yet local, scale-dependent air-sea couplings linking atmosphere, ocean and sea-surface temperature anomalies (SSTA) remain unclear. Using 30 years of daily fields (1993--2022), we compute detrended fluctuation/cross-correlation metrics over 5--50-day scales at every grid: the Hurst exponent (H), the cross-Hurst exponent ($λ$), and the DCCA coefficient (ρDCCA). Significance is assessed with iterative-AAFT surrogates and Benjamini--Hochberg false-discovery-rate control. Three robust features emerge. (1) During AO+ winters, the EKB--SPF corridor exhibits high SSTA variance and near-ballistic persistence (H ≈ 1.4--$1.5$), indicating increased susceptibility to marine heatwaves. (2) SSTA co-fluctuates positively with near-surface air-temperature anomalies, whereas turbulent heat-flux anomalies are largely anti-phased and show negligible cross-persistence, consistent with fast damping. (3) Oceanic fields impart persistent coupling: sea-surface height anomalies display basin-wide positive links with SSTA; meridional geostrophic velocity imprints advective cross-coupling along EKWC/SPF pathways, while zonal flow and vorticity yield patchy signatures. Winter SST variability in the EJS thus reflects a two-tier process in which mesoscale structure and along-front advection organize persistence, while synoptic forcing and turbulent heat exchange supply strong but non-persistent tendencies. The FDR-controlled, grid-point DFA/DCCA framework is transferable to other marginal seas.