This study examines how wind speed (WS), net surface heat flux (Q0), and freshwater flux (Fs) regulate upper-ocean mixing and sea surface temperature (SST) using a one-dimensional multi-slab ocean model in both idealized experiments driven by prescribed atmospheric forcing and coupled experiments with an atmospheric general circulation model (AGCM). The coupled configuration extends the idealized framework to spatially varying atmospheric forcing and background upper-ocean states, while single-forcing experiments isolate the response to each of the three forcing components. In the idealized experiments, increased wind speed strengthens vertical shear and turbulent mixing, deepens the ocean boundary layer, and enhances the entrainment of colder subsurface water, resulting in SST cooling. Surface heating strengthens upper-ocean stratification and increases SST, whereas surface cooling reduces static stability and enhances vertical mixing. Freshwater input strengthens near-surface stratification and suppresses vertical mixing. In the coupled experiments, wind forcing produces widespread SST cooling, with stronger responses in regions where strong background vertical shear promotes mixing. Net surface heat flux forcing produces warming over most of the analysis domain, whereas freshwater forcing yields a weaker and more spatially variable SST response. Decomposition of the combined SST response relative to the AMIP simulation indicates that net surface heat flux is the largest contributor to the domain-mean response, followed by wind forcing, the nonlinear residual, and freshwater forcing. At the regional scale, wind forcing dominates where vertical shear is strong, whereas net surface heat flux dominates where vertical shear is weak. Although the nonlinear residual makes a secondary contribution to the domain-mean response, it is locally important. These results highlight that regional SST responses are jointly governed by atmospheric forcing, background upper-ocean stratification and vertical shear, and nonlinear effects.
Arctic sea ice decline, a prominent feature of recent climate change, has increasingly been linked to tropical climate variability through atmospheric connections. This study investigates interdecadal shifts in the relationship between May Barents Sea Ice Concentration (SIC) and West African Summer Monsoon (WASM) rainfall over the period 1981–2023. Using observational datasets and reanalysis products, we identify a robust in-phase relationship between Barents SIC and WASM rainfall during 1981–2008, which weakened substantially after 2009. In the early period, Barents Sea ice in May enhanced upper-tropospheric divergence, triggering a Rossby wave train that propagated into the North Pacific Ocean, across the United States and Mexico, and further into the Tropical North Atlantic. This wave train modulated geopotential height anomalies and favored warm Sea Surface Temperature (SST) patterns over the Tropical North Atlantic (TNA), thereby strengthening low-level moisture convergence and monsoonal rainfall over West Africa in summer. In contrast, during the post-2009 period, the relationship weakened markedly, coinciding with reduced Barents SIC variability, diminished upper-tropospheric wave activity flux, weaker Rossby wave sources, and a breakdown of the Barents SIC-TNA coupling. The diminished tropical Atlantic response limited atmospheric moisture convergence and suppressed the influence of Arctic forcing on WASM variability. The NCAR Community Atmosphere Model version 5.3 (CAM5.3) reasonably reproduces the observed mechanisms linking increased Barents SIC to WASM variability in both periods. These results highlight the dynamic nature of Arctic-tropical interactions under ongoing climate change, with important implications for improving the predictability of WASM rainfall and informing regional adaptation planning.
Summer precipitation over the Haihe River Basin (HRB) exhibits a statistically significant decreasing trend during 1961–2020, posing increasing challenges to regional water resource security. Using station observations and ERA5 reanalysis data, this study provides a unified quantitative assessment of the physical processes responsible for the long-term decline in HRB summer precipitation. Moisture budget diagnostics indicate that the vertical transport term associated with anomalous vertical motion plays a dominant role, with the vertical-motion–related component accounting for approximately 129.5
