Future changes in the East Asian summer monsoon (EASM) are estimated from historical and Representative Concentration Pathway 6.0 (RCP6) experiments of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The historical runs show that, like the CMIP3 models, the CMIP5 models produce slightly smaller precipitation. A moisture budget analysis illustrates that this precipitation deficit is due to an underestimation in evaporation and ensuing moisture flux convergence. Of the two components of the moisture flux convergence (i.e., moisture convergence and horizontal moist advection), moisture convergence associated with mass convergence is underestimated to a greater degree. Precipitation is anticipated to increase by 10%–15% toward the end of the twenty-first century over the major monsoonal front region. A statistically significant increase is predicted to occur mostly over the Baiu region and to the north and northeast of the Korean Peninsula. This increase is attributed to an increase in evaporation and moist flux convergence (with enhanced moisture convergence contributing the most) induced by the northwestward strengthening of the North Pacific subtropical high (NPSH), a characteristic feature of the future EASM that occurred in CMIP5 simulations. Along the northern and northwestern flank of the strengthened NPSH, intensified southerly or southwesterly winds lead to the increase in moist convergence, enhancing precipitation over these areas. However, future precipitation over the East China Sea is projected to decrease. In the EASM domain, a local mechanism prevails, with increased moisture and moisture convergence leading to a greater increase in moist static energy in the lower troposphere than in the upper troposphere, reducing tropospheric stability.

The Coupled Model Intercomparison Project Phase 5 (CMIP5) 21st century climate change simulations exhibit a robust (slight) weakening of the Hadley cell (HC) during the boreal winter (summer, respectively) season in the future climate. Using 30 different coupled model simulations, we investigate the main mechanisms for both the multimodel ensemble mean changes in the HC strength and its intermodel changes in response to global warming during these seasons. A simple scaling analysis relates the strength of the HC to three factors: the meridional potential temperature gradient, gross static stability, and tropopause height. We found that changes in the meridional potential temperature gradients across the subtropics in a warming climate play a crucial role in the ensemble mean changes and model-to-model variations in the HC strength for both seasons. A larger reduction in the meridional temperature gradient in the Northern Hemisphere in boreal winter leads to the larger reduction of the HC strength in that season.

Four new hydrothermal vent fields were discovered on the slow spreading Central Indian Ridge (8–12°S; Segments 1–3), all located off‐axis on abyssal hill structures or Ocean Core Complexes (OCCs). Each site was characterized using seafloor observation (towed camera system), plume chemistry (Fe, Mn, and CH4; Conductivity, Temperature, and Depth sensor [CTD]/Miniature Autonomous Plume Recorder [MAPR]), and rock sampling (TVgrab/dredges). Different styles of venting on each segment reflect different geological settings, rock types, likely heat sources, and fluid pathways. The segment 1 field was located on the western flank of the axial valley at the base of OCC‐1‐1. High‐temperature venting was inferred from plume characteristics and extensive seafloor sulfide mineralization, but only diffuse venting was observed. This site appears to be a magmatic‐influenced basaltic‐hosted system despite its off‐axis location. Two low‐temperature diffusely venting sites were located on abyssal hills 6 and 9 km off‐axis on Segment 2. Plume particle, metal, and CH4 concentrations were all very low, suggesting dilution of hydrothermal fluids by intrusion of seawater into the highly permeable flank area fault zone. The “Onnuri Vent Field” (OVF), located at the summit of OCC‐3‐2, vented clear, low‐temperature fluids supporting abundant vent organisms (21 macrofaunal taxa). The plume particle signal was low to absent, but strong ORP anomalies correlated with high CH4 and low metal concentrations. Sulfide mineralization was present, which suggests both serpentinization and magmatic/lithospheric influence on fluid composition. The detachment fault is the likely pathway for hydrothermal fluid circulation at this off‐axis location. These new vent field discoveries, especially the OVF, contribute valuable information toward understanding Indian Ocean hydrothermal systems and their ecology/biogeography.

The regional distribution of hydrothermal vent activity in the northeastern (NE) Lau Basin was recently reported by the Ridge 2000 program; however, active venting sources have yet to be located. Here, we report geological and hydrological evidence that indicates the presence of three active hydrothermal venting sources in the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC), the Northeast Lau Spreading Center (NELSC), and an off-axis caldera (MTJ-1). These examples of hydrothermal activity were recognized by the appearance of hydrothermal plume signals in the water column, including anomalies in light-transmission, methane, adenosine 5′-triphosphate (ATP), and trace metal concentrations (TDMn and TDFe). Three active venting sources were identified by the observation of possible buoyant plumes during conductivity-temperature-depth (CTD) tow-yo surveys and by the recovery of hydrothermal precipitates (chimneys and altered rocks). The strongest light-transmission anomaly, an order of magnitude greater than those at other sites, was observed at the central cone of the MTJ-1 caldera. The recovery of eruption debris at a central volcanic cone, including molten sulfur, volcanic ash, and lapilli, indicates an active volcanic eruption and hydrothermal venting at the MTJ-1 caldera. Our results suggest extensive and various hydrothermal activity in the NE Lau Basin, thereby providing valuable insight into hydrothermal and volcanic processes in back-arc environments.

This work provides a new perspective on the major factors controlling the East Asian summer monsoon (EASM) in July and a promising physical–statistical forecasting of the EASM ahead of summer. Dominant modes of the EASM are revealed from the variability of large-scale air masses discerned by equivalent potential temperature, and they are found to be dynamically connected with the anomalous sea surface temperatures (SSTs) over the three major oceans of the world and their counterparts of prevailing atmospheric oscillation or teleconnection patterns. Precipitation over northern East Asia (NEA) during July is enhanced by the tropical central Indian Ocean warming and central Pacific El Niño–related SST warming, the northwestern Pacific cooling off the coast of NEA, and the North Atlantic Ocean warming. Using these factors and data from the preceding spring seasons, the authors build a multiple linear regression model for seasonal forecasting. The cross-validated correlation skill predicted for the period 1994 to 2012 is up to 0.84, which far exceeds the skill level of contemporary climate models.