Science Bulletin最新文献

El Niño-Southern Oscillation (ENSO) exhibits a strong asymmetry between warm El Niño and cold La Niña in amplitude and temporal evolution. An El Niño often leads to a heat discharge in the equatorial Pacific conducive to its rapid termination and transition to a La Niña, whereas a La Niña persists and recharges the equatorial Pacific for consecutive years preconditioning development of a subsequent El Niño, as occurred in 2020-2023. Whether the multiyear-long heat recharge increases the likelihood of a transition to a strong El Niño remains unknown. Here, we show that such a transition is rare but more likely under transient greenhouse warming. In boreal spring and early summer after a multiyear La Niña, despite a substantial recharge in the western Pacific, thermocline remains anomalously shallow and sea surface temperature (SST) remains anomalously cold in the equatorial central Pacific. The cold conditions inhibit an ensuing eastward movement of atmosphere deep convection out of the warm western Pacific, delaying onset of ocean-atmosphere coupling, and hence growth of an El Niño. Under a high emission scenario, such a transition is still rare but more than twice as likely. The projected change is consistent with a projected weakening in climatological zonal SST gradient that promotes the eastward movement of atmosphere convection and a projected intensification in upper-ocean stratification of the equatorial Pacific that enhances the ocean-atmosphere coupling. Our result provides predictive insight of El Niño after multiyear La Niña, and advances our understanding of ENSO transition under greenhouse warming.

The southeastern Tibetan Plateau (SETP) is the preeminent summer heavy precipitation region within the Tibetan Plateau (TP). However, the large-scale circulation types and dynamics driving summer heavy precipitation in the SETP remain inadequately elucidated. Using the hierarchical clustering method, two distinctive atmospheric circulation patterns associated with heavy precipitation were identified: the Tibetan Plateau vortex type (TPVT, constituting 56.6 % of the events) and the mid-latitude trough type (MLTT, 43.4 %). A comprehensive examination of the two atmospheric circulation patterns reveals a clear nexus between the occurrences of summer heavy precipitation and positive vorticity anomalies, moisture convergence, as well as the southeastward displacement of the westerly jet core. Specifically, TPVT events are characterized by the eastward and dry-to-wet potential vorticity progression processes, while MLTT events are linked to the intrusion of a deep extratropical trough into the SETP. This study advances our understanding of the complex mechanisms governing the summer heavy precipitation in the SETP, shedding light on critical meteorological processes in the region.

Divergent synthesis of valuable molecules through common starting materials and metal catalysis represents a longstanding challenge and a significant research goal. We here describe chemodivergent, highly enantio- and regioselective nickel-catalyzed reductive and dehydrogenative coupling reactions of alkynes, aldehydes, and silanes. A single chiral Ni-based catalyst is leveraged to directly prepare three distinct enantioenriched products (silyl-protected trisubstituted chiral allylic alcohols, oxasilacyclopentenes, and silicon-stereogenic oxasilacyclopentenes) in a single chemical operation. The use of a bulky C₂-symmetric N-heterocyclic carbene (NHC) ligand for nickel catalyst is the key to enable simultaneous exceptional control of stereo- and regioselectivity (up to 99% enantiomeric excess (ee), >99:1 regiomeric ratio (rr), >99:1 E/Z) and high efficiency (up to 99% yield). Computational studies elucidate the origin of chemodivergency and reveal the critical role of NHC in the enantioselectivity- and rate-determining oxidative cyclization step via an η²-aldehyde η²-alkyne Ni five-centered transition state. We expected that the enantioselective η²-activation mode be widely applicable in other Ni-catalyzed carbonyl couplings.