The record-breaking mei-yu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant ...precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the mei-yu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.
The visible light induced C–H bond thiocyanation on the α-site of tertiary enaminones has been realized under metal-free, photocatalytic conditions in the presence of Rose Bengal, which enables the ...synthesis of thiocyanated alkene derivatives and chromones using NH4SCN as the thiocyano source under an aerobic atmosphere. In addition, employing Ru(bpy)3Cl2·6H2O as the photocatalyst switches the reaction pathway to provide NH2-functionalized thiocyanated enamines via the difunctionalization process consisting of C–H bond thiocyanation and vinyl C–N bond transamination.
Sparse code multiple access (SCMA) is a novel non-orthogonal air-interface technology in which several users share a same frequency resource simultaneously. The SCMA decoder is based on a message ...passing algorithm (MPA) for the sparsity of codeword. In the original MPA, all the users update a message until the maximum number of iterations is reached, resulting in high computational complexity. This letter puts forward a threshold-based MPA, where a belief threshold is applied to control the algorithm process. Simulation results show that the proposed scheme obtains a low computational complexity with only a slight performance degradation when the threshold is set appropriately.
The prediction skill and source of the predictability of the East Asian summer monsoon (EASM) system are examined in this work based on four state‐of‐the‐art seasonal climate forecast models ...including BCC_CSM1.1, ECMWF_SYS4, NCEP_CFS2 and TCC_CPS2. The prediction of the climatology and interannual EASM pattern and the impact on the prediction are further investigated. It is noted that the four models have some skill in predicting summer rainfall in the East Asia, however, the skill is low on average and also largely regional dependence. The interannual variation of EASM measured by monsoon circulation index is well reproduced, implying that the broad‐scale feature/pattern of EASM has higher predictability than the detailed spatial variation of EASM rainfall. The possible sources of predictability of the interannual variability of EASM are associated with the El Niño‐Southern Oscillation (ENSO) and the north Indian Ocean (NIO) sea surface temperature (SST) anomalies. The correlation pattern of rainfall with the NIO SST is characterized by a tripole pattern from south to north of East Asia, which is different from the correlation distribution of the southern‐northern dipole with ENSO, suggesting that NIO SST may exert influence on the EASM independently. The major biases in climatology of EASM in the models are the northward shift of the western Pacific subtropical high (WPSH) and weak monsoonal southerly over the coast of East Asia, which leads to the prediction bias of the Meiyu/Baiu/Changma (MBC) rainfall belt. The prediction of the interannual EASM pattern presents two deficiencies: too weak rainfall variability and northward shift of the dipole rainfall pattern (opposite variation between MBC and the northwestern Pacific), that may be caused by the biases of WPSH in the models.
The broad‐scale feature of EASM has higher predictability than the detailed spatial variation of EASM rainfall in the seasonal climate forecast models, while the possible predictability sources of NIO SST may exert influence on the EASM independently from ESNO. Too weak rainfall variability and northward shift of the dipole rainfall pattern of EASM may be caused by the biases of WPSH in the models. The distribution of rainfall (shaded; units: mm day−1) and 850 hPa wind (vectors; units: m s−1) regressed onto the observed EASM index in (a) the observation, (b) MME and (c–f) each models.
The construction of 1,5-disubstituted 1,2,3-triazoles has been effected through the cascade dual C–N bond formation, N–N bond formation and an acyl migration-based C–C bond formation via the ...three-component reactions of enaminones, tosylhydrazine and primary amines. This metal- and azide-free, regioselective synthetic method proceeds in the presence of only molecular iodine.
The perfluoroalkylsulfonylation (CF3SO2, C2F5SO2 and CHF2SO2) in the enaminone CH bonds has been developed simply via the promotion of molecular iodine by using stable and cheap sodium perfluoroalkyl ...sulfinates as coupling partners. The stereoselective synthesis of E-configurated α-perfluoroalkylsulfonyl enaminones has been realized via unprecedented CH bond elaboration and CC double bond configuration inversion by free radical process.
The CH perfluoroalkylsulfonylation of enaminones leading to the synthesis diverse perfluoroalkyl functionalized enamines is realized via the promotion of molecular iodine. As the first method in enaminone CH perfluoroalkylsulfonylation, this work features advantage of metal-free conditions, novel and selective stereoselectivity and broad substrate tolerance. Display omitted
This work investigated the simulation and future changes in East Asian summer mean rainfall, interannual variability, and associated uncertainty based on the historical and representative ...concentration pathway (RCP) 4.5 runs of 26 CMIP5 models. It is noted that the present‐day mean rainfall was well simulated by most of the models, though underestimation is over the Meiyu/Baiu/Changma (MBC) rainfall belt, and overestimation is in the western North Pacific (WNP). Nevertheless, it is still a challenge for the CMIP5 models to well simulate the interannual variability. The approach of the multi‐model ensemble greatly improves the credibility of model simulations, especially for the rainfall variability. The East Asian summer rainfall is projected to a relatively consistent increase in the near future, while the spatial distributions of the summer rainfall changes by the end of the 21st century are similar to those in the near future, with twice magnitude of the mean rainfall amount increase. The rainfall changes are associated with the strengthened low‐level southerly wind over East China and intensified western North Pacific high. Also, the variation of rainfall interannual variability by the end of the 21st century over East Asia is larger than that in the near future, with similar spatial patterns. It may imply that the stronger rainfall interannual variability is associated with the increased mean rainfall amount in the future. The inter‐model spreads of both the mean and interannual variability changes are larger in the low latitudes than in the high latitudes over East Asia. The signal‐noise‐ratio (SNR) is largely determined by the rainfall change (signal) in the future. Lower SNR of interannual variability than that of mean rainfall over East Asia implies that the CMIP5 models are more robust to a certain extent in simulating the summer mean rainfall change in East Asia than the change of interannual variability.
(a) MME‐projected changes of mean rainfall by the end of the 21st century, (b) difference of mean rainfall between the periods of 2070–2099 and 2020–2049, (c) inter‐model spread, and (d) signal‐noise‐ratio. Stippling in (d) represents that more than 70% models agree on the sign of the MME changes.
Carbon-halogen (C-X) bonds are amongst the most fundamental groups in organic synthesis, they are frequently and widely employed in the synthesis of numerous organic products. The generation of a C-X ...bond, therefore, constitutes an issue of universal interest. Herein, the research advances on the copper-catalyzed and mediated C-X (X = F, Cl, Br, I) bond formation via direct C-H bond transformation is reviewed.
In the spring of 2021, southwestern China (SWC) experienced extreme drought, accompanied by the highest seasonal-mean temperature record since 1961. This drought event occurred in the decaying phase ...of a La Niña event with negative geopotential height anomalies over the Philippine Sea, which is distinct from the historical perspective. Historically, spring drought over SWC is often linked to El Niño and strong western North Pacific subtropical high. Here, we show that the extreme drought in the spring of 2021 may be mainly driven by the atmospheric internal variability and amplified by the warming trend. Specifically, the evaporation increase due to the high temperature accounts for about 30% of drought severity, with the contributions of its linear trend portion being nearly 20% and the interannual variability portion being about 10%. Since the sea surface temperature forcing from the tropical central and eastern Pacific played a minor role in the occurrence of drought, it is a challenge for a climate model to capture the 2021 SWC drought beyond one-month lead times.
PDF
