Temporal and Spatial Characteristics of Summer Extreme Precipitation in Eastern China and Possible Causalities

In the past decades, with the increasing frequency of extreme weather and climate events, the world has suffered huge losses. Based on NCEP/NCAR reanalysis data and China regional precipitation data provided by China Meteorological Administration, the extreme precipitation events in eastern China are defined by relative threshold method, and the temporal and spatial characteristics of summer extreme precipitation in eastern China from 1961 to 2016 are analyzed by empirical orthogonal function (EOF), and the reverse distribution of extreme precipitation in the middle and lower reaches of the Yangtze River and south China by Indian Ocean warm pool is revealed influence. The results show that the total amount and frequency of extreme precipitation in summer are concentrated in the Yangtze River Basin and south China. EOF1 decomposition of extreme precipitation reflects the interannual oscillation characteristics of reverse spatial distribution in the Yangtze River Basin and south China. The time series corresponding to EOF1 has significant interannual characteristics. The Pacific-Japan (PJ) teleconnection pattern is a circulation system that significantly affects the spatial-temporal pattern of extreme precipitation in southern China. When the PJ pattern is in the positive phase, the anticyclone controls the south China region, and restrains the convective activity, which results in the decrease of extreme precipitation. The anomalous southwest wind to the south of 30°N and the anomalous northerly wind to the north of 30°N converge in the middle and lower reaches of the Yangtze River. Combining with the sufficient water vapor carried by the anomalous southwest airflow at the edge of anticyclone, it is more conducive to the formation of extreme precipitation. The east propagating Kelvin wave in the warm pool of the Indian Ocean is an important reason for the formation of the PJ pattern and finally the formation of extreme precipitation anomalies in China.

Spatial-Temporal Distribution of Summer Extreme Precipitation in South China and Response of Tropical Ocean

In the study, the summer extreme precipitation in South China is divided into early rainy season (MJ) and late rainy season (JA). The percentile method (95%) is used to define the extreme precipitation threshold. Based on the international general definition method of extreme precipitation threshold: percentile method (95%), the extreme precipitation thresholds in flood season before and after South China are defined respectively. The total amount and frequency of extreme precipitation in flood season before and after 1979-2014 are calculated in this paper. The change trend of the two indicators is basically the same, and the two indicators have obvious interannual variation and an upward trend. According to the results of wavelet analysis of extreme precipitation frequency, the frequency of extreme precipitation in the first flood season mainly has a period of 3 - 5 years, while the frequency of extreme precipitation in the later flood season has a significant period of 6 - 8 years. The spatial distribution of extreme precipitation before and after the flood season shows that the extreme precipitation in the former flood season is mainly distributed in the central part of Guangdong, the northeast of Guangxi and the western part of Fujian, and the extreme precipitation in the latter flood season mainly occurs in the southern coastal area. The results show that there are different tropical SST regions affecting the extreme precipitation in South China. The former flood season is mainly the tropical Indian Ocean warm SST, and the latter flood season is mainly the tropical Pacific warm SST. The tropical Indian Ocean SST stimulates the anticyclonic anomaly over the South China Sea, which brings the southwest warm and humid air flow into South China, resulting in the increase of extreme precipitation in the first flood season of South China;the tropical Pacific SST stimulates the cyclonic anomaly over the South China Sea, which reduces the water vapor outflow caused by the seasonal northward jump of the subtropical high in South China, resulting in the increase of extreme precipitation in the later flood season of South China.

Ligand accommodation causes altered reactivity of silver clusters with iodomethane:superatomic stability of Ag_(9)I_(2)^(+)in mimicking XeF_(2)

Exploring metal cluster reactivity with alkyl halides enables to understand the related chemical mechanism of metal surfaces in terms of active sites.Here we report a study of Ag_(n)^(+)(n=1-27)clusters reacting with iodomethane by a flow tube apparatus in tandem with a customized triple quadrupole mass spectrometer.Strong even/odd alternation of the Ag_(n)^(+)is observed in their reactions with CH_(3)I,where silver clusters with even-number,Ag_(2n)^(+),find favorable products of Ag_(2n)I_(1,3)^(+)series,while the Ag_(2n−1)^(+)clusters form Ag_(2n−1)I_(2,4)^(+)products.Interestingly,Ag_(9)^(+)shows up with prominent mass abundance but allows for the formation of Ag_(9)I_(2)^(+),which finds an echo with the formation of Ag_(10)I_(3)^(+).We illustrate the enhanced stability of Ag_(9)I_(2)^(+)and Ag_(10)I_(3)^(+)by showing their significantly enlarged highest occupied molecular orbital(HOMO)-lowest unoccupied molecular orbital(LUMO)gaps and balanced charge distribution compared with the bare metal clusters,respectively.Also elucidated,is the superatomic nature of these bare and iodinated silver clusters,especially Ag_(9)I_(2)^(+)which mimics the rare-gas compound XeF_(2).This study expands a vivid example of special and general superatoms,and enriches the general knowledge on how a ligand stabilizes a metal cluster.

A comparative study on the reactivity of cationic niobium clusters with nitrogen and oxygen

We have prepared well-resolved Nb^(+)_(n)(n=1-10)clusters and report here an in-depth study on the es-sentially different reactivity with N_(2)and O_(2),by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer(MIFT-TQMS).As results,the Nb^(+)_(n)clus-ters are found to readily react with N_(2)and form adsorption products Nb_(n)N^(+)_(2m);in contrast,the reactions with O_(2)give rise to Nb_(n)O^(+)_(1−4)products,and the odd-oxygen products indicate O-O bond dissociation,as well as increased mass abundance of NbO^(+)pertaining to oxygen-etching reactions.We illustrate how N_(2) prefers a physical adsorption on Nb^(+)_(n)clusters with an end-on orientation for all the products,and allow for size-selective Nb^(+)_(n)clusters to act as electron donor or acceptor in forming Nb_(n)N^(+)_(2m).In contrast to these nitrides,the dioxides Nb_(n)O+2display much larger binding energies,with O_(2)always as an electron acceptor,corresponding to superoxide or peroxide states in the initial reactions.Density-of-states and orbital anal-yses show that the interactions between Nb^(+)_(n)and O_(2)are dominated by strongπ-backdonation indicative of incidental electron transfer;whereas weakπ-backdonation and simultaneousσdonation interactions exist in Nb_(n)N^(+)_(2).Further,reaction dynamics analysis illustrates the different interactions for N_(2)and O_(2) in approaching the Nb^(+)_(n)clusters,showing the energy diagrams for N_(2)adsorption and O-O bond dissoci-ation in producing odd-oxygen products.Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed,giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.

Pure Metal Clusters with Atomic Precision for Nanomanufacturing

Advances in cluster science have enabled the preparation of atomically precise metal clusters with one to a hundred atoms under controllable expansion conditions.After introducing typical gas-phase cluster preparation and reaction apparatuses,this work summarized recent progress in preparing pure metal clusters of single-atom resolution,including neutral and ionic ones,with typical examples of Al,V,Nb,Fe,Co,Ni,Rh,Pt,Ag,Cu,and Pb.With the development of soft-landing deposition technology,the size-selective pure metal clusters with strict atomic precision and predictive property will benefit nanomanufacturing down to atomic and near-atomic scales.This work serves as a modest motivation to stimulate the interest of scientists focusing on interdisciplinary subjects.