Fidelity of the APHRODITE Dataset in Representing Extreme Precipitation over Central Asia

Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network(V3.25)and the Chinese Surface Daily Climate Dataset(V3.0),this study investigates the fidelity of the AHPRODITE dataset in representing extreme precipitation,in terms of the extreme precipitation threshold value,occurrence number,probability of detection,and extremal dependence index during the cool(October to April)and warm(May to September)seasons in Central Asia during 1961–90.The distribution of extreme precipitation is characterized by large extreme precipitation threshold values and high occurrence numbers over the mountainous areas.The APHRODITE dataset is highly correlated with the gauge-observation precipitation data and can reproduce the spatial distributions of the extreme precipitation threshold value and total occurrence number.However,APHRODITE generally underestimates the extreme precipitation threshold values,while it overestimates the total numbers of extreme precipitation events,particularly over the mountainous areas.These biases can be attributed to the overestimation of light rainfall and the underestimation of heavy rainfall induced by the rainfall distribution–based interpolation.Such deficits are more evident for the warm season than the cool season,and thus the biases are more pronounced in the warm season than in the cool season.The probability of detection and extremal dependence index reveal that APHRODITE has a good capability of detecting extreme precipitation,particularly in the cool season.

Wave-Breaking Features of Blocking over Central Siberia and Its Impacts on the Precipitation Trend over Southeastern Lake Baikal

Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979–2018 and is closely related to blocking occurrence over central Siberia(45°–70°N,75°–115°E).This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking(AWB and CWB)blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area.Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia,as well as an evident Rossby wave train over midlatitude Eurasia.For AWB blocking events,the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution.In contrast,ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale,meridional,and more anisotropic signatures.Moreover,the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events.Therefore,CWB blocking events are more persistent.AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events,in which moderate above-normal rainfall is seen in the decaying periods of blockings.A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia,which may contribute to the downward trend of precipitation over southeastern Lake Baikal.

The development of a powerful Mongolian cyclone on 14-15 March 2021:Eddy energy analysis

2021年3月14-15日,强蒙古气旋引起的大范围强沙尘天气袭击了蒙古国和中国北方地区.本文从高频涡动能量学的角度分析了这一超强气旋的发展过程.2021年3月初,加强的极涡向中亚伸入,并与横跨东亚和东北亚的一个大型脊协同作用,由此形成了从中亚到贝加尔湖地区的强大斜压带.在这一有利的低频环流条件下,3月13日一个移动性小槽越过萨彦岭后触发了蒙古气旋.850 hPa涡旋动能的下传在气旋的加强和成熟阶段起到了关键作用.而这一机制主要由冷锋后侧的冷空气下沉过程完成.一旦气旋开始快速发展,锋面气旋波机制就变得至关重要.我们强调,高频涡动有效位能是首先从时间平均有效势能中提取能量,然后从低频有效位能中汲取能量而剧烈增长的,这正是该超强气旋的鲜明特征.“北冷南暖”的近地面温度气候异常型为时间平均有效位能的增多和向高频涡动有效位能的转换提供了条件,而“西北冷东南暖”的温度异常型则有利于低频有效位能的增加和向高频涡动有效位能的转换.分析结果表明,高低频波之间的相互作用对蒙古气旋的增强也很重要.

Visible-Light-Promoted Palladium-Catalyzed Cross-Coupling of lodocarboranes with Disulfides and Phenylselenyl Chloride

This work describes a general method for the synthesis of a series of sulfenylated and selenylated carboranes at room temperature using readily available iodocarboranes as starting materials via boron-centered carboranyl radicals.Such hypervalent boron radicals are generated by a visible-light-promoted Pd(O)/Pd(I)pathway.They are useful intermediates and can be trapped by disulfides and phenylselenyl chloride for the convenient construction of B-S/Sebonds.

Nickel-catalyzed regioselective B(3,4,5,6)-H tetra-alkylation of o-carboranes

Though transition metal-catalyzed cage BH methylation has been well documented, catalytic alkylation of cage BH bonds remained elusive because transition metal alkyl complexes are prone to undergo β-H elimination. We report herein a highly efficient 8-aminoquinoline-assisted nickel-catalyzed regioselective cage B(3,4,5,6)-H tetra-alkylation of o-carboranes employing unactivated alkyl bromides as alkylating agents in the absence of any oxidants, leading to the preparation of a class of tetra-alkylated o-carboranes with a broad substrate scope in good to very high yields. This method opens new avenues for oxidant-free, direct, efficient, sustainable, and regioselective multiple B–H alkylation of carboranes via base metal catalysis.

Copper Catalyzed Asymmetric [4＋2] Annulations of D-A Cyclobutanes with Aldehydes

Copper catalyzed enantioselective [4＋2] annulations of D-A cyclobutanes and aldehydes have been developed. In the presence of a side arm modified chiral bisoxazoline （SaBOX） ligand, the [4＋2] annulations proceeded smoothly with a broad substrate scope. 22 examples were studied, leading to the corresponding products with various functional groups in 41%-99% yields with 〉99/1 dr and 90%-96% ee. The resulting product with two ester groups was mono-reduced, giving the corresponding product in excellent diastereoselectivity without loss of the enantiopurity.

A Novel Identification of the Polar/Eurasia Pattern and Its Weather Impact in May

The Polar/Eurasia(POL) pattern was previously identified based on the empirical orthogonal function method and monthly mean data, in which the positive and negative phases are anti-symmetric in spatial distribution. This paper identifies the positive(POL+) and negative(POL-) phases of the POL pattern through applying a novel approach, i.e.,self-organizing maps, to daily 500-h Pa geopotential height fields in May over 1948–2017. The POL+, POL1-, and POL2-patterns defined by this method represent actual physical modes. The POL+ pattern features a wave train from the northeastern Atlantic/northern Europe via the subarctic regions of Eurasia to Lake Baikal. The POL1-pattern is characterized by a planetary-scale dipole pattern with a positive anomaly band over subarctic Eurasia and a negative anomaly band from central Asia to the Sea of Okhotsk. The anomaly centers of the POL2-pattern are basically antisymmetrical to those of the POL+ pattern. The POL+ pattern increases the blocking frequency over the northeastern Atlantic/northern Europe and northeastern Asia, where high-frequency transient eddies are highly recurrent in the north. Accordingly, precipitation increases apparently in the subarctic Asian continent and western Siberia, and decreases around Europe and Lake Baikal. A mimic wave train is also observed in the surface air temperature anomaly field. During the POL1-period, the blocking frequency is abnormally high over Eurasia, whereas high-frequency transient eddies are apparently suppressed over northern Eurasia. Correspondingly, significant precipitation deficits are observed in northern Eurasia. The POL1-pattern also causes a remarkable temperature increase in the subarctic seas of Eurasia and a considerable temperature drop in the midlatitude Asian continent. As the POL2-pattern prevails, the blocking frequency decreases over the North Atlantic/Europe but strengthens over the Asian continent. The POL2-pattern also causes wavelike anomalies of precipitation and surface air temperature over northern Eurasia.

One-Pot Process to Carborano-Coumarin via Catalytic Cascade Dehydrogenative Cross-Coupling

Summary of main observation and conclusion Ir-catalyzed cascade dehydrogenative CH/BH and BH/OH cross-coupling of carboranyl carboxylic acid with readily available benzolc acid has been achieved,leading to the facile synthesis of previously unavailable carborano-coumarin in a simple one-pot process.Two cage B-H,one aryl C--H and one 0-H bonds are activated to construct eficiently new B-C and B-0 bonds.The cascade cyclization can stop at the first B-H/C-H cross-coupling step by tuning the reaction conditions,resulting in a series of a-carboranyl benzoic acid and aryl carborane derivatives.Control experiments indicate that B-H/C-H dehydrocoupling proceeds preferentially over B-H/O-H dehydrocoupling,and both directing groups and oxidants are crucial for this reaction.An iridium(V)intermediate is proposed to be involved in the catalytic cycle.

Copper catalyzed/mediated direct B–H alkenylation/alkynylation in carboranes

Base metal catalyzed regioselective cage B–H functionalization has been achieved. Under the assistance of a bidentate directing group, Cu-catalyzed [4+2] annulation of carboranyl amides with internal alkynes affords unprecedented C,B-substituted carborane-fused-pyridone derivatives, whereas the use of terminal alkynes leads to B–H/C(sp)–H dehydrocoupling products. The isolation and structural identification of a notably stable Cu(Ⅰ) intermediate shed light on the reaction mechanism, which is proposed to involve a Cu(Ⅲ) intermediate.

Blocking Features for Two Types of Cold Events in East Asia

Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations over the Eurasian continent.Two categories of CAOs are recognized,namely,the ordinary cold wave events（CWEs）and the extensive and persistent extreme cold events（EPECEs）,with the latter having even stronger impacts.The blocking features associated with these two types of CAOs and their differences are investigated in this study on the intraseasonal timescale.What these two CAOs do have in common is that they are both preceded by the intensification and recurrence of a blocking high over the midlatitude North Atlantic.The difference between these events is primarily reflected on the spatial scale and duration of the corresponding blocking high.During the CWEs,blocking occurs around the Ural Mountains,and exhibits a regional feature.The resulting cold air temperature persists for only up to 8 days.In contrast,during the EPECEs,the blocking region is quite extensive and is not only confined around the Ural Mountains but also extends eastward into Northeast Asia in a southwest–northeast orientation.As a result,the cold air tends to accumulate over a large area and persists for a much longer time.The blocking activity is primarily induced by an increased frequency and eastward extension of the synoptic anticyclonic Rossby wave breaking（AWB）.Compared with the CWEs,characterized by a regional and short-lived synoptic AWB frequency,the EPE-CEs tend to be accompanied by more recurrent and eastward extensions of the synoptic AWB.

Reaction of o-Carboryne with Furans： Facile Synthesis of Carborane- Fused Oxanorbornenes and Their Derivatives

o-Carboryne （1,2-dehydro-o-carborane） is a very useful synthon for the synthesis of a variety of carborane-functionalized molecules. Diels-Alder reaction of o-carboryne with furans gave a series of carborane-fused oxanorbornenes in moderate to high yields using 1-OTf-1,2-C_2B_10H_11 as carboryne precursor. The resultant cycloadducts can undergo hydrogenation, cyclic oxidation, bromination, [4＋2]/[2＋2] cycloaddition and nucleophilic ring opening reaction to afford a variety of highly functionalized carboranes that may find applications as useful basic units in medicine and materials science.

How long a C–C bond can be? An example of extraordinary long C–C single bond in 1,2-diarylamino-o-carborane

How long a C-C bond can be?A question has long fascinated chemists.This work reports an example of extraordinary long C-C bond distance of 1.990(4)?observed in single-crystal X-ray structure of 1,2-(NHMes)2-o-carborane(2;Mes=2,4,6-trimethylphenyl).DFT calculations show that hyperconjugation of lone pairs of the nitrogen atoms into the emptyσ^*orbital of the cage C-C bond is the origin of the bond elongation.Such hyperconjugation can be suppressed if the two nitrogen atoms in 2 are linked to a Lewis acidic germanium(Ⅱ)center.

On Desilylation of 13-Vertex Carborane 1,2-Me_(2)Si(CH_(2))_(2)-1,2-C_(2)B_(11)H_(11)

The reasons for facile double desilylation of 13-vertex carborane 1,2-Me_(2)Si(CH_(2))_(2)-1,2-C_(2)B_(11)H_(11)(2)are discussed in this article.New 13-and 14-vertex ruthenacarboranes bearing the same-CH_(2)SiMe_(2)CH_(2)-linkage have been prepared and structurally characterized for comparison.Structural analyses of 13-and 14-vertex heteroboranes as well as control experiments suggest that the facile double desilylation of 2 on silica gel can be attributed to the joint actions of several factors involving the high ring-strain of exo five-membered C_(4)Si ring,Lewis acidity of Si atom and Brønsted acidity of silica surface.

Palladium-Catalyzed Oxidative Annulation of 1-Hydroxy-o-Carborane withInternal Alkynes:Facile Synthesis of Carborane-Fused Oxaborolest

of main observation and conclusion A palladium catalyzed oxidative annulation of 1-hydroxy-o-carborane with internal alkynes via regioselective B(3)—H bond activation has been developed for facile synthesis of a series of QB-substituted carborane-fused oxaboroles.These molecules can undergo intramolecular oxidative dehydrogenative coupling to afford carborane-fused large n systems for potential applications in organic materials.The reaction mechanism is also proposed,involving hydroxy deprotonation,nucleopalladation of alkyne,regioselective electrophilic B—H substitution and reductive eiiimination.