A CLIMATOLOGY OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

Based on best-track data and JRA-25 reanalysis, a climatology of western North Pacific extratropical transition (ET) of tropical cyclone (TC) is presented in this paper. It was found that 35% (318 out of 912) of all TCs underwent ET during 1979–2008. The warm-season (June through September) ETs account for 64% of all ET events with the most occurrence in September. The area 120°E–150°E and 20°N–40°N is the most favorable region for ET onsets in western North Pacific. The TCs experience ET at latitudes 30°N–40°N and have the greatest intensity in contrast to other latitude bands. The distribution of ET onset locations shows obviously meridional migration in different seasons. A cyclone phase space (CPS) method was used to analyze the TC evolution during ET. Except for some cases of abnormal ET at relatively high latitudes, typical phase evolution paths—along which TC firstly showed thermal asymmetry and an upper-level cold core and then lost its low-level warm core—can be used to describe the main features of ET processes in western North Pacific. Some seasonal variations of ET evolution paths in CPS were also found at low latitudes south of 15°N, which suggests different ET onset mechanisms there. Further composite analysis concluded that warm-season ETs have generally two types of evolutions, but only one type in cold season (October through next May). The first type of warm-season ETs has less baroclinicity due to long distance between the TC and upper-level mid-latitude system. However, significant interactions between a mid-latitude upper -level trough and TC, of either approaching or being absorbed into the trough, and TC’s relations with downstream and upstream upper-level jets, are the fingerprints for both a second type of warm-season ETs and almost all the cold-season ETs. For each type of ETs, detailed structural characteristics as well as precipitation distribution are illustrated by latitude.     

The Role of Land–sea Distribution and Orography in the Asian Monsoon. Part I： Land–sea Distribution

A number of AGCM simulations were performed by including various land--sea distributions (LSDs), such as meridional LSDs, zonal LSDs, tropical large-scale LSDs, and subcontinental-scale LSDs, to identify their effects on the Asian monsoon. In seven meridional LSD experiments with the continent/ocean located to the north/south of a certain latitude, the LSDs remain identical except the southern coastline is varied from 40^o to 4^oN in intervals of 5.6^o. In the experiments with the coastline located to the north of 21^oN, no monsoon can be found in the subtropical zone. In contrast, a summer monsoon is simulated when the continent extends to the south of 21^oN. Meanwhile, the earlier onset and stronger intensity of the tropical summer monsoon are simulated with the southward extension of the tropical continent. The effects of zonal LSDs were investigated by including the Pacific and Atlantic Ocean into the model based on the meridional LSD run with the coastline located at 21^oN. The results indicate that the presence of a mid-latitude zonal LSD induces a strong zonal pressure gradient between the continent and ocean, which in turn results in the formation of an East Asian subtropical monsoon. The comparison of simulations with and without the Indian Peninsula and Indo-China Peninsula reveals that the presence of two peninsulas remarkably strengthens the southwesterly winds over South Asia due to the tropical asymmetric heating between the tropical land and sea. The tropical zonal LSD plays a crucial role in the formation of cumulus convection.     

广西大暴雨期间西南低涡涡动动能收支分析

Based on the 6-hour-interval reanalysis data with 1°× 1°resolution from the National Center for Environmental Prediction/the National Center for Atmospheric Research （NCEP/NCAR）, the eddy kinetic energy （EKE） budget of a southwest vortex （SWV） that caused heavy rainfall in Guangxi over South China （from 1200 UTC 11 to 0000 UTC 13 June） is calculated. The results are as follows： （a） The SWV is a kind of subtropical vortex, with characteristics of both an extratropical vortex and a tropical vortex. （b） In the case examined, large-scale circulation and other perturbation fields contributed to the formation and development of the SWV. （c） When the SWV moved from weak large-scale circulation EKE areas to strong ones, the EKE of the SWV increased, and vice versa. （d） Sub-grid processes and frictional dissipation were the main sinks of the SWV EKE, which contributed to the decay of the SWV. （e） The residual term （RES） and the Total （composite effect of all right hand side （rhs） terms except the RES in the EKE equation） varied almost in the same tendency, which kept the EKE varying in a moderate way. （f） The EKE between 550 hPa and 850 hPa increased most intensively, corresponding to the vertical stretching of the SWV.     

东昆仑石榴石闪长玢岩的形成机制及其对埃达克岩成因的制约

本文报道在东昆仑地区发现的一种较为稀少的含石榴石英云闪长玢岩,这也是此类岩石在中国的首次发现。该次火山岩形成于晚三叠纪,主要由富钙(CaO5 wt%)、贫锰(MnO3 wt%)的石榴石,富铝的角闪石(15.9 wt%),中性斜长石和石英等斑晶以及基质物质组成。岩石含有中等的SiO_2(61.1～62.2wt%),低的MgO(2.0 wt%),K_2O(1.3 wt%)以及较高的Al_2O_3(17 wt%)含量,呈现出次铝质至轻微过铝质的特征(ACNK=0.89～1.05)。在微量元素方面,该岩石富集大离子亲石元素和轻稀土元素,同时亏损Nb-Ta-Ti,显示出典型的消减带特征。而异常低的重稀土(Yb0.8×10~(-6))和相对高的Sr/Y比值(约38)表明石榴石是一个残留相,而较高的Al_2O_3含量,大多为正的铕异常反映了斜长石因结晶受到抑制而在岩浆演化晚期的聚集,同时表明岩浆具有较高的水含量。Nd-Sr同位素组成(ε_(Nd)(t)=-2.33～-1.38;~(87)Sr/~(86)Sr=0.706 5～0.706 7)和斜长石的反向分带显示,壳幔间岩浆混合作用在岩体的形成过程中扮演了重要角色。石榴石斑晶和其中的钛铁矿包体均含有较低的MgO,且包裹石榴石的角闪石形成于较高的压力(8～10 kb)条件下,显示这些矿物结晶自一个长英质岩浆中,且很可能形成于壳幔过渡带附近。尽管该岩石在富铝、低重稀土、高Sr/Y等很多方面均类似于埃达克岩石,但其中等含量的Sr(260×10~(-6))和La/Yb比值(16～21)却明显低于典型的埃达克岩和太古代的TTG。结合石榴石斑晶中广泛存在的磷灰石包体以及其较高的Sr和轻稀土分配系数,本文提出在岩浆演化早期结晶的磷灰石有效地降低了残余熔体中的Sr和轻稀土。这进一步表明,即使在高水逸度的条件下,磷灰石在岩浆早期的大量结晶可以有效地阻止一些弧岩浆演化成为埃达克质岩石。     

Fluvial style changes during the last glacial-interglacial transition in the middle Tisza valley (Hungary)

The Weichselian Late Pleniglacial, Lateglacial and Holocene fluvial history of the middle Tisza valley in Hungary has been compared with other river systems in West and Central Europe, enabling us to define local and regional forcing factors in fluvial system change. Four Weichselian to Holocene floodplain generations, differing in palaeochannel characteristics and elevation, were defined by geomorphological analysis. Coring transects enabled the construction of the channel geometry and fluvial architecture. Pollen analysis of the fine-grained deposits has determined the vegetation development over time and, for the first time, a bio(chrono)stratigraphic framework for the changes in the fluvial system. Radiocarbon dating has provided an absolute chronology; however, the results are problematic due to the partly reworked character of the organic material in the loamy sediments. During the Late Pleniglacial, aggradation by a braided precursor system of the Tisza and local deflation and dune formation took place in a steppe or open coniferous forest landscape. A channel pattern change from braided to large-scale meandering and gradual incision occurred during the Late Pleniglacial or start of the Lateglacial, due to climate warming and climate-related boreal forest development, leading to lower stream power and lower sediment supply, although bank-full discharges were still high. Alternatively, this fluvial change might reflect the tectonically induced avulsion of the River Tisza into the area. The climatic deterioration of the Younger Dryas Stadial, frequently registered by fluvial system changes along the North Atlantic margin, is not reflected in the middle Tisza valley and meandering persisted. The Lateglacial to Holocene climatic warming resulted in the growth of deciduous forest and channel incision and a prominent terrace scarp developed. The Holocene floodplain was formed by laterally migrating smaller meandering channels reflecting lower bank-full discharges. Intra-Holocene river changes have not been observed.     

挤压域构造变换带内部构造类型研究——以准噶尔盆地南缘中段构造变换带为例

挤压域构造变换带的类型前人有许多分类方法,文章从分析构造变换带的基本特征入手,结合准噶尔盆地南缘中段地区地质构造特点,初步划分出红车—巴音沟传递带、乌鲁木齐—阿克苏传递带、然热克萨依调节带、玛纳斯调节带。     

http://www.sciencedirect.com/science/article/pii/S1674987110000034

<正>We synthesize significant recent results on the deep structure and origin of the active volcanoes in mainland China.Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge,whereas the intraplate magmatism in China has different origins.The active volcanoes in Northeast China(such as the Changbai and Wuda-lianchi) are caused by hot upwelling in the big mantle wedge(BMW) above the stagnant slab in the mantle transition zone and deep slab dehydration as well.The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate(or Indian plate). The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs' deep subduction in the east and the Indian slab's deep subduction in the west down to the lower mantle.The stagnant slab finally collapses down to the bottom of the mantle,which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab—plume interactions.     

Geomorphic controls and transition zones in the lower Sabine River

Instream flow science and management requires identification of characteristic hydrological, ecological, and geomorphological attributes of stream reaches. This study approaches this problem by identifying geomorphic transition zones along the lower Sabine River, Texas and Louisiana. Boundaries were delineated along the lower Sabine River valley based on surficial geology, valley width, valley confinement, network characteristics (divergent versus convergent), sinuousity, slope, paleomeanders, and point bars. The coincidence of multiple boundaries reveals five key transition zones separating six reaches of distinct hydrological and geomorphological characteristics. Geologic controls and gross valley morphology play a major role as geomorphic controls, as does an upstream‐to‐downstream gradient in the importance of pulsed dam releases, and a down‐to‐upstream gradient in coastal backwater effects. Geomorphic history, both in the sense of the legacy of Quaternary sea level changes, and the effects of specific events such as avulsions and captures, are also critical. The transition zones delineate reaches with distinct hydrological characteristics in terms of the relative importance of dam releases and coastal backwater effects, single versus multi‐channel flow patterns, frequency of overbank flow, and channel‐floodplain connectivity. The transitional areas also represent sensitive zones which can be expected to be bellwethers in terms of responses to future environmental changes. Copyright © 2007 John Wiley & Sons, Ltd.     

Lake‐level fluctuations at Lake Bourget (eastern France) around 4500–3500 cal. a BP and their palaeoclimatic and archaeological implications

On the basis of sedimentological analysis of two cores taken at Chatillon, Lake Le Bourget (northern French Pre‐Alps), and well dated by radiocarbon dates in addition to tree ring dates obtained from an archaeological layer, this paper presents a high‐resolution lake‐level record for the period 4500–3500 cal. a BP. The collected data provide evidence of a complex palaeohydrological (climatic) oscillation spanning the ca. 4300–3850 cal. BP time interval, with major lake‐level maxima at ca. 4200 and 4050–3850 cal. a BP separated by a lowering episode around 4100 cal. a BP. The lake‐level highstands observed at Chatillon between 4300 and 3850 cal. BP appear to be synchronous with (i) a major flooding period recorded in deep cores from the large lakes Le Bourget and Bodensee, and (ii) glacier advance and tree line decline in the Alps. Such wetter and cooler climatic conditions in west‐central Europe around 4000 cal. a BP may have been a nonlinear response to decrease and seasonal changes in insolation. They may also provide a possible explanation for the general abandonment of prehistoric lake dwellings north of the Alps between 4360 and 3750 cal. a BP. Copyright © 2012 John Wiley & Sons, Ltd.