EFFECTS OF TROPOPAUSE AND POTENTIAL VORTICITY ANOMALY ON FRONTOGENESIS*

A two-dimensional,semi-geostrophic numerical model incorporating the tropopause and stratosphere is used to investigate the effects of a positive potential vorticity anomaly and latent heat release on the frontogenetic process and the structure of the resulting frontal zone.It is demonstrated that(1) the inclusion of tropopause and stratosphere significantly changes the frontal structure only in the upper levels;(2) a clearly defined quasi-equivalent barotropic structure and a region of upward motion of finite width appear when a positive potential vorticity anomaly exists on the warm side of the maximum baroclinity in the lower troposphere,especially when it is located on the south edge of the baroclinic zone;(3) the above mentioned structure deteriorates as the frontogenesis proceeds in a dry atmosphere but can be maintained in a moist frontogenetic process with condensational heating;(4) the combination of a positive potential vorticity anomaly and the latent heat release is able to accelerate the frontogenesis significantly with the time needed to form an intense frontal zone reduced to less than 15 h.The results have significant theoretical importance in understanding the complex nature of frontal structure and frontogenesis,especially in understanding the dynamic structure of the subtropical frontal zone observed during early summer over East Asia.     

永登5.8级地震前后的重力变化

着重分析了１９９５年７月２２日永登５．８级地震前后的重力异常变化及其与地震的对应关系，对这次地震的探讨性分析，进一步说明流动重力测量对一些较大地震作出一定的预报是可行的。     

地壳磁化强度模型和居里等温面

利用卫星观测的长波磁异常，用等效偶极源方法推导了中国地区的视磁化强度分布．因卫星的高度远大于磁性地壳的厚度，将视磁化强度转换成磁化强度的垂直积分，它代表地壳内磁性物质的区域变化，利用视磁化强度与地表热流相应关系，计算了中国的新疆和东部一些地区居里等温面的深度．新疆地区的居里面深度为35-50km，其分布形态与塔里木盆地和准噶尔盆地的地貌比较相似；中国东部一些地区居里面深度在20-40km之间，与一些作者用航磁等数据得到的居里深度十分接近．     

华北夏季旱涝的前期环流异常及其与北太平洋海温的关系

文章分析了华北地区夏季旱涝的前期春季大气环流和北太平洋海温异常（ＳＳＴＡ）分布特征，探讨ＳＳＴＡ与异常环流的关系，并用ＯＳＵ－ＡＧＣＭ进行黑潮地区热源异常强迫的数值试验．结果表明，当春季北极低涡明显减弱，欧亚大陆中高纬度地区纬向环流加强，西太平洋副高位置偏北偏西，且存在负ＰＮＡ型异常环流时，华北地区夏季多雨涝；反之则少雨干旱．此时，西北太平洋和赤道东太平洋ＳＳＴ分别存在较大的正、负异常，它们与春季环流异常密切相关，黑潮区ＳＳＴＡ对北半球副热带及其以北的大气环流产生显著影响，正的ＳＳＴＡ是造成华北夏涝年的前期春季异常环流形势的重要因素．     

综合物探在鄱阳湖铁路特大桥勘察中的应用

鄱阳湖铁路特大桥桥址位于鄱阳湖入长江的交汇处。该区地质情况复杂,断裂构造十分发育,因此地质勘探对桥址方案的比选显得尤为重要。此次有效地利用了综合物探,采用多种方法查明了岩性分区和地质构造格局,取得了良好的地质效果。充分显示了综合勘探、综合物探的优势。     

提高航空物探网格化精度的一种方法

本文针对航空物探测量的特点,提出了一种在最佳拟合航空物探测量点基础上的网格化方法。从而,有效地保证了航空物探测量数据的网格化精度。     

用光盘转录航空物探数据

航空物探数据具有较高的保存开发价值,由于磁带保存的有效年限较短,航空物探勘查所获资料存在着丢失的危险。航空物探数据光盘转录将解决这些难题,为航空物探资料的二次开发和利用创造条件。本光盘数据从任一与RICOHRS-5060E型光盘机兼容的光盘机上均可读出。     

The Origin of the Early Proterozoic Kuandian Complex: Evidence from Geochemistry

The Kuandian Complex is scarcely preserved Early Proterozoic volcanic suite, formed2.3-2.4 Ga ago. It is located in an Early Proterozoic mobile belt bounded by the ArchaeanRangrim and Ryonggang Blocks of the northeastern Sino-Korean Craton. The Complex ismainly made up of amphibolites, gneisses, leucoleptite, leptite and layered granite. Petrologicaland geochemical studies show that the protoliths of the Complex are mainly assoctations ofbimodal volcanics and anorogenic granites. The Kuandian amphibolites are depleted in Nb, Ta,P and Ti, and enriched in LILE, e.g. K, Rb and Cs, with pronounced depletion of Sr relative toNd and Pb; La/Nb ratios are higher than 1(1.75 to 5.18). The trace element patterns of theamphibolites are similar to continental flood basalts formed by the Gondwana break-up, suchas those in South Karoo and Tasmania, which shows continental contamination. ε_(Nd) valuesranging from 0.70 to 1.94 of the Kuandian amphibolites and the relationships between Nb/Yband La/Yb suggest that contamination of basaltic magma happened in the mantle, rather thanalong the conduit. Isotope ratios of ~(208)Pb/~(204)Pb, ~(207)Pb/ ~(204)Pb, ~(206)Pb/~(204)Pb, ~(143)Nd/~(144)Ndand ~(87)Sr/~(86)Sr indicate that the magma was derived from a contaminated mantle source likeDMM or a mixture of DMM and EM2. The Kuandian Complex has Dupal anomaly, as is thecase with some continental basalts in the south hemisphere, e.g. in South Karoo and Tasmania.Petrochemical modelling proposes that the Kuandian gneiss, granite, and amphibolite camefrom the same parental magma, being products of strong fractional crystallization. Protoliths ofthe Kuandian Complex were formed in extensional tectonic setting during the transition fromcontinental crust to oceanic crust. The formation of the Kuandian Complex indicates that 2.3or 2.4 Ga ago tectonic evolution of the Sino-Korean craton was different from that of otherwell-studied Precambrian cratons, e.g. the North American shield, European platform andAustralian continent in that strong volcanic eruption resulted in its accretion. Besides, the con-taminated magma source with a Dupal anomaly for the Complex indicates that crust-mantleconvection whose scale was similar to that of the present plate tectonics had occurred at leastbefore the formation of the Kuandian Complex (2.3-2.4 Ga B.P).     

Study on the Gravity Field and Deep-Seated Crustal Structure at the North Margin of the Qinghai-Tibet Plateau

1.I~ductionThenorthernmarginoftheQinghai-TibetplateauincludestheAltllnMis.,theQilianMis.,KunlunMis.,theQaidambasinandthesouthernTarimbasin.ThisareaistCctonicallycharacterizedbyintensiveCenozoicdeformationwithcomplicateddeformationalmechedsm(Molnaretal.,1987;Zheng,1991;Culetal.,1994;Ding,1995andXuetal.,1996).Thedeformationalmechanismsincludethrust-napping,strike-slipping,extensionandblockrotation,aswellassimultaneousupliftingandtypicalbasin-rangetectonics(CulandXu,1996).IntermsofCenozoi…     

The Darwin Rise demise: the western Pacific guyot heights trace the trans-Pacific Mendocino fracture zone

The Darwin Rise has been proposed so many times and in so many forms and places that the time has come to make a more comprehensive examination of the region. Lying on the NW Pacific Plate between the Geisha Guyots, the Mid-Pacific Mountains, the equator, and the trenches, the region is roughly bounded by magnetic anomaly M20 (147 Ma). It was subjected to a massive outpouring of lava about 105 to 120 Ma, which created the guyots and seamounts in that region. Guyots are excellent tools for studying events of long ago because they eroded in the same lowstand in the Cretaceous and guyot relief, therefore, is a surrogate for paleo-sealevel. The relief is derived by subtracting the break depth of the summit plateau of a guyot from the regional depth. Guyot relief would necessarily be less in the center than to the periphery if the feature formed on a pre-existing rise, as has been postulated. The existence of a paleo-Darwin Rise would give concentric contours for the region in question. Of the sixty guyots used in this study, thirty-seven of these guyots were surveyed using SASS multibeam in the Marcus-Wake seamount group. Twenty-three guyots were surveyed using random track single-beam sonar surveys. An entirely different scenario is shown. Data revealed a major fracture passing through the area coevally or after the guyots formed. Because the depths to the summit are not the same now, vertical tectonics occurred after subaerial erosion. This means the fracture formed during and after the erosion (roughly 105 Ma) and influenced the normal sequence of events in guyot formation. Depending on how one deciphers trends through the Hess Rise morass, SASS bathymetry shows a continuation of the Surveyor/Mendocino fracture zone swarm inside the M20 region to the NE of these data. The fracture swarm continues to the western Pacific trench system. Based on this information, if the Darwin Rise ever existed, it had to have done so elsewhere.