IMPACT OF TROPICAL INTRASEASONAL OSCILLATIONS ON THE PRECIPITATION OF GUANGDONG IN JUNES

The impact of tropical intraseasonal oscillations on the precipitation of Guangdong in Junes and its physical mechanism are analyzed using 30-yr (1979 to 2008), 86-station observational daily precipitation of Guangdong and daily atmospheric data from NCEP-DOE Reanalysis. It is found that during the annually first rainy season (April to June), the modulating effect of the activity of intraseasonal oscillations propagating eastward along the equator (MJO) on the June precipitation in Guangdong is different from that in other months. The most indicative effect of MJO on positive (negative) anomalous precipitation over the whole or most of the province is phase 3 (phase 6) of strong MJO events in Junes. A Northwest Pacific subtropical high intensifies and extends westward during phase 3. Water vapor transporting along the edge of the subtropical high from Western Pacific enhances significantly the water vapor flux over Guangdong, resulting in the enhancement of the precipitation. The condition is reverse during phase 6. The mechanism for which the subtropical high intensifies and extends westward during phase 3 is related to the atmospheric response to the asymmetric heating over the eastern Indian Ocean. Analyses of two cases of sustained strong rainfall of Guangdong in June 2010 showed that both of them are closely linked with a MJO state which is both strong and in phase 3, besides the effect from a westerly trough. It is argued further that the MJO activity is indicative of strong rainfall of Guangdong in June. The results in the present work are helpful in developing strategies for forecasting severe rainfall in Guangdong and extending, combined with the outputs of dynamic forecast models, the period of forecasting validity.     

海南岛附近四季风场的中尺度环流

利用一层σ坐标原始方程数值诊断模式研究海南岛，雷州半岛及其四周海域的地面风场特征，在春夏秋冬四季典型盛行气流下试验，均明显呈现绕流，爬坡，辐合线、海陆风和山谷风效应，看出在不同季节下的中尺度环流存在一定的差异。试验表明，区域内的复杂地形和海陆分布是形成各种中尺度环流的重要原因，同时，揭示出本地气候分布的特征与中尺度环流间存在的密切的关系。     

我国新一代VLBI数字基带转换器研制进展

数字化是目前设备研制发展的趋势,介绍了中国科学院上海天文台利用超大规模集成电路结合软件无线电技术,自主研发的我国新一代VLBI数字基带转换器(Chinese Data Acquisition System,简称CDAS).文中描述了设备的工作原理及其组成,并以VLBI观测实验数据证明其可行性.与原有的模拟设备(Anal...     

利用IGS星历预报GPS卫星轨道

在动力学轨道拟合以及轨道积分的基础上,提出了基于IGS精密星历的GPS卫星轨道预报方法。该方法首先利用已知的IGS精密星历作为虚拟观测值,采用动力学方法拟合出GPS卫星的初始轨道和动力学参数,然后再通过积分来预报GPS卫星的轨道。主要讨论了基于不同弧段的IGS星历时,该方法对GPS卫星轨道的拟合和预报情况。研究结果显示:对于6 d弧段以内的IGS精密星历,其拟合轨道与IGS精密星历差值的三维RMS值均优于4 cm,随着拟合弧段的增加,拟合残差变大;当利用2～6 d弧段的IGS星历来预报GPS轨道时,大部分卫星第1天、第7天和第30天的三维预报精度可优于0.1 m、3 m和100 m。其中,2d弧段的IGS星历对GPS卫星第1天和第7天的预报结果最好,5 d弧段的IGS星历对GPS卫星第30天的预报结果最好。     

新疆乌恰康苏地区构造地貌与景观生态格局研究

新疆乌恰康苏地区位于西昆仑山与西南天山对冲作用形成的盆山耦合带,其构造地貌具有显著的山地-平原分布格局特征.文章以"3S"技术为基础进行构造地貌填图,划分新疆乌恰康苏地区的景观类型,研究构造地貌对该区域景观生态格局的影响.采用垂向山地-平原构造地貌为指标,划分5个景观类;以土地利用类型+植被覆盖为指标,划分6个景观型;...     

NDVI与气候因子关系在不同时间尺度上的结果差异

植被指数是反映地表植被覆盖状况的重要参数,分析气候因子与植被指数间的相互关系有助于揭示气候变化对植被的影响,然而当前研究有两种分析植被指数与气候因子关系的方法,分别为分析植被指数与生长季内和生长季间气候因子的关系,然而这两种法差异如何,何种方法更为合适需要进一步分析。利用2000年—2009年生长季的MODIS的归一化植被指数NDVI(Normalized Difference Vegetation Index)数据集和藏北那曲地区3个气象站逐月气象资料(月平均气温、≥0℃活动积温和月降水量),分析比较了生长季内和生长季间气候因子对植被生长影响的差异,并分析了两种方法的优劣。结果表明:(1)生长季内植被NDVI与同期气温和降水量均呈高度正相关,生长季内时滞时间尺度为1个月时,植被NDVI对月平均气温及降水响应均最为强烈。(2)生长季间NDVI与同期降水量相关性并不明显,气候因子的滞后效应在生长季间也较弱。(3)生长季内和生长季间植被NDVI与气候因子的关系所得出的结论有一定差异性,可能是因为两方面的原因:生长季内植被NDVI与水热因子的高相关性与中国季风季候造成的高温多雨出现在夏季有关,而生长季内高水热条件与高植被指数对应的多年重复必然造伪的高相关系数,但这种相关性不一定能真实反映植被与水热条件的关系,而生长季间水热等气候因子与植被指数年际变化相关性分析不存在水热与高植被指数同期问题,更能真实反映气候因子年际变化对植被的影响。     

Secular period decreasing of detached chromospherically active binaries

The long-term orbital period changes of a large sample of detached chromospherically active binaries (CABs) were studied. Eleven such systems were found to be undergoing secular period decreases with the rates of ?6.3×10^?9 to ?1.1×10^?6 days per year. The period decreasing rates are found to vary depending on the orbital period. The longer the orbital period is, the more rapidly the period decreases. Following Stepien (Mon. Not. R. Astron. Soc. 274:1019, 1995), the period decreasing rate predicted by angular momentum loss (AML) caused by magnetic wind is computed for each system. A comparison between the observed and calculated period decreasing rates shows that the former values are obviously larger than the latter by 1–3 orders of magnitude. It suggests that the magnetic wind is not likely the determinant mechanism driving the AML in these systems. Finally, the orbital angular momentum (AM) and the rate of AML, $\dot{J}$ , are computed for each system. It shows that the AM have a similar change with the orbital period like dP/dt does, but $\log\dot{J}/J$ presents no strict changing with the kinematical ages.     

Rainfall effect on wind waves and the turbulence beneath air-sea interface

Rainfall effects on wind waves and turbulence are investigated through the laboratory experiments in a large wind-wave tank. It is found that the wind waves are damped as a whole at low wind speeds, but are enhanced at high wind speeds. This dual effect of rain on the wind waves increases with the increase of rain rate, while the influence of rainfall-area length is not observable. At the low wind speed, the corresponding turbulence in terms of the turbulent kinetic energy （TKE） dissipation rate is significantly enhanced by rain- fall as the waves are damped severely. At the high wind speed, the augment of the TKE dissipation rate is suppressed while the wind waves are enhanced simultaneously. In the field, however, rainfall usually hin- ders the development of waves. In order to explain this contradiction of rainfall effect on waves, a possibility about energy transfer from turbulence to waves in case of the spectral peak of waves overlapping the inertial subrange of turbulence is assumed. It can be applied to interpret the damping phenomenon of gas trans- fer velocity in the laboratory experiments, and the variation of the TKE dissipation rates near sea surface compared with the law of wall.     

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

We present elemental and Sr–Nd–Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO₂ = 59.43–76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO₂ = 54.95–56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb) _n  = 2.40–12.44] and display weak Eu anomalies (Eu/Eu* = 0.30–0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harşit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr–Nd isotopic data for all of the samples display I _Sr = 0.70676–0.70708, ε _Nd(79 Ma) = −4.4 to −3.3, with T _DM = 1.09–1.36 Ga. The lead isotopic ratios are (²⁰⁶Pb/²⁰⁴Pb) = 18.79–18.87, (²⁰⁷Pb/²⁰⁴Pb) = 15.59–15.61 and (²⁰⁸Pb/²⁰⁴Pb) = 38.71–38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir–Ankara–Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr–Nd isotope modeling shows that the generation of these magmas involved ~65–75% of the lower crustal-derived melt and ~25–35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar–Ar plateau age on hornblende, combined with regional studies, imply that the Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least ~79 Ma in the Eastern Pontides.     

大别山岳西县石关混合岩锆石SHRIMP定年及其地质意义

安徽岳西县石关混合岩属于原北大别变质杂岩的一部分。锆石SHRIMPU-Pb定年结果:第一次变质时间为232Ma,相当于晚三叠世早期,第二次变质时间为207Ma,相当于晚三叠世晚期。复合锆石的核部(继承锆石)为发育韵律环带的岩浆碎屑锆石,其年龄值分别为560Ma、444Ma、394Ma、378Ma和331Ma,暗示其原岩非岩浆岩,而应为沉积岩;研究结果还表明,北大别石关混合岩经历了两次变质作用:①超高压变质作用,变质时间为232Ma(n=5加权平均年龄);②退变质作用,时间为207Ma。与苏鲁地区超高压变质和退变质时间一致。