地磁扰动事件的描述及处理

影响地磁观测的因素很多,只有充分了解干扰的机制,才能对其数据进一步的处理。而在GM3,GM4提供秒采样数据后,观测数据中干扰数据的形态就可以非常清晰。本文就是利用秒采样的数据对几种常见干扰情况进行了描述,并使用软件对干扰数据进行剔除。     

Gravitational effect of water circulation in the northwest Yunnan

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Influence of permeability on hydrothermal circulation in the sediment-buried oceanic crust

1 Introduction Hydrothermal circulation is the key process of hydrothermal activity. Modern seafloor hydrothermal circulation can be divided into three parts: convective cells in the oceanic curst, interface between seafloor and ocean and hydrothermal plume. Hydrothermal convection in the crust is the dominant part of the whole seafloor hydrothermal circulation. The distribu-tion and nature of hydrothermal system in the oceanic crust are controlled by crust thermal structures and permeability …     

Establishment and adjustment of monsoon-driven circulation in the South China Sea

The South China Sea (SCS) is one of the large marginal seas of the western Pacific Ocean. In comparison with open oceans, the SCS circulation has obviously transient characteristics due to its small basin-scale and semi-annually reversed monsoon forcing. …     

Nonlinear dynamics and recurrence analysis of extreme precipitation for observed and general circulation model generated climates

A statistical framework based on nonlinear dynamics theory and recurrence quantification analysis of dynamical systems is proposed to quantitatively identify the temporal characteristics of extreme (maximum) daily precipitation series. The methodology focuses on both observed and general circulation model (GCM) generated climates for present (1961–2000) and future (2061–2100) periods which correspond to 1xCO₂ and 2xCO₂ simulations. The daily precipitation has been modelled as a stochastic process coupled with atmospheric circulation. An automated and objective classification of daily circulation patterns (CPs) based on optimized fuzzy rules was used to classify both observed CPs and ECHAM4 GCM‐generated CPs for 1xCO₂ and 2xCO₂ climate simulations (scenarios). The coupled model ‘CP‐precipitation’ was suitable for precipitation downscaling. The overall methodology was applied to the medium‐sized mountainous Mesochora catchment in Central‐Western Greece. Results reveal substantial differences between the observed maximum daily precipitation statistical patterns and those produced by the two climate scenarios. A variable nonlinear deterministic behaviour characterizes all climate scenarios examined. Transitions’ patterns differ in terms of duration and intensity. The 2xCO₂ scenario contains the strongest transitions highlighting an unusual shift between floods and droughts. The implications of the results to the predictability of the phenomenon are also discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Heating status of the Tibetan Plateau from April to June and rainfall and atmospheric circulation anomaly over East Asia in midsummer

Based on the 1958-1999 monthly averaged reanalysis data of the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and the rainfall data of 160 Chinese surface stations, the relationship between rainfall and the atmospheric circulation anomaly over East Asia (EA) in July and the sensible heating (SH) over the Tibetan Plateau (TP) from April to June (AMJ) is investigated by using the rotational experimental orthogonal function (REOF) method. The results show that the TP is an isolated heating source in this period. The lagged correlation analysis between the first rotational principal component (RPC) of SH over the TP in May and rainfall of EA in July demonstrates that strong SH over the TP before July leads to a positive rainfall anomaly over the TP, the valley between the Yangtze River and Huaihe River, and the regions south and southeast of the TP, and the Sichuan Basin and Yunnan-Guizhou Plateau, but less rainfall anomaly over the regions north, northeas     

Annual variation of sea surface height,dynamic topography and circulation in the South China Sea

TOPEX/Poseidon satellite altimetry data from 1993 to 1999 were used to study mean annual variation of sea surface height anomaly (SSHA) in the South China Sea (SCS) and to reproduce its climatological monthly surface dynamic topography in conjunction with historical hydrographic data. The characters and rules of seasonal evolution of the SCS dynamic topography and its upper circulation were then discussed. Analyses indicate that annual variation of the SCS large-scale circulation could be divided into four major phases. In winter (from November to February), the SCS circulation is mainly controlled by double cyclonic gyres with domination of the northern gyre. Other corresponding features include the Kuroshio intrusion from the Luzon Strait and the northeastward off-shelf current in the area northwest off Kalimantan Island. The double gyre structure disassembled in spring (from March to April) when the northern gyre remains cyclonic, the southern gyre becomes anticyclonic, and the general circulation pattern shows a dipole. There is no obvious large-scale closed gyre inside the SCS basin in both summer (from May to July) and autumn (from August to October) when the SCS Monsoon Jet dominates the circulation, which flows northeastward across the SCS. Even so, circulation patterns of these two phases diverse significantly. From May to July, the SCS monsoon jet flows northward near the Vietnam coast and bends eastward along the topography southeast off Hainan Island at about 18°N forming an anticyclonic turn. It then turns northeastward after crossing the SCS. From August to October, however, the monsoon Jet leaves the coast of Vietnam and enters interior of the basin at about 13°N, and the general circulation pattern becomes cyclonic. The Kuroshio intrusion was not obvious in spring, summer and autumn. It is suggested from these observations that dynamic adjustment of the SCS circulation starts right after the peak period of the prevailing monsoon.     

Tidal and residual circulation in the St. Andrew Bay system,Florida

Two 24-h surveys were conducted in St. Andrew Bay, Florida, during spring and neap tides to describe the tidal and non-tidal circulation patterns and to determine the factors that affect these patterns. In particular, the effect of tidal forcing in modulating such circulation patterns was explored. Observed velocities were fitted to diurnal and semidiurnal harmonics separating tidal motions from sub-tidal motions. Residual flows were compared with an analytic model that allowed variations in the relative contributions from Coriolis acceleration and friction using the Ekman number. A solution with an Ekman number of 0.04 resembled the observations best and indicated that the hydrodynamics were governed by pressure gradient, Coriolis and friction. Locally, advective accelerations became important around headlands in sub-estuaries in the system. The consistency of the mean pattern from October to March suggests that tides play a minor role in modulating the exchange flow. Deviations from the long-term mean are mainly caused by wind-driven coastal setup and setdown.     

The earthquake-related disturbances in ionosphere and project of the first China seismo-electromagnetic satellite

Based on the case studies and statistical analysis of earthquake-related ionospheric disturbances mainly from DEMETER satellite, ground-based GPS and ionosounding data, this paper summarizes the statistical characteristics of earthquake-related ionospheric disturbances, including electromagnetic emissions, plasma perturbations and variation of energetic particle flux. According to the main results done by Chinese scientists, fusing with the existed study from global researches, seismo-ionospheric disturbances usually occurred a few days or hours before earthquake occurrence. Paralleling to these case studies, lithosphere-atmosphere-ionosphere (LAI) coupling mechanisms are checked and optimized. A thermo-electric model was proposed to explain the seismo-electromagnetic effects before earthquakes. A propagation model was put forward to explain the electromagnetic waves into the ionosphere. According to the requirement of earthquake prediction research, China seismo-electromagnetic satellite, the first space-based platform of Chinese earthquake stereoscopic observation system, is proposed and planned to launch at about the end of 2014. It focuses on checking the LAI model and distinguishing earthquake-related ionospheric disturbance. The preliminary design for the satellite will adopt CAST-2000 platform with eight payloads onboard. It is believed that the satellite will work together with the ground monitoring network to improve the capability to capture seismo-electromagnetic information, which is beneficial for earthquake monitoring and prediction researches.     

Annual variation of sea surface height, dynamic topography and circulation in the South China Sea —— A TOPEX/Poseidon satellite altimetry study

The South China Sea (SCS) is a semi-enclosed deep basin with complex topography includ-ing broad continental shelves, steep slopes, and a large deep basin. It is dominated by prevailing southwest monsoon in summer and by much stronger northeast monsoon in…     

冀豫环流动磁测异常与中等地震关系研究

利用冀豫环流动地磁观测资料,绘制单点时序变化曲线,采用常规差值法,计算相邻两期的差值,绘制整个测区的平面等值线;分析研究1998年以来测区周围发生的中等地震与流动地磁数据变化的关系。结果显示,冀豫环流磁异常与邻区的中等地震有一定的对应关系,震前有两个或多个测点同时出现异常,而且异常特征表现为上升正异常。     

Seasonal variation in the transverse and layered structure of estuarine circulation in Ariake Bay, Japan

Seasonal variation in the transverse and layered structure of estuarine circulation in Ariake Bay, Japan was investigated by box model analysis using monthly salinity data from 1990 to 2000. Two-layered gravitational estuarine circulation was intensified from autumn to spring (vertically well mixed season) accompanied by a small river discharge. Two-layered circulation was weakened accompanying the transversely segregated cyclonic circulation in the upper layer during summer (stratified season) with a large river discharge. Such seasonal variation in the transverse and layered structure of estuarine circulation is because the bay width of Ariake Bay (20 km) is narrower than the external Rossby deformation radius (235 km) but wider than the internal Rossby deformation radius (3–5 km).     

Explanatory analysis of the relationship between atmospheric circulation and occurrence of flood‐generating events in a coastal city

The aim of this study is to enhance the understanding of the occurrence of flood‐generating events in urban areas by analysing the relationship between large‐scale atmospheric circulation and extreme precipitation events, extreme sea water level events and their simultaneous occurrence, respectively. To describe the atmospheric circulation, we used the Lamb circulation type (LCT) classification and re‐grouped it into Lamb circulation classes (LCC). The daily LCCs/LCTs were connected with rare precipitation and water‐level events in Aarhus, a Danish coastal city. Westerly and cyclonic LCCs (W, C, SW and NW) showed a significantly high occurrence of extreme precipitation. Similarly, for extreme water‐level events westerly LCCs (W and SW) showed a significantly high occurrence. Significantly low occurrence of extreme precipitation and water‐level events was obtained in easterly LCCs (NE, E and SE). For concurrent events, significantly high occurrence was obtained in LCC W. We assessed the change in LCC occurrence frequency in the future based on two regional climate models (RCMs). The projections indicate that the westerly directions in LCCs are expected to increase in the future. Consequently, simultaneous occurrence of extreme water level and precipitation events is expected to increase in the future as a result of change in LCC frequencies. The RCM projections for LCC frequencies are uncertain because the representation of current LCCs is poor; a large number of days cannot be classified and the frequencies of the days that can be classified differ from the observed time series. Copyright © 2015 John Wiley & Sons, Ltd.     

A dynamically consistent analysis of circulation and transports in the southwestern Weddell Sea

An inverse model is applied for the analysis of hydrographic and current meter data collected on the repeat WOCE section SR4 in the Weddell Sea in 1989–1992. The section crosses the Weddell Sea cyclonic gyre from Kapp Norvegia to the northern end of the Antarctic Peninsula. The concepts of geostrophy, conservation of planetary vorticity and hydrostatics are combined with advective balances of active and passive properties to provide a dynamically consistent circulation pattern. Our variational assimilation scheme allows the calculation of three-dimensional velocities in the section plane. Current speeds are small except along the coasts where they reach up to 12 cm/s. We diagnose a gyre transport of 34 Sverdrup which is associated with a poleward heat transport of 28 × 10¹² W corresponding to an average heat flux of 15 Wm^–2 in the Weddell Sea south of the transect. This exceeds the estimated local flux on the transect of 2 Wm^–2. As the transect is located mostly in the open ocean, we conclude that the shelf areas contribute significantly to the ocean-atmosphere exchange and are consequently key areas for the contribution of the Weddell Sea to global ocean ventilation. Conversion of water masses occuring south of the section transform 6.6 ± 1.1 Sv of the inflowing warm deep water into approximately equal amounts of Weddell Sea deep water and Weddell Sea bottom water. The volume transport of surface water equals in the in-and outflow. This means that almost all newly formed surface water is involved in the deep and bottom water formation. Comparison with the results obtained by pure velocity interpolation combined with a hydrographic data subset indicates major differences in the derived salt transports and the water mass conversion of the surface water. The differences can be explained by deviations in the structure of the upper ocean currents to which shelf areas contribute significantly. Additionally a rigorous variance analysis is performed. When only hydrographic data are used for the inversion both the gyre transport and the poleward heat transport are substantially lower. They amount to less than 40% of our best estimate while the standard deviations of both quantities are 6.5 Sv and 37 × 10¹² W, respectively. With the help of long-term current meter measurements these errors can be reduced to 2 Sv and 8 × 10¹² W. Our result underlines the importance of velocity data or equivalent information that helps to estimate the absolute velocities.     

The response of circulation and salinity in a micro-tidal estuary to sub-tidal oscillations in coastal sea surface elevation

Conceptual models of circulation theorise that the dominant forces controlling estuarine circulation are freshwater discharge from the riverine section (landward), tidal forcing from the ocean boundary, and gravitational circulation resulting from along-estuary gradients in density. In micro-tidal estuaries, sub-tidal water level changes (classified as those with periods between 3 and 10 days) with amplitudes comparable to the spring tidal range can significantly influence the circulation and distribution of water properties. Field measurements obtained from the Swan River Estuary, a diurnal, micro-tidal estuary in south-western Australia, indicated that sub-tidal water level changes at the ocean boundary were predominantly from remotely forced continental shelf waves (CSWs). The sub-tidal water levels had maximum amplitudes of 0.8 m, were comparable to the maximum tidal range of 0.6 m, propagated into the estuary to its tidal limit, and modified water levels in the whole estuary over several days. These oscillations dominated the circulation and distribution of water properties in the estuary through changing the salt wedge location and increasing the bottom water salinity by 7 units over 3 days. The observed salt wedge excursion forced by CSW was up to 5 km, whereas the maximum tidal excursion was 1.2 km. The response of the residual currents and the salinity distribution lagged behind the water level changes by ∼24 h. It was proposed that the sub-tidal forcing at the ocean boundary, which changed the circulation, salinity, and dissolved oxygen in the upper estuary, was due to a combination of two processes: (1) a gravity current generated by a process similar to a lock exchange mechanism and (2) amplified along-estuary density gradients in the upper estuary, which enhanced the gravitational circulation in the estuary. The salt intrusions under the sub-tidal forcing caused the rapid movement of anoxic water upstream, with significant implications for water quality and estuarine health.     

IMF Bz周期震荡期间日间热层扰动风的经度差异分析

基于磁层-电离层-热层耦合模型(Coupled Magnetosphere-Ionosphere-Thermosphere Model,CMIT),本文探究了当行星际磁场Bz分量(Interplanetary magnetic field,IMF) 60 min周期震荡时,白天热层扰动风的经度差异特征.由于地磁构型、热...     

洪泽湖风生流对风场和水位变化响应特征

深入认识大型湖泊在不同风速、风向和水位下三维风生流结构特征对于湖泊污染控制、生态恢复及资源的开发利用具有重要意义.本文在构建笛卡尔坐标系下洪泽湖三维水动力模型的基础上,利用2次全湖30个点位流场监测数据验证了模型精度.基于1975-2020年长系列风场观测数据,确定了洪泽湖典型风速风向.在此基础上,模拟了16种不同风向,13种不同风速和20种不同水位工况条件下洪泽湖三维风生流结构.结果表明：水动力模型可以较好地刻画洪泽湖三维湖流变化特征.洪泽湖风生流结构随风向变化呈现出较大空间差异.风生流流速随着风速的升高呈加速上升趋势,其中表层水体流速上升幅度远高于其他水层.在2.4 m/s东风驱动下,溧河洼、成子湖和南部湖区垂向平均流速随着水位上升呈先升高后降低的趋势,3个湖区分别在12.7、12.4和12.2 m水位下流速达到最大值.     

南极涛动异常及其对冬春季北半球大气环流影响的数值模拟试验

利用IAP9L-AGCM模式考察了模式中与南极涛动异常相关的海温敏感区,发现南半球高纬海温异常能够强迫出南极涛动异常,而赤道东太平洋海温异常与太平洋南美型密切相关.研究了南极涛动异常对冬春季北半球大气环流及亚洲北部气温的影响,结果表明,南极涛动加强,能够引起北半球高纬环流异常和欧亚西风加强,以及亚洲北部地表气温和850 hPa气温显著增温.数值模拟支持了已有的诊断结果,也证实了冬春季节南极涛动异常下两半球高纬间的经向遥相关存在.     

Effects of spatial wind inhomogeneity and turbulence anisotropy on circulation in an elongated basin: A simplified analytical solution

The response of a closed basin to wind forcing has been studied extensively, but the role of turbulence anisotropy coupled with spatial wind inhomogeneity has never been considered explicitly. An analytical solution is presented for steady state hydrodynamics, considering the central part of a constant-depth, elongated basin with a laterally varying wind, and a homogeneous, yet anisotropic, eddy viscosity tensor. The solution is derived both for a single-layer and for a two-layer basin, which is representative of a stratified lake with a well-developed thermocline. Since the focus is on the short-term barotropic reaction to wind forcing, which determines the type of lake circulation, baroclinic effects are neglected as a first approximation. In this case, the development of planimetric (depth-averaged) circulation superimposed on circulation in the vertical plane can be determined as a function of wind lateral variation and a few dimensionless parameters. The relevance of such an analytical solution is twofold. Firstly, the knowledge of the prevailing circulation can help in the choice of the best type of numerical model (three-dimensional vs. two-dimensional, depth- or lateral-averaged). Secondly, it shows the importance of correct estimates of both vertical and horizontal eddy viscosity, whereas the latter is not usually considered as an important parameter in lake hydrodynamics modeling.     

南海礼乐盆地礁体水热循环及其对地温场的影响

南海礼乐盆地自渐新世以来持续发育碳酸盐岩礁体,礁体区地温场可能受到礁体与周围低温海水间水热循环的扰动.为了解礁体与周围海水间的热交换过程及其对礁体区地温场的影响,以便从位于礁体区的钻井测温数据中提取深部热信息,本文以过礁体区S-1井的地震剖面为基础,在流热耦合条件下对礁体内的水热活动进行数值模拟.结果表明,礁体与海水间存在水热交换,该水热活动对礁体区温度场有明显的扰动,使得礁体上部温度和地温梯度明显降低,进入礁体下伏地层后,地温梯度逐渐趋于正常;水热循环对礁体区地温场的影响程度与礁体的厚度和渗透率密切相关,礁体厚度越大、渗透率越高,礁体及其下伏地层温度越低;计算剖面中,2100 m厚礁体之下可能存在约400 m厚、渗透率约为3×10^-12 m²的高渗碎屑岩层,高渗层上覆礁体平均渗透率估计介于1×10^-13~5×10^-12 m²之间.分析表明,在受水热活动影响的礁体区,礁体下伏地层中的热流可近似代表礁体区的深部热背景,S-1钻井深部热流介于65~75 mW·m^-2之间.