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1.
正Bursty bulk flows(BBFs)and dipolarization fronts(DFs)are two important phenomena responsible for the transport of energy,mass and magnetic flux from the Earth's magnetotail to the inner magnetosphere during magnetosphere substorms.The BBFs are defined as the high-speed flows of several hundred km/s in the central plasma sheet lasting about 10 minutes,while DFs are defined as,with much shorter time scale of several seconds,sharp increases in the northward magnetic field component in the plasma sheet.These two phenomena  相似文献   

2.
The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.  相似文献   

3.
On 24 August 2005, an impulse of solar wind dynamic pressure(Psw) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of Psw at the trailing edge of the impulse. The results show that the sharp decrease of Psw can excite a global pulsation in the frequency range 4.3–11.6 m Hz. The pulsation has a reversal of polarization between two auroral latitude stations, a larger power spectral density(PSD) close to resonant latitude and increasing frequency with decreasing latitude. All these features indicate that the pulsations are associated with field line resonance(FLR). The fundamental resonant frequency(the peak frequency of PSD between 4.3 and 5.8 m Hz) is dependent on magnetic local time and is largest around magnetic local noon. This feature is due to the fact that the size of magnetospheric cavity is dependent on local time and smallest at noon. A second harmonic wave at about 10 m Hz is also observed, which is strongest in the daytime sector, and becomes heavily attenuated in the night sector. The comparison of the PSDs of the pulsations driven by sharp increase and sharp decrease of Psw shows that the frequency of pulsations is negatively proportional to the size of magnetopause. Since the FLR is excited by compressional cavity/waveguide waves, the above results indicate that the resonant frequency in the magnetospheric cavity/waveguide is controlled not only by solar wind parameters but also by magnetic local time of observation point.  相似文献   

4.
A high resolution lithospheric magnetic field model over China   总被引：4，自引：0，他引：4  
CHAMP satellite data and ground-based magnetic observations are used and combined to map the lithospheric magnetic field over China by means of the revised spherical cap harmonic analysis(R-SHCA)modeling technique.The magnetic field is described to a spatial resolution of 150 km at the mean Earth’s radius,which represents a good compromise between the resolutions afforded by surface and satellite data.We compare the magnetic anomalies modeled at the regional scale with composite regions containing large-scale of tectonic structures.These regions,including the Tarim Basin and the Tibetan Plateau,are correlated with regional magnetic anomalies at satellite altitude but contain a significant number of small-scale and complex magnetic structures at the mean Earth’s radius.These magnetic anomalies are globally consistent with the known geological features in China but also offer a way to delineate the contours of the geological blocks and to discuss the connection between magnetic anomalies and the heat flow distribution in this region.  相似文献   

5.
We have quantitatively investigated the radiation belt’s dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)-driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the Radiation Belt Content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions, radial diffusion, and adiabatic transport. Due to the limitation of numerical schemes, formal radiation belt models do not include the cross diffusion term of local wave-particle interactions. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders (depending on the pitch angle) if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field; the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model, which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere; the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell (the outer magnetosphere); in smaller L shell regions (the inner magnetosphere), the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.  相似文献   

6.
Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause. A global view of the auroral oval with throat aurora will be critical for inferring global processes at the magnetopause, but it has never been achieved. Using imaging spectrograph observations from Defense Meteorological Satellite Program satellites, for the first time, here we show typical throat auroras in a global view and reveal some important observational facts as follows.(1) The throat auroras can be as long as ～8 degrees in latitudinal direction,which is hardly to be fully seen in the ground-based camera.(2) The plasma flows and field aligned currents associated with throat aurora show consistences with previous radar observations, which have been suggested to be the observational evidence of magnetopause reconnection.(3) Most importantly, we confirmed that the electron and ion precipitations associated with throat aurora are always spatially separated, i.e., electrons in the east and ions in the west. The observational results not only establish a new picture of the aurora oval near local noon, but also provide important support to a conceptual model of throat aurora.  相似文献   

7.
This paper studies the effective polytropic index in the central plasma sheet(CPS) by using the method of Kartalev et al.(2006), which adopts the denoising technique of Haar wavelet to identify the homogeneous MHD Bernoulli integral(MBI) and has been frequently used to study the polytropic relation in the solar wind. We chose the quiet CPS crossing by Cluster C1 during the interval 08:51:00–09:19:00 UT on 03 August 2001. In the central plasma sheet, thermal pressure energy per unit mass is the most important part in MBI, and kinetic energy of fluid motion and electromagnetic energy per unit mass are less important. In the MBI, there are many peaks, which correspond to isothermal or near isothermal processes. The interval lengths of homogenous MBI regions are generally less than 1 min. The polytropic indexes are calculated by linearly fitting the data of lnp and lnn within a 16 s window, which is shifted forward by 8 s step length. Those polytropic indexes with |R|≥0.8(R is the correlation coefficient between lnp and lnn) and p-value≤0.1 in the homogeneous regions are almost all in the range of [0, 1]. The mean and median effective polytropic indexes with high R and low p-value in homogeneous regions are 0.34 and 0.32 respectively, which are much different from the polytropic index obtained by traditional method(?trad=?0.15). This result indicates that the CPS is not uniform even during quiet time and the blanket applications of polytropic law to plasma sheet may return misleading value of polytropic index. The polytropic indexes in homogeneous regions with a high correlation coefficient basically have good regression significance and are thus credible. These results are very important to understand the energy transport in magnetotail in the MHD frame.  相似文献   

8.
A regressive correction method is presented with the primary goal of improving ENSO simulation in regional coupled GCM. It focuses on the correction of ocean-atmosphere exchanged fluxes. On the basis of numerical experiments and analysis, the method can be described as follows: first, driving the ocean model with heat and momentum flux computed from a long-term observation data set; the pro-duced SST is then applied to force the AGCM as its boundary condition; after that the AGCM’s simula-tion and the corresponding observation can be correlated by a linear regressive formula. Thus the re-gressive correction coefficients for the simulation with spatial and temporal variation could be obtained by linear fitting. Finally the coefficients are applied to redressing the variables used for the calculation of the exchanged air-sea flux in the coupled model when it starts integration. This method together with the anomaly coupling method is tested in a regional coupled model, which is composed of a global grid-point atmospheric general circulation model and a high-resolution tropical Pacific Ocean model. The comparison of the results shows that it is superior to the anomaly coupling both in reducing the coupled model ‘climate drift’ and in improving the ENSO simulation in the tropical Pacific Ocean.  相似文献   

9.
Data on sediment flux at three hydrologic stations from the 1950s to 2006 are utilized to study the decadal,annual,and monthly variations in suspended sediment load delivered from the Pearl River to the ocean.Results show that variations in sediment flux from three main tributaries,including the West River,the North River and the East River,are spatially non-uniform.Since nearly 90%of the suspended sediment load comes from the West River,its variation has dominated the overall tendency of sediment flux in the entire Pearl River.Although a significant decreasing trend exists in the annual variation of the total sediment flux,the decadal change can be divided into an increasing phase and a decreasing phase,with the turning point between the two phases in the late 1980s.From the 1950s to the 1980s,the average annual river sediment flux increased by 30.43%.However,sediment flux has decreased significantly since the 1990s,with the average sediment flux being 38.60%less in the 2000s than that in the 1950s.The current sediment flux is also 52.93%less than its peak in the 1980s. The monthly variation pattern of the suspended sediment load transport to the sea is more interesting. For the West River,all months show a decreasing trend,and for most months the reduction values are significant.However,for the East River the sediment load shows a decrease trend in the dry season and an increase trend in the wet season.The method of regression analysis was used to study the influence of precipitation in the variation on the sediment flux.It was found that the climate change is not the main driving force behind the variation in suspended sediment load.Before the 1990s, intensive land use destroyed the vulnerable ecosystem of the upper Pearl River,and speeded up the process of rocky desertification.Consequently,aggravated soil erosion caused an increase in suspended sediment load.However,sediment retention within reservoirs had begun to play a dominant role after the massive construction of large dams after 1990,and resulted in a decrease in the suspended sediment load delivered to the ocean.  相似文献   

10.
The magnetic susceptibility (MS) of Chinese loess showing a general proportional relationship to pedogenic grade has been widely recognized and used for reconstruction of paleoclimate by Quaternary scientists. The in-situ pedogenic enhancement of ferrimagnetic content is normally believed to be the main reason for the increase of susceptibility in soil units. However, this pattern of high magnetic susceptibility in palaeosols, and low values in loess, are not replicated in some loess deposits. Siberian loess deposits display a completely opposite susceptibility behavior: high values in loess and low values in palaeosols. This inverse relationship has been explained by the idea that magnetic susceptibility is reflecting the magnitude of an aeolian ferrimagnetic component of consistent mineralogy, the grain size of which is related to average wind velocity. Our magnetic study of Siberian samples in this paper suggests that there are notable differences in magnetic properties between Siberian loess and developed palaeosols, not only in magnetic grain-size and concentration but also in magnetic mineralogy. This evidence is difficult to explain fully through variation in wind strength alone, but implies that the low magnetic susceptibility values in the Siberian paleosol units are a reflection, at least in part, of the alteration of the ferrimagnetic content by post-depositional processes. The Loess Plateau is a very arid area where potential evaporation is always higher than precipitation; pedogenesis occurs under dry oxidising conditions. The Siberian Kurtak region is located on the edge of the tundra where it is always wet and saturation during interglacials will lead to a reducing pedogenic environment. Ferrimagnetic minerals under this condition will be destroyed, resulting in lower magnetic susceptibility. Therefore, great care should be taken when using susceptibility values for paleoclimatic reconstruction.  相似文献   

11.
In order to understand the various processes responsible for siltation in the entrance channel and in the sand bar area near the old Mangalore port, variations in temperature, salinity, suspended sediment load, currents and extinction coefficient in the Netravathi-Gurpur Estuary and in the sea near the sand bar were studied in relation to tides during monsoon, post-monsoon and pre-monsoon seasons. The hydrographic characteristics in the estuary showed marked seasonal changes and were influenced by tides to a considerable extent. In the sea, seasonal variations of these parameters were less marked, and the effect of tides was not significant. Salinity and temperature values in the estuary and in the sea were maximum during the pre-monsoon season in general. The suspended sediment load values were always higher in the estuary than in the sea and they were found to be maximum in the monsoon season. Currents in the estuary were controlled by tides as well as by the river flow, particularly in the monsoon season, whereas currents in the sea mostly followed the general circulation pattern. Extinction coefficient values were higher in the monsoon season both in the estuary and in the sea due to increase in the particulate matter from inland drainage.  相似文献   

12.
Variations in annual numbers of earthquakes (the earthquake occurrence rate) that hit the Baikal region and Mongolia during the period from 1964 through 2001 are studied in this work. Correlation analysis of the different-length series of annual numbers N of earthquakes of representative energy classes makes it possible to reveal the effects of synchronous changes in the earthquake occurrence rate in seven regions and eleven areas in the Mongolia-Baikal region, located far apart. The analysis of the shock occurrence rate revealed episodes of short-period synchronization of seismic processes in the Mongolia-Baikal region at the end of the 1960s, early in the 1980s, and in the middle of the 1990s. The episode of synchronization in the earthquake occurrence rate in the early 1980s is observed in all the territories under study, but the episode at the end of the 1960s is less distinctly seen in Mongolia and is revealed mainly in the data series with a length of three years. The synchronization in the seismicity in Mongolia and in the southern PreBaikal region in 1995 requires further investigations, involving the dynamic parameters of the earthquake sources. The observed synchronism in the annual number of earthquakes indicates that the seismic processes become active nearly simultaneously over the huge territory of the Mongolia-Baikal region and produce a short-term coherent change in the shock occurrence rate in the spatial-temporal distribution of the seismicity. The observed spatial and temporal correlation in the seismicity is a sign of the seismogenic link between the Baikal region and Mongolia.  相似文献   

13.
During many PCAs at auroral zone stations in the daytime, a smooth decrease in the absorption, called the noon recovery effect, is observed. The manifestation of this effect in PCA events registered at various seasons of the year (in spring, summer, and fall under a completely illuminated ionosphere and in winter under a completely (or partially) dark ionosphere) is analyzed in this paper. In the summer PCA, the amplitude of the noon recovery (the strongest decrease in the absorption in the hours close to the noon) and the frequency of occurrence of this effect are lower than in equinox conditions. A decrease in temperature and the enhanced content of water vapor in the upper mesosphere in summer as compared to the equinox seasons are the main factors governing the small amplitude of the noon recovery in summer PCA. Using experimental and calculated data, the presence of the noon recovery effect in winter PCA is found for the first time. In winter PCA, the absorption variation during noon recovery has a complicated shape: a smooth decrease in the daytime hours and a short-term (pulse-type) increase in the absorption in the local noon. This increase is caused by the fact that the ionosphere over auroral stations in the winter season is illuminated for a short time interval (around the local noon), which causes a sharp increase in the absorption. The amplitude of the noon recovery in winter PCA is higher than in equinox and summer PCA.  相似文献   

14.
Regime observations 017 the zoobenthos state in the Balagansk transect in 1971, 1972 and in the Odissa bay in 1987-1993 of the Bratsk Reservoir were conducted.In 1991-1993 there is a change in the zoobenthos structure of the Bratsk Reservoir. In the depth zone of 0-5 m in the Balagansk transect in 1971-1972 the bottom community was considered as Gammaridae-Chiro-nomodae, in 1991 as Gammaridae-Ephemeroptera in 1992-1993 as Chironomidae-Ephemeroptera-Gammaridae. As compared with 1968-1972 the importance of Gammaridae decreased and the role of Ephemeroptera increased in the zoobenthos structure in 1991-1993.Changes were noted in the species composition of the Ologochaeta fauna and increase of the role of Oligochaeta in the zoobenthos in 1991-1993 as compared with 1965-1972.During all studies Chironomidae played a significant role in the zoobenthos. Since 1989 Paratanytarsus baialensis, bailialian endemic, has occurred in the Chironomidae fauna.The comparison of zoobenthos has shown that aver-age number and biomass of bortom invertebrates by 3-6 times and species diversity by 2.25 are higher^ in the Odissa bay than in the Balagansk transect.  相似文献   

15.
The scenario of climatic changes in the 20th century has been presented in the scope of the developed model concerning the effect of solar activity on the parameters of the climatic system governing the energy flux, outgoing from the Earth into space in the high-latitude regions. The regularities of changes in the circulation in the atmosphere and ocean are discussed. Specific attention is paid to the causes of a “cold snap” in 1940–1976 in the Northern Hemisphere and the nature of an anomalous increase in the heat content in the Earth climatic system (ocean) in 1969–1980. It has been indicated that these phenomena result from changes in the circulation in the atmosphere and ocean (specifically, a change in the thermohaline circulation in the Northern Atlantic), heat exchange between the ocean and the atmosphere and cryosphere.  相似文献   

16.
Tree-ring analysis is used successfully in studies of solar-terrestrial relations. We consider a linear dependence between the radial increment in conifers in Eastern Siberia and solar activity parameters: the length and amplitude of an 11-year solar cycle in the 20th century. It is shown that the increment in conifers in the region is larger in a longer and lower solar cycle than in a short and high one. A correlation between the increment in the width of annual rings of Pinus sylvestris and Siberian pine and the length of the ascending phase of an 11-year cycle is revealed: the longer the ascending phase, the larger the radial increment in conifers. The dynamics of the annual increment in conifers in the region is inversely related to the cycle amplitude and magnetic disturbances in the main solar cycle.  相似文献   

17.
This study aims to quantify the contribution of land use/cover change (LUCC) during the last three decades to climate change conditions in eastern China. The effects of farmland expansion in Northeast China, grassland degradation in Northwest China, and deforestation in South China were simulated using the Weather Research and Forecasting (WRF) model in addition to the latest actual land cover datasets. The simulated results show that when forestland is converted to farmland, the air temperature decreased owing to an increase in surface albedo in Northeast China. The climatic effect of grassland degradation on the Loess Plateau was insignificant because of the negligible difference in albedo between grassland and cropland. In South China, deforestation generally led to a decrease in temperature. Furthermore, the temperature decrease caused by the increase in albedo counteracted the warming effects of the evapotranspiration decrease, so the summer temperature change was not significant in South China. Excluding the effects of urbanization in the North China Plain, the LUCC effects across the entire region of East China presented an overall cooling trend. However, the variation in temperature scale and magnitude was less in summer than that in winter. This result is due mainly to the cooling caused by the increase in albedo offset partly by the increase in temperature caused by the decrease in evaporation in summer. Summer precipitation showed a trend of increasing–decreasing–increasing from southeast to northwest after LUCC, which was induced mainly by the decrease in surface roughness and cyclone circulations appearing northwest of Northeast China, in the middle of the Loess Plateau, and in Yunnan province at 700 hPa after forests were converted into farmland. All results will be instructive for understanding the influence of LUCC on regional climate and future land planning in practice.  相似文献   

18.
A close negative correlation was found to exist between oxygen concentration in winter and the latitude in rivers in the basins of the Ob and Volga. This can be explained by an increase in the duration of the freeze-up period (during which oxygen is consumed for oxidation of organic matter (OM) in water and bottom sediments) in the direction from the south to the north, while the input from oxygen from the atmosphere and photosynthesis is practically zero. No inverse relationship was found to exist between dissolved oxygen and the latitude, because in rivers of mountain and semimountain types, typical of this basin, organic matter (OM) does not accumulate in bottom sediments and the conditions of atmospheric circulation are better than in lowland rivers. The magnitude of seasonal variations in oxygen in lowland rivers is greater than in mountain ones because of an abrupt drop in oxygen concentration in slowly flowing rivers in winter and the saturation of their water by oxygen from photosynthesis in summer.  相似文献   

19.
以我国南方丘陵区红壤小流域为研究对象,对不同土地利用方式坡面下的4个水塘底泥中养分含量作了分层比较研究(0-5 cm,5-10 cm,10-15 cm,15-20 cm,20-25 cm,25-30 cm)．结果表明:4个水塘底泥养分含量差异明显,在0-15 cm泥层有机碳、全氮、速效氮和全磷含量以邻近村庄的水塘(简称C塘)底泥最高,其次为板栗园坡下的水塘(简称B塘),水稻田坡面下水塘(简称S塘)和花生地坡面下水塘(简称H塘)最低;在15-30 cm泥层,有机碳和速效氮含量以B塘最高,而全氮和全磷含量则以C塘最高;有效磷含量除C塘0-15 cm底泥外,其余均为痕量．表明土地利用方式对其坡面下水塘底泥养分含量影响明显．各水塘底泥养分随泥层加深均呈递减趋势,其中全氮和速效氮减幅以C塘最大,分别为36．0％和38．7％,有机碳和全磷减幅则以B塘最大,为29．4％和31．9％;各塘底泥养分含量的最大降幅主要在浅层底泥,水塘养分积累加速表明近年来农村面源污染加剧．传统农业耕作方式的改变是农村水体底泥养分含量增加的主要原因之一．  相似文献   

20.
中国异常增暖来年江淮流域易发生大洪水   总被引：1，自引：0，他引：1       下载免费PDF全文
在1987年以来全球气温明显增高的同时，中国气温也显著增高，1997年达到了峰值，2006年又出现了次峰值.为搞清异常增暖对中国旱涝等灾害的发生可能带来的影响，本文重点统计分析了中国年平均气温对全球年平均气温的响应关系，并分析研究了1951～2006年期间中国月年平均气温的年际变化特征和汛期主要多雨带类型及发生严重洪涝区域之间的对应关系.结果发现：（1）3个中国年平均气温异常偏高但8月气温不高的来年汛期主要多雨带和严重洪涝区域都发生在淮河流域（3/3）；（2）5个年平均气温偏高且8月气温也明显偏高的来年汛期长江流域发生了大洪水和严重洪涝（5/5），特别是其中2个8月气温特高的来年（1954、1998年）汛期长江流域发生了特大洪水和严重洪涝（2/2）.对这个前兆强信号的发现和揭示，不但证明了全球和中国异常增暖对来年中国汛期水旱灾害的重大影响，也对准确预测中国汛期主要多雨带分布类型和江淮流域的大洪水和特大洪水有特别重要的应用价值.  相似文献   

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