共查询到20条相似文献，搜索用时 778 毫秒
1.
Yan Feng Yong Jiang Yi Jiang Bao-Jia Liu Jin Jiang Zhong-Wei Liu Mei-Chen Ye Hong-Shen Wang Xiu-Ming Li 《应用地球物理》2016,13(3):561-569
We used CHAMP satellite vector data and the latest IGRF12 model to investigate the regional magnetic anomalies over mainland China. We assumed satellite points on the same surface (307.69 km) and constructed a spherical cap harmonic model of the satellite magnetic anomalies for elements X, Y, Z, and F over Chinese mainland for 2010.0 (SCH2010) based on selected 498 points. We removed the external field by using the CM4 model. The pole of the spherical cap is 36N° and 104°E, and its half-angle is 30°. After checking and comparing the root mean square (RMS) error of ΔX, ΔY, and ΔZ and X, Y, and Z, we established the truncation level at K max = 9. The results suggest that the created China Geomagnetic Referenced Field at the satellite level (CGRF2010) is consistent with the CM4 model. We compared the SCH2010 with other models and found that the intensities and distributions are consistent. In view of the variation of F at different altitudes, the SCH2010 model results obey the basics of the geomagnetic field. Moreover, the change rate of X, Y, and Z for SCH2010 and CM4 are consistent. The proposed model can successfully reproduce the geomagnetic data, as other data-fitting models, but the inherent sources of error have to be considered as well. 相似文献
2.
H. Nevanlinna 《Physics of the Earth and Planetary Interiors》1985,39(4):265-269
This paper is a short contribution to the debate on sources (external or internal) of the geomagnetic acceleration phenomenon (jerk) around 1970. Using annual means of very quiet days it is shown here that the external part in the jerk signal in in North Europe was rather small. There was a clear external part in but the corresponding change in was only 1 nT y?1. 相似文献
3.
—Maximum entropy spectral analysis (MESA) has been applied to 24 series of hourly daily data and only one daily mean series for the horizontal (H) and vertical (Z) components of the geomagnetic field for the year 1983 as observed at Narssarssuaq, Greenland (71.2°N, 36.7°E) (gm coordinate). The method has isolated some prominent medium frequency signal components. The maximum peaks for H are at 06 hr (0.174 cycles per day (cpd), 3.2 × 104 db) and 08 hr (0.09 cpd, 3.5 × 104 db). Similarly, the maximum peak in Z is observed at 04 hr (0.114 cpd, 5.7 × 104 db). The spectral results for the daily-mean data indicate periods are greater than two days, with 178.5 days (nearly semiannual) being common to both H and Z. Other harmonics have been found for all the series of H and Z components which are mainly caused by the "Effective Period", i.e., the period produced by the combined effect of the sunspot numbers and the sun’s rotation period. Such frequencies correspond very well with those found in the geomagnetic indices A p ?, C p and AE. This suggests that the disturbance transient variations are caused by viscous interaction of the solar energies emanating from sunspot regions with the outermost magnetospheric boundary which, in turn, influences the magnetosphere-iono sphere coupling and produces the medium intensity long-duration continuous auroral activities (MILD CAAs) over high latitude regions. Thus, the higher latitude geomagnetic activities are nothing but the "effective period driven MILDCAAs" having a recurrence tendency of 27/n, where n is an integer. 相似文献
4.
Variations of geomagnetic components X, Y, and Z recorded in 19 Intermagnet European observatories in 2004 were analysed. The original data from all observatories were preliminarily
processed. In the first step, periods longer than three hours were filtered out. In the second step, variations of vertical
geomagnetic component Z were separated into external and internal parts. We introduced a non-dimensional index η defined as the square root of a ratio of the energy of the external part of the vertical component to that of the horizontal
components. Maps of the surface distribution of a new magnetic index η for the area of Europe at selected time periods were created, and their time changes are presented. The time changes of η for selected observatories are also shown. Moreover, we discuss a very interesting phenomenon we discovered, that has never
been described in geophysical literature. Namely, in the recordings of all the observatories we noticed the presence of very
regular variations, observed almost exclusively in the vertical component Z, which is quite unusual. These regular variations occur in the form of sinusoidal “wave packets”. The amplitudes of these
variations do not depend on the geomagnetic latitude and appear in the records of all the observatories we analyzed. They
occur in quiet days, which suggests that their source is in the ionosphere. 相似文献
5.
《Journal of Atmospheric and Solar》2000,62(9):757-771
We present here a statistical study quantifying the errors associated with the most commonly used methods for propagating discontinuities in the interplanetary magnetic field (IMF) from an upstream monitor to the magnetosphere by the magnetospheric and ionospheric communities. The purpose of this paper is to show the quantified errors in the different techniques. Step changes in the IMF orientation were first identified at the WIND satellite. A total of 363 events were identified. Ninety percent of the events measured at WIND (330) were clearly observed in the IMP 8 data. Of those events, the time delay between the satellites could be determined to within 2 min in 288 events. Four propagation methods were used to estimate the time delay between WIND and IMP 8: (1) using only the X distance between the satellites; (2) assuming that the propagation front plane is in the plane of the Parker spiral; (3) using the IMF in the X–Y plane to estimate the propagation front plane; and (4) using the total IMF to determine the Z component of the propagation front plane. The average (Ē) and maximum (Emax) propagation error (in minutes) as a function of Y–Z distance (in Re) were determined for each method. It is concluded that the average uncertainty in propagation is 7.5–8.5 min for off-axis distances of 30 Re (which is the average WIND off-axis distance, and approximately the largest off-axis distance of IMP 8). For off-axis distances of 100 Re (the largest off-axis distance of WIND), the uncertainties are 17.5–25 min, depending on the propagation method. 相似文献
6.
In most lakes, phosphorus (P) is the nutrient controlling the trophic state. Thus, for effective control of eutrophication, the uncertainty in P-loading should be encoded as a probability density function (pdf). Specifically, the pdf of P-loading Y from non-point agricultural sources is sought by means of an event-based stochastic model.P-loading events are triggered by precipitation events (X1, X2, T), in which X1 is the rainfall amount, X2 the duration, and T the interarrival time between events. (X1, X2) are dependent random variables, while T is assumed to be exponentially distributed. The precipitation event causes runoff, which carries dissolved P into the lake with a concentration C1 and sediment yield, Z, which carries fixed or sorbed P into the lake in a fraction C2 of Z. Seasonal loading of P is calculated by adding random numbers of random variables. The model accounts separately for dissolved P and sorbed P. Explicit expressions are given for the mean and variance of each type of P-loadings. The case study of a sub-watershed of Lake Balaton, Hungary, is used to illustrate the methodology. Precipitation data, empirical rainfall-runoff-sediment yield relationships and a small number of observations of events are used to calibrate the model and estimate the means and variances of loading per event and per season. Then a simulation method is used to estimate complete pdf of these random variables. Use of the model for alternative methods of controlling P-loading is briefly discussed, as well as the economics of control. 相似文献
7.
Saralees Nadarajah Samuel Kotz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):164-170
Motivated by environmental applications, we derive the exact distributions of R = X+Y, P = X
Y and W = X/(X+Y) and the corresponding moment properties when X and Y follow Downton’s bivariate exponential distribution. The expressions turn out to involve several special functions. For practical
purposes, we also provide extensive tabulations of the percentage points associated with the distributions. 相似文献
8.
This work investigated an interrelationship between the monthly means of time derivatives of horizontal geomagnetic field, dH/dt, sunspot number, R z , and aa index for the period of substorms (from ?90 to ?1800 nT) during the years 1990–2009. A total of 232 substorms were identified during the period of study. The time derivative of horizontal geomagnetic field, dH/dt, used as a proxy for geomagnetically induced current (GIC) exhibited high positive correlation with sunspot number (0.86) and aa index (0.8998). The obtained geomagnetic activity is in 92.665% explicable by the combined effect of sunspot number and aa index. The distribution of substorms as a function of years gives a strong support for the existence of geomagnetic activity increases, which implies that as the sunspot number increases the base level of geomagnetic activity increases too. 相似文献
9.
10.
E. H. Lloyd D. Warren 《Stochastic Environmental Research and Risk Assessment (SERRA)》1990,4(3):227-240
The paper discusses the overflow (spillage) and yield rates and the total overflow and total yield over a specified time from a finite discrete stochastic reservoir, in which the yieldY
t
during the working interval (t,t+1) is a function of the storageZ
t
at timet, the inflow sequence {X
t
} being IID.The distribution vector of the spillage rate at timet is a telescoped version of the distribution of a certain Markovian variable whose transition matrix is derived. Formulae are given for the distribution of the total spillageW
h
given suitable initial conditions, forh=1,2,3; and a simple expression derived forE(W
h
).The distribution of the yield rateY
t
is a trivial modification of the storage distribution. As for the total yieldR
t
=Y
1+...+Y
t
, it is shown that the bivariate sequence {R
t
,Z
t
} is first-order Markovian, whereZ
t
is the storage at timet. The transition matrix of this process is obtained and the method of evaluating the marginal distribution of the total yieldR
t
is exemplified. 相似文献
11.
David W. Hughes 《Earth and Planetary Science Letters》1978,39(3):371-376
Near-spherical chondrules disaggregated from the meteorite Bjurböle are not found to give a good fit to Rosin's size distribution law but do obey with considerable precision a Weibull distribution law in which Y, the mass percentage of the chondrules which passes through a sieve of mesh size d mm, is given by: Y = 100{1?exp[?0.471 (d ?0.32)1.84]} 相似文献
12.
N. V. Yagova V. A. Pilipenko E. N. Fedorov A. D. Lhamdondog Yu. P. Gusev 《Izvestiya Physics of the Solid Earth》2018,54(5):749-763
The problem of estimating the time derivatives of the horizontal components of the geomagnetic field and forecasting the probability of the occurrence of perturbations that exceed a given threshold level (the over-threshold perturbations) arises in the applications concerned with the geomagnetically induced currents (GICs). In this work, we consider the temporal and spatial structure of the Pi3 pulsations with quasi-periods of 102 to 103 s during which the auroral and subauroral stations of the IMAGE network record over-threshold values in the derivatives of the meridional (along the longitudinal circle) BX component and latitudinal (along the latitudinal circle) BY component. The extreme |dBX/dt| values mainly develop against the background of the Pi3 pulsations with a complex frequency content, whereas the extreme |dBY/dt| values appear when the buildup (decay) phases of the bay-like disturbance associated with the evolution of a substorm coincide with the respective phases of the field of pulsations. The conditions under which the derivatives |dBX/dt| and |dBY/dt| reach their over-threshold values are studied for subauroral latitudes by the technique of superposed epoch analysis. The extreme values of the derivatives most frequently occur during the main phase of moderate magnetic storms or beyond the storm—during high substorm activity under the conditions of a negative vertical component of the interplanetary magnetic field. The probability of the occurrence of over-threshold values increases at high amplitudes of the Pi3 pulsations and depends on their spectral content. The problem of analyzing and forecasting the over-threshold |dBY/dt| perturbations is complicated by the fact that the scale of the perturbations is small along the lines of latitude and large along the meridians. This can result in GIC excitation in the North–South oriented electric power lines by the geomagnetic perturbations localized within a narrow band in longitude which can be missed during the measurements. 相似文献
13.
V. N. Pogrebnoi V. P. Golovkov T. I. Zvereva E. L. Mozoleva S. Moldobekova 《Geomagnetism and Aeronomy》2010,50(4):536-541
The results of investigations of the latitudinal distribution of annual variation of the geomagnetic field level in the seasons
of 1964 (International Quiet Sun Year) using the data from 95 world magnetic observatories located at various longitudes in
the latitude range 83° N–90° S are reported. The latitudinal features of the X, Y, and Z components of the geomagnetic field have been analyzed. It has been shown that the amplitudes (summer-winter differences)
of the annual variation are maximal in the polar regions, decrease continuously to zero towards the equator, and are identical
for both the Northern and Southern hemispheres with a half-year delay (local summer). The amplitudes of the equinox-winter
difference in the equinox periods are smaller than those in summer, but are manifested simultaneously in the Northern and
Southern hemispheres. An equivalent circumpolar current system has been constructed, which is responsible for the annual variation
of the geomagnetic field level. Its parameters have been determined. 相似文献
14.
Based on the moment magnitude scale, a probabilistic model was developed to predict the occurrences of strong earthquakes in the seismoactive area of Zemmouri, Algeria. Firstly, the distributions of earthquake magnitudes M i were described using the distribution function F 0(m), which adjusts the magnitudes considered as independent random variables. Secondly, the obtained result, i.e., the distribution function F 0(m) of the variables M i was used to deduce the distribution functions G(x) and H(y) of the variables Y i = Log M 0,i and Z i = M 0,i , where (Y i ) i and (Z i ) i are independent. Thirdly, some forecast for moments of the future earthquakes in the studied area is given. 相似文献
15.
Various methods have been used to study soil redistribution in the Loam Belt of Belgium. These methods have had contrasting levels of spatial coverage and time-scale. Ideally, a technique to assess soil redistribution patterns should provide the determination of dense networks of X, Y and Z terrain coordinates (digital elevation models) at different time intervals. Sequential stereoscopic aerial photographs contain this information, which can be extracted with standard photogrammetric techniques. In this study, aerial photographs taken by the National Geographic Institute of Belgium in 1947 and 1991 were used to determine the soil redistribution pattern between these years. This was done by overlaying the two digital elevation models and subtracting the corresponding Z coordinate values (heights). The results indicate that most severe surface lowering occurs on the top of the hillslope and on the hillslope convexities. Important deposition occurs on the lowermost parts of the hillslope, in most hillslope concavities and in the topographically defined concentration line. The observed pattern differs markedly from that expected from water erosion processes, and suggests that the soil redistribution is dominated by tillage operations. 相似文献
16.
17.
Saralees Nadarajah B. M. Golam Kibria 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):206-212
The generalized Pareto distribution is one of the popular models in the environmental sciences. Scientists in these areas
are often interested in comparing the values of an environmental variable under two different conditions, locations, etc.
This would require the study of the ratio X/(X+Y) where X and Y are independent generalized Pareto random variables. In this note, the exact distribution of X/(X+Y) is derived, which turns out to involve the Gauss hypergeometric function. An application of this result is provided to assess
the relative extremity of rainfall for 14 locations in Florida. Some computer programs for use in the applications are also
provided. 相似文献
18.
Leonie E.A. Jones Robert C. Liebermann 《Physics of the Earth and Planetary Interiors》1974,9(2):101-107
Fluorides are considered as models for the physical properties of oxides on the basis of Goldschmidt's crystal chemical arguments. The well-established bulk modulus (K)-volume (V) relationship KV = constant is sddddhown to hold for fluorides and oxides belonging to the four isostructural series. The bulk moduli of equivolume oxides and fluorides are scaled as 4S2, where S = ZO/2ZF is the ratio of the effective unit charges and is approximately 77% for all of the crystal structures. The fluorides have distinctly lower melting and Debye temperatures which offers the possibility of using these compounds as models for the high-temperature elastic behaviour of their oxide analogues. 相似文献
19.
Using the data set of about 1 Hz Lg amplitudes from 80 stations in the six eastern provinces of China, the ratios of horizontal to vertical amplitude of Lg waves,H/Z are determined. The mean lg(H/Z)-value is equal to 0.13. For the station bases of soft deposit,granite and sedimentary rock, lg(H/Z)-values average 0.55, 0.04 and 0.10, respectively. For the three kinds of station bases, the station terms of horizontal amplitude,C h average 0.65, ?0.09 and 0.00; that of vertical amplitude,C z average 0.32, ?0.04 and 0.00, respectively. There are the relations betweenC h ,C z and lg(H/Z):C h =0.01+2.10C z andC h =?0.15+1.46 lg(H/Z). 相似文献
20.
In applied studies on electromagnetic well-logging and electric prospecting, a medium is supposed to be either isotropic or
with conventional anisotropy of conductivity. However, in the meantime, there is a clear hint that a medium may exhibit even
biaxial anisotropy; i.e., the resistances along all three directions X, and Y, Z are different. Based on the analytical solution by the method of separation of variables, the paper considers an algorithm
for the calculation of the electromagnetic field in a layered medium with biaxial conductivity anisotropy involving an arbitrary
direction of horizontal conductivities in each layer. In this case, the theoretical solution and the algorithm display substantial
peculiarities, and the numerical implementation involves many complexities. These problems were examined and solved mainly
due to the constant comparison with the calculations carried by the finite element method and their analysis. Programs for
the calculation of electromagnetic fields in the frequency and time domains were developed, and results of geoelectric interest
were obtained. For example, the excitement of a horizontally-layered section by a magnetic dipole produces a vertical electric
component of the field. 相似文献