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1.
The Alaskar pipeline is a highly conducting anomaly extending 800 miles (1300 km) from about 62° to 69° geomagnetic latitude beneath the most active regions of the ionospheric electrojet current. The spectral behavior of the magnetic field from this current was analyzed using data from standard geomagnetic observatories to establish the predictable patterns of temporal and spatial changes for field pulsation periods between 5 min and 4 hr. Such behavior is presented in a series of tables, graphs and formulae. Using 2- and 3-layer models of the conducting earth, the induced electric fields associated with the geomagnetic changes were established. From the direct relationship of the current to the geomagnetic field variation patterns one can infer counterpart temporal and spatial characteristics of the pipeline current. The relationship of the field amplitudes to geomagnetic activity indices,A p, and the established occurrence of various levels ofA p over several solar cycles were employed to show that about half of the time the induced currents in the pipe would be under 1 A for the maximum response oscillatory periods near 1 hr. Such currents should be of minimal consequence in corrosion effects for even a section of the pipeline unprotected by sacrificial electrodes. Of greater interest was the result that the extreme surges of current should reach over one-hundred amperes in the pipeline during high activity.  相似文献   

2.
The planetary scale distribution of electrical currents in the Earth is still largely unknown. The role of the oceans for long period (hours to days) inducing electromagnetic fieldsB e of external origin has been investigated by several authors, while the role of telluric current channelling, from the planetary viewpoint, is still far from a satisfactory understanding. Canonical geomagnetic depth sounding (GDS) analysis can yield locally a direction parallel to the strike of a telluric current density flowing in a region around the recording site and which also has the property of being the most relevant source for the internal origin fieldB i observed at the given site at the given frequency. The use of such local information from 64 geomagnetic observatories is discussed here in a study to infer evidences of (a) the role of the polarization properties ofB e and (b) the role of the telluric current channelling within conductivity anomalies relevant to the planetary scale circuitry. The results show clear evidence of the influence of the equatorial electrojet on the polarization ofB e in a latitudinal band between ±(15°–20°) latitude. There is also evidence that theB e associated with the equatorial electrojet produces telluric currents which flow at a much shallower depth than the skin depth to be expected in the case of a plane Earth. This implies that the Parkinson planes in these regions reflect the conductivity structure underground more than the polarization ofB e due to the equatorial electrojet. Further, it clearly appears that some regular planetary scale pattern of telluric currents plays a more significant role than current channelling within some conductivity anomalies of fixed strike close to some geomagnetic observatories. Finally, the number of observatories used in this study appears to be insufficient to deduce any information concerning a seasonal evolution of the telluric current pattern on a planetary scale.  相似文献   

3.
The goal of cathodic protection is to prevent corrosion by maintaining buried pipelines at a constant potential with respect to the surrounding soil. In practice, however, the implementation is very complicated since many factors can contribute to the current flowing off the pipe. Design requires characterization of the parameters impacting the corrosion process, such as soil resistivity, size of the pipe and quality of the coating.In the present paper, we have studied the effect of geomagnetic fields on the pipe-induced currents considering it as an additional cause of corrosion. A theoretical method implemented to model the induced currents was tested in a previous work and the effect during disturbed days was quantified. This theoretical model indicated that the intensity of the current induced in a pipeline by the varying geomagnetic field depends on the intensity and rate of change of the field and the electrical resistivity of the soil. This induced current is in equilibrium with the host current and there is no current drainage between the pipeline and the host until, along the length of the pipeline, the host resistivity becomes different. At that point, current must flow between the pipe and host in order to establish a new equilibrium. It is this drainage current, flowing between the pipeline and the host, which causes corrosion problems.Following these results, experimental tests were performed in Tierra del Fuego. In this zone, a geophysical study was made to determine the discontinuities in soil resistivities and simultaneous measurements of the geomagnetic field and the drainage of current were recorded at different sites. The results obtained from the correlation of the data are consistent with the theoretical predictions.  相似文献   

4.
从杂散电流腐蚀的数学模型、监测手段、防护措施和可展望的问题等方面,对交流电引起的杂散电流腐蚀进行系统评述。首先,介绍杂散电流腐蚀的机理及数据模型,并从不同行业学者所选取的模型及软件入手,介绍杂散电流腐蚀的模型建立的相关类型;其次,对目前杂散电流监测的主要方法及其自动监测系统的发展进行阐述;最后,介绍基于杂散电流腐蚀防护原则建立的防护体系及其相应特点,并对杂散电流腐蚀的监测中具有可行性发展的技术进行探讨。  相似文献   

5.
根据场源不同可将地电场E分为大地电场ET和自然电场ESP。空间Sq电流系和固体潮一般被认为是大地电场ET的起源;自然电场ESP源于地下介质的物理化学作用,其局部性变化相对稳定。2013年南北地震带相继发生了芦山MS7.0地震（30.3°N,103.0°E）和岷县、漳县MS6.6地震（34.5°N,104.2°E）。两次地震周边约400 km范围内的地电场台站（成都、汉王）数据表明震前自然电场ESP出现明显的小幅度突跳或大幅度跃变,同时在时间上具有准同步性,其他地电场台站也有类似变化。基于大地电场岩体裂隙水（电荷）渗流（移动）模型,对两次地震周边自然电场ESP的变异机理进行探讨,尝试解析其物理过程。  相似文献   

6.
Relative variations in the number of sunspots and sunspot groups in activity cycles have been analyzed based on data from the Kislovodsk Mountain Astronomical Station and international indices. The following regularities have been established: (1) The relative fraction of small sunspots decreases linearly and that of large sunspots increase with increasing activity cycle amplitude. (2) The variation in the average number of sunspots in one group has a trend, and this number decreased from ～12 in cycle 19 to ～7.5 in cycle 24. (3) The ratio of the sunspot index (Ri) to the sunspot group number index (G gr) varies with a period of about 100 years. (4) An analysis of the sunspot group number index (G gr) from 1610 indicates that the Gnevyshev-Ohl rule reverses at the minimums of secular activity cycles. (5) Ratio of the total area to area of Ssp/Sum nuclei has long-term variation with a period approximately 8 cycles. Minimum ratio falls on 16–17 cycles of activity. (6) It has been indicated that the magnetic field intensity and sunspot area in the current cycle are related to the amplitude of the next activity cycle.  相似文献   

7.
The hourly values of the F-layer critical frequency from the ionospheric sounder in Dourbes (50.1°N, 4.6°E) during the time interval from 1957 to 2010, comprising five solar cycles, were analyzed for the effects of the solar activity. The hourly time series were reduced to hourly monthly medians which in turn were used for fitting a single station foF2 monthly median model. Two functional approaches have been investigated: a statistical approach and a spectral approach. The solar flux F10.7 is used to model the dependence of foF2 on the solar activity and is incorporated into both models by a polynomial expression. The statistical model employs polynomial functions to fit the F-layer critical frequency while the spectral model is based on spectral decomposition of the measured data and offers a better physical interpretation of the fitting parameters. The daytime and nighttime foF2 values calculated by both approaches are compared during high and low solar activity. In general, the statistical model has a slightly lower uncertainty at the expense of the larger number of fitting parameters. However, the spectral approach is superior for modeling the periodic effects and performs better when comparing the results for high and low solar activity. Comparison with the International Reference Ionosphere (IRI 2012) shows that both local models are better at describing the local values of the F-layer critical frequency.  相似文献   

8.
Relatively little is known about the long-term sediment accumulation dynamics of Naracoorte Cave Complex (NCC) solution pipe cavities, and many of the megafauna-bearing infill deposits at this globally significant Australian Pleistocene fossil locality remain partially dated or lack any numerical age control. In this study, we assess the suitability of three different luminescence dating signals for improving existing chronologies at six Late and Middle Pleistocene NCC sites (n = 22 samples), and we undertake multi-site examinations of NCC sediment infill dynamics spanning the last 550 thousand years (ka). Modern analogue samples collected from above and beneath two active cave entrances confirm that single-grain OSL, single-grain TT-OSL and multi-grain pIR-IRSL signals can be reset down to insignificant residual levels (<10−1–100 Gy) when compared with the natural dose ranges of interest for most NCC palaeontological applications. Replicate luminescence dating comparisons performed at six NCC fossil sites (n = 15 samples) reveal consistent ages for twenty-eight out of thirty-one paired OSL–TT-OSL, OSL–pIR-IRSL and TT-OSL–pIR-IRSL datasets. Nineteen of the twenty Middle to Late Pleistocene samples analysed from the NCC sites produce homogeneous OSL, TT-OSL and pIR-IRSL De datasets suggesting that the NCC solution pipe deposits considered here are generally not affected by syn-depositional mixing complications that can take place within closed karst cavities (i.e., the remobilisation of unbleached grains from pre-existing cave floor sediments, and their subsequent translocation and incorporation into deposits within deeper parts of the cavity along with externally bleached, allochthonous grain populations). Detailed examination of solution pipe dynamics at Smoke Tortoise Cave (SMT) reveals a complex accumulation history focused on the marine isotope stage (MIS) 9 and MIS 7 interglacial complexes, as well as the MIS 8e interstadial. The SMT case study highlights that NCC solution pipes are not simply associated with short-lived opening and sediment accumulation events, but may involve multiple, discontinuous deposition episodes and reactivation events. An initial multi-site examination of all published NCC infill chronologies (n = 70) appears to suggest statistically significant, preferential solution pipe development during the relatively wet parts of interglacial or interstadial cycles. The non-uniform infill age distribution implies that NCC solution pipe dynamics may have exerted taphonomic biases on fossil accumulation, which should be taken into consideration when reconstructing long-term palaeoecological histories from NCC solution pipe cavities.  相似文献   

9.
In the framework of the French participation in the International Equatorial Electrojet Year (IEEY), ten magnetotelluric stations were installed between November 1992 and November 1994 along a 1200-km-long meridian profile, between Lamto (latitude 6.2°N, CôCte dIvoire) to the south and Tombouctou (latitude 16.7°N, Mali) to the north. These stations measured digitally the three components of the magnetic field and the two components of the telluric electric field, and operated over a period of 20 months. The magnetic data is used to study the features of the equatorial electrojet (EEJ) in West African longitude. The measurement of the telluric electric field variations will be presented elsewhere. Hourly mean values are used to study the morphological structure of the regular diurnal variation SR of the three components (H, D, and Z) of the earth magnetic field and to characterize the EEJ during magnetically quiet days. The occurrences of the counter-electrojet (CEJ) are set forth, emphasizing its seasonal variability. Assumed to be a current ribbon, the EEJ main parameters (the position of its center, its width, and the amplitude of its current density at the center) are determined. A preliminary analysis of the time variations of these parameters is presented over period of 20 months (from January 1993 to August 1994). Results are compared with those obtained during previous experiments of the same kind.  相似文献   

10.
We study the cosmic ray modulation during different solar cycles and polarity states of the heliosphere. We determine (a) time lag between the cosmic ray intensity and the solar variability, (b) area of the cosmic ray intensity versus solar activity modulation loops and (c) dependence of the cosmic ray intensity on the solar variability, during different solar activity cycles and polarity states of the heliosphere. We find differences during odd and even solar cycles. Differences during positive and negative polarity periods are also found. Consequences and implications of the observed differences during (i) odd and even cycles, and (ii) opposite polarity states (A<0 and A>0) are discussed in the light of the modulation models, including drift effects.  相似文献   

11.
To make a long-term prediction of the solar cycle in a standard way (GOST 25645.302-83), it is necessary to know the instant of the activity minimum onset, the determination of which is difficult during the decline stage of the previous cycle. The dependence of the long-term prediction error on the time of shift (t) relative to the solar activity minimum instant (i.e., the situation when a certain time before the minimum onset, rather than the time of this minimum, is the initial point of calculations) has been studied. It has been indicated that one should not know the exact time of the activity minimum onset in order to make prediction according to GOST, and such a prediction can be performed with an approximately identical error if the lead time is t ～ 1 year and more relative to the activity minimum onset. An analysis of the dependence of prognostic W max values on t for cycles 18–23 indicated that prognostic W max values are overestimated at small (to ～ 1 year) uncertainties in the time of activity minimum onset. It has been obtained that W max = 96 ± 13 for cycle 24 on the assumption that this cycle began in April 2007.  相似文献   

12.
A database of the electron temperature (Te) comprising of most of the available LEO satellite measurements is used for studying the solar activity variations of Te. The Te data are grouped for two levels of solar activity (low LSA and high HSA), five altitude ranges between 350 and 2000 km, and day and night. By fitting a theoretical expression to the Te values we obtain variation of Te along magnetic field lines and heat flux for LSA and HSA. We have found that Te increases with increase in solar activity at low and mid-latitudes during nighttime at all altitudes studied. During daytime the Te response to solar activity depends on latitude, altitude, and season. This analysis shows existence of anti-correlation between Te and solar activity at mid-latitudes below 700 km during the equinox and winter day hours. Heat fluxes show small latitudinal dependence for daytime but substantial for nighttime.  相似文献   

13.
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   

14.
Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91E; dip Latitude 24.8°N), India, for the period 1975/80 and 1986/89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IECmax (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IECmax shows positive correlation with F10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F10.7 values, IECmax is substantially constant in all the seasons. IECmax and magnetic activity (Ap) are found to be positively correlated in summer in high solar activity. Winter IECmax shows positive correlation with Ap in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IECmax is independent of Ap in both solar cycles in low solar activity. A study of day-to-day variations in IECmax shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.  相似文献   

15.
Electron and ion temperature (Te and Ti) data observed using RPA on board SROSS C2 satellite are investigated for the variation with local time, season, latitude (0–30°N geographic) over a half of a solar cycle (1995–2000). The nighttime Te (∼1000 K) is independent of the season and the solar flux whereas Ti exhibits positive correlation with the solar activity during all three seasons. In the early morning hours during summer, Te is higher by ∼500 K than other seasons in all three levels of solar activity. During winter and equinox in the early morning hours, Te and Ti are higher during low solar activity, showing a negative correlation with solar flux. During daytime, the Ti increases with the solar flux in winter and summer solstice, but is independent in equinox. IRI underestimates Te and Ti during the morning period by 50–75% in the equatorial and near-equatorial stations during all levels of solar activities.  相似文献   

16.
The possibilities of improving the semiempirical model of cosmic ray (CR) modulation, proposed by us previously, are discussed. The following characteristics have been considered as model parameters in order to describe long-period CR variations using a unified model and to more completely reflect solar cycles in CR modulation as a complex interaction between two systems of fields (large-scale and local): the value and sign of the polar solar field, the average strength of the solar magnetic field (the B ss integral index), partial indices (zone-even (ZE) and zone-odd (ZO) and sector-even (SE) and sector-odd (SO) indices), the tilt of the heliospheric current sheet, and the special index (F x ) taking into account X ray flares. The role of each index in CR modulation has been revealed. When we described the long-term CR variations using many parameters and taking into account the integral index or one of four partial indices, the best results of modulation modeling during 1976–1999 were obtained for the B ss total energetic index and SO index. A difference between the model calculations and observations increases beginning from the middle of 2000; the problem features of the CR behavior and the specific features of modeling this behavior in cycle 23 of solar activity (SA) are discussed. It is assumed that a decrease in the CR density at the last SA minimums (from cycle to cycle) can be related to a decrease in the ZO index and to a recently detected similar decrease in the vertical component of the solar dipole magnetic moment.  相似文献   

17.
Summary The rotating nature of telluric field is simulated in an electrolytic model tank. Variations of this rotating field due to the presence of a few two and three dimensional geological models, simulated in the tank, are studied. The telluric ellipses, recorded on a C.R.O. Screen, are found to be useful for qualitative and quantitative interpretation of the non-linearly polarised telluric field data. Relative usefulnesses of the various parameters, e.g., (i)M=ratio of the semimajor and semiminor axis, (ii)K = square root of normalized surface areas, (iii) = linear eccentricity ((a 2/b 2-1) and (iv)e = conventional eccentricity ((1-b 2/a 2)), of a telluric ellipse are tested. Linear eccentricity appears to be the most sensitive parameter. Methods for determining depth and horizontal extent of a structure from a telluric map are suggested. Near surface inhomogeneities, as revealed from the experiment are unlikely to affect the telluric map due to a basement structure.  相似文献   

18.
An array designed to detect changes of resistivity in the upper 10 km of the crust has been in continuous operation since 1988. Long period (T=300–7200 s) telluric signals are recorded digitally on 5–16 km long dipoles. Telluric transfer functions are computed between field dipoles and two reference dipoles and then decomposed to examine daily fluctuations of those functions. Based on analysis of these daily fluctuations, stabilities of 0.1–0.3% are achieved. No intermediate term resistivity changes are seen associated with any of the 5 Mb>4.0 earthquakes that have occurred since 1989. Short term fluctuations are seen associated with most of these earthquakes, however. Minimum bounds on resistivity changes that could have caused the fluctuations in the telluric responses range from 1.7 to 13.0%. While these are within the ranges seen in other field studies, the statistical significance of these fluctuations is low because they also occur at many times that cannot be correlated to earthquakes. Comparison of the one potential resistivity change associated with a strain change results in a strain sensitivity that is unrealistically high. This possible resistivity change coincides spatially with a temporary variation in seismic travel time in May–June 1989, however. It is likely that many of the fluctuations in the telluric responses are random variations except for the one in 1989, and recording through the next M6 earthquake will be needed in order to detect a statistically significant resistivity change.  相似文献   

19.
This work represents a physical interpretation of cosmic ray modulation in the 22nd–24th solar cycles, including an interpretation of an unusual behavior of their intensity in the last minimum of the solar activity (2008–2010). In terms of the Parker modulation model, which deals with regularly measured heliospheric characteristics, it is shown that the determining factor of the increased intensity of the galactic cosmic rays in the minimum of the 24th solar cycle is an anomalous reduction of the heliospheric magnetic field strength during this time interval under the additional influence of the solar wind velocity and the tilt angle of the heliospheric current sheet. We have used in the calculations the dependence of the diffusion tensor on the rigidity in the form K ij ∝ R 2?μ with μ = 1.2 in the sector zones of the heliospheric magnetic field and with μ = 0.8 outside the sector zones, which leads to an additional amplification of the diffusion mechanism of cosmic ray modulation. The proposed approach allows us to describe quite satisfactorily the integral intensity of protons with an energy above 0.1 GeV and the energy spectra in the minima of the 22nd–24th solar cycles at the same value of the free parameter. The determining factor of the anomalously high level of the galactic cosmic ray intensity in the minimum of the 24th solar cycle is the significant reduction of the heliospheric magnetic field strength during this time interval. The forecast of the intensity level in the minimum of the 25th solar cycle is provided.  相似文献   

20.
The relationship between the ground-based inferred vertical E × B drifts, Vz, and the magnetic equatorial electrojet current during the year of solar minima was presented. Both the diurnal and seasonal Vz variations are positively directed during the daytime and negative at nighttime. The evening time pre-reversal enhancement occurs around 19:00 LT. The fairly strong linear relationship between the electrojet current strength and Vz exhibited higher correlations during the daytime (06:00–16:00 LT). The maximum morning time proxy parameter described by E = [d (ΔH ILR)/dt]max in the morning hours, indicating the east-west electric field in the EEJ, corresponds reasonably well with the E × B drift and, hence, can be used as a proxy parameter for representing Vz in the morning hours. The daytime EEJ magnitude seasonal changes are connected with a change in conductivity emerging from the action of turbulence and divergence of momentum flux. These waves above the dynamo region are suggested to lead to partial counter electrojet during the equinoctial months.  相似文献   

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