首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
In this study, we aim to improve the scaling between the moment magnitude (M W), local magnitude (M L), and the duration magnitude (M D) for 162 earthquakes in Shillong-Mikir plateau and its adjoining region of northeast India by extending the M W estimates to lower magnitude earthquakes using spectral analysis of P-waves from vertical component seismograms. The M W-M L and M W-M D relationships are determined by linear regression analysis. It is found that, M W values can be considered consistent with M L and M D, within 0.1 and 0.2 magnitude units respectively, in 90 % of the cases. The scaling relationships investigated comply well with similar relationships in other regions in the world and in other seismogenic areas in the northeast India region.  相似文献   

2.
The results of an analysis of the possible effect of auroral electron fluxes on the effective recombination coefficient αeff in the ionosphere are presented. It is shown that the αeff value in the E-region of the ionosphere is determined mainly by the physical-chemical properties of the medium. In the F1-layer of the ionosphere, the effective recombination coefficient becomes dependent on both the value of the energy flux and the type of the energy spectrum of the auroral electron flux.  相似文献   

3.
In this study, we have modeled the density(ρ) and bulk sound velocity(VΦ) profiles of the bottom lower mantle using the experimental thermal equation of state(EoS) parameters of lower-mantle minerals, including bridgmanite, ferropericlase,CaSiO3-perovskite, and post-perovskite. We re-evaluated the literature pressure-volume-temperature relationships of these minerals using a self-consistent pressure scale in order to avoid the long-standing pressure scale problem and to provide more reliable constraints on the thermal EoS parameters. With the obtained thermal EoS parameters, we have constructed the ρ and VΦ profiles of the bottom lower mantle in different composition, mineralogy, and temperature models. Our modelling results show that the variations of chemistry, mineralogy, and temperature have different seismic signatures from each other. The Fe and Al enrichment at the bottom lower mantle can cause an increase in ρ but greatly lower VΦ. A change in mineralogy needs to be considered with the lateral variation in temperature. The cold slabs will be shown as denser regions compared to the normal mantle because of the combined effect of a lower temperature and the presence of a denser post-perovskite at a shallower depth,whereas the hot regions will have a 1–2% lower ρ than the normal mantle. VΦ of both cold slabs and hot regions will be lower than the normal mantle when bridgmanite is the dominant phase in the normal mantle, yet they will be greater once bridgmanite transforms into post-perovskite in the normal mantle. Our modeling also shows that the presence of a(Fe, Al)-enriched bridgmanite thermal pile above the core-mantle boundary will exhibit a seismic signature of enhanced ρ and VΦ, but a reduced VS,which is consistent with the observed seismic anomalies in the large-low-shear-velocity-provinces(LLSVPs). The existence of such a(Fe, Al)-enriched bridgmanite thermal pile thus can help to understand the origin of the LLSVPs. These results provide new insights for the chemical and structure of the deepest lower mantle.  相似文献   

4.
Aftershock sequences of some strong earthquakes of Kamchatka, the Kurile Islands, and Japan are examined. Such source parameters as the length L, along-dip width W, motion on fault D, and stress drop Δσ are determined from the aftershock sequences considered. The values of these parameters were obtained by the formal estimation of linear source parameters (lower bound estimates) and visually (upper bound estimates). The correlation dependences of the obtained parameters on the surface wave (M S ) and seismic moment (M W ) magnitudes are calculated.  相似文献   

5.
The powerful solar flares that occurred on September 4–10, 2017 are analyzed based on a quantitative diagnostics method for proton flares developed at the Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation (IZMIRAN) in the 1970–1980s. We show that the fluxes and energy spectra of the protons reached the Earth with the energies of tens of MeV qualitatively and quantitatively correspond to the intensity and frequency spectra of the microwave radio bursts in the range of 2.7–15.4 GHz. Specifically, the flare of September 4 with a peak radio flux S ~ 2000 sfu at the frequency f ~ 3 GHz (i.e., with the soft radio spectrum) was accompanied by a significant proton flux J (>10 MeV) ~100 pfu and a soft energy spectrum with the index γ ~3.0, while the strong flare on September 10 with S ~ 21000 sfu at f ~ 15 GHz (i.e., with the hard radio spectrum) led to a very intense proton event with J (>10 MeV) ~1000 pfu with a hard spectrum (γ ~ 1.4), including the ground level enhancement (GLE72). This is further evidence that microwave radio data can be successfully used in diagnostics of proton flares independently of a specific source of particle acceleration at the Sun, in particular, with the IZMIRAN method.  相似文献   

6.
Parameters of the interplanetary magnetic field and solar wind plasma during periods of 163 isolated substorms have been studied. It is shown that the solar wind velocity V and plasma density N remain approximately constant for at least 3 h before substorm onset Т o and 1 h after Т o . On average, the velocity of the solar wind exhibits a stable trend toward anticorrelation with its density over the whole data array. However, the situation is different if the values of V and N are considered with respect to the intensity of substorms observed during that period. With the growth of substorm intensity, quantified as the maximum absolute value of AL index, an increase in both the solar wind plasma velocity and density, at which these substorms appear, is obsreved. It has been found that the magnitude of the solar wind dynamic pressure P is closely related to the magnetosphere energy load defined as averaged values of the Kan–Lee electric field EKL and Newell parameter dΦ/dt averaged for 1 h interval before Т o . The growth of the dynamic pressure is accompanied by an increase in the load energy necessary for substorm generation. This interrelation between P and values of EKL and dΦ/dt is absent in other, arbitrarily chosen periods. It is believed that the processes accompanying increasing dynamic pressure of the solar wind result in the formation of magnetosphere conditions that increasingly impede substorm generation. Thus, the larger is P, the more solar wind energy must enter the Earth’s magnetosphere during the period of the growth phase for substorm generation. This energy is later released during the period of the substorm expansion phase and creates even more intense magnetic bays.  相似文献   

7.
The reaction of the lower ionosphere to the solar proton events that occurred in 2011–2012 is studied in this paper based on the results of measurements of the propagation velocity and the E z /H τ ratio of the low-frequency electromagnetic pulses (atmospherics) in the ELF range at the high-latitude observatories Lovozero and Barentsburg. With numerical modeling methods, it is shown that horizontal local irregularities of the lower ionosphere conductivity profile could be a cause of the splashes in the E z /H τ ratio observed in the experiment during the solar proton event of March 7, 2012, which was a unique event in both the proton flux value and energy.  相似文献   

8.
The Dinghushan flux observation site, as one of the four forest sites of ChinaFLUX, aims to acquire long-term measurements of CO2 flux over a typical southern subtropical evergreen coniferous and broad-leaved mixed forest ecosystem using the open path eddy covariance method. Based on two years of data from 2003 to 2004, the characteristics of temporal variation in CO2 flux and its response to environmental factors in the forest ecosystem are analyzed. Provided two-dimensional coordinate rotation, WPL correction and quality control, poor energy-balance and underestimation of ecosystem respiration during nighttime implied that there could be a CO2 leak during the nighttime at the site. Using daytime (PAR > 1.0 μmol?1·m?2·s?1) flux data during windy conditions (u* > 0.2 m·s?1), monthly ecosystem respiration (Reco) was derived through the Michaelis-Menten equation modeling the relationship between net ecosystem C02 exchange (NEE) and photosynthetically active radiation (PAR). Exponential function was employed to describe the relationship between Reco and soil temperature at 5 cm depth (Ts05), then Reco of both daytime and nighttime was calculated respectively by the function. The major results are: (i) Derived from the Michaelis-Menten equation, the apparent quantum yield (α) was 0.0027±0.0011 mgCO2·μmol?1 photons, and the maximum photosynthetic assimilation rate (Amax) was 1.102±0.288 mgCO2·m?2·s?1. Indistinctive seasonal variation of α or Amax was consistent with weak seasonal dynamics of leaf area index (LAf) in such a lower subtropical evergreen mixed forest, (ii) Monthly accumulated Reco was estimated as 95.3±21.1 gC·m?2mon?1, accounting for about 68% of the gross primary product (GPP). Monthly accumulated WEE was estimated as ?43.2±29.6 gC·m?2·mon?1. The forest ecosystem acted as carbon sink all year round without any seasonal carbon efflux period. Annual NEE of 2003 and 2004 was estimated as ?563.0 and ?441.2 gC·m?2·a?1 respectively, accounting for about 32% of GPP.  相似文献   

9.
The dynamics of energetic electrons (E e =0.17–8 MeV) and protons (E p =1 MeV) of the outer radiation belt during the magnetic storm of May 15, 2005, at high (GOES-10 and LANL-84 geosynchronous satellites) and low (Meteor-3M polar satellite) altitudes is analyzed. The data have been compared to the density, plasma velocity, solar wind, and magnetic field measurements on the ACE satellite and geomagnetic disturbances. During the magnetic storm main phase, the nighttime boundary of the region of trapped radiation and the center of westward electrojet shifted to L ～ 3. Enhancements of only low-energy electrons were observed on May 15, 2005. The belt of relativistic electrons with a maximum at L ～ 4 was formed during the substorm, the amplitude of which reached its maximum at ～0630 UT on May 16. The results are in good agreement with the regularity relating the position of a maximum of the new relativistic electron belt, boundaries of the trapped radiation region, and extreme low-latitude position of westward electrojet center to the Dst variation amplitude.  相似文献   

10.
The dependence of the zonal geomagnetic indices (AE, Ap, Kp, Kn, and Dst) on the solar wind parameters (the electric field E y component, dynamic pressure P d and IMF irregularity σB) has been studied for two types of events: magnetic clouds and high-speed streams. Based on the empirical relationships, it has been established that the AE, Ap, Kp, and Kn indices are directly proportional to the E y value at E y < 12 mV m?1 and are inversely proportional to this value at E y > 12 mV m?1 for the first-type events. On the contrary, the dependence of Dst on E y is monotonous nonlinear. A linear dependence of all geomagnetic indices on E y is typical of the second-type events. It has been indicated that the specific features of geoeffectiveness of magnetic clouds and high-speed solar wind streams are caused by the dependence of the electric field potential across the polar cap on the electric field, solar wind dynamic pressure, and IMF fluctuations.  相似文献   

11.
The position of the auroral oval poleward and equatorward boundary projections on the equatorial plane in the nightside MLT sector during magnetically quiet periods (|AL| < 200 nT, |Dst| < 10 nT) has been determined. The oval boundary positions were determined according to the precipitation model developed at Polar Geophysical Institute (http://apm.pgia.ru/). The isotropy of the averaged plasma pressure and the experimentally confirmed balance of pressures during the nighttime have been taken into account. The morphological mapping method has been used to map the oval poleward and equatorward edges without the use of any magnetic field model on the assumption that the condition of magnetostatic equilibrium is valid. Ion pressures at ionospheric altitudes and in the equatorial plane have been compared. It has been shown that the auroral oval equatorward boundary in the midnight sector is localized at geocentric distances of ~7 RE, which is in good agreement with the position of the energetic particle injection boundary in the equatorial plane. The oval poleward edge is localized at the ~10 RE geocentric distance, which is in good agreement with the position of the equatorward boundary of the region with a high turbulence level in the Earth’s magnetosphere plasma sheet.  相似文献   

12.
During the ruptures of an earthquake,the strain energy.△E,.will be transferred into,at least,three parts,i.e..the seismic radiation energy(E_s),fracture energy(E_g),and frictional energy(E_f),that is,△E = E_s + E_g + E_f.Friction,which is represented by a velocity- and state-dependent friction law by some researchers,controls the three parts.One of the main parameters of the law is the characteristic slip displacement.D_c.It is significant and necessary to evaluate the reliable value of D_c from observed and inverted seismic data.Since D_c controls the radiation efficiency.η_R = E_s/(E_s+ E_g),the value of η_r is a good constraint of estimating D_c.Integrating observed data and inverted results of source parameters from recorded seismograms.the values of E_s and E_g of an earthquake can be measured,thus leading to the value of η_R.The constraint used to estimate the reliable value of D_c will be described in this work.An example of estimates of D_c.based on the observed and inverted values of source parameters of the September 20,1999 M_S 7.6 Chi-Chi(Ji-Ji).Taiwan region,earthquake will be presented.  相似文献   

13.
Rhythms of heliogeomagnetic activity and their dynamics in the solar activity (SA) cycles are analyzed. Heliogeomagnetic rhythms are the mixture of a periodic signal and noise component, which differs from a periodic signal by a substantial suddenness. Therefore, the filtering methods optimized for smoothness were used to analyze these rhythms and to separate rhythm periodic components. Short-period rhythms of the Kp index of geomagnetic activity and Wolf numbers (W) have been revealed. The rhythm dynamics in SA cycles has been indicated. Clearly defined near-seven-day, semi-seven-day, and other components, which are harmonics of the solar rotation period, are present in the rhythms of the Kp index in contrast to W. A comparison of the Kp and Dst rhythms indicates that the seasonal and annual variations in these indices are substantially similar. It has been indicated that the rhythms of heliogeomagnetic activity could be the external synchronizers of biological rhythms, having integrated into the endogenous temporal structure of these rhythms in the process of evolution, and that the dependence of the population macroparameters on W is much weaker than on Kp.  相似文献   

14.
Long-period geomagnetic pulsations during the SSC of July 14, 2012, are studied. The prenoon longitudinal sector (09:20–11:30) MLT, from the boundaries of which pulsations propagate azimuthally onto the dawn and dusk sides with an opposite polarization direction and increased amplitude, has been distinguished. The position of this sector relative to noon (a shift to the dawn side) depends on the front azimuthal inclination. It has been found that the polarization direction reverses in going from low (<30°) to middle/subauroral (≥50°) latitudes on the entire dayside. The geomagnetic pulsations mainly fluctuate near the f1 = 2.9 and f2 = 4.4 mHz frequencies. Fluctuations with frequency f1, which coincide with the fluctuation frequency of the IMF х component, predominate at the polar cap latitudes (the open field line region) in the form of rapidly attenuating impulses and at low latitudes with a much smaller amplitude. Fluctuations with frequency f2 are globally registered at all latitudes in the dayside sector below the magnetopause projection as a train of several fluctuations. It is assumed that fluctuations with frequency f1 penetrate from the solar wind, and fluctuations with frequency f2 are radial magnetopause oscillations.  相似文献   

15.
Using model simulations, the morphological picture (revealed earlier) of the disturbances in the F 2 region of the equatorial ionosphere under quiet geomagnetic conditions (Q-disturbances) is interpreted. It is shown that the observed variations in the velocity of the vertical E × B plasma drift, related to the zonal E y component of the electric field, are responsible for the formation of Q-disturbances. The plasma recombination at altitudes of the lower part of the F 2 region and the dependence of the rate of this process on heliogeophysical conditions compose the mechanism of Q-disturbance formation at night. The daytime positive Q-disturbances are caused exclusively by a decrease in the upward E × B drift, and this type of disturbances could be related to the known phenomenon of counter electrojet. Possible causes of formation of the daytime negative Q-disturbances are discussed.  相似文献   

16.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F NEE, F GPP and R E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux.LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.The forest was a net sink of atmospheric CO2 and sequestered ?449 g C·m?2 during the study period; ?278 and ?171 gC·m?2 for 2003 and 2004 respectively. F GPP and F RE over 2003 and 2004 were ?1332, ?1294 g C·m?2. and 1054, 1124 g C·m?2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2.There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F GPP, and 60.4, 62.1% of R E of the entire year.  相似文献   

17.
The variations in the density of the ionospheric F2 layer maximum (NmF2) under the action of the zonal plasma drift perpendicularly to the magnetic (B) and electric (E) fields in the direction geomagnetic west-geomagnetic east have been studied using the three-dimensional nonstationary theoretical model of electron and ion densities (N e and N i ) and temperatures (T e and T i ) in the low-latitude and midlatitude ionospheric F region and plasmasphere. The method of numerical calculations of N e , N i , T e , and T i , including the advantages of the Lagrangian and Eulerian methods, is used in the model. A dipole approximation of the geomagnetic field (B), taking into account the non-coincidence of the geographic and geomagnetic poles and differences between the positions of the Earth’s and geomagnetic dipole centers, is accepted in the calculations. The calculated NmF2 and altitudes of the F2 layer maximum (hmF2) have been compared with these quantities measured at 16 low-latitude ionospheric sounding stations during the geomagnetically quiet period October 11–12, 1958. This comparison made it possible to correct the input model parameters: the NRLMSISE-00 model [O], the meridional component of the neutral wind velocity according to the HWW90 model, and the meridional component of the equatorial plasma drift due to the electric field specified by the empirical model. It has been indicated that the effect of the zonal E × B plasma drift on NmF2 can be neglected under daytime conditions and changes in NmF2 and hmF2 under the action of this drift are insignificant under nighttime conditions north of 25° and south of ?26° geomagnetic latitude. The effect of the zonal E × B plasma drift on NmF2 and hmF2 is most substantial in the nightside ionosphere approximately from ?20° to 20° geomagnetic latitude, and the neglect of this drift results in an up to 2.4-fold underestimation of NmF2. The found dependence of the effect of the zonal E × B plasma drift on NmF2 and hmF2 on geomagnetic latitude is related to the longitudinal asymmetry of B, asymmetry of the neutral wind about the geomagnetic equator, and changes in the meridional E × B plasma drift at a change in geomagnetic longitude.  相似文献   

18.
The forecasting of evaporative loss (E) is vital for water resource management and understanding of hydrological process for farming practices, ecosystem management and hydrologic engineering. This study has developed three machine learning algorithms, namely the relevance vector machine (RVM), extreme learning machine (ELM) and multivariate adaptive regression spline (MARS) for the prediction of E using five predictor variables, incident solar radiation (S), maximum temperature (T max), minimum temperature (T min), atmospheric vapor pressure (VP) and precipitation (P). The RVM model is based on the Bayesian formulation of a linear model with appropriate prior that results in sparse representations. The ELM model is computationally efficient algorithm based on Single Layer Feedforward Neural Network with hidden neurons that randomly choose input weights and the MARS model is built on flexible regression algorithm that generally divides solution space into intervals of predictor variables and fits splines (basis functions) to each interval. By utilizing random sampling process, the predictor data were partitioned into the training phase (70 % of data) and testing phase (remainder 30 %). The equations for the prediction of monthly E were formulated. The RVM model was devised using the radial basis function, while the ELM model comprised of 5 inputs and 10 hidden neurons and used the radial basis activation function, and the MARS model utilized 15 basis functions. The decomposition of variance among the predictor dataset of the MARS model yielded the largest magnitude of the Generalized Cross Validation statistic (≈0.03) when the T max was used as an input, followed by the relatively lower value (≈0.028, 0.019) for inputs defined by the S and VP. This confirmed that the prediction of E utilized the largest contributions of the predictive features from the T max, verified emphatically by sensitivity analysis test. The model performance statistics yielded correlation coefficients of 0.979 (RVM), 0.977 (ELM) and 0.974 (MARS), Root-Mean-Square-Errors of 9.306, 9.714 and 10.457 and Mean-Absolute-Error of 0.034, 0.035 and 0.038. Despite the small differences in the overall prediction skill, the RVM model appeared to be more accurate in prediction of E. It is therefore advocated that the RVM model can be employed as a promising machine learning tool for the prediction of evaporative loss.  相似文献   

19.
It is proposed to determined minimums of the 11-year solar cycles based on a minimal flux of the large-scale open solar magnetic field. The minimal fluxes before the finished cycle 23 (Carrington rotation CR 1904) and the started cycle 24 (CR 2054, April 2007) were equal to 1.8 × 1022 and 1.2 × 1022 μs, respectively. The long-term tendency toward an approach to a deep minimum of solar activity is confirmed. On the assumption that magnetic flux variations from minimums to maximums are proportional to each other, the anticipated value of the maximal Wolf number during cycle 24 is estimated as W max = 80.  相似文献   

20.
The distribution of the ionospheric currents during the geomagnetic storms of November 20–21, 2003, November 7–8, 2004, and November 9–10, 2004, depending on the IMF B y component, has been studied based on the data from the global network of magnetic stations. It has been indicated that, during geomagnetic disturbances, the westward electrojet intensity maximum is localized in the evening sector at IMF B y < 0 and in the morning sector at IMF B y > 0. The region of the westward electrojet intensity maximum shifts to morning hours with increasing positive B y values. Thus, the IMF azimuthal component forms not only the magnetospheric convection pattern during magnetic storms but is also responsible for the longitudinal position of ionospheric structures.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号