共查询到20条相似文献，搜索用时 46 毫秒
1.
M. I. Divlekeev 《Geomagnetism and Aeronomy》2012,52(8):1044-1049
The observations of active region (AR) NOAA 10792 in the Ca II 8498 ? line with an ATB-1 solar telescope at the Sternberg State Astronomical Institute, Moscow State University (SSAI MSU) on July 30, 2005, are illustrated, and the events are analyzed using the data obtained on spacecraft. Three flares and accompanying coronal mass ejections (CMEs) are considered. It has been indicated that the beginning of the first compact CME lagged behind the flare onset by 3 min. Plasma ascended with acceleration that reached 0.4 km/s2 at the flare maximum. The matter was also apparently accelerated after the flare maximum, since an ejection could only appear at the edge of the occulting C 2 LASCO coronograph disk at 0557 UT when acceleration is about 0.5 km/s2. The second CME (of the halo type) leaded the beginning of the corresponding flare. 相似文献
2.
A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 1022 Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 1022 Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ～1022 Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines. 相似文献
3.
Ali A. Nowroozi 《Pure and Applied Geophysics》2010,167(12):1459-1474
The active faults near Tehran are capable of producing Mw magnitudes of 6.62?C7.23; at epicentral distances of 25?km from the active faults, and Mw?=?7.23, the peak ground horizontal acceleration, PGH, is between 386 and 730?cm/s2 and peak ground vertical acceleration, PGV, is between 192 and 261?cm/s2; the historic earthquake of the fourth century BC, Mw?=?7.16 produced the highest estimated PGH acceleration in Tehran, between 254 and 479?cm/s2 and PGV acceleration between 127 and 173?cm/s2. Earthquakes from 1909 to 2008, within 300?km from Tehran, are used for calculation of magnitude frequency relation, and results are applied to estimate PGH and PGV accelerations as a function of magnitudes for a set of fixed epicentral distance and site conditions; also as a function of epicentral distances for a set of fixed magnitudes and site conditions. Poisson??s distribution is used for probability calculation of PGH and PGV accelerations for several exposure times, site conditions and epicentral distances; accelerations with very high probability, near 1, are presented. At an epicentral distance of 10?km and exposure time of 450?years, in the northern part of Tehran, close to Mosha and the Northern Tehran faults, PGH acceleration is 800?C420?cm/s2 and PGV is 400?C220?cm/s2 with high probability. At an epicentral distance of 25?km and 1,000?years exposure time, PGH is 610?C320?cm/s2 and PGV is 310?C160?cm/s2 with high probability, where larger values are for soft soil and smaller values are for hard rock. 相似文献
4.
The results of a three-dimensional MHD simulation and data obtained using specialized spacecraft made it possible to construct
an electrodynamic model of solar flares. A flare results from explosive magnetic reconnection in a current sheet above an
active region, and electrons accelerated in field-aligned currents cause hard X rays on the solar surface. In this review,
we considered works where the boundary and initial conditions on the photosphere were specified directly from the magnetic
maps, obtained by SOHO MDI in the preflare state, in order to simulate the formation of a current sheet. A numerical solution
of the complete set of MHD equations, performed using the new-generation PERESVET program, demonstrated the formation of several
current sheets before a series of flares. A comparison of the observed relativistic proton spectra and the simulated proton
acceleration along a magnetic field singular line made it possible to estimate the magnetic reconnection rate during a flare
(∼107 cm s−1). Great flares (of the X class) originate after an increase in the active region magnetic flux up to 1022 Mx. 相似文献
5.
In order to investigate crustal structure beneath the eastern Marmara region, a seismic refraction survey was conducted across
the North Anatolian Fault (NAF) zone in north west Turkey. Two reversed profiles across two strands of the NAF zone were recorded
in the Armutlu Highland where a tectonically active region was formed by different continents. We used land explosions in
boreholes and quarry blasts as seismic sources. A reliable crustal velocity and depth model is obtained from the inversion
of first arrival travel times. The velocity-depth model will improve the positioning of the earthquake activities in this
active portion of the NAF. A high velocity anomaly (5.6–5.8 km s−1) in the central highland of Armutlu block and the low velocity (4.90 km s−1) pattern north of Iznik Lake are the two dominant features. The crustal thickness is about 26 ± 2 km in the north and increases
to about 32 ± 2 km beneath the central Armutlu block in the south. P-wave velocities are about 3.95 km s−1 to 4.70 km s−1 for the depth range between about 1 km and 5 km in the upper crust. The eastern Marmara region has different units of upper
crust with velocities varying with depth to almost 8 km. The high upper crust velocities are associated with Armutlu metamorphic
rocks, while the low velocity anomalies are due to unconsolidated sedimentary sequences. The western side of Armutlu block
has complex tectonics and is well known for geothermal sources. If these sources are continuous throughout the portions of
the crust, it may be associated with a granitic intrusion and deformation along the NAF zone. That is, the geothermal sources
associated with the low velocity may be due to the occurrence of widespread shear heating, even shear melting. The presence
of shear melting may indicate the presence of crustal fluid imposed by two blocks of the NAF system. 相似文献
6.
A. S. N. Murty H. C. Tewari Prakash Kumar P. R. Reddy 《Pure and Applied Geophysics》2005,162(12):2409-2431
A 2-D subcrustal velocity model for the central Indian continental lithosphere has been derived by travel time and relative
amplitude modeling of a digitally normalized analog seismic record section of the Hirapur-Mandla DSS profile, using a ray-tracing
technique. Some prominent wave groups with apparent velocities slightly higher than the Moho reflection phase (PMP) are identified on the normalized record sections assembled with a reduction velocity of 6 km s−1. We interpret these phases as the wide-angle reflections from subcrustal lithospheric boundaries. Comparison of synthetic
seismograms with the observed record section shows that the observed phases cannot be explained either by multiples or by
the P-to-S converted phase (PMS) from the Moho. Subcrustal velocity models either with a velocity increase or with a single low velocity layer (LVL) also
do not provide a satisfactory fit. We infer that a subcrustal velocity model with two alternate LVLs (velocity 7.2 km s−1), separated by a 6-km thick high velocity layer (velocity 8.1 km s−1), can satisfy both the observed travel times and amplitudes. The prominent reflection phases are modeled at depths of 49,
51, 57 and 60 km. It is inferred that the subcrustal lithosphere in the central Indian region has a lamellar structure with
varying structural and mechanical properties. The alternating LVLs, occurring at relatively shallow depths below Moho, may
be associated with the zones of weakness and lower viscosity suggesting continued mobility, with a possible thermal source
in the upper mantle. This explains the source of observed high heat flow values in the central Indian region. 相似文献
7.
The specific features in the development of an X1 solar flare, which occurred on September 22, 2011, and was registered with the Atmospheric Imaging Assembly (AIA) device onboard the Solar Dynamics Observatory (SDO) in the UV line (λ = 304 Å, He II), are analyzed. During the flare, which lasted about 12 h, cold plasma was sucked up with an increasing velocity from a very distant region into the low-lying hot region of flare energy release along a flat helical trajectory. This phenomenon fundamentally differs from a surge ejection, when matter previously ejected from the flare region returns to the flare hot zone under the action of gravity. Suction of cold plasma “from outside” into the hot flare region is interpreted in the scope of the rope flare mechanism, according to which an extremely inhomogeneous plasma density distribution in the cross-section originates in an emerging magnetic rope. In the region with a sharply decreased density (which is the suction region), the drift velocity in the current chanel can reach the ion thermal velocity, which inevitably results in the excitation of plasma turbulence and anomalous resistance, i.e., in the development of a flare. 相似文献
8.
9.
The following results have been achieved in this work. The distribution of the recurrence times of solar flare events is generally lognormal. The typical flare recurrence times at the cycle 23 minimum and maximum are different: the average times (100–200 min) are most typical of the maximum; at the same time, the minimum is simultaneously characterized by short (several tens of seconds) and long (from several hundreds to a thousand of minutes). The minimal flare recurrence time tends to decrease in an active region with increasing sunspot group area in this region. The average flare recurrence times in an active region have typical values of 120m, 210m, 300m, 400m, and 530m, which is close to the typical periods of long-period sunspot oscillations. The total number of flares in an active region depends on the sunspot area in this region and the flare energy release rate. 相似文献
10.
Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm 总被引：1，自引：0，他引：1
T. K. Yeoman J. A. Davies N. M. Wade G. Provan S. E. Milan 《Annales Geophysicae》2000,18(9):1073-1087
On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s-1, whilst the eastward edge also expands eastward at ~0.6 km s-1. Typical flows of 600 m s-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s-1 and 10–20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it. 相似文献
11.
A. Joshi 《Journal of Seismology》2001,5(4):499-518
Garhwal Himalaya has been rocked by two major earthquakes in the span of just eight years, viz. Uttarkashi earthquake of 20th Oct, 1991 and Chamoli earthquake of 28th March, 1999. Chamoli earthquake of March 28, 1999 was recorded at 11 different stations of a strong motion array installed in the epicentral region. The maximum peak ground acceleration (353 cm/s2) was recorded at an accelerograph located at Gopeshwar. The data from eleven stations has been used for comparison with the simulated acceleration envelopes due to a model of the rupture responsible for this earthquake. For simulation of acceleration envelope the method of Midorikawa (1993) has been modified for its applicability to Himalayan region. This method has earlier been used by Joshi and Patel (1997) and Joshi (1999) for the studyof Uttarkashi earthquake of 20th Oct, 1991. The same method has been used for study of Chamoli earthquake. Layered earth crust has been introduced in place of homogeneous one in this method. The model of rupture is placed at a depth of 12 km below the Munsiari thrust for modelling Chamoli earthquake. Peak ground acceleration was calculated from simulated acceleration envelope using layered as well as homogeneous earth crust. For the rupture placed in a layered crust model peak ground acceleration of order 312 cm/s2 was simulated at Gopeshwar which is quite close to actually recorded value. The comparison of peak ground acceleration values in terms of root mean square error at eleven stations suggests that the root mean square error is reduced by inclusion of a layered earth crust in place of homogeneous earth crust. 相似文献
12.
The occurrence of PMSEs with time of day shows a semi-diurnal variation with minima at 8 and 20 h LT. PMSE layers observed for more than 30 min show an average rate of descent of 2 km h−1. These characteristics suggest the influence of tidal winds. When the observed steady wind and diurnal and semi-diurnal tides at EISCAT are added, the overall magnitude shows a time-variation which matches the occurrence of PMSEs, and the observed rate of descent, approximately 2 km h−1. Atmospheric gravity waves also contribute to the velocity of the neutral wind. When the wave reinforces the background wind, the PMSEs are stronger and descend more rapidly, but when the wave-related velocity opposes the background wind the PMSE is weaker and it descends more slowly. 相似文献
13.
Recent seismic activity in southern Lebanon is of particular interest since the tectonic framework of this region is poorly understood. In addition, seismicity in this region is very infrequent compared with the Roum fault to the east, which is seismically active. Between early 2008 and the end of 2010, intense seismic activity occurred in the area. This was manifested by several swarm-like sequences and continuous trickling seismicity over many days, amounting in total to more than 900 earthquakes in the magnitude range of 0.5?≤?M d?≤?5.2. The region of activity extended in a 40-km long zone mainly in a N-S direction and was located about 10 km west of the Roum fault. The largest earthquake, with a duration magnitude of M d?=?5.2, occurred on February 15, 2008, and was located at 33.327° N, 35.406° E at a depth of 3 km. The mean-horizontal peak ground acceleration observed at two nearby accelerometers exceeded 0.05 g, where the strongest peak horizontal acceleration was 55 cm/s2 at about 20 km SE of the epicenter. Application of the HypoDD algorithm yielded a pronounced N-S zone, parallel to the Roum fault, which was not known to be seismically active. Focal mechanism, based on full waveform inversion and the directivity effect of the strongest earthquake, suggests left-lateral strike-slip NNW-SSE faulting that crosses the NE-SW traverse faults in southern Lebanon. 相似文献
14.
The 2-D crustal velocity model along the Hirapur-Mandla DSS profile across the Narmada-Son lineament in central India (Murty et al., 1998) has been updated based on the analysis of some short and discontinuous seismic wide-angle reflection phases. Three layers, with seismic velocities of 6.5–6.7, 6.35–6.40 and 6.8 km s–1, and upper boundaries located approximately at 8, 17 and 22 km depth respectively, have been identified between the basement (velocity 5.9 km s–1) and the uppermost mantle (velocity 7.8 km s–1). The layer with 6.5–6.7 km s–1 velocity is thin and is less than 2-km deep between the Narmada north (at Katangi) and south (at Jabalpur) faults. The upper crust shows a horst feature between these faults, which indicates that the Narmada zone acts as a ridge between two pockets of mafic intrusion in the upper crust. The Moho boundary, at 40–44 km depth and the intra-crustal layers exhibit an upwarp suggesting that the Narmada faults have deep origins, involving deep-seated tectonics. A smaller intrusive thickness between the Narmada faults, as compared to those beyond these faults, suggests that the intrusive activities on the two sides are independent. This further suggests that the two Narmada faults may have been active at different geological times. The seismic model is constrained by 2-D gravity modeling. The gravity highs on either side of the Narmada zone are due to the effect of the high velocity/high density mafic intrusion at upper crustal level. 相似文献
15.
A. S. N. Murty B. Rajendra Prasad P. Koteswara Rao S. Raju T. Sateesh 《Pure and Applied Geophysics》2010,167(3):233-251
2-D shallow velocity structure is derived by travel-time inversion of the first arrival seismic refraction and wide-angle reflection data along the E–W trending Narayanpur–Nandurbar and N–S Kothar–Sakri profiles, located in the Narmada–Tapti region of the Deccan syneclise. Deccan volcanic (Trap) rocks are exposed along the two profiles. Inversion of seismic data reveals two layered velocity structures above the basement along the two profiles. The first layer with a P-wave velocity of 5.15–5.25 km s?1 and thickness varying from 0.7–1.5 km represents the Deccan Trap formation along the Narayanpur–Nandurbar profile. The Trap layer velocity ranges from 4.5 to 5.20 km s?1 and the thickness varies from 0.95 to 1.5 km along the Kothar–Sakri profile. The second layer represents the low velocity Mesozoic sediments with a P-wave velocity of 3.5 km s?1 and thickness ranging from about 0.70 to 1.6 km and 0.55 to 1.1 km along the E–W and N–S profiles, respectively. Presence of a low-velocity zone (LVZ) below the volcanic rocks in the study area is inferred from the travel-time ‘skip’ and amplitude decay of the first arrival refraction data together with the prominent wide-angle reflection phase immediately after the first arrivals from the Deccan Trap formation. The basement with a P-wave velocity of 5.8–6.05 km s?1 lies at a depth ranging from 1.5 to 2.45 km along the profiles. The velocity models of the profiles are similar to each other at the intersection point. The results indicate the existence of a Mesozoic basin in the Narmada–Tapti region of the Deccan syneclise. 相似文献
16.
M. A. Livshits 《Geomagnetism and Aeronomy》2009,49(8):1069-1071
Data on high-energy processes on the Sun are summarized. We refine the classification of flares and substantiate the view
that a coronal mass ejection and a flare proper are manifestations of the same common process, at least for the most powerful
events. Next, we analyze data on the acceleration of electrons (RHESSI, Mars Odyssey) and protons. The existence of two peaks
of hard X-ray emission spaced 10–20 min apart and the evolution of its spectra are shown to be indicative of two acceleration
episodes. We have analyzed the spectra of 172 proton increases identified with the ratio of the proton fluxes at energies
above 10 and 100 MeV near the Earth. These spectra turn out to be virtually the same for most of the large flares under favorable
conditions for the escape of particles from the corona and their propagation in the interplanetary space. This is an argument
for the invariance of the main features of efficient particle acceleration in powerful events. This process takes place at
the explosive phase of a flare and its source is located low, immediately above the chromosphere, in the region adjacent to
sunspots. There is a reason to believe that, in this case, a rapid simultaneous acceleration of electrons and protons takes
place with the capture of some fraction of the particles into magnetic traps. However, there exist a few events in which an
additional number of protons with energies as high as 10–30 MeV escape from the corona at the post-eruptive phase of flare
development. Analysis of these cases with softer particle spectra more likely suggests an additional particle acceleration
at coronal heights (about 30 000 km) than the facilitation of particle escape from magnetic traps. We estimate the contribution
from the proton flux at an energy above 10 MeV arising at the post-eruptive phase of a flare to the total particle flux at
the maximum of a proton increase and discuss possible particle acceleration mechanisms at significant coronal heights. 相似文献
17.
《Journal of Atmospheric and Solar》2007,69(16):1936-1983
The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H+, He+ and O+ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to ∼50,500 km, and revealed several important features in the polar wind that are unexpected from “classical” polar wind theories. These include the day–night asymmetry in polar wind velocity, which is 1.5–2.0 times larger on the dayside; appreciable O+ flow at high altitudes, where the velocity at 5000–10,000 km is of 1–4 km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5–2. These features are attributable to a number of “non-classical” polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of ∼0.2–0.3 eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (<4000 km for H+). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H+ and smallest for O+. Near solar maximum, H+, He+, and O+ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000 km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized “non-polar-wind” ion such as a low-energy “cleft ion fountain” ion that has convected into a polar wind flux tube from an energized “polar-wind” ion that is accelerated locally by “non-classical” polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O+ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H+ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He+ and other minor ion species in the polar wind population. 相似文献
18.
Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock 相似文献
19.
Morgachev A. S. Tsap Yu. T. Smirnova V. V. Motorina G. G. 《Geomagnetism and Aeronomy》2018,58(8):1113-1122
Geomagnetism and Aeronomy - Millimeter (93 and 140 GHz) emission of the М6.4 solar flare detected on April 2, 2017 in the NOAA 12644 active region by the RT-7.5 telescope of the Bauman Moscow... 相似文献
20.
JIAN PING WU RONG SHENG ZENG YUE HONG MING Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):677-686
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