共查询到20条相似文献，搜索用时 31 毫秒
1.
Devendraa Siingh A. K. Singh R. P. Patel Rajesh Singh R. P. Singh B. Veenadhari Madhuparna Mukherjee 《Surveys in Geophysics》2008,29(6):499-551
Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and
mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many efforts
have been made towards understanding lightning, thunderstorms and their consequences. Recent observations of optical phenomena
above an active lightning discharge along with the availability of modern technology both for data collection and data analysis
have renewed interest in the field of thunderstorms and their consequences in the biosphere. In this paper, we review the
electrification processes of a thunderstorm, lightning processes and their association with global electric circuit and climate.
The upward lightning discharge can cause sprites, elves, jets, etc. which are together called transient luminous events. Their
morphological features and effects in the mesosphere are reviewed. The wide spectrum of electromagnetic waves generated during
lightning discharges couple the lower atmosphere with the ionosphere/magnetosphere. Hence various features of these waves
from ULF to VHF are reviewed with reference to recent results and their consequences are also briefly discussed. 相似文献
2.
3.
A theory of electromagnetic radiation generation by random electric discharges in the troposphere and VHF radiowave scattering by these discharges has been developed. The discharge model, which makes it possible to calculate the spatiotemporal distribution of the discharge channel conductivity depending on the electric current value in this discharge, has been obtained. The electromagnetic radiation spectrum in the troposphere occupied by random discharges has been calculated. VHF electromagnetic wave scattering by random electric discharges in the troposphere has been considered. Equations have been derived, and the method for calculating the average value of the electromagnetic wave field scattered by random discharges has been developed. The calculations indicated that the scattered wave field amplitude is much larger than the diffraction wave field amplitude behind the horizon. The theoretical results agree with the observations of the electromagnetic radiation and VHF transmitter signals behind the horizon relative to the earthquake epicenter during the earthquake preparation. 相似文献
4.
HUANG Suiliang 《国际泥沙研究》1998,(2)
ＶＡＲＩＡＴＩＯＮＳＯＦＷＡＴＥＲＳＵＲＦＡＣＥＧＲＡＤＩＥＮＴＡＮＤＶＥＬＯＣＩＴＹＤＩＳＴＲＩＢＵＴＩＯＮＣＡＵＳＥＤＢＹＷＡＴＥＲＪＥＴＳＨＵＡＮＧＳｕｉｌｉａｎｇ１ＡＢＳＴＲＡＣＴＵｓｉｎｇｆｌｕｍｅｅｘｐｅｒｉｍｅｎｔｓ,ｔｈｉｓｐａｐｅｒ... 相似文献
5.
L. P. Babich 《Geomagnetism and Aeronomy》2007,47(5):664-670
The results of the experiments, during which we revealed that the flux of neutrons in the atmosphere increases in correlation with electromagnetic pulses of lightning discharges, have been analyzed. The mechanisms of charged particle acceleration and nuclear reactions that can be responsible for neutron generation have been analyzed. It has been indicated that the probability of nuclear synthesis reactions in a lightning channel, which is traditionally considered as the source of neutrons in a thunderstorm atmosphere, is extremely low. The generation of neutrons in thunderstorm electric fields is related to photonuclear reactions in gigantic upward atmospheric discharges caused by relativistic runaway electron bremsstrahlung. 相似文献
6.
7.
利用闪电宽带干涉仪系统对闪电的观测表明，地闪和云闪的云内闪电通道都存在双向发展的特征. 闪电在云中负电荷区域初始激发以后，在通道两端发生向不同方向同时发展的击穿过程. 这两种击穿过程均产生较强的辐射，且辐射频谱特征十分相似，表明云内闪电通道两端发生的击穿过程可能均为负击穿过程. 相应电场变化表明闪电通道双向发展期间伴随着负电荷的向上转移. 这一观测事实与Kasemir早期提出的闪电通道双向发展的概念有一定的差异. 相似文献
8.
A field study evaluating wetted radius (Wr), downward depth (Dd), and upward movement (Um) under different emitter discharges and lateral depths was conducted. Four emitter discharges (2, 4, 8, and 16 L/h) and four lateral depths (0, 10, 20, and 30 cm) were tested in a clay loam soil. Relationships were found between the emitter discharge and lateral depth versus Wr, Dd, and Um. Wetting area at the surface occurs under different emitter discharges and lateral depths except at 30 cm lateral depth. At lateral depth of 0 and 10 cm, Wr and emitter discharge were positively correlated. The Dd was not affected by emitter discharge except for laterals installed at 20 cm depth. At 30 cm lateral depth, the correlations between each of Wr, Um, and Dd with emitter discharge were poor. The ratios of Wr/Dd and Um/Dd, with respect to emitter position, were less than unity over different emitter discharges and lateral depths. These results shed some light on the design of subsurface drip irrigation scheme so that the spacing between emitters should be determined based on the lateral depths and discharge of emitters. Evaporation losses were negligible for the 30‐cm‐lateral depth since the upward moisture movement has not reached the soil surface area at all discharge rates tested in the study. 相似文献
9.
The aim of this study is to investigate tide–surge interaction in narrow channels with complex and relatively shallow topography. A high-resolution depth-integrated tidal and storm surge model has been implemented for the Tjeldsund channel which is an important sailing lane in northern Norway. A horizontal grid resolution down to 50 m is applied in order to represent the complex bottom topography and the formation of jets and small-scale eddies. Two typically storm surge events in December 2004 have been examined in detail. The tide–surge interaction is found to influence the generation of higher harmonics and the formation of eddies in the current field. In some cases, the magnitude of storm surge currents may reach the same magnitude as the tidal currents enhancing the formation of jets and eddies. 相似文献
10.
In recent years the gas hydrothermal activity of Ebeko Volcano has been characterized by a constant heat flow and a constant chemical composition of water and fumarole gases. The volcano’s activity suddenly increased on January 27, 2005. Two high-output steam-gas jets 5 m across formed in the Active Funnel of the North Crater. A new high-output, high-temperature, fumarole field originated in the funnel in July 2005. Changes have been recorded in the chemical composition of fumarole gases. Ratios between individual components of the gas were calculated, with the ratios being geochemical precursors of eruptions for the volcano under study. Based on these results and on the very fact of increased fumarole activity on Ebeko, an intermediate-term forecast of explosive eruptions has been developed. Atmospheric contamination by a toxic gas (hydrogen sulfide) is described. It was previously thought that toxic gases pose a short-lived threat only to the population of the town of Severo-Kuril’sk because of frequent strong winds prevailing there. It is shown that the presence of a snow cover during increased activity on Ebeko sharply enhances the hazard of contamination by toxic gases, the hazard being constant both on the volcano itself and in the Severo-Kuril’sk area. 相似文献
11.
Based on subsurface wave energy flows calculated in the previous paper for strong motion records at 30 vertical array sites by assuming vertical propagation of SH waves, upward energy ratios between layers have been correlated to corresponding impedance ratios. This indicates that the upward energy tends to decrease almost in proportion to the power of 0.70 of the impedance ratio from deep-seated stiff rock (equivalent to seismological bedrock) to soft soil near ground surface. The upward energies at the seismological bedrock have been estimated from the observed energy at the deepest level for all vertical array sites by using this relationship and plotted versus hypocentral distances. 相似文献
12.
Noor Azlinda Ahmad M. Fernando Z.A. Baharudin M. Rahman V. Cooray Ziad Saleh Joseph R. Dwyer Hamid K. Rassoul 《Journal of Atmospheric and Solar》2010,72(2-3):143-150
In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as ‘small’, ‘medium’ and ‘large’, depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same. 相似文献
13.
Guang-ming Chen Jiyao Xu Wenbin Wang Jiuhou Lei Yue Deng 《Journal of Atmospheric and Solar》2009,71(8-9):967-974
O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from electron density profiles retrieved from CHAMP radio occultation (RO) measurements. The velocities and fluxes from January 2002 to December 2003 at low- and mid-latitudes have been statistically analyzed. The results show that daytime diffusive fluxes changed gradually from downward to upward as altitude increases. The largest values of the upward diffusive fluxes and velocities occurred at around ±25° geomagnetic latitude. During solstices the plasma fluxes in the winter hemisphere were larger than those in the summer hemisphere. 相似文献
14.
James D. L. White 《Bulletin of Volcanology》1996,58(4):249-262
The subaqueous phases of an eruption initiated approximately 85 m beneath the surface of Pleistocene Lake Bonneville produced
a broad mound of tephra. A variety of distinctive lithofacies allows reconstruction of the eruptive and depositional processes
active prior to emergence of the volcano above lake level. At the base of the volcano and very near inferred vent sites are
fines-poor, well-bedded, broadly scoured beds of sideromelane tephra having local very low-angle cross-stratification (M1
lithofacies). These beds grade upward into lithofacies M3, which shows progressively better developed dunes and cross-stratification
upsection to its uppermost exposure approximately 10 m below syneruptive lake level. Both lithofacies were emplaced largely
by traction from relatively dilute sediment gravity flows generated during eruption. Intercalated lithofacies are weakly bedded
tuff and breccia (M2), and nearly structureless units with coarse basal layers above strongly erosional contacts (M4). The
former combines products of deposition from direct fall and moderate concentration sediment gravity flows, and the latter
from progressively aggrading high-concentration sediment gravity flows. Early in the eruption subaqueous tephra jetting from
phreatomagmatic explosions discontinuously fed inhomogeneous, unsteady, dilute density currents which produced the M1 lithofacies
near the vent. Dunes and crossbeds which are better developed upward in M3 resulted from interaction between sediment gravity
flows and surface waves triggered as the explosion-generated pressure waves and eruption jets impinged upon and occasionally
breached the surface. Intermingling of (a) tephra emplaced after brief transport by tephra jets within a gaseous milieu and
(b) laterally flowing tephra formed lithofacies M2 along vent margins during parts of the eruption in which episodes of continuous
uprush produced localized water-exclusion zones above a vent. M4 comprises mass flow deposits formed by disruption and remobilization
of mound tephra. Intermittent, explosive magma–water interactions occurred from the outset of the Pahvant eruption, with condensation,
entrainment of water and lateral flow marking the transformation from eruptive to "sedimentary" processes leading to deposition
of the mound lithofacies.
Received: 10 October 1995 / Accepted: 18 April 1996 相似文献
15.
V. G. Vorobjev V. B. Belakhovsky O. I. Yagodkina V. K. Roldugin M. R. Hairston 《Geomagnetism and Aeronomy》2008,48(2):154-164
The optical observations on Heiss Island and the ion drift measurements on the DMSP F8 satellite were used to study the aurora characteristics and ionospheric convection before and after SC registered at 2330 UT on January 13, 1988. It has been indicated that two zones of luminosity can be distinguished in morning-time auroras during the quiet period before SC: the soft zone with auroral arcs and the harder diffuse auroral zone (equatorward of the first zone). After SC, a gradual smooth activation of auroras in both zones was followed (4–5 min later) by a more abrupt intensification of diffuse luminosity and by the appearance of numerous bright discrete auroras throughout the sky. In the diffuse auroral zone, the variations in the luminosity intensity with a period of 6–7 min were observed after SC. Auroral and geomagnetic field pulsations are closely correlated. During the quiet period before SC, sunward convection was concentrated in the soft precipitation region in the form of jets located in the vicinity of auroral arcs. After SC, considerable sunward convection was observed in the diffuse auroral zone. Peaks of the upward ion drift velocity were registered in the vicinity of auroral arcs. 相似文献
16.
Measurements made with a new fast-response suspended sand sensor have for the first time enabled the turbulence characteristics of a natural sand suspension to be studied. Suspended sand concentration measurements, together with fast-response current measurements, were made 18 cm above a sandy bed under a strong tidal current. They showed a highly variable concentration field, dominated by clouds of sand which took 2 to 10 s to sweep past the sensor. The concentration spectrum had peak energy at a wavelength of about 3 m, and exhibited a −5/3 power dependence at high frequencies. Damping of the turbulence intensity of the current was observed when sand was suspended. A spectral approach produced more plausible values for the upward Reynolds flux of sediment than the direct covariance technique. The calculated upward fluxes were appreciably smaller than the settling fluxes around the time of maximum current, contrary to the expectation for an equilibrium concentration profile. The turbulence characteristics of the concentration field displayed marked similarities with standard results from atmospheric temperature measurements, strengthening assumptions commonly made in the prediction of sediment transport rates. 相似文献
17.
Short-lived plasma jets of various scales, from giant X-ray jets more than 300 Mm in extent to numerous small jets with sizes
typical of macrospicules, are the phenomena observed in the solar corona in extreme ultraviolet and X-ray emission. Small
jets are particularly prominent in polar coronal holes. They are close neighbors of tiny bright loops and coincide in time
with their sudden brightening and increase in size. The geometric shape of the jets and their location suggest that they arise
near singular null points of the coronal magnetic field. These points appear in coronal holes due to the emergence of small
bipolar or unipolar magnetic structures within large-scale unipolar cells. Polar jets show a distinct vertical plasma motion
in a coronal hole that introduces significant momentum and mass into the solar wind flow. Investigating the dynamics of polar
jets can elucidate certain details in the problem of fast solar wind acceleration. 相似文献
18.
A Lagrangian technique is developed and applied to calculate stratosphere-troposphere exchange in an extratropical cyclone. This exchange is computed from the potential vorticity or PV along trajectories, calculated from ECMWF circulation data. Special emphasis is put on the statistical significance of the results. The computed field of the cross-tropopause flux is dominated by elongated patterns of statistically significant large downward and small upward fluxes. The downward fluxes mainly occur in the lower part of the considered tropopause folds. The upward fluxes are found near the entrance of the folds, in the tropopause ridges. The ratio between the area averaged downward and upward cross-tropopause fluxes increases with increasing strength of the cyclone. Since the largest fluxes are shown to occur in the regions with the largest wind shear, where PV-mixing is thought to cause large cross-tropopause fluxes, the results are expected to be reliable, at least in a qualitative sense. The position of a tropopause fold along the northwest coast of Africa is confirmed by total ozone observations. The results indicate that the applied Lagrangian technique is an appropriate tool for diagnosing stratosphere-troposphere exchange. 相似文献
19.
In order to study the impact of produced water (PW) from a North Sea oil field on blue mussels (Mytilus edulis), chemical and biological markers were selected. A laboratory exposure (0.125%, 0.25% and 0.5% of PW) and a field study (6 stations 0.2-2 km from a PW discharge point) were conducted. In the laboratory study, PAH bioaccumulation increased in mussel soft tissue even at the lowest exposure dose. Micronuclei frequency demonstrated a dose-response pattern, whereas lysosomal membrane stability showed tendency towards a dose-response pattern. The same markers were assessed in the field study, biomarker analyses were consistent with the contamination level, as evaluated by mussel polycyclic aromatic hydrocarbons body burden. Overall, obtained results confirmed the value of an ecotoxicological approach for a scientifically sound characterisation of biological effects induced by offshore oilfield operational discharges. 相似文献
20.
S. O. Feofilaktov S. N. Rychagov Yu. Yu. Bukatov I. A. Nuzhdaev A. A. Nuzhdaev 《Journal of Volcanology and Seismology》2017,11(5):353-366
This paper is concerned with a discussion of a fundamental problem in geothermal research, that of reaching an understanding of the structure and physical nature of zones of thermal discharges, taking the Pauzhetka hydrothermal system as an example along with the eponymous geothermal field situated at the southern tip of Kamchatka. We combined geological and geophysical results from magnetic surveying, electrical surveying, gravity surveying, soil thermometry, pitting and well drilling in hydrothermal clay, to carry out a detailed study of a large zone of hydrothermal discharges in the structure of this hydrothermal system, that is, the East Pauzhetka thermal field. We identified a system of blocks that control aquifers, mineralization zones at the base of the sequence of hydrothermal clay, steam-charged and water-saturated volumes, and volumes where ascending hydrothermal brines circulate via fissures and pores. We hypothesize the existence of a shallow (a few tens of meters) top of a subintrusive body of an intermediate or basic composition. The intrusion of that body may have given rise to the formation of a tectono-magmatic uplift in the East Pauzhetka thermal field. The resulting geological and geophysical data stimulate multidisciplinary surveys of other areas in the Pauzhetka geothermal field and make their contribution to the solution of a major scientific and applied problem, which is to determine the source of heat for the field. 相似文献