共查询到20条相似文献，搜索用时 31 毫秒
1.
The relation between the long-term variations in the thunderstorm VLF radio noise intensity and solar activity in 1979–2006
has been studied. The sunspot number (the Wolf number) was used as a parameter characterizing solar activity. The intensity
of VLF noise registered in Yakutsk characterizes thunderstorm activity in Eastern Siberia (0100–0500 UT) and in the African
thunderstorm center (1300–1700 UT). Using the results of a correlation analysis, it has been found that thunderstorm activity
in Eastern Siberia and in the African world centre is in antiphase with a change in the sunspot number. The highest anticorrelation
coefficients between solar activity and thunderstorm discharge intensity were obtained for thunderstorms in Eastern Siberia.
In this case the maximal correlation coefficients (R = −0.59 and −0.75) were obtained for the average monthly values of the VLF radio noise intensity in August, measured at 0400
UT and 1600 UT, respectively. 相似文献
2.
M. G. Ogurtsov 《Geomagnetism and Aeronomy》2007,47(1):85-93
Present-day data on 14C and 10Be concentration in natural archives have been statistically analyzed. It has been established that it is difficult to extract information about solar activity variations on long (several Myr and longer) and, especially, short (to 30 years) time scales using radiocarbon data. It has been indicated that beryllium series bear reliable information about short-term, secular, and, probably, 1000-year variations in solar activity. Moreover, 10Be concentration in polar ice can also be used to study the internal dynamics of solar activity. It has been concluded that beryllium data are more promising than radiocarbon ones from the viewpoint of solar paleoastrophysics. 相似文献
3.
V. I. Larkina 《Geomagnetism and Aeronomy》2010,50(3):320-328
The complex geophysical pattern of the development of geomagnetic storm in VLF emissions has been studied based on the satellite
data. It has been established that the variations in the LF noise emission intensity (0.1–20.0 kHz) and the energetic electron
(E ≥ 40 keV) flux density reflect the processes of magnetospheric plasma reconstruction during geomagnetic disturbances. It
has been indicated that a distinct structure of the inner and outer radiation belts is observed under quiet conditions, and
the VLF emission maximum was registered at L = 4–5. The inner boundary of the outer radiation belt shifted to lower latitudes, the intensity of the noise VLF emissions
increased, and the intensity maximum was displaced to L = 2.5–3.5 during the geomagnetic storm, when the energetic electron flux density increased. The VLF noise spectrum widened
toward higher frequencies. The VLF noise level continued increasing, the noise maximum shifted to L = 4–5, and the fluxes of precipitating electrons abruptly increased during the storm recovery phase, when the density of
the flux of quasitrapped electrons remained increased for a long time. 相似文献
4.
An analysis of the geomagnetic field variations between 3 min and 2 h at L’Aquila (L=1.6) shows that the power level in the low-frequency range (i.e. for periods longer than approximately 10 min) at solar maximum (1989/90) is much higher than at solar minimum (1985/86). Conversely, at solar minimum, it emerges that there is a greater relative importance of fluctuations with periods smaller than 10 min which might be related to the greater percentage of solar wind speeds greater than approximately 540 km s−1. Diurnal, seasonal and solar cycle variations of both the high- and the low-frequency power are also discussed. We found that several aspects of these variations might be correlated with ionospheric features such as the ionisation of the F2 layer and the location and the intensity of the S current system. 相似文献
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7.
V. A. Dergachev P. B. Dmitriev O. M. Raspopov H. Jungner 《Geomagnetism and Aeronomy》2006,46(1):118-128
Direct and indirect data on variations in cosmic rays, solar activity, geomagnetic dipole moment, and climate from the present to 10–12ka ago (the Holocene Epoch), registered in different natural archives (tree rings, ice layers, etc.), have been analyzed. The concentration of cosmogenic isotopes, generated in the Earth’s atmosphere under the action of cosmic ray fluxes and coming into the Earth archives, makes it possible to obtain valuable information about variations in a number of natural processes. The cosmogenic isotopes 14C in tree rings and 10Be in ice layers, as well as cosmic rays, are modulated by solar activity and geomagnetic field variations, and time variations in these concentrations gives information about past solar and geomagnetic activities. Since the characteristics of natural reservoirs with cosmogenic 14C and 10Be vary with climate changes, the concentrations of these isotopes also inform about climate changes in the past. A performed analysis indicates that cosmic ray flux variations are apparently the most effective natural factor of climate changes on a large time scale. 相似文献
8.
《Journal of Atmospheric and Solar》2002,64(5-6):617-624
The variations in the fluxes of the relativistic electrons in the planetary radiation belts are due to a set of different physical processes which violate one or more of the adiabatic invariants. We survey the mechanisms which break down these invariants and investigate the time scales for the processes and the resulting effects on the observed fluxes. The mechanisms include (a) sudden deformation of the magnetic field configuration, (b) radial diffusion due to low-frequency electromagnetic oscillations, (c) transit-time damping due to fast waves and (d) diffusion due to electromagnetic ion-cyclotron (emic) or whistler waves. It is indicated how the waves which interact resonantly with the relativistic electrons are responsible for enhancement in the radiative spectra of the gyrosynchrotron emissions in the GHz frequency range and the X-ray bremsstrahlung emissions at the MeV energy range. 相似文献
9.
Magnetic Pulsations: Their Sources and Relation
to Solar Wind and Geomagnetic Activity 总被引：1，自引：1，他引：0
Ultra low frequency (ULF) waves incident on the Earth are produced by processes in the magnetosphere and solar wind. These
processes produce a wide variety of ULF hydromagnetic wave types that are classified on the ground as either Pi or Pc pulsations
(irregular or continuous). Waves of different frequencies and polarizations originate in different regions of the magnetosphere.
The location of the projections of these regions onto the Earth depends on the solar wind dynamic pressure and magnetic field.
The occurrence of various waves also depends on conditions in the solar wind and in the magnetosphere. Changes in orientation
of the interplanetary magnetic field or an increase in solar wind velocity can have dramatic effects on the type of waves
seen at a particular location on the Earth. Similarly, the occurrence of a magnetospheric substorm or magnetic storm will
affect which waves are seen. The magnetosphere is a resonant cavity and waveguide for waves that either originate within or
propagate through the system. These cavities respond to broadband sources by resonating at discrete frequencies. These cavity
modes couple to field line resonances that drive currents in the ionosphere. These currents reradiate the energy as electromagnetic
waves that propagate to the ground. Because these ionospheric currents are localized in latitude there are very rapid variations
in wave phase at the Earth’s surface. Thus it is almost never correct to assume that plane ULF waves are incident on the Earth
from outer space. The properties of ULF waves seen at the ground contain information about the processes that generate them
and the regions through which they have propagated. The properties also depend on the conductivity of the Earth underneath
the observer. Information about the state of the solar wind and the magnetosphere distributed by the NOAA Space Disturbance
Forecast Center can be used to help predict when certain types and frequencies of waves will be observed. The study of ULF
waves is a very active field of space research and much has yet to be learned about the processes that generate these waves. 相似文献
10.
The model of variations in the orthohelium 1083 nm emission intensity has been constructed based on the measurements at different stations. The analytical approximations of the nighttime intensity variations depending on the phase age of the Moon, season, solar activity during the 11-year cycle, and geomagnetic disturbances are presented. 相似文献
11.
We discuss the results of an analysis of digital high-sensitivity ground-based observations of very low frequency (VLF) emissions, carried out in Northern Finland (L = 5.3) in May–June 2012. During this period of time, we found that three high-speed solar wind streams approached the Earth’s magnetosphere and at the front of these fluxes long-lasting intense daytime bursts of VLF emissions were generated in two frequency bands: above and below ～2.5 kHz. At frequencies above ～2.5–3.0 kHz, there were VLF hiss waves, the temporal structure of which consisted of a quasi-periodic sequence of separate stronger spots of noise signals. The low-frequency band was represented by chorus waves, superimposed on intense hiss emissions at frequencies below ～1.5 kHz. The high-frequency (f > 2.5 kHz) waves were elliptic and, predominately, left-hand polarized and the low-frequency waves were right-hand polarized. It was supposed that high-frequency VLF hiss waves were generated at L < 5 and VLF chorus waves were generated at L > 5. We discuss a possible scenario of the generation and propagation of the VLF emissions observed. 相似文献
12.
Pauline Green 《Pure and Applied Geophysics》1972,101(1):194-204
Summary Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given. 相似文献
13.
The empirical model of variations in the emitting layer height and parameters has been developed based on an analysis of the rocket measurements of the vertical distributions in the 630 nm intensity. The dependences on the solar zenith angle during a day are most substantial. This dependence is responsible for the character of seasonal variations at different latitudes. The height of the emitting layer increases with increasing solar activity, reflecting a temperature rise in the upper atmosphere. The negative trend—0.35 km yr?1 in the interval 1964–1990—has been revealed. 相似文献
14.
Signatures of thunderstorms in the variations of the secondary cosmic rays registered in Mexico City
We studied the effect of thunderstorms (TS) in the intensity variations of the electromagnetic and muon components of the Cosmic Rays during the year 2004, a year of minimum solar activity. We analyzed the variations in the counting rates of the upper and lower scintillators of the muon telescope installed in Mexico City at times of reported TS and compared those with variations during quiet times. The data were filtered to eliminate long trends, then a wavelet spectrum was calculated, searching for the temporal evolution of diverse periods of high significance; recurrent periodicities and total power distributions were obtained. The results show variations of short period whose main periodicities are arranged in a distribution where the most important are the shortest periodicities. These may be associated to the electric fields of the TS. Significant long period variations were found too, these could be due to other processes linked to rainstorms. No systematic effect on the power of variations due to TS was found. 相似文献
15.
Magnetohydrodynamic compressive fluctuations of the interplanetary plasma in the region from 0.3 to 1 AU have been characterized in terms of their polytropic index. Following Chandrasekhar’s approach to polytropic fluids, this index has been determined through a fit of the observed variations of density and temperature. At least three different classes of fluctuations have been identified: (1) variations at constant thermal pressure, in low-speed solar wind and without a significant dependence on distance, (2) adiabatic variations, mainly close to 1 AU and without a relevant dependence on wind speed, and (3) variations at nearly constant density, in fast wind close to 0.3 AU. Variations at constant thermal pressure are probably a subset of the ensemble of total-pressure balanced structures, corresponding to cases in which the magnetic field magnitude does not vary appreciably throughout the structure. In this case the pressure equilibrium has to be assured by its thermal component only. The variations may be related to small flow-tubes with approximately the same magnetic-field intensity, convected by the wind in conditions of pressure equilibrium. This feature is mainly observed in low-velocity solar wind, in agreement with the magnetic topology (small open flow-tubes emerging through an ensemble of closed structures) expected for the source region of slow wind. Variations of adiabatic type may be related to magnetosonic waves excited by pressure imbalances between contiguous flow-tubes. Such imbalances are probably built up by interactions between wind flows with different speeds in the spiral geometry induced by the solar rotation. This may account for the fact that they are mainly found at a large distance from the sun. Temperature variations at almost constant density are mostly found in fast flows close to the sun. These are the solar wind regions with the best examples of incompressible behaviour. They are characterized by very stable values for particle density and magnetic intensity, and by fluctuations of Alfvénic type. It is likely that temperature fluctuations in these regions are a remnant of thermal features in the low solar atmosphere. In conclusion, the polytropic index appears to be a useful tool to understand the nature of the compressive turbulence in the interplanetary plasma, as far as the frozen-in magnetic field does not play a crucial role. 相似文献
16.
V. A. Dergachev P. B. Dmitriev O. M. Raspopov H. Jungner 《Geomagnetism and Aeronomy》2007,47(1):109-117
A joint analysis of paleodata on variations in cosmic ray fluxes, solar activity, geomagnetic field, and climate during the period from ～10000 to ～100000 years ago has been performed. Data on the time variations in the concentration of 14C and 10Be cosmogenic isotopes, which are generated in the Earth’s atmosphere under the action of cosmic ray fluxes modulated by solar activity and geomagnetic field variations, were used to detect variations in solar activity and the geomagnetic dipole. Information about climate changes has been obtained mainly from variations in the concentration of stable isotopes in the natural archives. A performed analysis indicates that the variations in cosmic ray fluxes under the action of variations in the geomagnetic field and solar activity are apparently one of the most effective natural factors of long-term climate changeability on a large time scale. 相似文献
17.
《Journal of Atmospheric and Solar》2000,62(4):239-248
Based on long-term observations of the resonance structure in the electromagnetic background noise spectrum (resonance spectrum structure, RSS), recorded in the frequency range 0.1–10 Hz over one complete solar cycle (11 years, from 1985 to 1995), it was found that the resonance conditions for Alfven waves in the ionosphere (ionospheric Alfven resonator) are determined at midlatitudes by the level of solar activity. RSS are regularly observed in years of minimum solar activity, and are practically absent in years of maximum solar activity. It is shown that consideration of the ionospheric Alfven resonator explains the dependence of the RSS on solar activity. 相似文献
18.
V. I. Vlasov 《Geomagnetism and Aeronomy》2011,51(1):28-38
We analyzed the variations of the interplanetary plasma parameters, obtained from radio astronomical observations of scintillations
of cosmic radio sources during four 11-year cycles of solar activity, from 1966 to present. It is shown that the state of
the interplanetary plasma permanently changes in conformity with cyclicity in the solar activity. In the studied time period,
besides the 11-year variations in the velocity and scintillation index, there is also an increasing linear trend of these
variables, which is presumably due to a secular 80–90-year cycle of solar activity. The observed differences between the 11-year
variations and trends in the solar wind velocity and interplanetary scintillation index suggest that the 11-year and secular
cycles have different origins. It is found that these trends occur in this time period in each link of the Sun-Earth system:
in the solar activity indices, in the characteristics of the interplanetary medium, and practically in all characteristics
of the geophysical, demographical, medical, and other Earth’s processes. From the entire set of facts we can conclude that
most of the analyzed Earth’s processes are dominated not by anthropogenic factors, but by the effects of the secular cyclic
processes of the solar activity. 相似文献
19.
A. A. Kovalev A. G. Kolesnik S. A. Kolesnik A. A. Kolmakov 《Geomagnetism and Aeronomy》2010,50(1):127-133
Based on the data of the long-term monitoring of the electromagnetic background at frequencies of 1–30 MHz in Tomsk, new main
regularities of the daily and seasonal variations in this background in different frequency ranges at a low level of solar
activity (the annual average values are 68.6 = F
10.7 <= 80.9) have been established. 相似文献
20.
Possible correlation between variations of the intensity of lightnings, which are estimated from the flux of thunderstorm-generated
VLF-signals, and variations of the solar wind parameters has been investigated. The signals representing the intensity of
local thunderstorms in summer and winter are received in Yakutsk (the Eastern Siberia) and in the African World Thunderstorm
Center, respectively. The highest correlation coefficient has been obtained between the thunderstorm activity and variations
of the solar-wind particle density. This correlation has a season-dependent sign-alternating character. The maximum positive
and negative correlation coefficients are observed in August–September and February, respectively; i.e., the manifestation
of solar wind density variations in the thunderstorm activity is maximal in the near-equinoctial periods. This may be associated
with the peculiarities of the transfer of the magnetospheric electric field “from morning to evening,” which is induced by
the solar-wind particle flux, to ionospheric heights. 相似文献