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1.
The occurrence of a large number of high and low amplitude anisotropic wave train events over the years 1981–1994 has been examined along with the different solar features. The results indicate that the time of maximum of diurnal variation significantly remains in the 18-h direction for majority of the high and low amplitude wave trains. The amplitude of diurnal anisotropy remains significantly high and phase shifts towards earlier hours as compared to the quite day annual average values for majority of the HAEs. The diurnal amplitude remains significantly low and phase shifts towards earlier hours as compared to the quiet day annual average values for majority of the LAEs. The occurrence of these enhanced/low amplitude events is found to be dominant during the positive polarity of the Bz component of the interplanetary magnetic field. The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar wind streams do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases. 相似文献
2.
《Planetary and Space Science》2007,55(14):2077-2086
Several workers have attempted to find out the possible origin of the “high amplitude wave trains” of enhanced diurnal variation of cosmic rays and to develop a suitable realistic theoretical model that can explain the different harmonics in individual days. The various observed harmonics of the cosmic-ray variation may be understood on a unified basis if the free-space cosmic-ray anisotropy is non-sinusoidal in form. The major objective of this paper is to study the first three harmonics of high-amplitude wave trains of cosmic-ray intensity over the period 1981–1994 for Deep River neutron monitoring station. The main characteristic of these events is that the high-amplitude wave trains show a maximum intensity of diurnal component in a direction earlier than 18:00 h/co-rotational direction. It is noteworthy that the amplitude significantly enhanced and the phase remains in the co-rotational direction during the years close to solar-activity maximum for first harmonic. Significant deviations have been observed in the semi-diurnal amplitude after the onset of solar-activity maximum. This leads us to conclude that the amplitude as well as direction of the first harmonic and the amplitude of second harmonic are correlated with solar-activity cycle during these HAEs. The amplitude and phase of all the three harmonics (diurnal/semi-diurnal/tri-diurnal) are not found to depend on the polarity of Bz component of interplanetary magnetic field for long-term variation. The occurrence of high-amplitude events is dominant for the positive polarity of Bz component of IMF. The occurrence of HAEs is dominant during the period of average solar-wind velocity, but their occurrence during HSSWSs cannot be denied. The possibility of occurrence of these events is more during the periods of co-rotating streams. The occurrence of HAE is dominant when Dst-index remains negative and this point is not reported earlier in the litterature. All the high amplitude events occurred, when geomagnetic activity index, Ap, remains ⩽20. 相似文献
3.
We studied the cosmic ray intensity variation due to interplanetary magnetic clouds during an unusual class of low amplitude
anisotropic wave train events. The low amplitude anisotropic wave train events in cosmic ray intensity have been identified
using the data of ground based Deep River neutron monitor and studied during the period 1981–1994. Even though the occurrence
of low amplitude anisotropic wave trains does not depend on the onset of interplanetary magnetic clouds, but the possibility
of occurrence of these events cannot be overlooked during the periods of the interplanetary magnetic cloud events. It is observed
that the solar wind velocity remains higher (> 300) than normal and the interplanetary magnetic field B remains lower than normal on the onset of the interplanetary magnetic cloud during the passage of low amplitude wave trains.
It is also noted that the proton density remains significantly low during high solar wind velocity, which is expected. The
north south component of interplanetary magnetic field Bz turns southward to one day before the arrival of cloud and remains in the southward direction after the arrival of a cloud.
During these events the cosmic ray intensity is found to increase with increase of solar wind velocity. The superposed epoch
analysis of cosmic ray intensity for these events during the onset of interplanetary magnetic clouds reveals that the decrease
in cosmic ray intensity starts not at the onset of the cloud but after a few days. The cosmic ray intensity increases on arrival
of the magnetic cloud and decreases gradually after the passage of the magnetic cloud. 相似文献
4.
Large amplitude wave-trains of cosmic-ray intensity 总被引：1，自引：0，他引：1
H. Mavromichalaki 《Astrophysics and Space Science》1980,71(1):101-110
The large amplitude wave-trains of cosmic-ray intensity observed during June, July and August, 1973, were analysed. These events exhibit the same characteristics as the event of May, 1973. During these days the phase of the enhanced diurnal anisotropy is shifted to a point earlier than either the corotation direction or the anti-garden-hose direction. For this analysis we used data from high- and middle-latitude neutron monitors and from the satellites HEOS-2, IMP-7 and IMP-8. The diurnal variation of these days is well understood in terms of a radially outward convective vector and a field-aligned inward diffusive vector yielding a diurnal anisotropy vector along about 1600 h in space. 相似文献
5.
Long-term changes in the cosmic-ray diurnal anisotropy 总被引：1，自引：0，他引：1
A detailed study has been conducted on the long-term changes in diurnal anisotropy of cosmic rays for the two solar cycles (20 and 21) during the period 1965–1990; this shows that the amplitude of the anisotropy is related to the characteristics of high and low amplitude days. The occurrence of high amplitude days are found to be positively correlated with the sunspot cycle while the low amplitude days are correlated negatively with the sunspot cycle. Further, the variability of the time of maximum of the aniotropy indicates that it essentially is composed of two components; one in the 1800 hours (corotation) direction and the other, an additional component in the 1500 hours direction (45° east of the S-N line) apparently caused by the reversal of the solar polar magnetic field. Our observations also suggest that the direction of the anisotropy of high- and low-amplitude days contribute significantly to the long-term behaviour of the diurnal anisotropy as it produces an additional component of cosmic rays in the radial (1200 hours) direction. 相似文献
6.
The occurrence of a large number of high- and low-amplitude cosmic-ray diurnal wave trains during the two solar cycles (20 and 21) over the years 1965–1990 has been examined as a function of solar activity. The high-amplitude days with the time of maximum in the 18:00 hr corotation direction do not indicate any significant correlation with solar activity. But, the low-amplitude days are inversely correlated with solar activity and the time of maximum shifts to earlier hours ( 15:00 hr direction). The slope of the power-specrum density roughly characterized by power spectral index n in the high-frequency range 3.5 x 10–5 Hz to 8.3 x 10–4 Hz (time scales of 20 min to 8 hr) is different for the two classes of events. A suggestion is made that the enhanced and low-amplitude cosmic-ray diurnal variations are produced by different types of interplanetary magnetic field distributions. 相似文献
7.
The unusually low amplitude anisotropic wave train events (LAEs) in cosmic ray intensity using the ground based Deep River
neutron monitor data has been studied during the period 1991–94. It has been observed that the phase of the diurnal anisotropy
for the majority of the LAE events remains in the co-rotational direction. However, for some of the LAE events the phase of
the diurnal anisotropy shifts towards earlier hours as compared to the annual average values. On the other hand, the amplitude
of the semi-diurnal anisotropy remains statistically the same, whereas phase shift-towards later hours; a similar trend has
also been found in case of tri-diurnal anisotropy. The high-speed solar wind streams do not play a significant role in causing
the LAE events. The occurrence of LAE is independent of the nature of the Bz component of IMF polarity.
Published in Astrofizika, Vol. 50, No. 2, pp. 313–324 (May 2007). 相似文献
8.
The unusually low amplitude anisotropic wave train events (LAWEs) in cosmic ray intensity using the ground based Deep River neutron monitor data has been studied during the period 1991–1994. It has been observed that the amplitude of the diurnal anisotropy for LAWE events significantly remains quite low and statistically constant as compared to the quiet day annual average amplitude for majority of the events. The time of maximum of the diurnal anisotropy of LAWE significantly shifts towards earlier hours as compared to the co-rotational direction and remains in the direction of quiet day annual average anisotropy for majority of the events. On the other hand, the amplitude of the semi/tri-diurnal anisotropy remains statistically the same and high whereas, phase shift towards later hours as compared to the quiet day annual average values for majority of the LAWEs. The diurnal anisotropy vectors are found to shifts towards earlier hours for 50% of the events; whereas they are found to shifts towards later hours for rest of the events (50%) relative to the average vector for the entire period. It is also noted that the amplitude of these vectors are found to increase significantly with the shift of the diurnal anisotropy vectors towards later hours. The high-speed solar wind streams do not play a significant role in causing the LAWE events on short-term basis, however it may be responsible in causing these events on long-term basis (Mishra and Mishra 2007). Occurrence of LAWE is dominant, when the polarity of Bx and Bz remains positive and polarity of By remains negative, which is never been reported earlier. The amplitude of first harmonic shows good anti-correlation and direction of first and third harmonic shows nearly good anti-correlation with solar wind velocity, whereas the direction of second harmonic shows nearly good anti-correlation with interplanetary magnetic field strength. 相似文献
9.
10.
H. Mavromichalaki 《Earth, Moon, and Planets》1989,47(1):61-72
The diurnal anisotropy of cosmic-ray intensity observed over the period 1970–1977 has been analysed using neutron-monitor data of the Athens and Deep River stations. Our results indicate that the time of the maximum of diurnal variation shows a remarkable systematic shift towards earlier hours than normally beginning in 1971. This phase shift continued until 1976, the solar activity minimum, except for a sudden shift to a later hour for one year, in 1974, the secondary maximum of solar activity.This behavior of the diurnal time of maximum has been shown to be consistent with the convective- diffusive mechanism which relates the solar diurnal anisotropy of cosmic-rays to the dynamics of the solar wind and of the interplanetary magnetic field. Once again we have confirmed the field-aligned direction of the diffusive vector independently of the interplanetary magnetic field polarity. It is also noteworthy that the diurnal phase may follow in time the variations of the size of the polar coronal holes. All these are in agreement with the drift motions of cosmic-ray particles in the interplanetarty magnetic field during this time period. 相似文献
11.
C. O. Lee J. G. Luhmann D. Odstrcil P. J. MacNeice I. de Pater P. Riley C. N. Arge 《Solar physics》2009,254(1):155-183
We present results of solar-wind parameters generated by 3D MHD models. The ENLIL inner-heliosphere solar-wind model together
with the MAS or Wang – Sheeley – Arge (WSA) coronal models, describe the steady solar-wind stream structure and its origins
in the solar corona. The MAS/ENLIL and WSA/ENLIL models have been tuned to provide a simulation of plasma moments as well
as interplanetary magnetic-field magnitude and polarity in the absence of disturbances from coronal transients. To investigate
how well the models describe the ambient solar wind structure from the Sun out to 1 AU, the model results are compared to
solar-wind measurements from the ACE spacecraft. We find that there is an overall agreement between the observations and the
model results for the general large-scale solar-wind structures and trends, such as the timing of the high-density structures
and the low- and high-speed winds, as well as the magnetic sector structures. The time period of our study is the declining
phase of Solar Cycle 23 when the solar activity involves well-defined stream structure, which is ideal for testing a quasi-steady-state
solar-wind model. 相似文献
12.
The purpose of this work is to investigate the first three harmonics of low-amplitude anisotropic wave trains (LAEs) of cosmic ray intensity and their association with solar and heliospheric parameters. The significant behaviour of these events is that the amplitude remains low for the first harmonic and high for the second/third harmonics, whereas direction of the anisotropy shift is towards earlier hours for the first harmonic and towards later hours for the second/third harmonic compared to annual average anisotropy. The first two harmonics are found to correlate well with the solar activity cycle during these LAEs. The amplitude and the direction of the first two harmonics do not show any significant association with the polarity change of the Bx/By component of the interplanetary magnetic field during LAEs. However, the third harmonic (amplitude and phase) shows some positive correlation with the Bx and negative correlation with the By component. The occurrence of LAEs is dominant for the positive polarity of Bx and the negative polarity of By. The occurrence of LAEs is dominant during the period of average solar wind velocity but their occurrence during high-speed solar wind streams cannot be overlooked. The frequency of occurrence of these LAEs is more during co-rotating streams.The amplitude of first and second harmonic shows deviations for different values of geomagnetic activity index Ap. However, the amplitude of second harmonic and direction of all the three harmonics do not show any significant association with the Ap-index. The Ap-index consistently remains in the range 14?Kp?31 during these events.The amplitude of first and third harmonic and the direction of first harmonic show deviations for different values of proton density. However, the amplitude of the second harmonic and the direction of the second and third harmonics do not show any significant association with proton density. The occurrence of LAEs is dominant when proton density remains ?20. The cosmic ray intensity during LAEs has good anti-correlation with interplanetary magnetic field strength (B) and its Bx component, whereas it shows a good correlation with its By component. However, it shows significant anti-correlation with sunspot number, the product (R×V) and (R×B). 相似文献
13.
In the present study the occurrence of an unusual class of low amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of low amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of low amplitude anisotropic wave trains of cosmic ray intensity over the period 1981–1994 for Deep River neutron monitoring station. The significant characteristic of these events is that the low amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 18:00 h/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. However the possibility of occurrence of these events during high-speed solar wind streams cannot be denied. The occurrence of low amplitude events is dominant for positive polarity of Bz. The disturbance storm time index i.e. Dst, remains consistently negative only for majority of the low amplitude wave train events, which is never been reported earlier. The amplitude as well as direction of first two harmonics seems to remain unaffected with the variation in the Dst and Ap-index. However, the amplitude as well as direction of third harmonic found to deviates with the increase of Dst and Ap-index. The corotating streams produce significant deviations in cosmic ray intensity as well as in solar wind speed during low amplitude anisotropic wave train events. 相似文献
14.
Over the last few years, the pre-decreases or pre-increases of the cosmic-ray intensity observed before a Forbush decrease, called the precursor effect and registered by the worldwide neutron monitor network, have been investigated for different cases of intense events. The Forbush decreases presented in this particular study were chosen from a list of events that occurred in the time period 1967?–?2006 and were characterized by an enhanced first harmonic of cosmic-ray anisotropy prior to the interplanetary disturbance arrival. The asymptotic longitudinal cosmic-ray distribution diagrams for the events under consideration were studied using the “Ring of Stations” method, and data on solar flares, solar-wind speed, geomagnetic indices, and interplanetary magnetic field were analyzed in detail. The results revealed that the use of this method allowed the selection of a large number of events with well-defined precursors, which could be separated into at least three categories, according to duration and longitudinal zone. Finally, this analysis showed that the first harmonic of cosmic-ray anisotropy could serve as an adequate tool in the search for precursors and could also be evidence for them. 相似文献
15.
The high/low-amplitude anisotropic wave train events (HAE/LAE) in CR intensity have been investigated during the period 1981–1990, using the neutron monitoring data for different latitudes. In all, 21 HAE and 15 LAE cases have been studied. It has been observed that the phase of the diurnal anisotropy remains in the same co-rotational direction for the majority of the HAE/LAE cases. However, it has also been observed that the phase of the diurnal anisotropy changes to later hours in some of the HAE cases, whereas it changes to early hours in some of the LAE cases. Further, the amplitude of the semi-diurnal anisotropy for HAE/LAE cases remains statistically the same; however, the phase of the semi-diurnal anisotropy for HAE has been found to shift to later hours for all events. Furthermore, the HAE occur dominantly during the declining phase of solar activity, whereas LAE occur dominantly during the minimum solar activity period. The geomagnetic activity index-Ap has been observed to remain low during the period of each HAE/LAE. The possible phenomenon to cause the enhanced/low-amplitude daily variation has been proposed to appear on the back side of the Sun. 相似文献
16.
F. R. Allum R. A. R. Palmeira K. G. McCracken U. R. Rao D. H. Fairfield L. J. Gleeson 《Solar physics》1974,38(1):227-256
Concurrent interplanetary magnetic field and 0.7–7.6 MeV proton cosmic-ray anisotropy data obtained from instrumentation on Explorers 34 and 41 are examined for five cosmic-ray events in which we observe a persistent eastern-anisotropy phase late in the event (t ? 4 days). The direction of the anisotropy at such times shows remarkable invariance with respect to the direction of the magnetic field (which generally varies throughout the event) and it is also independent of particle species (electrons and protons) and particle speed over the range 0.06 ? β ? 0.56. The anisotropy is from the direction 38.3° ± 2.4° E of the solar radius vector, and is inferred to be orthogonal to the long term, mean interplanetary field direction. Both the amplitude of the anisotropy and the decay time constant show a strong dependence on the magnetic field azimuth. Detailed comparison of the anisotropy and the magnetic field data shows that the simple model of convection plus diffusion parallel to the magnetic field is applicable for this phase of the flare effect. It is demonstrated that contemporary theories do not predict the invariance of the direction as observed, even when the magnetic field is steady; these theories need extension to take into account the magnetic field direction ψ varying from its mean direction ψ o. It is shown that the late phase anisotropy vector is not expected to be everywhere perpendicular to the mean magnetic field. The suggestion that we are observing kinks in the magnetic field moving radially outwards from the Sun leads to the conclusion that the parallel diffusion coefficient varies as 1/cos2 (ψ ? ψ o). Density gradients in the late decay phase are estimated to be ≈ 700%∣AU for 0.7–7.6 MeV protons. A simple theory reproduces the dependence of the decay time constant on anisotropy; it also leads to a radial density gradient of about 1000%∣AU and diffusion coefficient of 1.3 × 1020 cm2 s?1. 相似文献
17.
G. F. Krymsky P. A. Krivoshapkin S. K. Gerasimova P. Yu. Gololobov 《Astronomy Letters》2014,40(4):230-233
Long-termobservations of the muon intensity of galactic cosmic rays at the Nagoya (35°10′ N, 136°58′ E) and Yakutsk (62°01′ N, 129°43′ E) stations have revealed amplitude-phase annual and semiannual oscillations of the semidiurnal variation. These oscillations are attributable to the properties of the cosmic-ray anisotropy tensor that result from shielding by the interplanetary magnetic field and solar-wind shear flow. The mentioned tensor is also shown to have a north-south asymmetry. 相似文献
18.
We have bounded the upper cut-off rigidity (Rc) of the cosmic-ray diurnal anisotropy during the period 1968–1995. This period covers almost three solar cycles and includes three epochs of the solar polar field reversals. The diurnal variation observed by two detectors characterized by linearly independent kernels has been inverted in order to estimate the greatest lower bound (GLB) of Rc. We obtain a step function solution for the cosmic-ray anisotropy in free space which vanishes at the GLB of Rc. The greatest lower bound shows a magnetic cycle variation. The highest value of the amplitude of the anisotropy in free space at the GLB have been estimated as well. 相似文献
19.
Forbush decreases (FDs) are sharp reductions of the cosmic-ray (CR) intensity, following intense solar activity such as coronal mass ejections (CMEs) and their corresponding interplanetary shocks. In some cases, shocks create sudden storm commencements (SSCs) at the Earth’s magnetosphere with significant interest for space-weather studies. Preincreases and/or predecreases of CR intensity before the onset of FDs, known as precursory signals, have been widely examined by many authors. In this work, an attempt to define precursory signals that are not related to SSCs is presented. For the present analysis, CR data recorded by the ground-based Neutron Monitor Network as well as data on solar flares, CMEs, solar-wind speed, interplanetary magnetic field, and geomagnetic indices for the years 1969?–?2019 are used. To identify FDs that present precursors, the adopted criteria are mainly the FD amplitude (> 2%) and the equatorial CR anisotropy before the onset time (> 0.8%). The analysis of FDs and the study of their asymptotic-longitude CR distribution for precursors are based on the Global Survey Method and the Ring of Stations Method, respectively. Precursory signals are identified in 17 out of 27 events without SSCs.
相似文献20.
J. Xanthakis H. Mavromichalaki B. Petropoulos E. Marmatsouri A. Vassilaki 《Earth, Moon, and Planets》1988,43(2):165-179
A three-dimensional model for the calculation of cosmic-ray intensity of the Inuvik station during the 20th and 21st solar cycles is given. Especially we have studied the coefficient K of the used parameter of sunspot number in terms of high-speed solar-wind streams and have tried enough successfully to relate this coefficient with the diffusion process of cosmic rays in the interplanetary space.Analyzing these two data sets for the time-period 1964–1985 into a network of trigonometric series we have observed similar period in the two sets. It means that we have the same in general line variations in the high-speed streams as well as to the coefficient K expressed by this way the diffusion coefficient of cosmic-rays. 相似文献