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1.
We analyze the evolution of cosmic ray intensity detected by six neutron monitors located at high altitude from 1990 to 1999,
that includes most of solar cycle 22 and the start of cycle 23. This set of neutron monitors covers a wide range of geomagnetic
cutoff rigidities. We discuss the most significant characteristics of the cosmic ray modulation during the period as: the
extraordinary decreases produced by the events of the first half of 1991, the significant two step evolution of the recovery
phase of solar cycle 22 and the start of cycle 23. We also determine the rigidity dependence of the different phases of the
modulation cycle. Cosmic ray intensity correlations with several solar activity parameters as sunspots, microwave flux at
10.7 cm and solar flares and with the intensity of the interplanetary magnetic field are studied. 相似文献
2.
The modulation of galactic cosmic rays, as derived from ground-based neutron monitors over a solar cycle appears to be a good indicator of solar activity. Especially good correlation was found between short-term variations of cosmic ray flux and solar UV emission in the region of 250 nm during one year (1982). 相似文献
3.
Abdullrahnan Maghrabi Mohammed AlAnazi A. Aldosari M. Almuteri 《Journal of Astrophysics and Astronomy》2017,38(1):1
Solar disturbances modulate primary cosmic rays on different time scales. Studying cosmic ray variation is an important subject that attracts scientists from different disciplines. We have constructed and installed (in Riyadh, Saudi Arabia, Rc =14.4 GV) a three-layer small (20 × 20 cm2) MultiWire Chamber (MWC) telescope to study cosmic ray variations and investigate their influence on various atmospheric and environmental processes. Preliminary results obtained from the developed detector are given. The influence of both atmospheric pressure and temperature was studied. Both the temperature and pressure coefficients were calculated and were consistent with those previously obtained. Short-term cosmic ray periodicities, such as the 27-day period, and its two harmonics, have been identified. Sporadic variations caused by some solar activity processes have been inspected. The obtained results from this detector have been compared to the existing 1 m2 scintillator detector, as well as to some of the neutron monitors, showing comparable results. 相似文献
4.
In this work the galactic cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the years 1996??C?2010 covering solar cycle 23 and the solar minimum between cycles 23 and 24 is studied. A new perspective of this contribution is that cosmic ray data with a rigidity of 10 GV at the top of the atmosphere obtained from many ground-based neutron monitors were used. The proposed empirical relation gave much better results than those in previous works concerning the hysteresis effect. The proposed models obtained from a combination of solar activity indices and heliospheric parameters give a standard deviation <?10?% for all the cases. The correlation coefficient between the cosmic ray variations of 10?GV and the sunspot number reached a value of r=?0.89 with a time lag of 13.6±0.4 months. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 7.15?% for all of solar cycle 23; it also works very well during the different phases of the cycle. Moreover, the use of the cosmic ray intensity of 10?GV during the long minimum period between cycles 23 and 24 is of special interest and is discussed in terms of cosmic ray intensity modulation. 相似文献
5.
North/south directional telescopes operating at the surface and vertical and inclined telescopes operating at a depth of 60 m.w.e. underground in London have been employed to study changes in the cosmic ray solar diurnal variation over the past few years. In order to extend the study to the low rigidity end of the spectrum, results obtained by the NM64 neutron monitors operating at Deep River and Goose Bay in Canada have also been examined. The surface telescope data require that the full corotation amplitude of 0.59 per cent should have been observed during almost the entire solar cycle with the possible exception of the year 1965 when cosmic ray intensity was a maximum. However, the effective amplitude observed by neutron monitors during most of the solar cycle was only about 0.52 per cent and this reduction has been ascribed to the lower value of the exponent of the energy spectrum which prevails amongst the latitude sensitive primaries. Nevertheless, the upper limiting rigidity was varying during the course of the solar cycle, its value being high when solar activity was high and low when solar activity decreased. During 1965, even though the upper limiting rigidity assumed its lowest value, the free space amplitude was also diminished by a little over 10 per cent. Even though the theory of rigid corotation invoking a purely azimuthal streaming of the cosmic ray gas successfully predicts the free space amplitude, it fails to explain the phase changes observed by both types of monitor and which are quite significant. The underground data require that the component due to atmospheric temperature effects is negligibly small and that throughout the rigidity range covered by the recorder response, there is present an apparent anisotropy due to the orbital motion of the Earth around the Sun. Also the underground data roughly confirm the changes in upper limiting rigidity which were observed by the surface instruments. 相似文献
6.
Cosmic ray intensity variations near the heliospheric current sheet—both above and below it—have been studied during 1964–1976. Superposed epoch analysis of the cosmic ray neutron monitor data with respect to sector boundaries (i.e., heliospheric current sheet crossings) has been performed. In this analysis we have used the data from neutron monitors well distributed in latitude over the Earth's surface. First, this study has been made during the two solar activity minimum periods 1964–1965 and 1975–1976, using the data from Thule (cut-off rigidity 0 GV), Deep River (cut-off rigidity 1.02 GV), Rome (cut-off rigidity 6.32 GV) and Huancayo (cut-off rigidity 13.45 GV) neutron monitors. We have also analyzed the data from Deep River, Rome and Huancayo neutron monitors, for whom we have the data for full period (1964–1976), by dividing the periods according to the changes in solar activity, interplanetary magnetic field polarity and coronal holes. All these studies have shown a negative gradient with respect to heliomagnetic latitude (current sheet). These results have been discussed in the light of theoretical and observational evidences. Suggestions have been given to overcome the discrepancy between the observational and theoretical results. Further, possible explanations for these observational results have been suggested. 相似文献
7.
We study the temporal evolution of cosmic ray intensity during ～27-day Carrington rotation periods applying the method of superposed epoch analysis. We discuss about the average oscillations in the galactic cosmic ray intensity, as observed by ground based neutron monitors, during the course of Carrington rotation in low solar activity conditions and in different polarity states of the heliosphere (A<0 and A>0). During minimum and decreasing phases in low solar activity conditions, we compare the oscillation in one polarity state with that observed in other polarity state in similar phases of solar activity. We find difference in the evolution and amplitude of ～27-day variation during A<0 and A>0 epoch. We also compare the average variations in cosmic ray intensity with the simultaneous variations of solar wind parameters such as solar wind speed and interplanetary magnetic field strength. From the correlation analysis between the cosmic ray intensity and the solar wind speed during the course of Carrington rotation, we find that the correlation is stronger for A>0 than A<0. 相似文献
8.
《New Astronomy》2016
The diurnal variation of cosmic ray intensity, based on the records of two neutron monitor stations at Athens (Greece) and Oulu (Finland) for the time period 2001 to 2014, is studied. This period covers the maximum and the descending phase of the solar cycle 23, the minimum of the solar cycles 23/24 and the ascending phase of the solar cycle 24.These two stations differ in their geographic latitude and magnetic threshold rigidity. The amplitude and phase of the diurnal anisotropy vectors have been calculated on annual and monthly basis.From our analysis it is resulted that there is a different behaviour in the characteristics of the diurnal anisotropy during the different phases of the solar cycle, depended on the solar magnetic field polarity, but also during extreme events of solar activity, such as Ground Level Enhancements and cosmic ray events, such as Forbush decreases and magnetospheric events. These results may be useful to Space Weather forecasting and especially to Biomagnetic studies. 相似文献
9.
A lead-free neutron monitor operating at High Altitude Research Laboratory (HARL), Gulmarg optimized for detecting 2.45 MeV neutron bursts produced during the atmospheric lightning discharges is also concurrently used for studying background neutron component present in the atmosphere. These background neutrons are produced due to the interaction of primary cosmic rays with the atmospheric constituents. In order to study and extract the information about the yield of the neutron production during transient atmospheric lightning discharges, the system is continuously operated to monitor and record the cosmic ray produced background secondary neutrons in the atmosphere. The data analysis of the background neutrons recorded by Lead-Free Gulmarg Neutron Monitor (LFGNM) has convincingly established that the modulation effects due to solar activity phenomena compare very well with those monitored by the worldwide IGY or NM64 type neutron monitors which have optimum energy response relatively towards the higher energy regime of the cosmic rays. The data has revealed various types of modulation phenomena like diurnal variation, Forbush decrease etc. during its entire operational period. However, a new kind of a periodic/seasonal variation pattern is also revealed in the data from September 2007 to September 2012, which is seen to be significantly consistent with the data recorded by Emilio Segre observatory, Israel (ESOI) Neutron Monitor. Interestingly, both these neutron monitors have comparable latitude and altitude. However, the same type of consistency is not observed in the data recorded by the other conventional neutron monitors operating across the globe. 相似文献
10.
C. Plainaki H. Mavromichalaki A. Belov E. Eroshenko M. Andriopoulou V. Yanke 《Solar physics》2010,264(1):239-254
In this work we present a cosmic ray model that couples primary solar cosmic rays at the top of the Earth’s atmosphere with
the secondary ones detected at ground level by neutron monitors during Ground-Level Enhancements (GLEs). The Neutron Monitor
Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model constitutes a new version of the already existing NMBANGLE model,
differing in the solar cosmic ray spectrum assumed. The total output of the model is a multi-dimensional GLE picture that
reveals part of the characteristics of the big solar proton events recorded at ground level. We apply both versions of the
model to the GLE of 15 April 2001 (GLE60) and compare the results. 相似文献
11.
The pressure-corrected hourly counting rate data of four neutron monitor stations have been employed to study the variation
of cosmic ray diurnal anisotropy for a period of about 50 years (1955–2003). These neutron monitors, at Oulu (
R
c = 0.78 GV), Deep River (
R
c = 1.07 GV), Climax (
R
c = 2.99 GV), and Huancayo (
R
c = 12.91 GV) are well distributed on the earth over different latitudes and their data have been analyzed. The amplitude of
the diurnal anisotropy varies with a period of one solar cycle (∼11 years), while the phase varies with a period of two solar
cycles (∼22 years). In addition to its variation on year-to-year basis, the average diurnal amplitude and phase has also been
calculated by grouping the days for each solar cycle, viz. 19, 20, 21, 22, and 23. As a result of these groupings over solar
cycles, no significant change in the diurnal vectors (amplitude as well as phase) from one cycle to other has been observed.
Data were analyzed by arranging them into groups on the basis of the polarity of the solar polar magnetic field and consequently
on the basis of polarity states of the heliosphere (
A > 0 and
A < 0). Difference in time of maximum of diurnal anisotropy (shift to earlier hours) is observed during
A < 0 (1970s, 1990s) polarity states as compared to anisotropy observed during
A > 0 (1960s, 1980s). This shift in phase of diurnal anisotropy appears to be related to change in preferential entry of cosmic
ray particles (via the helioequatorial plane or via solar poles) into the heliosphere due to switch of the heliosphere from
one physical/magnetic state to another following the solar polar field reversal. 相似文献
12.
13.
Several studies show that temporal variations in the Galactic cosmic ray (GCR) intensity display a distinct 11-year periodicity due to solar modulation of the galactic cosmic rays in the heliosphere. The 11-year periodicity of GCRs is inversely proportional to, but out of phase with, the 11-year solar cycle, implying that there is a time lag between actual solar cycle and the GCR intensity, which is known as the hysteresis effect. In this study, we use the hysteresis effect to model the relationship between neutron counting rates (NCRs), an indicator of the GCR intensity, and sunspot numbers (SSNs) over the period that covers the last four solar cycles (20, 21, 22, and 23). Both linear and ellipse models were applied to SSNs during odd and even cycles in order to calculate temporal variations of NCRs. We find that ellipse modeling provides higher correlation coefficients for odd cycles compared to linear models, e.g. 0.97, 0.97, 0.92, and 0.97 compared to 0.69, 0.72, 0.53, and 0.68 for data from McMurdo, Swarthmore, South Pole, and Thule neutron monitors, respectively, during solar cycle 21 with overall improvement of 31 % for odd cycles. When combined to a continuous model, the better correlation observed for the odd cycles increases the overall correlation between observed and modeled NCRs. The new empirical model therefore provides a better representation of the relationship between NCRs and SSNs. A major goal of the ongoing research is to use the new non-linear empirical model to reconstruct SSNs on annual time scales prior to 1610, where we do not have observational records of SSNs, based on changes in NCRs reconstructed from 10Be in ice cores. 相似文献
14.
Sankar Narayan Patra Koushik Ghosh Subhash Chandra Panja 《Astrophysics and Space Science》2011,334(2):317-323
In the present paper we have analyzed the daily Forbush decrease indices from January 1, 1967 to December 31, 2003. First
filtering the time series by Simple Exponential Smoothing, we have applied Scargle Method of Periodogram on the processed
time series in order to search for its time variation. Study exhibits periodicities around 174, 245, 261, 321, 452, 510, 571,
584, 662, 703, 735, 741, 767, 774, 820, 970, 1062, 1082, 1489, 1715, 2317, 2577, 2768, 3241 and 10630 days with confidence
levels higher than 90%. Some of these periods are significantly similar to the observed periodicities of other solar activities,
like solar filament activity, solar electron flare occurrence, solar-flare rate, solar proton events, solar neutrino flux,
solar irradiance, cosmic ray intensity and flare, spectrum of the sunspot, solar wind, southern coronal hole area and solar
cycle, which may suggest that the Forbush decrease behaves similarly to these solar activities and these activities may have
a common origin. 相似文献
15.
The flux rate of cosmic rays incident on the Earth’s upper atmosphere is modulated by the solar wind and the Earth’s magnetic
field. The amount of solar wind is not constant due to changes in solar activity in each solar cycle, and hence the level
of cosmic ray modulation varies with solar activity. In this context, we have investigated the variability and the relationship
of cosmic ray intensity with solar, interplanetary, and geophysical parameters from January 1982 through December 2008. Simultaneous
observations have been made to quantify the exact relationship between the cosmic ray intensity and those parameters during
the solar maxima and minima, respectively. It is found that the stronger the interplanetary magnetic field, solar wind plasma
velocity, and solar wind plasma temperature, the weaker the cosmic ray intensity. Hence, the lowest cosmic ray intensity has
good correlations with simultaneous solar parameters, while the highest cosmic ray intensity does not. Our results show that
higher solar activity is responsible for a higher geomagnetic effect and vice versa. 相似文献
16.
Recent helioseismic observations have found strong fluctuations at a period of about 1.3 years in the rotation speed around
the tachocline in the deep solar convection layer. Similar mid-term quasi-periodicities (MTQP; periods between 1–2 years)
are known to occur in various solar atmospheric and heliospheric parameters for centuries. Since the deep convection layer
is the expected location of the solar magnetic dynamo, its fluctuations could modulate magnetic flux generation and cause
related MTQP fluctuations at the solar surface and beyond. Accordingly, it is likely that the heliospheric MTQP periodicities
reflect similar changes in solar dynamo activity. Here we study the occurrence of the MTQP periodicities in the near and distant
heliosphere in the solar wind speed and interplanetary magnetic field observed by several satellites at 1 AU and by four interplanetary
probes (Pioneer 10 and 11 and Voyager 1 and 2) in the outer heliosphere. The overall structure of MTQP fluctuations in the different locations of the heliosphere
is very consistent, verifying the solar (not heliospheric) origin of these periodicities. We find that the mid-term periodicities
were particularly strong during solar cycle 22 and were observed at two different periods of 1.3 and 1.7 years simultaneously.
These periodicities were latitudinally organized so that the 1.3-year periodicity was found in solar wind speed at low latitudes
and the 1.7-year periodicity in IMF intensity at mid-latitudes. While all heliospheric results on the 1.3-year periodicity
are in a good agreement with helioseismic observations, the 1.7-year periodicity has so far not been detected in helioseismic
observations. This may be due to temporal changes or due to the helioseismic method where hemispherically antisymmetric fluctuations
would so far have remained hidden. In fact, there is evidence that MTQP fluctuations may occur antisymmetrically in the northern
and southern solar hemisphere. Moreover, we note that the MTQP pattern was quite different during solar cycles 21 and 22,
implying fundamental differences in solar dynamo action between the two halves of the magnetic cycle. 相似文献
17.
In the present work an analysis has been made of the extreme events occurring during July 2005. Specifically, a rather intense
Forbush decrease was observed at different neutron monitors all over the world during 16 July 2005. An effort has been made
to study the effect of this unusual event on cosmic ray intensity as well as various solar and interplanetary plasma parameters.
It is noteworthy that during 11 to 18 July 2005 the solar activity ranged from low to very active. Especially low levels occurred
on 11, 15, and 17 July whereas high levels took place on 14 and 16 July 2005. The Sun is observed to be active during 11 to
18 July 2005, the interplanetary magnetic field intensity lies within 15 nT, and solar wind velocity was limited to ∼500 kms-1.
The geomagnetic activity during this period remains very quiet, the Kp index did not exceed 5, the disturbance storm time
Dst index remains ∼-70 nT and no sudden storm commencement has been detected during this period. It is noted that for the
majority of the hours, the north/south component of the interplanetary magnetic field, Bz, remains negative, and the cosmic
ray intensity increases and shows good/high correlation with Bz, as the polarity of Bz tends to shift from negative to positive
values, the intensity decreases and shows good/high anti-correlation with Bz. The cosmic ray intensity tends to decrease with
increase of interplanetary magnetic field strength (B) and shows anti-correlation for the majority of the days.
Published in Astrofizika, Vol. 51, No. 2, pp. 255–265 (May 2008). 相似文献
18.
A study has been made of the yearly variation of the cosmic ray intensity for the years 1961–67 inclusive using pressure corrected neutron monitor data from both hemispheres to minimize seasonal meteorological effects. An annual wave is found in the data with an amplitude which varied between 0.2 and 1.0 per cent during the period but which had a sensibly constant phase, the time of maximum being in March. These observations, which are shown to be consistent with the observed heliolatitude distribution of coronal 5303Å emission, indicate the existence of a southerly directed asymmetrical gradient of up to 8 per cent perpendicular to the solar equatorial plane. It is found that the cosmic ray intensity at the Earth is controlled by the solar activity in a narrow band of heliolatitudes ±10° or ±20° centred at the heliolatitude of the Earth. Also, the results indicate that there was a phase lag of 1 ± 1 month between solar activity and the resulting changes in the cosmic ray intensity at the Earth giving a radius for the modulating region of ? 10 A.U. during the period of low solar activity considered. 相似文献
19.
The purpose of the present communication is to identify the short-term (few tens of months) periodicities of several solar indices (sunspot number, Caii area and K index, Lyman , 2800 MHz radio emission, coronal green-line index, solar magnetic field). The procedure used was: from the 3-month running means (3m) the 37-month running means (37m) were subtracted, and the factor (3m – 37m) was examined for several parameters. For solar indices, considerable fluctuations were seen during the ± 4 years around sunspot maxima of cycles 18–23, and virtually no fluctuations were seen in the ± 2 years around sunspot minima. The spacings between successive peaks were irregular but common for various solar indices. Assuming that there are stationary periodicities, a spectral analysis was carried out which indicated periodicities of months: 5.1–5.7, 6.2–7.0, 7.6–7.9, 8.9–9.6, 10.4–12.0, 12.8–13.4, 14.5–17.5, 22–25, 28 (QBO), 31–36 (QBO), 41–47 (QTO). The periodicities of 1.3 year (15.6 months) and 1.7 years (20.4 months) often mentioned in the literature were seen neither often nor prominently. Other periodicities occurred more often and more prominently. For the open magnetic flux estimated by Wang, Lean, and Sheeley (2000) and Wang and Sheeley (2002), it was noticed that the variations were radically different at different solar latitudes. The open flux for < 45 solar latitudes had variations very similar (parallel) to the sunspot cycle, while open flux for > 45 solar latitudes had variations anti-parallel to the sunspot cycle. The open fluxes, interplanetary magnetic field and cosmic rays, all showed periodicities similar to those of solar indices. Many peaks (but not all) matched, indicating that the open flux for < 45 solar latitudes was at least partially an adequate carrier of the solar characteristics to the interplanetary space and thence for galactic cosmic ray modulation. 相似文献
20.
Ambika Singh Anil Kumar Tiwari S. P. Agrawal 《Journal of Astrophysics and Astronomy》2010,31(2):89-96
A detailed study has been conducted on the long-term changes in the diurnal variation of cosmic rays in terms of high and
low amplitude wave trains event (HAEs/LAEs) during the period 1996–2008 (solar cycle 23), using the neutron monitor data from
Kiel neutron monitoring station. As such, 17 HAE and 48 LAE cases have been detected and analyzed. These HAEs appear quite
dominantly during the declining phase as well as near the maximum of the solar activity cycle 23. In contrast, the low amplitude
events (LAEs) are inversely correlated with solar activity cycle. In fact, LAEs appear quite dominantly during the minimum
phase of the solar activity. When we compare our results for diurnal phase with that observed on an annual average basis,
we notice no significant diurnal phase shift for HAEs as well as for LAEs. Moreover, we find that the high-speed solar wind
streams (HSSWS) do not play any significant role in causing these variations. These results are discussed on the basis of
that observed in earlier cycles. 相似文献