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1.
We have studied Forbush decreases (FD) with solar flare data and major solar proton event (SPE) data (E > 10 MeV) for the years 1976–1986 and have found that FD solar flare data exhibit periods around 0.95, 2.4, and 4.75 years at >99% level of confidence (CL), while SPE data exhibit periods around 2.6 and 5.0 years (at >95% CL). Because of a common periodicity around 2.5 years, it is suggested that FD with the solar flare data and major SPE data, together with solar diameter and solar neutrino variations, behave similarly and may have a common origin.  相似文献   

2.
We propose to build a large water-Cherenkov-type muon-detector array (Tibet MD array) around the 37 000 m2 Tibet air shower array (Tibet AS array) already constructed at 4300 m above sea level in Tibet, China. Each muon detector is a waterproof concrete pool, 6 m wide × 6 m long × 1.5 m deep in size, equipped with a 20 inch-in-diameter PMT. The Tibet MD array consists of 240 muon detectors set up 2.5 m underground. Its total effective area will be 8640 m2 for muon detection. The Tibet MD array will significantly improve gamma-ray sensitivity of the Tibet AS array in the 100 TeV region (10–1000 TeV) by means of gamma/hadron separation based on counting the number of muons accompanying an air shower. The Tibet AS+MD array will have the sensitivity to gamma rays in the 100 TeV region by an order of magnitude better than any other previous existing detectors in the world. The Tibet ASγ Collaboration.  相似文献   

3.
A nearly complete sample of 24 Magellanic Cloud WC/WO subclass Wolf–Rayet stars is studied spectroscopically and photometrically to determine its binary frequency. Theory predicts the Roche lobe overflow produced Wolf–Rayet binary frequency to be 52±14 per cent in the Large Magellanic Cloud and 100 per cent in the Small Magellanic Cloud, not counting non-Roche lobe overflow Wolf–Rayet binaries. Lower ambient metallicity ( Z ) leads to lower opacity, preventing all but the most massive (hence luminous) single stars from reaching the Wolf–Rayet stage. However, theory predicts that Roche lobe overflow even in binaries of modest mass will lead to Wolf–Rayet stars in binaries with periods below approximately 200 d, for initial periods below approximately 1000 d, independent of Z . By examining their absolute continuum magnitudes, radial velocity variations, emission-line equivalent widths and full widths at half-maximum, a WC/WO binary frequency of only 13 per cent, significantly lower than the prediction, is found in the Large Magellanic Cloud. In the unlikely event that all of the cases with a less certain binary status actually turn out to be binary, current theory and observation would agree. (The Small Magellanic Cloud contains only one WC/WO star, which happens to be a binary.) The three WC+O binaries in the Large Magellanic Cloud all have periods well below 1000 d. The large majority of WC/WO stars in such environments apparently can form without the aid of a binary companion. Current evolutionary scenarios appear to have difficulty explaining either the relatively large number of Wolf–Rayet stars in the Magellanic Clouds, or the formation of Wolf–Rayet stars in general.  相似文献   

4.
The pressure-corrected hourly counting rate data of ground-based super neutron monitor stations, situated in different latitudes, have been employed to study the characteristics of the long-term variation of cosmic-ray diurnal anisotropy for a long (44-year) period (1965?–?2008). Some of these super neutron monitors are situated in low latitudes with high cutoff rigidity. Annual averages of the diurnal amplitudes and phases have been obtained for each station. It is found that the amplitude of the diurnal anisotropy varies with a period of one solar activity cycle (11 years), whereas the diurnal phase varies with a period of 22 years (one solar magnetic cycle). The average diurnal amplitudes and phases have also been calculated by grouping the days on the basis of ascending and descending periods of each solar cycle (Cycles 20, 21, 22, and 23). Systematic and significant differences are observed in the characteristics of the diurnal variation between the descending periods of the odd and even solar cycles. The overall vector averages of the descending periods of the even solar cycles (20 and 22) show significantly smaller diurnal amplitudes compared to the vector averages of the descending periods of the odd solar cycles (21 and 23). In contrast, we find a large diurnal phase shift to earlier hours only during the descending periods of even solar cycles (20 and 22), as compared to almost no shift in the diurnal phase during the descending periods of odd solar cycles. Further, the overall vector average diurnal amplitudes of the ascending period of odd and even solar cycles remain invariant from one ascending period to the other, or even between the even and odd solar cycles. However, we do find a significant diurnal phase shift to earlier hours during the ascending periods of odd solar cycles (21 and 23) in comparison to the diurnal phase in the ascending periods of even solar cycles (20 and 22).  相似文献   

5.
Singh  Jagdev  Cowsik  R.  Raveendran  A. V.  Bagare  S. P.  Saxena  A. K.  Sundararaman  K.  Krishan  Vinod  Naidu  Nagaraja  Samson  J. P. A.  Gabriel  F. 《Solar physics》1997,170(2):235-252
An experiment to search for short-period oscillations in the solar corona was conducted during the total solar eclipse of 1995 October 24 at Kalpi, India. The intensity in the continuum, centred around 5500 Å and with a passband having a half-width of 240 Å, was recorded at a counting rate of 20 Hz using a thermoelectric-liquid cooled photomultiplier. The power-spectrum analysis of the data reveals that most of the power is contained in 6 frequencies below 0.2 Hz. A least-square analysis gives the periods of the 6 frequency components to be 56.5, 19.5, 13.5, 8.0, 6.1, and 5.3 s. These oscillations are found to be sinusoidal, and their amplitudes are found to lie in the rangeinebreak 0.2–1.3% of the coronal brightness. Assuming these oscillations to be fast magnetosonic modes, the calculations indicate the availability of enough flux for the heating of the active regions in the solar corona.  相似文献   

6.
We present the results of our study of Jupiter and its radiation belts with a resolution of 6 arcsec at a frequency of 30 GHz using the RATAN-600 radio telescope and a MARS matrix radiometer with a sensitivity of about 6 mK ?1/2. We monitored the integrated emission from the Jovian disk with a signal-to-noise ratio of more than 1000 for 30 days and showed its radio emission to be highly stable (≈1%). Based on daily data for the one-dimensional radio brightness distribution over the disk, we mapped the longitudinal radio brightness distribution over 100 rotation periods of Jupiter around its axis. Neither hot nor cold spots with a temperature contrast of more than 1 K were detected; their contribution to the total radio flux from the Jovian disk was no more than 0.2%. The one-dimensional latitudinal (longitude-averaged) distribution obtained on VLA with a similar resolution is shown to be an order of magnitude less uniform than the one-dimensional longitudinal (latitude-averaged) distribution obtained on RATAN-600. We have studied the radiation belts at such high frequencies for the first time and estimated their intensities and variability levels under the effect of external factors. The variable component of the radiation belts was shown to have not exceeded 0.5% of the integrated spectrum of Jupiter over the entire period of its observations. We estimated the contribution of the Galilean satellites (“Galilean noise”) in low-resolution observations; the accuracy of allowing for this noise is determined by the accuracy of estimating the temperatures of the satellites at the observing frequency. The uncertainty in the total flux does not exceed 0.1%.  相似文献   

7.
This paper addresses the influence of external forcing (changes in tectonics, sea level and climate) on the downstream and long-term (103–105 years) evolution of sediment composition along a fluvial longitudinal profile. The River Meuse served as a case study for a semi 2-D forward-modelling approach to simulate the downstream sediment transport in the 200- to 0-ka period. This has been related to bulk geochemical properties of the tributary catchments to quantify the bulk composition of the sediment load in the main river. The model was used to test the hypothesis that long-term fluvial dynamics influences sediment composition.The simulation exercise showed that long-term fluvial dynamics can yield systematic temporal changes in fluvial sediment composition, especially in high-relief areas. We tested a scenario of minimal discharges and maximum hillslope erosion during cold glacial periods (weathering-limited sediment supply), alternating with maximal discharges and minimal hillslope erosion during prolonged interstadials or interglacials (transport-limited sediment supply). This scenario largely reproduced the timing and direction of measured changes in the bulk and clay geochemistry of fine-grained sediments, which were deposited in the River Meuse lower reach from 13 to 0 ka. However, it failed to reproduce the measured amplitude of change, which was five to six times larger than the modelled amplitude. This suggests that climate-dependent changes in weathering intensity of rocks and saprolite in the source areas were more important and that aeolian inputs from outside the drainage basin have co-determined the sediment composition.  相似文献   

8.
De Meyer  F. 《Solar physics》1998,181(1):201-219
The modulation model of the solar magnetic cycle for the time interval from 1650 to 1996 A.D. describes an harmonic oscillator with a basic (22.13 ± 0.05)-yr period, which is subjected to amplitude and phase variations that can be represented by a sum of trigonometric series. The simulated sunspot data explain 97.9% of cycle peak height variance and the residual standard deviation is 8.6 mean annual sunspots. A peak height of 139 for cycle 23 occurring in 2001 is predicted, whereas cycle 24 would have a maximum around 132 in 2014. Simulation of the sunspot numbers from 1000 until 2400 A.D. shows that the model recreates recurring minima (Maunder and Spörer Minimum). The prediction also expects a high level of amplitude modulation in the interval 1950–2010 with a rapid decrease afterwards. A greatly reduced cycle activity is reproduced by the simulation from about 2065 to 2100 A.D. No direct explanation of the long-term periodicities of the model can be advanced. The high-frequency contribution of the phase modulation, which accounts for the skewness of the solar cycle, shows coincidences with the orbital periods of Jupiter and Saturn, but no physical basis for the matching periodicities can be conceived.  相似文献   

9.
Watari  Shinichi  Kunitake  Manabu  Watanabe  Takashi 《Solar physics》2001,204(1-2):425-438
One of the large Sun–Earth connection events in solar cycle 23 occurred between 14 and 16 July 2000. Anomalies occurring on several satellites were reported in association with this event. Statistical study of extreme events is important not only for a view of space weather but for seeking ways to predict such kinds of large events. The Bastille Day event was characterized by a large flux (24 000 p.f.u. at its maximum) of solar energetic protons and a fast average transit speed of approximately 1500 km s−1 of the interplanetary disturbance. A geomagnetic Kp index of more than 9 was observed after an interval of approximately eleven years since 1989. We found that return periods of extreme space weather (e.g., large flares, solar energetic proton events, and large geomagnetic storms) satisfied the Weibull distribution.  相似文献   

10.
The wavelet analysis of the period of solar activity   总被引：1，自引：0，他引：1  
Using the wavelet technique, we analyzed the time series of solar radio fluxes at 2800 MHz as well as sunspot numbers and areas. The results are as follows: (1) These three data sets demonstrate that the most prominent period is 10.69 years and that all other periods are not obvious. (2) The wavelet power spectrum displays the changes of the power spectrum over the entire time-period range and shows the variations in the local power of a given period in a given time interval. Our analysis shows that periods shorter than one year are distinct only around solar activity maximum. (3) The time curves of the wavelet power at three periods (10.69 years, 5.11 years and 155.5 days) for the three times series are rather alike, with the same times of peaks and similar undulations. The shorter the period, the more frequent the fluctuations.  相似文献   

11.

The radio frequency emission at 10.7 cm (or 2800 MHz) wavelength (considered as solar flux density) out of different possible wavelengths is usually selected to identify periodicities because of its high correlation with solar extreme ultraviolet radiation as well as its complete and long observational record other than sunspot related indices. The solar radio flux at 10.7 cm wavelength plays a very valuable role for forecasting the space weather because it is originated from lower corona and chromospheres region of the Sun. Also, solar radio flux is a magnificent indicator of major solar activity. Here in the present work the solar radio flux data from 1965 to 2014 observed at the Domimion Radio Astrophysical Observatory in Penticton, British Columbiahas been processed using Date Compensated Discrete Fourier Transform (DCDFT) to identify predominant periods within the data along with their confidence levels. Also, the multi-taper method (MTM) for periodicity analysis is used to validate the observed periods. Present investigation exhibits multiperiodicity of the time series F10.7 solar radio flux data around 27, 57, 78, 127, 157, 4096 days etc. The observed periods are also compared with the periods of MgII Index data using same algorithm as MgII Index data has 99.9% correlation with F10.7 Solar Radio Flux data. It can be observed that the MgII index data exhibits similar periodicities with very high confidence levels.Present investigation also clearly indicates that the computed results are very much confining with the results obtained in different communication for the similar data of 10.7 cm Solar Radio Flux as well as for the other solar activities.

  相似文献   

12.
We have analysed intermediate-term periodicities in the green corona by dividing 10° latitudinal belts for the solar cycles 18, 19, and 20 (1947–1976). Discrete Fourier transform technique was used and three noticeable periodicities (3.48, 2.57, and 2.27 years) were found. The physical origin of these periods is not known, but evidence in our results exclude the possibility that the observed periods are a harmonic due to the method of analyse. The period of 3.48-year is the strongest one. 17.6-month periodicity was found only on around +40° belt while 155-day periodicity was not found in our analysis.  相似文献   

13.
Statistical analyses on available archaeomagnetic intensity data mainly from the Aegean area and supplemented by some from Bulgaria and Czechoslovakia have revealed the existence of periodicities.The power spectrum analysis showed the existence of periods of 100–120, 200, 250, 540, 800 and 1600 years with an overall significance level of around 95%.Maximum entropy method showed the existence of significant periods of 100–130, 200, 240, 400–450 and 1200–1350 years.Emphasis is given to the 200-year period in relation to similar periods of other solar-terrestrial phenomena as well as to theoretical calculations.  相似文献   

14.
David Pieri 《Icarus》1976,27(1):25-50
The distribution of small channels on Mars has been mapped from Mariner 9 images, at the 1:5 000 000 scale, by the author. The small channels referred to here are small valleys ranging in width from the resolution limit of the Mariner 9 wide-angle images (～1 km) to about 10 km. The greatest density of small band occurs in dark cratered terrain. This dark zone forms a broad subequatorial band around the planet. The observed distribution may be the result of decreased small-channel visibility in bright areas due to obscuration by a high albedo dust or sediment mantle. Crater densities within two small-channel segments show crater size-frequency distributions consistent with those of the oldest of the heavily cratered plains units. Such crater densities coupled with the almost exclusive occurrence of small channels in old cratered terrain and the generally degraded appearance of small channels in the high-resolution images (～100 m) imply a major episode of small-channel formation early in Martian geologic history.  相似文献   

15.
The results of galaxy counts on plates taken with the Tautenburg Schmidt telescope in a 36□° region around the globular cluster M3 are presented and discussed. More than 26000 galaxies on four blue plates (covering the whole region) and nearly 18000 galaxies on two red plates (covering half the region) have been counted in 5′ × 5′ cells. The discussion in the present paper includes a first determination of the two-point correlation function and a dispersion curve analysis. The results are not very different from those obtained for the Jagiellonian field. It is suggested that counting errors may influence the conclusions drawn for the space distribution of galaxies and its possible secular change.  相似文献   

16.
We report the discovery of large-amplitude (∼0.25 mag) pulsations in the bright ( V =12.8) sdB star, PG 1605+072. The dominant period is 480 s, but more than 20 periods were present on at least three separate occasions. Frequency analysis of the complete data set yields more than 30 periods. A few of these are harmonics or linear combinations of the strongest modes. Excluding the latter, the periods span a range of almost 400 s, which contrasts with the typical range <20 s for most other EC 14026 stars.
Analysis of multicolour photometry limited any cool companion to being a main-sequence star of type M0 or later. Balmer line profile fitting yielded an effective temperature of 32 100±1000 K and a log g of 5.25±0.10, significantly smaller than in the other stars of the EC 14026 class, and possibly indicative of a more evolved state. The lower gravity is probably responsible for the fact that the pulsation periods and amplitudes are respectively much longer and larger than in other stars of the class. This star is an obvious target for asteroseismological investigation using a multilongitude photometric campaign.  相似文献   

17.
研究了Blazar天体3C 66A光学波段的准周期光变行为.收集了3C 66A光学V波段将近18 yr (2003—2021年)的测光数据,观测数据主要来源是:上海天文台(ShAO)、 AAVSO (The American Association of Variable Star Observers)数据库、Steward天文台.使用了Jurkevich和Lomb-Scargle两种方法分析了光变数据.Jurkevich方法得到了(850±90) d (～2.3 yr)和(1150±140) d (～3.2 yr)的光变周期,而Lomb-Scargle方法在充分考虑了“红噪声”效应之后同样得到了(869±70) d和(1111±90) d的光变周期,它们的置信水平分别为>99%和> 95%.通过与之前的研究结果比较,发现～2.3 yr的光变周期在3C 66A的历史光变数据中是一个稳定的周期,而～3.2 yr的周期则是不稳定的.  相似文献   

18.
Sediment samples were collected from a borehole in the northern South China Sea with the depositional age back to 400 ka BP, for grain size and geochemical analyses to constrain the sediment provenance and paleoenvironmental variability. Geochemical indices of Th/Sc, Ti/Nb and Th/Nb ratios suggest that the Zhujiang (Pearl River) was the main provenance of the inner shelf sediments of Hong Kong deposited during interglacial periods, whereas the locally-derived granitoids contributed significantly to the exposed inner shelf through the incision of local streams during glacial periods. Furthermore, the influence of the Zhujiang-derived sediments on the inner shelf of Hong Kong varied spatially and temporally with different sea-level changes during the past 400 kyr. Chemical weathering indices suggest hot and wet climate conditions were dominant in South China during interglacial periods of marine isotope stages (MIS) 7, 9 and 11 whereas a dry and cold paleoclimate prevailed during glacial periods of MIS 6 which accounts for weak chemical weathering and coarse-grained deposition on the inner shelf. The Holocene and last interglacial period did not see more intense chemical weathering in the Zhujiang drainage basin than other interglacial periods. Although the high resolution paleoenvironmental changes can not be easily reconstructed due to ubiquitous unconformity in the sedimentary strata and weak age controls compared to the deep sea sedimentation, the present study sheds new lights on the understanding of the transport process of the Zhujiang sediment in the deep ocean and provides a teleconnection of East Asian palaeomonsoon activity between South China, the inland and open sea areas.  相似文献   

19.
The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.  相似文献   

20.
Abstract— The enrichment of F on Antarctic meteorites is the result of their exposure to the atmosphere, and its measurement allows a subdivision of the terrestrial age into a duration of exposure on the ice and the time a meteorite was enclosed by the ice. In many cases, the periods of surface exposure are only small fractions of the terrestrial ages of meteorites collected in Antarctica. The enrichment of F on the surfaces of Antarctic achondrites was investigated by means of nuclear reaction analysis (NRA): scanning proton beams with an energy of 2.7 and 3.4 MeV were used to induce the reactions 19F(p,αγ)16O and 19F(p, p'γ)19F, respectively. Gamma signals proportional to the F content were measured. The following Antarctic achondrites were investigated: Martian meteorite ALH 84001; diogenite ALHA77256; the eucrites ALHA81011 and ALHA78132; and in addition, the H5 chondrite ALHA79025. For ALH 84001, our data indicate a period of exposure on the ice of <500 years. Thus, this specimen was enclosed in the ice >95% of its terrestrial age of 13 000 years.  相似文献   

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