The Periodicity of High-Latitude Solar Activity     

K. J. Li  Q. X. Li  T. W. Su  P. X. Gao 《Solar physics》2006,239(1-2):493-501

The periodicity of high-latitude solar activity has been studied with the use of the Carte Synoptique solar filaments archive. The Morlet wavelet is utilized to analyze the periodicity of the number of solar filaments at latitudes over 50° during Carrington solar rotations 876 – 1823. For solar filaments at latitudes over 50°, the most eminent periods are about 10.23 and 10.90 years, which correspond to the Schwabe period of high-latitude solar activity, and the these periods make-up a highly significant proportion of the time span considered. The periods of 1.3 and 1.7 years and the quasi-biennial 2 – 3-year oscillation often mentioned in the literature are not found to be a feature of every solar cycle but seem to appear only from time to time.  相似文献   

Multifrequency study of the Large Magellanic Cloud supernova remnant (SNR) B0513−692 and new SNR candidate J051327−6911     

I. S. Boji&#;i&#;  M. D. Filipovi&#;  Q. A. Parker  J. L. Payne  P. A. Jones  W. Reid  A. Kawamura  Y. Fukui 《Monthly notices of the Royal Astronomical Society》2007,378(4):1237-1247

We present a new multiwavelength study of supernova remnant (SNR) B0513−692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324−691049. This is identified as a likely compact H  ii region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz  (λ≃ 6 cm and λ≃ 3.5 cm)  to determine the large-scale morphology, spectral index and polarization characteristics of B0513−692 for the first time. We detect a strongly polarized region (49 per cent) in the remnant's southern edge  (λ≃ 6 cm)  . Interestingly, we also detect a small (∼40 arcsec) moderately bright, but distinct optical, circular shell in our Hα imagery which is adjacent to the compact H  ii region and just within the borders of the north-eastern edge of B0513−692. We suggest that this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in three imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [S  ii ] emission relative to Hα).  相似文献   

Catastrophic Behavior of Multiple Coronal Flux Rope System     

J. Y. Ding  Y. Q. Hu  J. X. Wang 《Solar physics》2006,235(1-2):223-234

A major solar active event called Bastille Day Event occurred in AR 9077 on July 14, 2000. Simultaneous occurrence of a filament eruption, a flare and a coronal mass ejection was observed in this event. Previous analyses of this event show that before the event, there existed an activation and eruption of a huge trans-equatorial filament, which might play a crucial role in triggering the Bastille Day event. This implies that independent flux systems are closely related to and affect each other, which has encouraged us to investigate the catastrophic behavior of a multiple coronal flux rope system with the use of a 2.5-D time-dependent MHD model. A force-free field that contains three separate coronal flux ropes is taken to be the initial state. Starting from this state, we increase either the annular or the axial flux of a certain flux rope to examine the catastrophic behavior of the system in two regimes, the ideal MHD regime and the resistive MHD regime. It is found that a catastrophe occurs if the flux exceeds a certain critical value, or the magnetic energy of the system exceeds a certain threshold: the rope of interest breaks away from the base and escapes to infinity, leaving a current sheet below. Moreover, the destiny of the remainder flux ropes relies on whether reconnection takes place across the current sheet. In the ideal MHD regime, i.e., in the absence of reconnection, these ropes remain to be attached to the base in equilibrium, whereas in the resistive MHD regime they abruptly erupt upward during reconnection and escape to infinity. Reconnection causes the field lines to close back to the base and thus changes the background field outside the attached flux ropes in such a way that the constraint on these ropes is substantially relaxed and the corresponding catastrophic energy threshold is reduced accordingly, leading to a catastrophic eruption of these ropes. Since magnetic reconnection is generally inevitable when a current sheet forms and develops through an eruption of one flux rope, the eruption of this flux rope must lead to an eruption of the others. This provides an example to demonstrate the interaction between several independent magnetic flux systems in different regions, as implied by the Bastille Day event, and may serve as a possible mechanism for sympathetic events occurring on the Sun.  相似文献   

Energy cascades in the upper ocean     

Ray Q. Lin Scott Chubb 《中国海洋湖沼学报》2006,24(3):225-235

1 INTRODUCTION Wave-wave interactions play a key role in the evolution of the dynamics of upper ocean phenomena. Even though they conserve total wave energy, these interactions cause energy cascades to occur in which wave-energy is transferred at the surf…  相似文献   

The effect of differential refraction on wave propagation in rotating pulsar magnetospheres     

D. Fussell  Q. Luo 《Monthly notices of the Royal Astronomical Society》2004,349(3):1019-1026

  相似文献   

Vertical vibration of an elastic strip footing on saturated soil     

Y. Q. Cai  Y. M. Cheng  S. K. Alfred Au  C. J. Xu  X. H. Ma 《国际地质力学数值与分析法杂志》2008,32(5):493-508

Based on Biot's dynamic coupled equations, the vertical vibration of an elastic strip footing on the surface of saturated soil is studied. Utilizing the Fourier transform, the governing dynamic differential equations for saturated poroelastic medium are solved. Considering the mixed boundary value conditions at the bottom of the foundation, a pair of dual integral equations about the vertical vibration of an elastic strip footing is derived, which can be converted to a set of linear equations by means of infinite series of orthogonal functions. The relation between the dynamic compliance coefficients and the dimensionless frequency tends to be gentle with decreasing footing rigidity, while the dimensionless frequency has only small effect on the dynamic compliance coefficients. When the dynamic permeability is large, its effect on the dynamic compliance coefficients should be taken into consideration. Furthermore, the dynamic compliance coefficients are found to be not sensitive to Poisson's ratio of the soil for footing on saturated soil. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Finite element analyses of layered visco‐elastic system under vertical circular loading     

Q. Xu  M. S. Rahman 《国际地质力学数值与分析法杂志》2008,32(8):897-913

Analyses for the response of a linear visco‐elastic system subjected to axi‐symmetric vertical circular loading are presented. Hankel transforms with respect to the radial spatial coordinate are used to reduce the three‐dimensional problem to that involving only a single spatial dimension, which is then discretized using the finite element method. Three techniques are employed to handle the time factor in the visco‐elastic material: (i) direct time integration; (ii) Fourier transforms; and (iii) Laplace transforms. These methods are compared and evaluated through their numerical results. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

On Both the Time Histories of the 0.511 MeV Line and 2.223 MeV Line from the X4.8 Flare of 23 July 2002 Observed with Rhessi     

Gan  W.Q. 《Solar physics》2004,219(2):279-287

High-spectral-resolution measurements of the 2.223 MeV neutron capture line and the 0.511 MeV positron-electron annihilation line have been made with the Reuven Ramaty High-Energy Solar Spectroscopic Imager during the X4.8 flare of 23 July 2002. We have tried to explain both the time histories of the 2.223 MeV line and the 0.511 MeV line, adopting a power-law spectrum of accelerated ions. The results show that with a power-law spectral index of 3.52, the calculational time histories can roughly reproduce the observations. An improved fit between the calculated 2.223 MeV line and the observed 2.223 MeV line can be achieved if we allow the spectrum of accelerated ions to vary with time.  相似文献   

An Improved Method to Derive the Lower Energy Cutoff of non-Thermal Electrons From Hard x-Rays of Solar Flares     

Gan  W.Q.  Li  Y.P.  Chang  J.  Tiernan  James M. 《Solar physics》2002,207(1):137-147

By changing a dimensionless calculation to a dimensional one, introducing a more accurate bremsstrahlung cross section, and using a more reasonable fitting energy range, we have recalculated the hard X-ray bremsstrahlung produced by a beam of power-law electrons with a lower energy cutoff (E _c). The method to deduce E _c from the hard X-ray spectral observations has therefore been refined in comparison with our previous one. The universality of this method has been clarified and discussed. We have applied this improved method to the 54 BATSE/Compton Gamma Ray Observatory (CGRO) hard X-ray events. It was found that about 44% of sample hard X-ray spectra can be directly explained by a beam of power-law electrons with a lower energy cutoff. The value of E _c, varying from 45 keV to 97 keV, is on average 60 keV. Another 44% of sample hard X-ray spectra might be explained by a beam of power-law electrons with the energy cutoff lower than 45 keV, which is however beyond the availability of BATSE/CGRO. Still another 11% sample hard X-ray spectra cannot be explained by a beam of power-law electrons with a lower energy cutoff. These results, based on the lower energy resolution data, however, should be compared in the future with that based on a higher energy resolution data, like the data from HESSI.  相似文献   

The INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS)     

Janet E. Drew  R. Greimel  M. J. Irwin  A. Aungwerojwit  M. J. Barlow  R. L. M. Corradi  J. J. Drake  B. T. Gänsicke  P. Groot  A. Hales  E. C. Hopewell  J. Irwin  C. Knigge  P. Leisy  D. J. Lennon  A. Mampaso  M. R. W. Masheder  M. Matsuura  L. Morales-Rueda  R. A. H. Morris  Q. A. Parker  S. Phillipps  P. Rodriguez-Gil  G. Roelofs  I. Skillen  J. L. Sokoloski  D. Steeghs  Y. C. Unruh  K. Viironen  J. S. Vink  N. A. Walton  A. Witham  N. Wright  A. A. Zijlstra  A. Zurita 《Monthly notices of the Royal Astronomical Society》2005,362(3):753-776

  相似文献