Study of Ribbon Separation and Magnetic Reconnection Rates in a Two-Ribbon Flare     

W. Xie  H. Zhang  H. Wang 《Solar physics》2009,254(2):271-283

In this paper, we present a study of the correlation between the speed of flare ribbon separation and the magnetic flux density during the 10 April 2001 solar flare. The study includes the section of the neutral line containing the flare core and its peripheral area. This event shows clear two-ribbon structure and inhomogeneous magnetic fields along the ribbons, so the spatial correlation and distribution of the flare and magnetic parameters can be studied. A weak negative correlation is found between the ribbon separation speed (V _r) and the longitudinal magnetic flux density (B _z ). This correlation is the weakest around the peak of the flare. Spatially, the correlation is also weakest at the positions of the hard X-ray (HXR) sources. In addition, we estimate the magnetic reconnection rate (electric field strength in the reconnection region E _rec) by combining the speed of flare ribbons and the longitudinal magnetic flux density. During flare evolution, the time profiles of the magnetic reconnection rate are similar to that of the ribbon separation speed, and the speeds of ribbon separation are relatively slow in the strong magnetic fields (i.e., V _r is negatively correlated with B _z ). However, along the flare ribbons, E _rec fluctuates in a small range except near the HXR source. A localized enhancement of the reconnection rate corresponds to the position of the HXR source.  相似文献   

Short-Term Periodicities in Sunspot Activity and Flare Index Data during Solar Cycle 23     

H. Kiliç 《Solar physics》2009,255(1):155-162

The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum, and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion of Pap, Tobiska, and Bouwer (1990, Solar Phys. 129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys. 65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23.  相似文献   

A Century of Solar Ca <Emphasis Type="SmallCaps">ii</Emphasis> Measurements and Their Implication for Solar UV Driving of Climate     

Peter Foukal  Luca Bertello  William C. Livingston  Alexei A. Pevtsov  Jagdev Singh  Andrey G. Tlatov  Roger K. Ulrich 《Solar physics》2009,255(2):229-238

Spectroheliograms and disk-integrated flux monitoring in the strong resonance line of Ca ii (K line) provide the longest record of chromospheric magnetic plages. We compare recent reductions of the Ca ii K spectroheliograms obtained since 1907 at the Kodaikanal, Mt. Wilson, and US National Solar Observatories. Certain differences between the individual plage indices appear to be caused mainly by differences in the spectral passbands used. Our main finding is that the indices show remarkably consistent behavior on the multidecadal time scales of greatest interest to global warming studies. The reconstruction of solar ultraviolet flux variation from these indices differs significantly from the 20th-century global temperature record. This difference is consistent with other findings that, although solar UV irradiance variation may affect climate through influence on precipitation and storm tracks, its significance in global temperature remains elusive.  相似文献   

Periodicities in Global Mean TEC from GNSS Observations     

L. H. Ma  Y. B. Han  Z. Q. Yin 《Earth, Moon, and Planets》2009,105(1):3-10

As an important measurement parameter, global total electron content (TEC) is appropriate for the study of the Sun–Earth connection. In this paper, the wavelet technique is employed to investigate the periodicities in global mean TEC during 1995–2008. Analysis results show several remarkable components (including 27-day, semiannual and annual cycles) existing in global mean TEC with obvious time-variable characteristics, besides 11-year cycle. After analyzing sunspot numbers and solar extreme ultra-violet (EUV) radiation variations during this time period, except for semiannual variations, close correlation between global mean TEC and solar variations is found, especially, a strong resemblance of the 27-day fluctuation exists in global mean TEC, sunspot and solar EUV radiation variations.  相似文献   

The annual period of the Earth’s seismic activity for 1964–2007     

A. E. Volvach  N. N. Gor’kavyi  A. I. Dmitrotsa  L. S. Levitsky 《Bulletin of the Crimean Astrophysical Observatory》2009,105(1):150-155

The catalog of the United States National Earthquake Information Center (NEIC, 2007) was used for a Fourier analysis of planetary seismic activity from 1964 to 2007 (401219 earthquakes with M ≥ 3 and hypocenter depths H ≥ 1 km) for the Northern Hemisphere (248291 events) and for the Southern Hemisphere (152928 events). The annual periodicity of weak earthquakes (M < 5.0) was verified with a high degree of reliability. All regularities (depending on the geographic latitude, hypocenter depths, and north-south asymmetry) revealed earlier (in 1964–1990) for this period are shown to exist for the period of 1964–2007.  相似文献   

The DynaMICCS perspective     

S. Turck-Chièze  P. Lamy  C. Carr  P. H. Carton  A. Chevalier  I. Dandouras  J. M. Defise  S. Dewitte  T. Dudok de Wit  J. P. Halain  S. Hasan  J. F. Hochedez  T. Horbury  P. Levacher  M. Meissonier  N. Murphy  P. Rochus  A. Ruzmaikin  W. Schmutz  G. Thuillier  S. Vivès 《Experimental Astronomy》2009,23(3):1017-1055

The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface layers, the photosphere/chromosphere layers and the low corona. The mission delivers data and knowledge that no other known mission provides for understanding space weather and space climate and for advancing stellar physics (internal dynamics) and fundamental physics (neutrino properties, atomic physics, gravitational moments...). The science objectives are achieved using Doppler and magnetic measurements of the solar surface, helioseismic and coronographic measurements, solar irradiance at different wavelengths and in-situ measurements of plasma/energetic particles/magnetic fields. The DynaMICCS payload uses an original concept studied by Thalès Alenia Space in the framework of the CNES call for formation flying missions: an external occultation of the solar light is obtained by putting an occulter spacecraft 150 m (or more) in front of a second spacecraft. The occulter spacecraft, a LEO platform of the mini sat class, e.g. PROTEUS, type carries the helioseismic and irradiance instruments and the formation flying technologies. The latter spacecraft of the same type carries a visible and infrared coronagraph for a unique observation of the solar corona and instrumentation for the study of the solar wind and imagers. This mission must guarantee long (one 11-year solar cycle) and continuous observations (duty cycle > 94%) of signals that can be very weak (the gravity mode detection supposes the measurement of velocity smaller than 1 mm/s). This assumes no interruption in observation and very stable thermal conditions. The preferred orbit therefore is the L1 orbit, which fits these requirements very well and is also an attractive environment for the spacecraft due to its low radiation and low perturbation (solar pressure) environment. This mission is secured by instrumental R and D activities during the present and coming years. Some prototypes of different instruments are already built (GOLFNG, SDM) and the performances will be checked before launch on the ground or in space through planned missions of CNES and PROBA ESA missions (PICARD, LYRA, maybe ASPIICS).  相似文献   

High resolution spectroscopy of two young active late type stars within 20 parsecs of the Sun     

Hui-Juan Wang Jian-Yan Wei 《中国天文和天体物理学报》2009,9(3)

We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. It will help us to have a better understanding of the structure and evolutionary history of the Milky Way. The radial ve-locities (RV) of HIP 544 and HIP 46843 are measured to be -6.88±0.13km s-1 and 8.30±0.16km s-1, respectively, which are more accurate than before. The equivalent widths (EW) of the Li I 6707.8 A absorption line of HIP 544 and HIP 46843 are mea-sured to be 110±5mA and 195±5mA respectively. Based on these properties, HIP 544 is estimated to be 100-800Myr old and HIP 46843 30-100Myr old using three relatively creditable methods.  相似文献   

Flare-induced signals in polarization measurements during the X2.6 flare on 2005 January 15     

Meng Zhao  Jing-Xiu Wang  Sarah Matthews  Ming-De Ding  Hui Zhao  Chun-Lan Jin 《中国天文和天体物理学报》2009,9(7)

Flare-induced signals in polarization measurements which were manifested as apparent polarity reversal in magnetograms have been reported since 1981. We are motivated to further quantify the phenomenon by asking two questions: can we distinguish the flare-induced signals from real magnetic changes during flares, and what we can learn about flare energy release from the flare-induced signals? We select the X2.6 flare that occurred on 2005 January 15, for further study. The flare took place in NOAA active re-gion (AR) 10720 at approximately the central meridian, which makes the interpretation of the vector magnetograms less ambiguous. We have identified that flare-induced signals during this flare appeared in six zones. The zones are located within an average distance of 5 Mm from their weight center to the main magnetic neutral line, have an average size of (0.6±0.4)×1017 cm2, duration of 13±4 min, and flux density change of 181±125 G in the area of reversed polarity. The following new facts have been revealed by this study: (1) the flare-induced signal is also seen in the transverse magnetograms but with smaller magnitude, e.g., about 50 G; (2) the flare-induced signal mainly manifests itself as apparent polarity reversal, but the signal starts and ends as a weakening of flux density; (3) The flare-induced signals appear in phase with the peaks of hard X-ray emission as observed by the Ramaty High Energy Solar Spectroscopic lmager (RHESSI), and mostly trace the position of RHESSI hard X-ray footpoint sources. (4) in four zones, it takes place cotemporally with real magnetic changes which persist after the flare. Only for the other two zones does the flux density recover to the pre-flare level immediately after the flare.The physical implications of the flare-induced signal are discussed in view of its relevance to the non-thermal electron precipitation and primary energy release in the flare.  相似文献   

Simulation of Tsaoling landslide, Taiwan, based on Saint Venant equations over general topography     

C.Y. Kuo  Y.C. Tai  F. Bouchut  A. Mangeney  M. Pelanti  R.F. Chen  K.J. Chang 《Engineering Geology》2009,104(3-4):181-189

The 1999 Chi-Chi earthquake triggered the catastrophic Tsaoling landslide in Taiwan. The geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0.126 km³ and 0.15 km³ respectively. The debris material ran over a distance of 1.6 km with 500 m descent in elevation. In this paper, we use the continuum model of hydraulic flow, SHALTOP^2D, based on the equations of Bouchut and Westdickenberg to simulate numerically the landslide dynamics. When the mass is moving, the flow is assumed hydrostatic with a basal Coulomb friction. The best fit is obtained using the basal friction angle equal to 6°, the only parameter of the simulation, uniformly applied in the calculation domain. The landslide front reaches the Chinshui river valley, the foothill of the slope, within only about 25 s after initiation and the motion settles in about 113 s. The maximum speed is estimated 75 m/s. The spreading of the deposit agrees well with the field measurement.  相似文献   

On the swelling potential of compacted high plasticity clays     

Valry Ferber  Jean-Claude Auriol  Yu-Jun Cui  Jean-Pierre Magnan 《Engineering Geology》2009,104(3-4):200-210

We conducted a study of the spatial distributions of seismicity and earthquake hazard parameters for Turkey and the adjacent areas, applying the maximum likelihood method. The procedure allows for the use of either historical or instrumental data, or even a combination of the two. By using this method, we can estimate the earthquake hazard parameters, which include the maximum regional magnitude Mˆ_max, the activity rate of seismic events and the well-known bˆ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. These three parameters are determined simultaneously using an iterative scheme. The uncertainty in the determination of the magnitudes was also taken into consideration. The return periods (RP) of earthquakes with a magnitude M ≥ m are also evaluated. The whole examined area is divided into 24 seismic regions based on their seismotectonic regime. The homogeneity of the magnitudes is an essential factor in such studies. In order to achieve homogeneity of the magnitudes, formulas that convert any magnitude to an M_S-surface scale are developed. New completeness cutoffs and their corresponding time intervals are also assessed for each of the 24 seismic regions. Each of the obtained parameters is distributed into its respective seismic region, allowing for an analysis of the localized seismicity parameters and a representation of their regional variation on a map. The earthquake hazard level is also calculated as a function of the form Θ = (Mˆ_max,RP_6.0), and a relative hazard scale (defined as the index K) is defined for each seismic region. The investigated regions are then classified into five groups using these parameters. This classification is useful for theoretical and practical reasons and provides a picture of quantitative seismicity. An attempt is then made to relate these values to the local tectonics.  相似文献