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951.
P. Pappa Kalaivani S. Umapathy A. Shanmugaraju O. Prakash 《Astrophysics and Space Science》2010,330(2):237-242
We have studied the characteristics of coronal mass ejections (CMEs) associated with Deca-Hectometric (DH) type II radio bursts (1–14 MHz) in the interplanetary medium during the year 1997–2005. The DH CMEs are divided into two parts: (i) DH CMEs (All) and (ii) DH CMEs (Limb). We found that 65% (177/273) of all events have the speed >900 km?s?1 and the remaining 35% (96/273) events have the speed below 900 km?s?1. The average speed of all and limb DH CMEs are 1230 and 1288 km?s?1, respectively, which is nearly three times the average speed of general population of CMEs (473 km?s?1). The average widths of all and limb DH CMEs are 105° and 106°, respectively, which is twice the average width (52°) of the general population of CMEs. We found a better correlation between the speed and width of limb DH CMEs (R=?0.61) than all DH CMEs (R=?0.53). Only 28% (177/637) of fast >900 km?s?1 general population of CMEs are reported with DH type II bursts counterpart. The above results gives that the relation between the CME properties is better for limb events. 相似文献
952.
H. S. Jeon S. Cho Y. S. Kwak J. K. Chung J. U. Park D. K. Lee M. Kuzmicz-Cieslak 《Astrophysics and Space Science》2011,332(2):341-351
The atmospheric mass density of the upper atmosphere from the spherical Starlette satellite’s Precise Orbit Determination
is first derived with Satellite Laser Ranging measurements at 815 to 1115 km during strong solar and geomagnetic activities.
Starlette’s orbit is determined using the improved orbit determination techniques combining optimum parameters with a precise
empirical drag application to a gravity field. MSIS-86 and NRLMSISE-00 atmospheric density models are compared with the Starlette
drag-derived atmospheric density of the upper atmosphere. It is found that the variation in the Starlette’s drag coefficient
above 800 km corresponds well with the level of geomagnetic activity. This represents that the satellite orbit is mainly perturbed
by the Joule heating from geomagnetic activity at the upper atmosphere. This result concludes that MSIS empirical models strongly
underestimate the mass density of the upper atmosphere as compared to the Starlette drag-derived atmospheric density during
the geomagnetic storms. We suggest that the atmospheric density models should be analyzed with higher altitude acceleration
data for a better understanding of long-term solar and geomagnetic effects. 相似文献
953.
K. A. Firoz J. Hwang I. Dorotovič T. Pintér Subhash C. Kaushik 《Astrophysics and Space Science》2011,331(2):469-484
Cosmic rays registered by Neutron Monitor on the surface of the Earth are believed to originate from outer space, and sometimes
also from the exotic objects of the Sun. Whilst the intensities of the cosmic rays are observed to be enhanced with sudden,
sharp and short-lived increases, they are termed as ground level enhancements (GLEs). They are the occurrences in solar cosmic
ray intensity variations on short-term basis, so different solar factors erupted from the Sun can be responsible for causing
them. In this context, an attempt has been made to determine quantitative relationships of the GLEs having peak increase >5%
with simultaneous solar, interplanetary and geophysical factors from 1997 through 2006, thereby searching the responsible
factors which seem to cause the enhancements. Results suggest that GLE peaks might be caused by solar energetic particle fluxes
and solar flares. The proton fluxes which seemed to cause GLE peaks were also supported by their corresponding fluences. For
most of the flares, the time integrated rising portion of the flare emission refers to the strong portion of X-ray fluxes
which might be the concern to GLE peak. On an average, GLE peak associated X-ray flux (0.71×10−4 w/m2) is much stronger than GLE background associated X-ray flux (0.11×10−6 w/m2). It gives a general consent that the GLE peak is presumably caused by the solar flare. Coronal mass ejection alone does
not seem to cause GLE. Coronal mass ejection presumably causes geomagnetic disturbances characterized by geomagnetic indices
and polarities of interplanetary magnetic fields. 相似文献
954.
L. Zaninetti 《Astrophysics and Space Science》2011,333(1):99-113
A classical and a relativistic law of motion for a supernova remnant (SNR) are deduced assuming an inverse power law behavior
for the density of the interstellar medium and applying the thin layer approximation. A third equation of motion is found
in the framework of relativistic hydrodynamics with pressure, applying momentum conservation. These new formulas are calibrated
against a decade of observations of SN 1993J. The existing knowledge of the diffusive processes of ultrarelativistic electrons
is reviewed in order to explain the behavior of the ‘U’ shaped profile of intensity versus distance from the center of SN 1993J. 相似文献
955.
R. Chandra B. Schmieder C. H. Mandrini P. Démoulin E. Pariat T. Török W. Uddin 《Solar physics》2011,269(1):83-104
We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501
on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections
(CMEs). The central flare ribbons were located at the site of an emerging bipole in the centre of the active region. The negative
polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ≈ 110° within 32 hours.
We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time
to each flare. In particular, we calculate the location of quasi-separatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501,
the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points.
For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally
unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology.
However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable
during each flare, so that magnetic reconnection proceeds differently in both events. 相似文献
956.
Based on the extended Greenwich – NOAA/USAF catalogue of sunspot groups, it is demonstrated that the parameters describing
the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and
the growth of the activity leads to the expansion of the SGZ. The ratio of the sunspot number to the width of the SGZ shows
saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly
due to the expansion of the SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes
of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (Solar Phys.
179, 189, 1998), the latitude distribution of sunspot groups (“the Maunder butterfly diagram”) for the eighteenth and the first half of
the nineteenth centuries is reconstructed and compared with historical sunspot observations. 相似文献
957.
As part of a program to estimate the solar spectrum back to the early twentieth century, we have generated fits to UV spectral
irradiance measurements from 1 – 410 nm. The longer wavelength spectra (150 – 410 nm) were fit as a function of two solar
activity proxies, the Mg ii core-to-wing ratio, or Mg ii index, and the total Ca ii K disk activity derived from ground based observations. Irradiance spectra at shorter wavelengths (1 – 150 nm) where used
to generate fits to the Mg ii core-to-wing ratio alone. Two sets of spectra were used in these fitting procedures. The fits at longer wavelengths (150
to 410 nm) were derived from the high-resolution spectra taken by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)
on the Upper Atmospheric Research Satellite (UARS). Spectra measured by the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite were used for the fits at wavelengths from 1 to 150 nm. To generate fits between solar irradiance and solar
proxies, this study uses the above irradiance data, the NOAA composite Mg ii index, and daily Ca ii K disk activity determined from images measured by Big Bear Solar Observatory (BBSO). In addition to the fitting coefficients
between irradiance and solar proxies, other results from this study include an estimated relationship between the fraction
of the disk with enhanced Ca ii K activity and the Mg ii index, an upper bound of the average solar UV spectral irradiance during periods where the solar disk contains only regions
of the quiet Sun, as was believed to be present during the Maunder Minimum, as well as results indicating that slightly more
than 60% of the total solar irradiance (TSI) variability occurs between 150 and 400 nm. 相似文献
958.
Similarity model of feed support system for FAST 总被引:1,自引:0,他引:1
A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper.
According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on
the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated.
A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed
support system can satisfy the observation accuracy requirement of FAST. 相似文献
959.
Victor G. Kornilov Vladimir M. Lipunov Evgeny S. Gorbovskoy Aleksander A. Belinski Dmitry A. Kuvshinov Natalia V. Tyurina Nikolai I. Shatsky Anatoly V. Sankovich Aleksander V. Krylov Pavel V. Balanutsa Vadim V. Chazov Artem S. Kuznetsov Dmitry S. Zimnuhov Victor A. Senik Andrey G. Tlatov Aleksander V. Parkhomenko Denis V. Dormidontov Vadim V. Krushinsky Ivan S. Zalozhnyh Aleksander A. Popov Sergey A. Yazev Nikolai M. Budnev Kirill I. Ivanov Evgeny N. Konstantinov Oleg A. Gress Oleg V. Chvalaev Vladimir V. Yurkov Yury P. Sergienko Irina P. Kudelina 《Experimental Astronomy》2012,33(1):173-196
Presented paper describes the basic principles and features of the implementation of a robotic network of optical telescopes MASTER, designed to study the prompt (simultaneous with gamma radiation) optical emission of gamma-ray bursts and to perform the sky survey to detect unknown objects and transient phenomena. With joint efforts of Sternberg astronomical institute, High altitude astronomical station of the Pulkovo observatory, Ural state university, Irkutsk state university, Blagoveshchensk pedagogical university, the robotic telescopes MASTER?II near Kislovodsk, Yekaterinburg, Irkutsk and Blagoveshchensk were installed and tested. The network spread over the longitudes is greater than 6?h. A further expansion of the network is considered. 相似文献
960.
The possibility of investigating the sky region near the Galactic center with instruments of the INTEGRAL orbital astrophysical gamma-ray observatory by the method of its occultation by the Earth and the Moon is considered. Existing engineering constraints on the observing conditions, such as the admissible orientation of the INTEGRAL satellite relative to the direction to the Sun and the performance of measurements only outside the Earth??s radiation belts, are taken into account. Long time intervals during which the lunar occultation center passes at angular distances of less than 2° from the Galactic center have been found. Such events occur under the adopted constraints two or three times per year without any correction of the INTEGRAL satellite orbit. The orbit can be corrected to reduce the angular distance between the Moon and the Galactic center in occultation events. The required velocity impulses do not exceed several meters per second. The possibility of the Galactic center being occulted by the Earth has been analyzed. In this case, to perform measurements, the admissible (in radiation exposure) height of the working segment of the orbit should be reduced to 25 000 km, which can be problematic. At the same time, part of the Galaxy??s equatorial region is shadowed by the Earth for a time long enough to carry out the corresponding experiments. 相似文献