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981.
Second and sub-second structures were simultaneously detected in optical, radio and hard X-ray (HXR) band, respectively by
the GanYu Station of Purple Mountain Observatory, Nobeyama Radio Observatory, and RHESSI satellite in the November 1, 2004 flare (Ji et al., in Astrophys. J. 636:L173, 2006), which may be contributed to the energy transport of the continuous heat flux from the hot corona or chromosphere evaporation
and of the accelerated electrons. The linear correlations between the amplitudes of these fluctuations and their flare emissions,
and those between the cross-correlation coefficients of the fluctuations at two H
α
kernels, or two radio frequencies, or two X-ray energies and their flare emissions may support the causal relationship of
the flare and these time structures. While, the cross-correlations of the fluctuations at three different bands suggest that
the fluctuations are caused by the common thermal or nonthermal processes in the flare. Moreover, some new features of the
fluctuations are reported in the flare: (1) The sub-second fluctuations in radio and HXR bands have a same timescale, which
is evidently larger than that in H-alpha band. The difference may be explained by the downward movements of nonthermal electrons
or the upward motion of chromosphere evaporation. (2) The power-law distributions of the amplitudes of the second and the
sub-second structures are obtained at optical, radio and HXR bands with different indices. (3) The peak-to-peak correspondence
of Stokes I and V components in the sub-second structures at radio band suggests that they may be resulted from a periodical
particle acceleration and particle injection in this event. However, the second structures may be caused by the modulations
of Alfvén waves with an upward speed of 103 km/s. 相似文献
982.
An analytically derived distribution function of reflected and accelerated electrons at a nearly perpendicular shock is presented. Then this distribution in a simplified form is introduced into a 1.5-D relativistic electromagnetic particle-in-cell (PIC) model and a generation of waves is studied. Numerical modeling shows not only a generation of Langmuir and high-frequency electromagnetic waves as expected, but also an efficient generation of whistler waves. Their role in emission processes of type II solar radio bursts is discussed. 相似文献
983.
三峡库首区最小一维速度模型研究 总被引:3,自引:0,他引:3
根据三峡台网2001~2006年记录的490个地震事件中的7 330条P波和3 524条S波到时资料,利用Kissling方法得到了三峡库区最小一维P波和S波速度模型以及台站校正值,并应用于地震的精定位.重新定位后地震走时残差均方根从原来的0.56 s下降到0.41 s,地震定位精度在经度、纬度、深度方向上有了较大提高. 相似文献
984.
985.
M. W. B. Anderson M. D. Filipovi 《Monthly notices of the Royal Astronomical Society》2007,381(3):1027-1030
We report the 6-cm radio-continuum detection of a previously unknown radio star, HIP 68718, identified by the Hipparcos satellite as an EB or β-Lyrae type optical variable. Only five prior radio detections of this type are reported in the literature. The radio source (VLA J140402−002145) was detected at the 6σ level, with an associated <1 arcsec position error. The radio-optical separation is 0.2 arcsec and is well within the position errors. A ROSAT X-ray source (RXJ 1404.0−0021) is located 4.5 arcsec from the radio position. Based on the component spectral types (F5V + G5V), 1.52 d period, variations in the peak of the light curve and the X-ray and 6-cm radio luminosities, we conclude the star is a candidate RS CVn. The binary is in a near-contact phase based on the asymmetric light curve (O'Connell effect). Evidence of two faint possible companion objects was also found in the J - and K -band Two-Micron All-Sky Survey images. 相似文献
986.
S. Dehaes † M. A. T. Groenewegen L. Decin S. Hony G. Raskin J. A. D. L. Blommaert 《Monthly notices of the Royal Astronomical Society》2007,377(2):931-944
It is generally acknowledged that the mass-loss of asymptotic giant branch (AGB) stars undergoes variations on different time-scales. We constructed models for the dust envelopes for a sample of AGB stars to assess whether mass-loss variations influence the spectral energy distribution. To constrain the variability, extra observations at millimetre wavelengths (1.2 mm) were acquired. From the analysis of the dust models, two indications for the presence of mass-loss variations can be found, being (1) a dust temperature at the inner boundary of the dust envelope that is far below the dust condensation temperature and (2) an altered density distribution with respect to ρ( r ) ∝ r −2 resulting from a constant mass-loss rate. For five out of the 18 studied sources a two-component model of the envelope is required, consisting of an inner region with a constant mass-loss rate and an outer region with a less steep density distribution. For one source an outer region with a steeper density distribution was found. Moreover, in a search for time variability in our data set at 1.2 mm, we found that WX Psc shows a large relative time variation of 34 per cent which might partially be caused by variable molecular line emission. 相似文献
987.
Huib Jan Van Langevelde Ylva PihlstrÖm Anthony Beasley 《Astrophysics and Space Science》2005,295(1-2):249-255
Centaurus A, the nearest AGN shows molecular absorption in the millimeter and radio regime. By observing the absorption with VLBI, we try to constrain the distribution of the gas, in particular whether it resides in the circumnuclear region. Analysis of VLBA observations in four OH and two H2CO transitions is presented here, as well as molecular excitation models parameterized with distance from the AGN. We conclude that the gas is most likely associated with the tilted molecular ring structure observed before in molecular emission and IR continuum. The formaldehyde absorption shows small-scale absorption which requires a different distribution than the hydroxyl. 相似文献
988.
989.
Evaluation of dynamically downscaled reanalysis precipitation data for hydrological application 下载免费PDF全文
Skilful and reliable precipitation data are essential for seasonal hydrologic forecasting and generation of hydrological data. Although output from dynamic downscaling methods is used for hydrological application, the existence of systematic errors in dynamically downscaled data adversely affects the skill of hydrologic forecasting. This study evaluates the precipitation data derived by dynamically downscaling the global atmospheric reanalysis data by propagating them through three hydrological models. Hydrological models are calibrated for 28 watersheds located across the southeastern United States that is minimally affected by human intervention. Calibrated hydrological models are forced with five different types of datasets: global atmospheric reanalysis (National Centers for Environmental Prediction/Department of Energy Global Reanalysis and European Centre for Medium‐Range Weather Forecasts 40‐year Reanalysis) at their native resolution; dynamically downscaled global atmospheric reanalysis at 10‐km grid resolution; stochastically generated data from weather generator; bias‐corrected dynamically downscaled; and bias‐corrected global reanalysis. The reanalysis products are considered as surrogates for large‐scale observations. Our study indicates that over the 28 watersheds in the southeastern United States, the simulated hydrological response to the bias‐corrected dynamically downscaled data is superior to the other four meteorological datasets. In comparison with synthetically generated meteorological forcing (from weather generator), the dynamically downscaled data from global atmospheric reanalysis result in more realistic hydrological simulations. Therefore, we conclude that dynamical downscaling of global reanalysis, which offers data for sufficient number of years (in this case 22 years), although resource intensive, is relatively more useful than other sources of meteorological data with comparable period in simulating realistic hydrological response at watershed scales. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
990.