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11.
Magnetic reconnection is commonly accepted to play a key role in flare energy release, but only poor information about the
main characteristics of this process is available so far. An intrinsic feature of reconnection is plasma density enhancement
in current sheets. A unique method to detect this effect is provided by analysis of drifting bursts, whose emission frequency
is close to the local Langmuir frequency or its harmonics. With this purpose, we analyze a series of several tens of drifting
microwave bursts during the 30 March 2001 flare. The burst drift rates range from −10 to 20 GHz s−1. Using one-dimensional scans recorded with the SSRT interferometer at two different frequencies near 5.7 GHz, we have measured
relative positions of burst sources and their velocities along a flare loop revealed from soft X-ray and extreme-ultraviolet
images. It is argued that the contribution of the increasing density effect into the observed frequency drift rates is about
6 GHz s−1, which is shown to be consistent with theoretical models of magnetic reconnection with reasonable boundary conditions. 相似文献
12.
利用国家天文台微波(1.0-2.0 GHz和2.6-3.8GHz)射电频谱仪于1998年9月23日观测到了一个稀少事件,它是一个伴生多重周期脉动、Ⅲ型爆发和类I型噪暴的复杂射电Ⅳ型爆发,着重介绍该爆发所具有的多重长周期(约7.3、4.9、3.7、1.2和0.4分钟)脉动成分。这个长周期脉动可能是归因于在封闭环中的驻波模式,由于光球层速度场驱动的MHD的Alfven驻波横穿磁场,导致了对射电辐射的调制。此外,由于这些脉动存在向下的运动,也不排除在一个封闭环或开放场结构中传播的扰动引起振荡的可能性。因为Alfven波的共振与光球层5分钟振荡模式相联系,所以甚长周期的脉动可能来自光球层驱动源的假设,可以说明日冕磁环和光球层之间存在一个互相耦合的可能性。 相似文献
13.
The areas of the active zone of five large forest fires among those occurring in Irkutsk Oblast in 1996 and 1997 and the burned-over areas formed by them were determined using an Advanced Very High Resolution Radiometer (AVHRR) carried aboard satellites of the American NOAA series. Comparative estimates of the burned-over areas, determined using AVHRR (NOAA satellite) and MSU-SK (medium-resolution scanner) (Russian Federation Resurs satellite) imagery, were obtained. 相似文献
14.
N. S. Meshalkina A. T. Altyntsev D. A. Zhdanov S. V. Lesovoi A. A. Kochanov Y. H. Yan C. M. Tan 《Solar physics》2012,280(2):537-549
The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows one to obtain unique information about the primary energy release mechanisms in solar flares. The SSRT (Siberian Solar Radio Telescope) spatially resolved images and its high spectral and temporal resolution allow for direct determination not only of the source positions but also of the exciter velocities along the flare loop. Practically, such measurements are possible during some special time intervals when SSRT is observing the flare region in two high-order fringes near 5.7?GHz; thus, two 1D brightness distributions are recorded simultaneously at two frequency bands. The analysis of type III-like bursts recorded during the flare 14?April 2002 is presented. Using multiwavelength radio observations recorded by the SSRT, the Huairou Solar Broadband Radio Spectrometer (SBRS), the Nobeyama Radio Polarimeters (NoRP), and the Radio Solar Telescope Network (RSTN), we study an event with series of several tens of drifting microwave pulses with drift rates in the range from ?7 to 13?GHz?s?1. The sources of the fast-drifting bursts were located near the top of a flare loop in a volume of a few Mm in size. The slow drift of the exciters along the flare loop suggests a high pitch anisotropy of the emitting electrons. 相似文献
15.
The ten-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the Local Area Network (LAN). The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West–East–South subarray of the SSRT. The radioheliograph will be fully constructed in the autumn of 2012. We plan to reach the brightness temperature sensitivity of about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and a polarization measurement accuracy about a few percent. First results with the ten-antenna prototype are presented of observations of solar microwave bursts. The prototype’s abilities to estimate source size and locations at different frequencies are discussed. 相似文献
16.
Wu Ji Li Dihui Zhang Xiaohui Jiang Jingshan A. T. Altyntsev B. I. Lubyshev 《Journal of Earth System Science》2005,114(6):627-632
Among many scientific objectives of lunar exploration, investigations on lunar soil become attractive due to the existence
of He3 and ilmenite in the lunar soil and their possible utilization as nuclear fuel for power generation. Although the composition
of the lunar surface soil can be determined by optical and γ/X-ray spectrometers, etc., the evaluation of the total reserves
of He3 and ilmenite within the regolith and in the lunar interior are still not available. In this paper, we give a rough analysis
of the microwave brightness temperature images of the lunar disc observed using the NRAO 12 meter Telescope and Siberian Solar
Radio Telescope. We also present the results of the microwave dielectric properties of terrestrial analogues of lunar soil
and, discuss some basic relations between the microwave brightness temperature and lunar soil properties. 相似文献
17.
We examine the problem related to the scattering of a solar radio pulse in a turbulent coronal plasma, taking into account
strong regular refraction. Based on an integral representation of the wave field as an interference integral, we analyze the
distortions of the mean profile of the radio pulse in spike events, for the case of the sources located in high coronal arches.
It is shown that strong regular refraction of radio emission in the coronal arch plays an important role for pulse structuring
during spike events. 相似文献
18.
A. T. Altyntsev V. M. Bardakov V. I. Krasov N. V. Lebedev V. L. Paperny V. G. Simonov 《Solar physics》1986,106(1):131-145
A laboratory simulation method is proposed for energy release processes occurring in a fragment of the flare current sheet on the Sun. The method relies on the assumption that the spatial scale of such processes is represented by the current sheet's thickness whose values can be close for both the solar and laboratory conditions. It is shown that in an extended current sheet, current dissipation on anomalous resistivity that ensures the specific power of energy release close to that observed in a flare, is the main energy release mechanism. A rapid compression of the sheet by external magnetic fields can provide the condition for switching on a powerful energy release. The tearing instability developing in a homogeneous neutral sheet, leads to the formation of magnetic islands in which the energy release is localized. 相似文献
19.
In this paper we determined the wave mode of subsecond pulses (SSP). We used data on pulses with a degree of polarization
over 30%, with the sources located at −60 to +60 deg from the central meridian, for the period 2000–2002. The superposition
of SSRT radio maps and MDI magnetograms has shown that radio SSP sources are typically located near the polarity inversion
line of the active region magnetic field. Such an arrangement indicates that SSP sources are located at the tops of magnetic
loops. The ordinary mode of electromagnetic radiation is recorded in SSP sources located from the inversion line by no less
than about 10 arc sec. 相似文献
20.
The new generation of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz. It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes. The flare occurred in the central part of the solar disk, which allows reconstructing the magnetic field in the flare region using vector magnetogram data. We have investigated the three possible known reasons of the circular polarization sense reversal – mode coupling, positron contribution, and the effect of beamed angular distribution. We excluded polarization reversal due to contribution of positrons because there was no relevant response in the X-ray emission. We find that a beam-like electron distribution can produce the observed polarization behavior, but the source thermal density must be much higher than the estimate from to the X-ray data. We conclude that the apparent ordinary wave emission in the optically thin mode is due to radio wave propagation across the quasi-transverse (QT) layer. The abnormally high transition frequency (above 35 GHz) can be achieved reasonably low in the corona where the magnetic field value is high and transverse to the line of sight. This places the microwave source below this QT layer, i.e. very low in the corona. 相似文献