|
|
|
|
|
|
| A.T. Altyntsev, A.A. Kuznetsov, N.S. Meshalkina |
| Fine temporal and spatial structure of the microwave emission sources from the SSRT and NoRH observations |
| One of the remarkable phenomena in the solar activity is the subsecond pulses of radio emission. Indirect estimates shows that their source sizes are considerably less than the beam width of NoRH and SSRT heliographs. Nevertheless, the fine structure observations with spatial resolution are extremely useful to study their nature. The localization of the fine structure sources in the flare region provides chance to determine the plasma parameters at the source. The analysis of the first events at 17 GHz have shown that the subsecond pulses are generated due to gyrosynchrotron mechanism by electron beams with energy of 100-200 keV, precipitating into tiny sites close to footpoints. In some events there is a contribution of plasma emission, which predominates at the SSRT receiving frequency (5.7 GHz). At this wavelength a joint analysis of data with high spatial and spectral resolution (NAOC spectropolarimeters) permits us to connect directly the frequency drift with the electron beam propagation. Secondly, it was shown that the short pulse appearance can be a response not to a dynamic of the electron acceleration, but to an impulsive heating of the bulk plasma within tiny regions of the flare loops. Also, the first observations of the zebra-pattern in cm-wave range came into view, which can be used to measure magnetic field in the fine structure source directly. The work was carried out with support of grants of RFBR 03-02-16229,02-02-39030 |
| A. Asai |
| Flare Associated Oscillations Observed with NoRH |
| We present an examination of the multi-wavelength observation of a C7.9 flare which occurred on 1998 November 10. This is the first time of imaging observation of the quasi-periodic pulsations (QPPs) observed with Yohkoh/HXT and NoRH. We found that the Alfven transit time was almost equal to the period of the QPP. We therefore suggest that variations of macroscopic magnetic structures, such as oscillations of coronal loops, affect the efficiency of particle injection/acceleration. We also review flare associated oscillations observed with NoRH. |
| T. Bastian |
| Flares and Particle Acceleration 1. |
| *** |
| G.D. Fleishman |
| Gyrosynchrotron Emission from Anisotropic Electron Distributions |
|
The change of the intensity, degree of polarization and spectral index
of gyrosynchrotron emission produced by fast electrons with
anisotropic pitch-angle distributions are analyzed as the pitch-angle
anisotropy increases. The anisotropy is found to affect the emission
substantially. The low-frequency harmonic structure is found to be
rather sensitive to the pitch-angle distribution. The emission
intensity can change up to a few orders of magnitude at the optically
thin region compared with the isotropic case. The local value of
spectral index changes considerably (up to a factor of 3-4) with the
anisotropy. X-mode polarization increases for loss-cone distributions and decreases for beam-like distributions. Moreover, the sense of polarization can correspond to ordinary wave-mode at the optically thin region for a certain range of the view angles for beam-like distributions. Above some threshold in the angular gradient, the electron cyclotron maser instability can develop provided that standard gyrosynchrotron emission is accompanied by a lower-frequency intense coherent emission. We present a few evidences of the important role of the pitch-angle anisotropy in the observations of solar microwave continuum bursts, e.g., based on Owens Valley Solar Array and Nobeyama Radioheliograph data. |
| D. Gary |
| FASR Flare Science: Lessons from the Nobeyama Radioheliograph |
| *** |
| G.B. Gelfreikh |
| Global Development of the Solar Cycle as Found from the Nobeyama Radio Observations |
|
The theory of physical nature of the solar activity and its cyclicity
needs an analysis of different types of its appearance over the whole
disk of the sun. For a long time, study of the 11-year cycles was
based mainly on observations of the active regions at low heliographic
latitudes. It is obvious, however, that the cycle is a global process
and needs the knowledge at least of the magnetic field over the whole
solar surface. More than that, it was found in some studies (e.g. by
V. I. Makarov et al.) that oscillations of the faculae in the polar
zone activity in some 5 or 6 years later are repeated in the main
activities at lower latitudes of the next 11-year cycle. That implies
that the real duration of a cycle in fact lasts about 17 years, and
two successive cycles do overcome each other. The other problem of
interpretation of the nature of solar cycles is the obvious necessity
to study it at all levels of the solar atmosphere. Today we do posses
brilliant pictures of the solar corona obtained from space
laboratories in EUV and X rays. However, no bank of such observations
include data necessary for homogeneous analysis of 11-year cycle. The
main reason is the time limitations of working conditions of such
instruments. The radio data, however, could be the solution of the
problem. At present stage, however, only the Nobeyama radio heliograph
is capable to present the necessary information. The point is that
only it presents high quality homogeneous 2D mapping of the whole sun
with reasonably high spatial resolution of about 10 arcsec. It is
especially so, if it will work at least to 2008, when the present 23-d
solar cycle will come to an end. The radio maps of the sun at wavelength 1.76 cm made with the NRH made it possible to investigate the following parameters of the progress of the cycles: - Development of the flocculae/faculae regions at all heliographic latitudes; - Sunspots with the high magnetic field strength at low corona levels; - Magnetic strength and structure of the active regions at the level of the upper chromosphere; - Development of differential rotation of the sun; - Filament and prominence development in the solar cycle; - Quasi-periodic oscillations of the plasma structures of the solar atmosphere; - Neutral line enhancements in ARs reflecting coronal arches structure. In this report the illustrations of the above method of investigation of the solar activity and its development are demonstrated and some samples of analysis of the 11-year solar cycles are shown. The problems and possible ways of developments of investigations of the solar activity and its 11-year cycle are discussed. The work was carried out with support of grant of RFBR 02-02-16548, programs of RAS "Astronomy", "Integration" (I0208.1173), "Scientific Schools" (477.2003). |
| G.B. Gelfreikh |
| Quasi-Periodic Oscillations of the Radio Emission of the Solar Plasma Structures and their Nature |
|
Observations of periodic oscillations play an important role in modern
physics of the sun and stars. So, detailed study of the five-minute
oscillations resulted even in a new branch of science ?
helioseismology. The latter is essential for a much deeper
understanding of the interior structure of the sun and other
stars. Limited in space plasma structures usually may be characterized
by some typical period of resonance oscillation. Each period is
connected with the size of the structure, its construction and
particular MHD mode of the wave/oscillation. Observations of the
quasi-periodic pulsations of the microwave solar radio emission are
being made for about 40 years. These were initiated by the group of
Prof. Kobrin in Gorkiy (Nizhniy Novgorod) and then developed by the
team of the Pulkovo observatory and Siberian Institute of the
Solar-terrestrial physics and Leningrad university. Small spacing
interferometers and large dishes were used to select the region of
oscillations with the accuracy of several arc minutes. The new era
came to the problem when the Nobeyama radio heliograph became
available to proceed in studying QPO. There are several reasons
essential for this progress: - comparatively high 2D resolution of the instrument; - covering the whole solar disk simultaneously; - full time every day coverage of observations for many years; - simultaneous intensity and circular polarization registration; - ability to choose optimum averaging of the signal. The main results discussed in this presentation illustrate a successful usage of these advantages of the instrument and desirable future development of the method and its astrophysical applications. The main conclusions concerning the QPO found from the NRH observations include: - the sunspot associated sources usually demonstrate well known 3-minute oscillations, however, the sensitivity to oscillations of the magnetic field in the radio observations are much high than using optical magnetography; - In sunspots also present shorter periods and much longer ones (tens of minutes and even hours), in some spots these are dominating; - different plasma structures in one active region oscillate with somewhat different periods; - most of the plasma structures of the solar atmosphere registered at the Nobeyama radio maps at the wavelength of 1.76 cm at all heliographic latitudes show the presence of the QPO (prominences including). In observations of the QPO at microwaves we deal mostly with nonstationary processes. So, using the wavelet analysis the quality of the proper plasma resonators responsible for QPO were estimated. Three types of plasma oscillators were proposed to be of importance: - the resonators coincides with the emitting region; - the resonators outside but close to the radio emitter; - the resonators of global solar nature. The work was supported by Program of the Presidium of RAS "Non-stationary phenomena in astronomy", INTAS 00-0543, grant of OFN-16 and grant of RFBR 02-02-16548. |
| N. Gopalswamy |
| Radio Observations of Solar Eruptions |
| Coronal mass ejections are composed of multithermal plasmas, which make them produce different radio signatures at different wavelengths. The prominence core of CMEs are of the lowest temperature and hence optically thick at microwave frequencies and hence are readily observed. The Nobeyama radioheliograph has exploited this fact and observed a large of prominence eruptions over most of solar cycle 23 and parts of cycle 22. In this paper, I review recent studies on prominence eruptions and how they helped understand the CME phenomenon. In particular, I will discuss (i) the statistical and physical relationship between CMEs and the radio prominence eruptions and how this relationship manifests as a function of the solar cycle; (ii) The asymmetry of prominence eruptions between northern and southern hemispheres; (iii) the relationship between the high latitude prominence eruptions and the tilt angle of the heliospheric current sheet; (iv) the implications of the cessation of high-latitude before the reversal of the global solar magnetic field. |
| V.V. Grechnev, A.M. Uralov, V.G. Zandanov, N.Y. Baranov, S.V. Lesovoi |
| Observations of Eruptive Events with Two Radioheliographs, SSRT and NoRH |
| Simultaneous microwave observations with two radioheliographs, SSRT (5.7 GHz) and NoRH (17 GHz), have significant advantages in studies of eruptive prominences and filaments. They are overlapping observational daytimes with three times different frequencies. Also important is that, unlike long-wave radio observations, microwaves show initial stages of the eruption. Observations of three events are discussed, i.e., September 27, 1997; September 4, 2000; and January 14, 2001. We have identified three stages of the eruptive process: 1) slow pre-eruptive ascension; 2) explosive acceleration; 3) self-similar expansion. We have measured velocities, accelerations, and brightness temperatures of eruptive prominences. The ejecta observed had twin-loop configuration in accord with a model we developed. Wide field of view of the SSRT allowed us identifying the radio prominence and CME core. Two-frequency microwave data allowed estimating the kinetic temperature of the erupting filament. It was established that 1) the CME's frontal structure is formed near the solar surface; 2) the CME's core is not heated, and it may consist of cool material with a temperature of order 5000 K. |
| V.V. Grechnev, M.R. Kundu, A. Nindos |
| A Study of Accelerated Electrons in Solar flares from Nobeyama, Yohkoh, and Other Observations |
| We study manifestations of accelerated electrons in solar flare microwave and hard X-ray emissions. To make our points, we discuss two events - those of March 16 and February 16, 1999. The analysis of the first event leads to the conclusion that: 1) a seemingly single-loop configuration can be actually a double-loop one, and 2) pitch-angle distribution can be beamlike, with practically no nonzero pitch angles. The second event shows seemingly intersecting flaring loops in microwaves - cosidered as possible radio evidence for magnetic reconnection in flares; it also shows a post-eruptive arcade that can proceed as a series of double-loop interactions. From these and other published results we conclude that: 1) different types of flares can proceed in closed double-loop configurations, 2) the acceleration site is localized between two or more interacting loops, i.e. close to a footpoint of one of them in impulsive flares, 3) pitch-angle distribution of accelerated electrons is anisotropic, with an excess of small angles, and 4) electron energies responsible for the microwave emission in impulsive flares are 50-200 keV. |
| V.V. Grechnev |
| Methods to Analyze Imaging Radio Data on Solar Flares |
| Putting additional constraints on physical conditions based on the observed quantities, microwave imaging data crucially enhance the reliability of results and consistency of interpretations. This is why microwave imaging data is a necessary constituent of observational data sets on solar flares and are widely used in their analyses. However, to identify essential features and study their behavior, one has to deal with large data sets of hundreds frames. This allows a single image, a variance map, to represent the overall dynamics of the event. Methods are presented that allow investigation of the detected positions of sources in both Stokes I and V using the analysis of variance maps, combined difference images, and total flux time profiles. By analyzing the similarity of time profiles for different-polarity Stokes V sources, one reveals magnetic connectivity. Imaging techniques at the NoRH both in the local and remote modes as well as interactive data analyses using IDL are also briefly discussed. |
| V.V. Grechnev, SSRT team |
| Observations of Quiet Solar Features with the SSRT and NoRH |
| We demonstrate observations of such well-known relatively quiet solar features as filaments & prominences, coronal holes, bright points, and arcades with two radioheliographs, SSRT at 5.7 GHz and NoRH at 17 GHz. Simultaneous microwave observations with the two radioheliographs are promising and fruitful due to overlapping observational daytimes and three times different frequencies. Last circumstance determines significantly different coronal contribution at those frequencies, which governs different appearance of coronal features in images produced by the NoRH and SSRT. The emphasis is made on SSRT observations, which are not yet well known. We overview some results obtained with the two radioheliographs and discuss new opportunities of radioheliographic observations. Microwave observations are also compared with magnetograms. Observations at several radio frequencies only assure correct estimates of the magnetic field. |
| V.V. Grechnev, V.N. Borovik, O.I. Bugaenko, S.A. Bogachev, I.Y. Grigorieva, S.V. Kuzin, S.V. Lesovoi, M.A. Livshits, A.A. Pertsov, G.V. Rudenko, V.A. Slemzin, A.I. Stepanov, K. Shibasaki, A.M. Uralov, V.G. Zandanov, I.A. Zhitnik |
| Observations of a Posteruptive Arcade on October 22, 2001 with the CORONAS-F, Other Spacebone Telescopes, and in Microwaves |
| The CORONAS-F/SPIRIT sometimes observes large-scale hot features existing for many hours high in the corona. We identify such a feature observed on October 22, 2001 at ~100 Mm with a posteruptive arcade. Using multi-spectral data, we estimate plasma parameters in the arcade and reveal the coronal large-scale magnetic field configuration. Several hours after the eruption, T = 6 MK, Ne ~ 10^10 cm-3. We state a problem of long-term existence of the hot arcade high in the corona: either the magnetic field surrounding the arcade well exceeds 20 G at that height, or beta > 1 both inside and outside the arcade. A downflow observed in soft X-rays can also contribute to the equilibrium conditions. |
| K. Hori, Y. Katsukawa, M. Oka, Y. Sakamoto, K. Watanabe, H. Kurokawa |
| RHESSI and NoRH Observations of the 3 July 2002 Flare |
|
By combining the spatially resolved X-ray and radio data from the
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the
Nobeyama Radioheliograph (NoRH), we report the morphology and spectral
evolution of a GOES X1.5 class flare of 3 July 2002. This event belongs to "Hanakoka-Nishio type" flares; i) it was an impulsive flare accompanied by high-energy electrons (< 50 keV), ii) it involved in two non-equal-sized magnetic loops that share one footpoint in the same magnetic polarity (thus a three-legged structure), and iii) it was induced by an emergence of magnetic flux (EMF), a twisted dipole in this event, through the photosphere. Across the magnetic neutral line that was heavily distorted by the EMF activity, the X1.5 flare occurred. In addition to a compact (< 20") hard X-ray (HXR) source that is typically seen at footpoints of the interacting loops in Hanaoka-Nishio type flares, our event shows a brightening of a longer loop (40") in 20-50 keV with a duration of < 15 sec. This elongated HXR source appeared immediately after a 17 GHz radio source with a brightness temperature Tb > 5 x 10^6 K propagetd along the longer loop from one footpoint (where the flare kernel existed) to the other. The propagation speed was about 1500 km/s. We suppose that this dynamic evolution was observed because the flare region had a high confinedness of the released energy. |
| G. Huang |
| Radio Signature of Coronal Magnetic Fields and Reconnections |
| The observations of solar radio spectra may provide important information of coronal magnetic fields and reconnections. Some recent works with the data of Chinese Radio Spectrometers, Nobeyama Radio Heliograph, Owens-Valley Solar Arrays, and the other wavelengths are reviewed on this topic. The coronal magnetic field and density of non-thermal electrons may be calculated with the spectral index, the brightness temperature, the turnover frequency and frequency in a give microwave burst source. The radio fine structures as the signature of reconnections (particle accelerations, inflows and outflows) may be indicated at different locations in coronal loops. The key problem is how to get the spatial distribution of coronal magnetic fields as well as the location of the reconnection sites from radio observations. Nobeyama Radio Heliograph with high-quality mapping at 17 and 34 GHz may give the possibility to test and improve the diagnosis of coronal magnetic fields and reconnection sites before the construction of the new instruments, such as FASR. |
| H.S. Hudson |
| Overview of RHESSI Results |
| *** |
| S. Kamio |
| Periodic Acceleration of Electrons in Solar Flares |
| We analyzed quasi-periodic oscillation in microwave and hard X-ray flux during the impulsive phase of flares, and investigated the relationship between the period of pulsation and the magnetic configuration of flare loops. Since microwave and hard X-ray are emitted by non-thermal electrons, they are important for understanding the particle acceleration process in the flares. We selected 4 flares observed by Nobeyama Radio Heliograph (NoRH) and Hard X-ray Telescope (HXT) on board Yohkoh Satellite, which showed oscillation of 6-16 sec. We estimated the geometry, density, and magnetic field strength of the flare loops using Yohkoh/SXT, TRACE, and SOHO/MDI data. Our results suggest that the observed oscillation periods are comparable to the periods of fast sausage mode of the flare loops. We discuss the possible mechanism which causes the observed pulsation from the analysis of spectral indices of hard X-ray and microwave. |
| T. Kosugi |
| Solar-B |
| *** |
| M.R. Kundu, E.J. Schmahl, V.I. Garaimov, P. Grigis |
| NoRH Observations of RHESSI Microflares |
| We present a summary of the analysis of more than two dozen microflares, observed simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz). The RHESSI microflares are observed in the energy range 3-25 keV. The observations were made on May 2-6, 2002. We describe the imaging characteristics of these microflares including their locations in hard X-rays and microwaves, and the relative positions of the micro-flaring sources relative to MDI magnetograms. We discuss the brightness temperatures, emission measures, and their hard X-ray spectral properties. One sees the mini flaring loops clearly in NoRH images. The microwave emission often seems to come from the RHESSI foot points (for higher energies), and from the entire small (mini) flaring loop (for lower energies). Sometimes the two (microwave & HXR) sources coincide, at other times they are at opposite ends of the mini flaring loop. The hard X-ray spectrum of the microwave associated RHESSI microflares can be fit by a thermal component at low energies (3-6 keV) and a nonthermal component at higher energies (12-25 keV). |
| S.V. Lesovoi, V.G. Zandanov, G.Ya. Smolkov, A.T. Altyntsev, A.V. Gubin |
| Upgrade of the Siberian Solar Radio Telescope |
|
Siberian Solar Radio Telescope, the SSRT, is a direct imaging
radio heliograph. The working frequency of the SSRT is 5730 MHz.
The SSRT is cross-shaped interferometer consisting of two
128-element linear arrays. The angular resolution of the SSRT is
up to 21 arc seconds. Because the direct imaging is performed using both
the Earth rotate scanning and the frequency scanning, the temporal
resolution of the SSRT depends on the observation time and is in range
2-10 minutes. Studying of coronal magnetic fields requires both spectral and temporal resolutions of a radio heliograph. Because we plan to change the Earth imaging of the SSRT to the Fourier synthesis imaging technique and to expand the frequency range up to 4500-9000 MHz. We plan to reach the temporal resolution unless 0.02 second for a given frequency and the angular resolution up to 13 arc seconds at 9000 MHz. In order to improve the SSRT capability to study the dynamic events with spectral resolution we plan to use redundancy of the SSRT antenna array. I.e. we plan to form up to five nested antenna arrays operating at different frequencies simultaneously. We plan to develop the 12-element antenna array with frequency agile receiver as first stage of this upgrade. We hope to obtain spatially resolved spectra in range 4500-9000 MHz every day by use Earth rotate aperture synthesis for this array. |
| R. MacDowall, N. Gopalswamy, M. Kaiser, S. Bale, R. Howard, D. Jones, J. Kasper, M. Reiner, & K. Weiler |
| Low Frequency Radio Astronomy from Space: The Solar Radio Imaging Array |
| The Solar Imaging Radio Array (SIRA) is a mission to perform aperture synthesis imaging of low frequency solar, magnetospheric, and astrophysical radio bursts. The primary science targets are coronal mass ejections (CMEs), which drive radio emission producing shock waves. A space-based interferometer is required, because the frequencies of observation (<15 MHz) do not penetrate the ionosphere. As such, the SIRA mission serves as a low frequency counterpart to LWA, LOFAR, and similar ground-based radio imaging arrays. SIRA will require 12 to 16 microsatellites to establish a sufficient number of baselines with separations on the order of kilometers. The microsat constellation consists of microsats located quasi-randomly on a spherical shell, initially of radius 5 km or less. The baseline microsat is 3-axis stabilized with body-mounted solar arrays and an articulated, earth pointing high gain antenna. A retrograde orbit at ~500,000 km from Earth was selected as the preferred orbit because it reduces the downlink requirement while keeping the microsats sufficiently distant from terrestrial radio interference. Also, the retrograde orbit permits imaging of terrestrial magnetospheric radio sources from varied perspectives. The SIRA mission serves as a pathfinder for space-based satellite constellations and for spacecraft interferometry at shorter wavelengths. It will be proposed to the NASA MIDEX proposal opportunity in mid-2005. |
| V.P. Maksimov, D.V. Prosovetsky, V.V. Grechnev, B.B. Krissinel, K. Shibasaki |
| On the Relation of Brightness Temperature in a Coronal Hole at 5.2 and 1.76 cm |
| From the analysis of simultaneous observations with the SSRT and NoRH we show that coronal holes are not uniform. In particular, in coronal holes small-scale features exist with anticorrelating brightness temperatures at 5.7 and 17 GHz. The features are disposed radially, which suggests radial heat transfer in them. We propose that the favorable heating mechanism within those features is dissipation of Alfven waves. |
| S. Masuda |
| Nonthermal Electrons in an Ejecta Associated with a Solar Flare |
|
An X-class flare, occurring near the west limb on 30 September 2000,
was well observed with Yohkoh. During the impulsive phase of this flare,
there are two large spikes in the hard X-ray time profile.
Accompanied with them, two plasma ejections were observed in soft X-rays.
The second ejecta was decelerated soon and had stayed about 15,000 km high
in the altitude above the flaring loop even in the gradual phase.
At the same location as the ejecta, a hard X-ray (> 30 keV) source was
observed with HXT and nonthermal emission was also observed with Nobeyama
Radio Heliograph. We analyzed the soft X-ray intensity variations of the flare loop and the ejecta. The soft X-ray intensity of the loop reached its maximum at the end of the nonthermal hard X-ray emission (23:21 UT)as expected. However, the intensity of the ejecta continued to increase and at 23:29 UT, showed almost the same brightness as the flare loop. Why did they have such a difference in time variation? To realize such an increase of soft X-ray intensity (due to increase of emission measure) in the ejecta, the supply of chromospheric plasma is needed. So this ejecta magnetically connected to the solar surface. This is consistent with the very slow (or almost no) upward motion of the ejecta. |
| V.F. Melnikov |
| Electron Acceleration and Transport in Microwave Flaring Loops |
| Nobeyama Radioheliograph has high spatial and temporal resolution at two frequencies where a nonthermal radio source is often optically thin. Such capabilities provide us with unique opportunity to get constraints on properties of mildly relativistic electrons accelerated and propagating in flaring magnetic loops. In this paper we review recent studies of Nobeyama observations concerning 1) spatial distribution of microwave brightness and spectral slope along flaring loops; 2) peculiarities of their temporal dynamics in different parts of a loop; 3) consequences of the obtained findings on spatial, spectral and pitch-angle distributions of high energy electrons. |
| T. Minoshima |
| Mutual Dependence of Physical Variables in Hard X-ray Flares Observed with Yohkoh |
|
Hard X-rays emitted during the impulsive phase of a solar flare result
from the interaction between non-thermal electrons and the solar
atmosphere (free-free bremsstrahlung). The analysis of solar hard
X-ray flares can thus provide information about non-thermal electrons
in a solar flare, and they may provide an explanation about the
acceleration process in a solar flare. Our purpose of study is to
explain mutual dependence of physical variables in solar hard X- ray
flares by analyzing observational data. The lower energy cutoff in the spectrum of non-thermal electrons is important to estimate physical variables of non- thermal component. But it's not easy to obtain it directly from the observed hard X-ray spectrum because of contamination due to thermal emission. Consequently, we deduce it indirectly by assuming the energy balance between non-thermal energy and thermal energy build-up during the impulsive phase. We apply this method to 7 hard X-ray flare events observed with Yohkoh and GOES. Physical variables of thermal component can be estimated from Yohkoh/SXT and GOES observational data. Then the lower energy cutoff in the spectrum of non-thermal electrons can be obtained by using these variables and Yohkoh/HXT observational data, and physical variables of non-thermal component are estimated. We examine their relationships in detail. The results are as follows: (1)The derived lower energy cutoff in the spectrum of non-thermal electrons is ranging in 20-40 keV. (2)When the derived lower energy cutoff in the spectrum of non-thermal electrons is relatively high (>30 keV), the observed hard X-ray spectrum shows the broken-down form at 20-30 keV in the initial phase. (3)When the derived lower energy cutoff in the spectrum of non-thermal electrons is relatively low (<30 keV), on the other hand, the observed hard X-ray spectrum indicates the existence of super-hot thermal plasma in the initial phase. (4)Positive correlation between the derived non-thermal electrons injection rate and the derived thermal plasma density in the pre-impulsive phase is shown. |
| H. Nakajima, J. Sato, Y. Hanaoka, M. Shimojo |
| Energetic Electrons in a Flaring Loop |
|
We have analyzed the 2002 August 24 flare which occurred on or behind
the west limb. This flare showed a clear loop-like structure in
microwave and hard X-ray images. We have gotten the following results
in the rising phase of the flare when the microwave and hard X-ray
data were available. (1) The flaring loop at 34 GHz had roughly a
uniform width of 14.4 +- 0.5 arcsec which suggested a small mirror
ratio of the magnetic loop. It also had a brighter loop top
source. (2) The decay time constant in the first major peak at 34 GHz
is about 30 s which is small as compared with the life time ( > 100 s)
of high energy electrons responsible for the 34 GHz emission. This
suggests that high energy electrons responsible for the 34 GHz
emission consists of a precipitation component and a trapping
component. (3) The hard X-ray flaring loop was located slightly above
the microwave loop in the energy range of 30 - 50 keV, and decreased
in height with decreasing energies. Since major hard X-ray emission
was confined in the loop top region, electrons responsible for the
hard X-rays were trapped in the flaring loop, which is consistent with
a thick-thin hard X-ray spectrum. (4) Electrons responsible for the
microwaves had a significantly harder spectrum than those for the hard
X-rays. We discuss about some implications from the above results for pitch angle distributions of electrons of hard X-rays and microwaves. |
| A. Nindos |
| Two Years of NoRH and RHESSI Observations: What Have we Learned? |
| *** |
| S. Pohjolainen |
| Moving Magnetic Features, Loop-Loop Interactions and Repeated Flaring |
| Repeated radio flaring was observed within a complex magnetic topology in AR 8996 during May 18--20, 2000. The same location, similar radio spectra, and temporal evolution in radio and in X-rays suggest that the repeated flaring could be homologous. In soft X-rays interacting loops were observed, and magnetograms revealed moving magnetic features. No emerging flux was visible. The radio flaring at the footpoint of one loop was due to strong magnetic field near the large sunspot region, while at the footpoint of the other interacting loop the electrons could precipitate and emit only in hard X-rays. The simultaneous emission and fluctuations in radio and X-rays -- at two different loop ends -- further support the idea of a single acceleration site at the loop intersection. |
| B.I. Ryabov |
| Coronal Magnetograms of Solar Active Regions Derived from Polarization Inversion in Microwaves |
|
Microwave observations are the most direct way to provide the
intensities of coronal magnetic fields. The state of the art in the
coronal magnetography through quasi-transverse (QT-) propagation of
microwaves is discussed in this presentation. The measurements are based on the fact that the circular polarization modification depends on the intensity of the magnetic field in the QT-region, where microwaves pass through the magnetic field lines at the right angle. The obtained coronal megnetograms are a series of 2D partial magnetograms, covering on each day a part of the active region: the following part near the eastern limb and the leading one near the western limb. The size of the microwave source portion affected by polarization inversion is of the order of 50" x 100". 2D coronal magnetograms in the range of 110 ~ 50 G corresponding to the coronal height of about (1.5 ~ 3.8) x 10^9 cm are derived using radio maps at 1.76 cm taken with the Nobeyama Radioheliograph. The Siberian Solar Radio Telescope observations at 5.2 cm provide the coronal magnetograms of 30 ~ 10 G at the heights of (5 ~ 9) x 10^9 cm. The first results obtained with this technique are encouraging in the sense that the features of the measured coronal magnetograms are consistent with the geometry of the QT-region and with the general tendency of the coronal magnetic fields to decrease with height. Two problems of this coronal magnetography will be discussed with more details: (i) under what circumstances the polarization inversion interpretation as the result of the QT-propagation run into difficulties; and (ii) whether the coronal field oscillations are represented by the oscillations of the depolarization line, V=0. This work has been supported by INTAS grant 00-0543. |
| K. Shibasaki |
| Quiet Sun and Active Region Studies by Nobeyama Radioheliograph |
| Although the major objective of the Nobeyama Radioheliograph (NoRH) is particle acceleration in solar flares, studies of the quiet sun and active regions are also important subjects for NoRH. Due to its full disk imaging capability and uniform data set for more than one solar cycle, NoRH is a unique instrument for these studies. Studies of QS and ARs done by NoRH are reviewed. Among them, polar brightenings and umbral oscillations for longer period are described in detail. Umbral oscillations are used as a sunspot thermometer and the solar cycle variation of the temperature is described. |
| M. Shimojo |
| NoRH Observations of Prominence Eruptions |
|
A prominence (filament) eruption is a most spectacular and interesting
phenomenon in the solar atmosphere since eruptions are sometimes associated
with solar flares and coronal mass ejections.
Nobeyama Radioheliograph (NoRH) has a wide field of view, covering the whole
Sun, a daily 8-hr observation and high image dynamic range of about 25 dB.
Furthermore, the large line-of-sight velocities of prominence do not have
an effect on the radioheliogram since the emission mechanism of radio from
prominence is thermal continuum emission. These properties of NoRH observations
are very useful for studies of prominence eruptions. Hence, many author studied
the phenomenon using NoRH. In this paper, at first, I review the studies of prominence eruptions using NoRH, and discuss the meaning of the prominence eruption observation using NoRH. Secondary, I present the result of the automatic detection of prominence eruptions using NoRH 11-years observations. |
| A.V. Stepanov, Yu.G. Kopylova, Yu.T.Tsap, K.Shibasaki, V.F.Melnikov, and T.B.Goldvarg |
| Diagnostics of Flare Plasma Using Pulsations in Microwave and X-ray Emission |
| Modulations of microwave (NT-gyrosynchrotron) and HXR emission from solar flares by both ballooning and radial oscillations of coronal loops are considered. The damping mechanisms of loop MHD-modes are analyzed. The method for diagnosing of loop flare plasma using peculiarities of the microwave and X-ray pulsations is proposed. Based on observational data obtained with the Nobeyama Radioheliograph and Yohkoh we determined the particle density n ~ 3.7x10^10 cm^-3, the temperature T ~ 4x10^7 K, and the magnetic field strength B ~ 220 G in the region of flare energy release G for the event of May 8, 1998. A wavelet analysis for the solar flare of August 28, 1999 revealed two main types of microwave oscillations with periods P1 ~ 7, 14 s, and P2 ~ 2.4 s, which we attribute to the ballooning and radial oscillations of compact and extended flare loops respectively. Analysis of the time profile for microwave emission supports an evidence of loop-loop interaction. We determined the plasma parameters for the compact (T ~ 5x10^7 K, n ~ 5x10^10 cm^-3, B ~ 200 G) and extended (T ~ 2x10^7 K, n ~ 2x10^10 cm^-3, B ~ 160 G) loops. The results of soft X-ray observations are consistent with the adopted model. |
| H. Takasaki, J. Kiyohara, A. Asai, T. Yokoyama, H. Nakajima, S. Masuda, J. Sato, T. Kosugi |
| The Spatially Resolved Spectrum Analysis of Gradual Hardening Flare |
| We present examination of the multi-wavelength observation of a M8.2 flare which occurred on 2000 November 25. This flare gives us more detailed pictures of the gradual hardening flare and high energy particles than before the previous studies. We mainly discussed the magnetic trapping effect for them and the spatial distribution and the temporal variation of the indices of the electron energy spectrum inferred from hard X-ray (HXR) and microwave. The preliminary results are as follows. (1) In this flare, the HXR emission is mainly produced by electrons which precipitate into choromosphere after magnetic mirroring in flare loops and their energy is under about 1 MeV. (2) The microwave emission at flare loop top is produced by trapped electrons and their energy is over about 1 MeV. (3) There are a break in the electron spectral index between lower energy electrons which have over 1 MeV and higher energy ones under 1 MeV. |
| S. Tanuma |
| Internal Shocks in the Reconnection Jet in Solar Flares |
| The Nobeyama Radioheliograph observes the radio emission from energetic electrons in solar flares. The energization mechanism of these particles, however, is not fully known. In this paper, we suggest that the internal shocks are created in the reconnection jet and that they are possible sites of particle acceleration. We examine how the magnetic reconnection creates the multiple shocks by performing 2D resistive MHD simulations. In this paper, we use very small grid to resolve the diffusion region to remove the numerical resistivity. As the results, we find that the current sheet evolves as follows: (1) Current sheet thinning due to the tearing instability, (2) Sweet-Parker reconnection. (3) Further current sheet thinning by secondary tearing instability, (4) Onset of anomalous resistivity and Petschek-like (fast) reconnection During the fast reconnection, the secondary tearing instability continues in the diffusion region where the anomalous resistivity is enhanced. Many plasmoids are created and ejected along the current sheet so that internal shocks are created in the reconnection jet. This situation is a turbulent reconnection. We suggest that the multiple fast shocks are created inside the reconnection jet in the solar flares. The energetic electrons can be accelerated in the multiple shocks. Furthermore, the plasmoid ejections due to the secondary tearing instability could explain the quasi-periodic pulsations in the flares, slowly drifting structures, and narrowband dm-spikes in the upward jet. |
| A.M. Uralov, G.V. Rudenko |
| Comparison of 5.7 and 17 GHz solar images with extrapolated magnetograms of coronal magnetic field. Active regions of the October/November 2003 period and forecast of powerful solar flares |
| A direct comparison of microwave images of a solar active region with MDI magnetograms of the longitudinal component of solar magnetic fields cannot correctly specify where a microwave source is located within an active region far from the solar disk center. We propose a way to do this by using coronal magnetic field magnetograms extrapolated from a single MDI magnetogram, which is the nearest to the time of observation. The method is illustrated for the October/November 2003 active regions period. Appearance and long-duration existence of Neutral Line associated Sources were detected. Such sources can be regarded as predictors of powerful flares. |
| S.M. White |
| NoRH Flare Studies with RHESSI and TRACE |
| *** |
| S.M. White |
| Radio Observations of EIT Waves and Coronal Dimmings |
| *** |
| S.M. White, T.S. Bastian, R. Bradley, C. Parashare, L. Wye |
| Low-Frequency Solar Radio Bursts from Green Bank |
| *** |
| J. Kiyohara, H. Takasaki, N. Narukage, S. Masuda, H. Nakajima, T. Yokoyama |
| Comparison between Microwave and Hard X-ray Spectral Indices of Temporally and Spatially Resolved Non-Thermal Sources |
| We analyzed flares which are observed with the Nobeyama Radioheliograph (NoRH) and the hard X-ray telescope (HXT) on board Yohkoh. Power-law indices, delta_m, of electron distribution functions are derived from the microwave spectra in the impulsive phase of the selected events as functions of time and position. They are compared with the corresponding power-law indices, delta_x, derived from the hard X-ray spectra of the same events. We found: (1) The selected events are categorized in three types by the temporal behavior of the delta. (2) The microwave spectrum near the footpoints is softer than that near the looptop. (3) Hard X-ray sources are located at the area where such softer microwave spectra are seen. The previous studies show by using spatially-unresolved data that delta_x is generally larger than delta_m. Our findings, however, suggest that the previous results are because of the relatively weighted signal of microwave from the loop top which is emitted by trapped electrons. There still remains a possibility that the electron power indices have a single value from hard X-ray emitting energy around 100keV up to microwave emitting energy, which is believed to be > 0.3 MeV. |
|
|
|
|
T. Bastian, N. Gopalswamy, T. Kosugi, K. Shibasaki (chair), T. Yokoyama |
|
|
A. Asai, H. Kodama, K. Shibasaki (chair), M. Shimojo |
|
|
nbym04@NRO (NRO: nro.nao.ac.jp) |