Spectral and fine polarization
features of cyclotron emission passing through filament.
V.M.Bogod and S.Kh. Tokhchukova
A gradual microwave darkening during several days on the pre-flare phase in the active region (AR) NOAA 9077, before the powerful proton event on July 14, 2000 was detected. The effects were revealed in a wide range radio observations at the RATAN-600 radiotelescope and were confirmed by data from the Nobeyama Radio Heliograph (NRH) at 17 GHz and Siberian Solar Radio Telescope (SSRT, Irkutsk) at 5.8 GHz. The associated change of the circular polarization structure in the form of narrow-band double inversion of the sign was marked. We propose an interpretation of the observed effects as an indication of gradual formation of a cold matter of filament in the vertical structure of the AR and its influence for transmitted emission of underlying sunspot associated sources. Destabilization of this filament apparently caused the major flare with a coronal mass ejection (CME).
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III Radio Bursts and Solar Energetic Particles (PDF)
H. V. Cane
Type III radio bursts are observed prior to all solar energetic particle events. Since the radio emissions trace out propagation paths of the causative electrons (and associated ions) they can be used to probe conditions for particle acceleration at the Sun and the means by which particles arrive near Earth. Such observations indicate, for example, that scatter-free propagation does not occur very often, particularly near solar maximum.
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On decimetric transition
radiation in solar flares.
Fleishman, G.D., Melnikov, V.F., Shibasaki, K.
We report a few events demonstrating strong decimetric component of microwave gyrosynchrotron bursts. The examples are characterized by smoothed time profiles and spectral shapes. The brightness temperature is relatively low for a coherent mechanism to be responsible for the component. The degree of polarization is exceedingly large (when available), the sense of polarization corresponds to ordinary wave-mode. The observed properties of the decimetric emission can be easily interpreted on the basis of the transition Radiation theory, which provides us with estimates of the level of small-scale plasma density inhomogeneities.
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On the problem of the magnetic
field measurements in coronal holes
using solar radio observations
Borovik V.N. (1), Gelfreikh G.B. (1), Korzhavin A.N. (2)
1- Main (Pulkovo)
Astronomical Observatory of RAS, St.Petersburg, Russia
2- St.Petersburg Branch of Special Astrophysical Observatory of RAS, St.Petersburg, Russia
The study of the magnetic field 3d-structure in coronal holes is very important for understanding the origin of high-speed streamers of solar wind and their influence on the space weather and Earth's ecology. The first measurements of the magnetic field strength at coronal level in the coronal hole have been made on the basis of multifrequency solar radio observations at microwaves (2-30cm) on the RATAN-600 radiotelescope based on the analysis of circular polarization. HPBW of the antenna was 70"x50' at 8.0cm. The polarized emission associated with the isolated equatorial coronal hole was registered during two solar rotations (CPM - 12.10.1996 and 9.11.1996) at wavelengths longer than 8cm. The measured maximum degree of polarization in the hole was (0.2-0.3)% at 9cm and increased up to (3-4)% at 30cm (rms about 0.01%). The magnetic field strength (for longitudinal component) was determined in the frame of thermal bremsstrahlung of the solar plasma in the presence of the weak magnetic field. Taken into account the magnetic field measurements at the photosphere level (Stanford data) we have came to conclusion on an increase of the longitudinal component of the magnetic field in the coronal hole with the height from 0.2Gs at the photosphere level to 7-10Gs at the level of the generation of radio emission at 18cm with further stabilization or small decreasing of this value up to the region of generation 30cm emission. It may be reflect the real complex topology of the magnetic field in the coronal hole. We believe that this interesting fact needs further detailed investigation. It must be taken into account that the moderate spatial resolution and the fan beam pattern of the RATAN-600 radiotelescope allowed us to obtain this result only during the period of the deep minimum of solar activity. One can hope that the problem of the magnetic field 3D-structure in coronal holes and related solar wind acceleration phenomena may be succesfully resolved on the radioastronomical instrument like FASR providing success in very fine polarization measuruments. Short cm part of the spectra in this case could be used for magnetography.
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of Solar Images by the Steer-type Algorithm
Solar images are more complex combinations of various-size components than non-solar images, such as a solar disk component, bright and compact sources, faint and compact sources, and diffuse features. Solar observations also possess an another unique feature in the data processing, namely, the enormous time-series images obtained in daily observations with high temporal resolution.
Each image can be carefully processed with a specified algorithm, and with manually controlled parameters in similar way to non-solar observations. However, every image must, first, be processed automatically without any parameter adjustments in order to determine when and where remarkable phenomena occurred. Initial data processing in solar observations is, therefore, requires the ability of data processing with a single set of parameters which are independent from solar activities, and also of less computational time.
The modified CLEAN algorithm proposed by Steer, Dewdney, and Ito in 1984 has been incorporated into the 17-GHz routine data processing of the Nobeyama Radioheliograph. This is a key-solution restoration procedure for the above requirements, which uses a single set of parameters covering a wide range of solar activities. Performance of restoration for complicated and time-variable brightness structures on daily solar images obtained by the Nobeyama Radioheliograph, and processed by the Steer-type algorithm are discussed. Proposal of the Steer-type algorithm to FASR data processing, considering a few array-configuration cases, are also discussed.
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Solar Millimeter Telescope
Alejandro Lara, Eduardo Mendoza and Jean-Pierre Raulin
We present the project of construction of a millimeter wavelength solar telescope at Puebla, México. The instrument consists of a 5 meters antenna dish, and will operate at few frequencies in the 100 - 200 GHz range. The location will be at 4600 m above the sea level at the same site where the Large Millimeter Telescope (LMT, non solar dedicated instrument) is being constructed. This site is at the top of a death volcano called ``Sierra Negra'' near the Mexico's highest peak ``Pico de Orizaba''. The atmospheric opacity, as measured by a 225 GHz tipping radiometer, is low for most of the year, although summer months may be relatively humid. The 5 meters diameter dish is a donation from the University of Texas at Austin, The tracking system will be constructed at INAOE-México. The comunication and computing systems will be constructed at UNAM.
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observations of the solar corona in the metric radio band (PDF)
I will present, in this poster, a summary of thermal observations of the solar corona in the metric range, performed with the Nancay Radioheliograph. This includes large scale structures: coronal plateau, coronal holes, and recently discovered structures associated with filaments. New thermal observations of eruptive events will also be presented.
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Spatially resolved microwave
oscillations above a sunspot
A. Nindos, C.E. Alissandrakis, G.B. Gelfreikh, V.M. Bogod, C. Gontikakis
Using high quality VLA observations, we detected for the first time spatially resolved oscillations in the microwave total intensity (I) and circular polarization (V) emission of a sunspot--associated gyroresonance (g--r) source. Oscillations were detected at 8.5 and 5 GHz during several time intervals of our 10--hour--long dataset. The oscillations are intermittent: they start suddenly and are damped somehow more gradually. Despite their transient nature when they are observed they show significant positional, amplitude and phase stability. The spatial distribution of intensity variations is patchy and the location of the patches of strong oscillatory power is not the same at both frequencies. The strongest oscillations are associated with a small region where the 8.5 GHz emission comes from the second harmonic of the gyrofrequency while distinct peaks of weaker oscillatory power appear close to the outer boundaries of the 8.5 and 5 GHz g--r sources, where the emissions come from the third harmonic of the gyrofrequency. Overall, the 5 GHz oscillations are weaker than the 8.5 GHz oscillations (the rms amplitudes of the I oscillations are 1.3-2.5 x 104 K and 0.2-1.5 x 105 K, respectively). At both frequencies the oscillations have periods in the three--minute range: the power spectra show two prominent peaks at 6.25--6.45 mHz and 4.49--5.47 mHz. Our models show that the microwave oscillations are caused by variations of the location of the third and/or second harmonic surfaces with respect to the base of the chromosphere--corona transition region (TR), i.e. either the magnetic field strength or/and the height of the base of the TR oscillates. The best--fit model to the observed microwave oscillations can be derived from photospheric magnetic field strength oscillations with an rms amplitude of 40 G or oscillations of the height of the base of the TR with an rms amplitude of 25 km. Furthermore small variations of the orientation of the magnetic field vector yield radio oscillations consistent with the observed oscillations.
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First detection of the
impulsive phase of a solar flare at 405 GHz
Raulin JP, Makhmutov VS, Kaufmann P, Luethi T, Hudson HS,
Gary DE, Yoshimori M
We present multi-frequency observations obtained with high temporal and spatial resolutions, of the August, 25, 2001, X5.3 solar flare. The corrected flux densities at 212 and 405 GHz as detected by the Solar Submillimeter Telescope reached 10000 and 4000 sfu respectively. Spectral analysis in the 1-405 GHz range show the presence of different phases (thermal and non-thermal) that will be discussed. Soft X-ray spatially resolved observations allow to describe the temporal evolution of magnetic field structures through the flare development. In particular we found a close temporal and spatial relation between the appearance of a new compact and low-lying loop system, and the production of high-energy electrons which produced submillimeter and GR (above 10 MeV) emissions. The comparison of both emissions allow us to discuss precipating/trapping effects during this solar event.
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radio emission time structures as observed by the Submillimeter Solar Telescope
V. S. Makhmutov, J.-P. Raulin, C.G. Gimenez de Castro, P. Kaufmann, E. Correia
We present the results of the analysis of experimental data obtained with high time resolution (1 ms), related to the observations of Quiet Sun Regions, Active Regions and Solar Flares by the multibeam Submillimeter Solar Telescope (SST) at 212 / 405 GHz. A multiresolution analysis technique based on Wavelet transformation is applied to study the radio emission time structures well above noise level. As a preliminary result, we show (1) the existence of 212 / 405 GHz emission time variations in the range from a few tens of millisecond up to few seconds during Quiet Sun, Active region and Solar Flare observations, (2) when a solar flare is in progress the amplitude of the time variations is increasing, especially in the subsecond time range.
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Radiophysics with HF Radars (PDF)
High frequency radars provide a method to study the dynamics of the solar corona through active sounding. Among the anticipated capabilities of solar radars will be the detection of earthward-moving coronal mass ejections, measurements of coronal electron densities, and studies of plasma wave interactions and instabilities. Existing and planned HF transmitting and receiving arrays will open a new window on solar coronal physics that will complement and support the FASR scientific objectives. We review the history of solar radars and discuss recent and future investigations.
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Results of Researches at the SSRT (PDF)
Smolkov G.Ya., Altyntsev A.T., Grechnev V.V., Krissinel B.B., Lesovoi S.V.,
Maksimov V.P., Uralov A.M. and Zandanov V.G.
Some results of the researches of power flares predictors, fast processes in time of flares, coronal mass ejections and weak contrast events in solar corona with Siberian Solar Radio Telescope (SSRT) have been presented.
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Balun/Dipole Development for the Low Frequency Array (PDF)
K. P. Stewart, W. C. Erickson, Brian C. Hicks
We are developing and testing active baluns and electrically short dipoles for possible use as the primary wideband receiving elements in the Low Frequency Array (LOFAR) for long wavelength radio astronomy in the 10 to 100 MHz frequency range. Two dipoles, with dimensions scaled approximately by a factor of three, have been built and tested. The antenna temperatures varied from about 25 % to 100 % of the average brightness temperature of the Galactic background. With these parameters it is easy to make the amplifier noise levels low enough that final system temperature is dominated by the Galactic background.
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