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High-sensitivity, high-spectral-resolution solar observations in the millimeter wavelength are scanty. A sensitive radiometer
with 1 GHz resolution, operating between 18 and 23 GHz in conjunction with a 13.7 m diameter antenna has been in regular operation
since the end of 1987. At present, each frequency is sampled for 100 ms, soon to be improved to 50 ms. Details of this instrumentation,
including the processes of calibration, data acquisition, and reduction are described here. Also, preliminary observations
of an active region and of the burst components are briefly described. 相似文献
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The mechanism of the double plasma resonance has been applied to the dot-like emission structures observed in the decimetric band. In particular, the existence of dot-emissions on definite trajectories in the dynamic spectra offers a rare opportunity to delineate the details of the double resonance mechanism as well as the diagnostics of the radio source and the ambient corona. The modeling of the chains of dots points to the excitation of the electron Bernstein modes predominantly at the second cyclotron harmonic and their subsequent coalescence to produce the observed dot-emissions. The coalescence process doubles the cyclotron harmonic number and thereby reduces the cyclotron absorption significantly. The discrete nature of the emissions results from the finite extent of the resonant region due to the presence of inhomogeneities. The determination of the relative scales of spatial variation of the magnetic field and the electron density in the region of the decimetric emission is particularly desirable as it has important consequences for the energy release, acceleration processes and the configuration of the participating plasma structures. 相似文献
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H. S. Sawant R. Ramesh J. R. Cecatto C. Faria F. C. R. Fernandes R. R. Rosa M. C. Andrade S. Stephany L. B. T. Cividanes C. A. I. Miranda L. C. L. Botti J. W. S. V. Boas J. H. Saito C. E. Moron N. D. Mascarenhas K. R. Subramanian M. S. Sundararajan E. Ebenezer M. R. Sankararaman 《Solar physics》2007,242(1-2):213-220
An East – West, one-dimensional radio interferometer array consisting of five parabolic dish antennas has been set up at Cachoeira
Paulista (longitude 45°0′20″ W, latitude 22°41′19″ S) for observations of the Sun and some of the strong sidereal sources
by the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. This is Phase-I of the proposed Brazilian Decimetric Array
and can be operated at any frequency in the range 1.2 – 1.7 GHz. The instrument has been in operation since November 2004
onwards at 1.6 GHz. The angular and temporal resolutions at this frequency are ∼3′ and 100 ms, respectively. Details of the
array, analog/digital receiver system, and a preliminary East – West one-dimensional solar image at the 1.6 GHz are presented
in this paper. 相似文献
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Sawant H.S. Subramanian K.R. Faria C. Fernandes F.C.R. Sobral J.H.A. Cecatto J.R. Rosa R.R. Vats H.O. Neri J.A.C.F. Alonso E.M.B. Mesquita F.P.V. Portezani V.A. Martinon A.R.F. 《Solar physics》2001,200(1-2):167-176
Digital, decimetric (200–2500 MHz) Brazilian Solar Spectroscope (BSS) with high time (10–1000 ms) and frequency (1–10 MHz) resolution is in regular operation since April, 1998, at National Space Research Institute (INPE) at São José dos Campos, Brazil. BSS operates in conjunction with a 9-m diameter polar mounted antenna. It allows to select suitable observing frequency range, frequency and time resolutions and data can be digitized up to 100 channels. BSS has capabilities of quasi-real time display of the ongoing dynamic spectra of the solar activity that enables the observer to modify observational parameters so as to suit a specific type of activity such as spikes and improve the quality of data acquisition and storage. Minimum detectable flux density of the spectroscope, for different combinations of the observational parameters, is 3 s.f.u. Observations are carried out routinely from 11 UT to 19 UT. Necessary software for data acquisition and reductions has been developed in IDL 5.3 environment. Data are available in FITS and ASCII formats. Absolute timing accuracy of the station is less than 3 ms. Here, we present examples of the bursts which have been recorded by BSS and available display facilities. 相似文献
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A millimeter-wavelength (23–18 GHz) variable frequency radiometer with frequency resolution of 1 GHz and time resolution of 0.1–16 s has been developed in conjunction with a 13.7 m-diameter antenna. In this paper we describe briefly this new instrument, and its use to observe active regions.Spectra of four active regions show that: (i) spectra of the quiet-Sun region and those of the active region were of the same nature and the spectral index of both varied between –0.4 and +0.3; (ii) for two cases the spectra of the active region remained almost flat during the observing period of about one hour; (iii) spectra of the two other active regions exhibited frequency fine structures similar to the trough and crest type with a width of the order of 2 GHz in frequency and lasting about 40 to 90 min.The spectra of the quiet-Sun region and those of the active regions are attributed to bremsstrahlung emission. Fine structures in frequency type crest and trough are attributed to the radio signatures of the temperature plateau in the chromosphere. 相似文献
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