Multilevel Analysis of Oscillation Motions in Active Regions of the Sun

We present a new method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots were analyzed to study the oscillation processes in the chromosphere-corona transition region in the layer with magnetic field B=2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk. A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio results with respect to optical ones. This implies a MHD wave traveling upward inside the umbral magnetic tube of the sunspot. Besides three-minute and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records.Comment: 17 pages, 9 figures, accepted to Solar Physics (18 Jan 2011). The final publication is available at http://www.springerlink.co

Coronal magnetograms of solar active regions

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Allen Telescope Array Multi-Frequency Observations of the Sun

We present the first observations of the Sun with the Allen Telescope Array (ATA). We used up to six frequencies, from 1.43 to 6 GHz, and baselines from 6 to 300 m. To our knowledge, these are the first simultaneous multifrequency full-Sun maps obtained at microwave frequencies without mosaicing. The observations took place when the Sun was relatively quiet, although at least one active region was present each time. We present multi-frequency flux budgets for each sources on the Sun. Outside of active regions, assuming optically thin bremsstrahlung (free--free) coronal emission on top of an optically thick ~10 000 K chromosphere, the multi-frequency information can be condensed into a single, frequency-independent, "coronal bremsstrahlung contribution function" [EM/sqrt(T)] map. This technique allows the separation of the physics of emission as well as a measurement of the density structure of the corona. Deviations from this simple relationship usually indicate the presence of an additional gyroresonance-emission component, as is typical in active regions.Comment: 16 pages, 11 figures. Accepted for publication in Solar Physic

Visual Explorations of Dynamics: the Standard Map

The Macintosh application \textit{StdMap} allows easy exploration of many of the phenomena of area-preserving mappings. This tutorial explains some of these phenomena and presents a number of simple experiments centered on the use of this program.Comment: Corrections in a couple of equations, and updated to the latest version of StdMa

Review of Coronal Oscillations - An Observer's View

Recent observations show a variety of oscillation modes in the corona. Early non-imaging observations in radio wavelengths showed a number of fast-period oscillations in the order of seconds, which have been interpreted as fast sausage mode oscillations. TRACE observations from 1998 have for the first time revealed the lateral displacements of fast kink mode oscillations, with periods of ~3-5 minutes, apparently triggered by nearby flares and destabilizing filaments. Recently, SUMER discovered with Doppler shift measurements loop oscillations with longer periods (10-30 minutes) and relatively short damping times in hot (7 MK) loops, which seem to correspond to longitudinal slow magnetoacoustic waves. In addition, propagating longitudinal waves have also been detected with EIT and TRACE in the lowest density scale height of loops near sunspots. All these new observations seem to confirm the theoretically predicted oscillation modes and can now be used as a powerful tool for ``coronal seismology'' diagnostic.Comment: 5 Figure

A study of the development of global solar activity in the 23rd solar cycle based on radio observations with the Nobeyama radio heliograph

Daily radio maps of the Sun at the wavelength of 1.76 cm were used to analyze the parameters of solar activity at all heliographic latitudes for the period 1992–2001. As a criterion of the level of solar activity, we analyzed the area/number of regions with an excess of brightness above a certain fixed level as well as regions with brightness below a certain level. The distribution of such “bright” and “dark” regions with heliographic latitude as function of time was found. Special attention was paid to the high latitude polar regions where the ways of analyzing solar activity are rather limited and have no generally accepted methods. The results are compared with some other indices of high latitude solar activity, such as polar faculae and magnetic field measurements. They appear to be in general agreement with the radio observations. The advantage of using radio observations is a more homogeneous database and a stable method of analysis

A study of development of global solar activity in the 23rd solar cycle based on radio observations with the Nobeyama radio heliograph

An analysis of solar rotation as a function of heliographic latitude and time is made using daily radio maps of the Sun at the wavelength of 1.76 cm. Variations of the velocity as a function of the latitude during the period 1992–2001 have been studied. The mean synodical rotation rate of the intensity features is best fit by \omega = 13.41 - 1.66\sin^2 \theta -2.19 \sin^4 \theta \:\mbox {(deg/day)} where θ is the latitude. We have found alternating bands of faster and slower rotation. They travel from higher latitudes towards the equator during the current solar cycle.
Radio observations with high accuracy and reliability thus confirm the reality of torsional oscillations in the higher levels of the solar atmosphere