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

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

Spatially resolved microwave oscillations above a sunspot

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  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 $\times 10^4$ K and 0.2–1.5 $\times 10^5$ 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