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Kupriyanova E.G.,Russian Academy of Sciences | Melnikov V.F.,Russian Academy of Sciences | Nakariakov V.M.,University of Warwick | Shibasaki K.,Nobeyama Solar Radio Observatory
Solar Physics | Year: 2010

Quasi-periodic pulsations (QPP) of microwave emission generated in single flaring loops observed with the Nobeyama Radioheliograph (NoRH) and Nobeyama Radio Polarimeters (NoRP) are studied. Specific features of the time profiles, i.e. the visible presence or absence of QPPs, are not accounted for in the selection. The time evolution of the periods of the QPPs is examined using wavelet and correlation analyses. In ten out of twelve considered events, at least one or more significant spectral components with periods from 5-60 s have been found. The quality of the oscillations is rather low: Q=πN, where N is the number of cycles, mostly varies in the range 12 to 40, with an average of 25. We suggest that the detected QPPs can be classified into four types: i) those with stable mean periods (e.g. of 15-20 s or 8-9 s, the prevailing type); ii) those with spectral drift to shorter periods (mostly in the rise phase of the microwave emission); iii) those with drift to longer periods (mostly in the decay phase); iv) those with multiple periods showing an X-shaped drift (e.g. in the range from 20-40 s in the rise phase). © 2010 Springer Science+Business Media B.V.

Iwai K.,Tohoku University | Miyoshi Y.,Nagoya University | Masuda S.,Nagoya University | Shimojo M.,Nobeyama Solar Radio Observatory | And 5 more authors.
Astrophysical Journal | Year: 2012

The first coordinated observations of an active region using ground-based radio telescopes and the Solar Terrestrial Relations Observatory (STEREO) satellites from different heliocentric longitudes were performed to study solar radio type-I noise storms. A type-I noise storm was observed between 100 and 300 MHz during a period from 2010 February 6 to 7. During this period the two STEREO satellites were located approximately 65° (ahead) and -70° (behind) from the Sun-Earth line, which is well suited to observe the earthward propagating coronal mass ejections (CMEs). The radio flux of the type-I noise storm was enhanced after the preceding CME and began to decrease before the subsequent CME. This time variation of the type-I noise storm was directly related to the change of the particle acceleration processes around its source region. Potential-field source-surface extrapolation from the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) magnetograms suggested that there was a multipolar magnetic system around the active region from which the CMEs occurred around the magnetic neutral line of the system. From our observational results, we suggest that the type-I noise storm was activated at a side-lobe reconnection region that was formed after eruption of the preceding CME. This magnetic structure was deformed by a loop expansion that led to the subsequent CME, which then suppressed the radio burst emission. © 2012 The American Astronomical Society. All rights reserved.

Abramov-Maximov V.E.,Russian Academy of Sciences | Gelfreikh G.B.,Russian Academy of Sciences | Kobanov N.I.,Institute of Solar Terrestrial Physics | Shibasaki K.,Nobeyama Solar Radio Observatory | Chupin S.A.,Institute of Solar Terrestrial Physics
Solar Physics | Year: 2011

The nature of the three-minute and five-minute oscillations observed in sunspots is considered to be an effect of propagation of magnetohydrodynamic (MHD) waves from the photosphere to the solar corona. However, the real modes of these waves and the nature of the filters that result in rather narrow frequency bands of these modes are still far from being generally accepted, in spite of a large amount of observational material obtained in a wide range of wave bands. The significance of this field of research is based on the hope that local seismology can be used to find the structure of the solar atmosphere in magnetic tubes of sunspots. We expect that substantial progress can be achieved by simultaneous observations of the sunspot oscillations in different layers of the solar atmosphere in order to gain information on propagating waves. In this study we used 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 the optical ones. This implies an MHD wave traveling upward inside the umbral magnetic tube of the sunspot. For the five-minute oscillations the similarity in spectral details could be found only for optical oscillations at the chromospheric level in the umbral region or very close to it. The time delays seem to be similar. Besides three-minute and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records. Their nature still requires further observational and theoretical study for even a preliminary discussion. © 2011 Springer Science+Business Media B.V.

Gopalswamy N.,NASA | Yashiro S.,NASA | Yashiro S.,Catholic University of America | Makela P.,NASA | And 4 more authors.
Astrophysical Journal Letters | Year: 2012

Using magnetic and microwave butterfly diagrams, we compare the behavior of solar polar regions to show that (1) the polar magnetic field and the microwave brightness temperature during solar minimum substantially diminished during the cycle 23/24 minimum compared to the 22/23 minimum. (2) The polar microwave brightness temperature (Tb) seems to be a good proxy for the underlying magnetic field strength (B). The analysis indicates a relationship, B = 0.0067Tb - 70, where B is in G and Tb in K. (3) Both the brightness temperature and the magnetic field strength show north-south asymmetry most of the time except for a short period during the maximum phase. (4) The rush-to-the-pole phenomenon observed in the prominence eruption (PE) activity seems to be complete in the northern hemisphere as of 2012 March. (5) The decline of the microwave brightness temperature in the north polar region to the quiet-Sun levels and the sustained PE activity poleward of 60oN suggest that solar maximum conditions have arrived at the northern hemisphere. The southern hemisphere continues to exhibit conditions corresponding to the rise phase of solar cycle 24. © © 2012. The American Astronomical Society. All rights reserved..

Song Q.,CAS National Astronomical Observatories | Huang G.,CAS National Astronomical Observatories | Nakajima H.,Nobeyama Solar Radio Observatory
Astrophysical Journal | Year: 2011

Solar microwave and hard X-ray spectral evolutions are co-analyzed in the 2000 June 10 and 2002 April 10 flares, and are simultaneously observed by the Owens-Valley Solar Array in the microwave band and by Yohkoh/Hard X-ray Telescope or RHESSI in the hard X-ray band, with multiple subpeaks in their light curves. The microwave and hard X-ray spectra are fitted by a power law in two frequency ranges of the optical thin part and two photon energy ranges, respectively. Similar to an earlier event in Shao & Huang, the well-known soft-hard-soft pattern of the lower energy range changed to the hard-soft-hard (HSH) pattern of the higher energy range during the spectral evolution of each subpeak in both hard X-ray flares. This energy dependence is actually supported by a positive correlation between the overall light curves and spectral evolution in the lower energy range, while it becomes an anti-correlation in the higher energy range. Regarding microwave data, the HSH pattern appears in the spectral evolution of each subpeak in the lower frequency range, which is somewhat similar to Huang & Nakajima. However, it returns back to the well-known pattern of soft-hard-harder for the overall spectral evolution in the higher frequency range of both events. This frequency dependence is confirmed by an anti-correlation between the overall light curves and spectral evolution in the lower frequency range, but it becomes a positive correlation in the higher frequency range. The possible mechanisms are discussed, respectively, for reasons why hard X-ray and microwave spectral evolutions have different patterns in different energy and frequency intervals. © 2011. The American Astronomical Society. All rights reserved.

Reznikova V.E.,Nobeyama Solar Radio Observatory | Reznikova V.E.,Radiophysical Research Institute | Melnikov V.F.,Nobeyama Solar Radio Observatory | Melnikov V.F.,Russian Academy of Sciences | And 2 more authors.
Astrophysical Journal | Year: 2010

We studied the spatial dynamics of the flaring loop in the 2005 August 22 event using microwave (NoRH) and hard X-ray (RHESSI) observations together with complementary data from SOHO/MDI, SMART at Hida, SOHO/EIT, and TRACE. We have found that (1) the pre-flare morphology of the active region exhibits a strongly sheared arcade seen in Hα and the J-shape filament seen in EUV; (2) energy release and high-energy electron acceleration occur in a sequence along the extensive arcade; (3) the shear angle and the parallel (to the magnetic neutral line) component of the footpoint (FP) distance steadily decrease during the flare process; (4) the radio loop shrinks in length and height during the first emission peak, and later it grows; after the fourth peak the simultaneous descending of the brightest loop and formation of a new microwave loop at a higher altitude occur; (5) the hard X-ray coronal source is located higher than the microwave loop apex and shows faster upward motion; (6) the first peak on microwave time profiles is present in both the loop top and FP regions. However, the emission peaks that follow are present only in the FP regions. We conclude that after the first emission peak the acceleration site is located over the flaring arcade and particles are accelerated along magnetic field lines. We make use of the collapsing magnetic trap model to understand some observational effects. © 2010. The American Astronomical Society. All rights reserved.

Kupriyanova E.G.,Russian Academy of Sciences | Melnikov V.F.,Russian Academy of Sciences | Shibasaki K.,Nobeyama Solar Radio Observatory
Solar Physics | Year: 2013

Quasi-periodic pulsations (QPPs) with at least three simultaneously existing spectral components with periods P≥30 s, P≈20 s, and about P≈10 s were detected during the decay phase of a solar flare on 3 July 2002, observed with the Nobeyama Radioheliograph (NoRH). A detailed study of the spatial structure of the Fourier amplitudes of QPPs along a flaring loop has revealed different spatial distributions of the three components. It is shown that the source of the QPPs with period P≥30 s has its maximum amplitude in the inner region of the loop, between the footpoints. QPPs with period P≈20 s are localized at the periphery of the loop, mainly in the outer parts of the footpoints. The spatial distribution of oscillations with period about P≈10 s contains three regions of high QPP amplitudes: two near the footpoints and one in the middle of the flaring region. It is shown that the observed properties of the spectral components are most accurately described by the fundamental, second, and third harmonics of the kink mode standing waves. This is the first identification of the kink mode in flare loops which is based on strict limitations derived from data on the spatial structure of a pulsating flare region. © 2012 Springer Science+Business Media Dordrecht.

Kawate T.,Kwasan and Hida Observatory | Nishizuka N.,Japan Aerospace Exploration Agency | Oi A.,Ibaraki University | Ohyama M.,Shiga University | Nakajima H.,Nobeyama Solar Radio Observatory
Astrophysical Journal | Year: 2012

We analyze 10 flare events that radiate intense hard X-ray (HXR) emission with significant photons over 300keV to verify that the electrons that have a common origin of acceleration mechanism and energy power-law distribution with solar flares emit HXRs and microwaves. Most of these events have the following characteristics. HXRs emanate from the footpoints of flare loops, while microwaves emanate from the tops of flare loops. The time profiles of the microwave emission show delays of peak with respect to those of the corresponding HXR emission. The spectral indices of microwave emissions show gradual hardening in all events, while the spectral indices of the corresponding HXR emissions are roughly constant in most of the events, though rather rapid hardening is simultaneously observed in some for both indices during the onset time and the peak time. These characteristics suggest that the microwave emission emanates from the trapped electrons. Then, taking into account the role of the trapping of electrons for the microwave emission, we compare the observed microwave spectra with the model spectra calculated by a gyrosynchrotron code. As a result, we successfully reproduce the eight microwave spectra. From this result, we conclude that the electrons that have a common acceleration and a common energy distribution with solar flares emit both HXR and microwave emissions in the eight events, though microwave emission is contributed to by electrons with much higher energy than HXR emission. © 2012. The American Astronomical Society. All rights reserved.

De Wit T.D.,University of Orléans | Bruinsma S.,French National Center for Space Studies | Shibasaki K.,Nobeyama Solar Radio Observatory
Journal of Space Weather and Space Climate | Year: 2014

The specification of the upper atmosphere strongly relies on solar proxies that can properly reproduce the solar energetic input in the UV. Whilst the microwave flux at 10.7 cm (also called F10.7 index) has been routinely used as a solar proxy, we show that the radio flux at other wavelengths provides valuable complementary information that enhances their value for upper atmospheric modelling. We merged daily observations from various observatories into a single homogeneous data set of fluxes at wavelengths of 30, 15, 10.7, 8 and 3.2 cm, spanning from 1957 to today. Using blind source separation (BSS), we show that their rotational modulation contains three contributions, which can be interpreted in terms of thermal bremsstrahlung and gyro-resonance emissions. The latter account for 90% of the rotational variability in the F10.7 index. Most solar proxies, such as the MgII index, are remarkably well reconstructed by simple linear combination of radio fluxes at various wavelengths. The flux at 30 cm stands out as an excellent proxy and is better suited than the F10.7 index for the modelling the thermosphere-ionosphere system, most probably because it receives a stronger contribution from thermal bremsstrahlung. This better performance is illustrated here through comparison between the observed thermospheric density, and reconstructions by the Drag Temperature Model. © T. Dudok de Wit et al., Published by EDP Sciences 2014.

Abramov-Maximov V.E.,Russian Academy of Sciences | Gelfreikh G.B.,Russian Academy of Sciences | Shibasaki K.,Nobeyama Solar Radio Observatory
Solar Physics | Year: 2011

The sunspot-associated sources at the frequency of 17 GHz give information on plasma parameters in the regions of magnetic field about B=2000 G at the level of the chromosphere-corona transition region. The observations of short period (from one to ten minutes) oscillations in sunspots reflect propagation of magnetohydrodynamic (MHD) waves in the magnetic flux tubes of the sunspots. We investigate the oscillation parameters in active regions in connection with their flare activity. We confirm the existence of a link between the oscillation spectrum and flare activity. We find differences in the oscillations between pre-flare and post-flare phases. In particular, we demonstrate a case of powerful three-minute oscillations that start just before the burst. This event is similar to the cases of the precursors investigated by Sych et al. (Astron. Astrophys. 505, 791, 2009). We also found well-defined eight-minute oscillations of microwave emission from sunspot. We interpret our observations in terms of a relationship between MHD waves propagating from sunspots and flare processes. © 2011 Springer Science+Business Media B.V.

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