We report here, for the —rst time, on spatial oscillations of coronal loops, which were detected in extreme-ultraviolet wavelengths (171 with the T ransition Region and Coronal Explorer, in the tem- Ae ) perature range of MK. The observed loop oscillations occurred during a —are that began at T e B 1.0¨1.5 1998 July 14, 12:55 UT and are most prominent during the —rst 20 minutes. The oscillating loops connect the penumbra of the leading sunspot to the —are site in the trailing portion. We identi—ed —ve oscillating loops with an average length of L \ 130,000 ^ 30,000 km. The transverse amplitude of the oscillations is A \ 4100 ^ 1300 km, and the mean period is T \ 280 ^ 30 s. The oscillation mode appears to be a standing wave mode (with —xed nodes at the footpoints). We investigate diUerent MHD wave modes and —nd that the fast kink mode with a period q \ 205(L /1010 cm~3)1@2 cm)(n e /109 (B/10 G)~1 s provides the best agreement with the observed period. We propose that the onset of loop oscillations in distant locations is triggered by a signal or disturbance that propagates from the central —are site with a radial speed of B700 km s~1. Because the observed loop oscillation periods are compa- rable to photospheric 5 minute oscillations, a resonant coupling between the two systems is possible. We further —nd evidence for global extreme-UV dimming in the entire active region possibly associated with a coronal mass ejection. Subject headings: Sun: coronaSun: —aresSun: oscillationsSun: UV radiation

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Coronal Loop Oscillations Observed with the Transition Region and Coronal Explorer

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections We also discuss flare soft X-ray spectroscopy and the energetics of the process The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations

An Observational Overview of Solar Flares

http://sourcedb.igsnrr.cas.cn/zw/lw/200906/P020090625750860369861.pdf

Growth, Population and Industrialization and Urban Land Expansion of China

Quasi-periodic pulsations (QPP) are a common feature of flaring energy releases in the solar atmosphere, observed in all bands, from radio to hard X-ray. In this review we concentrate on QPP with the periods longer than one second. Physical mechanisms responsible for the generation of long QPP split into two groups: “load/unload” mechanisms and MHD oscillations. Load/unload mechanisms are repetitive regimes of flaring energy releases by magnetic reconnection or by other means. MHD oscillations can affect all elements of the flaring emission generation: triggering of reconnection and modulation of its rate, acceleration and dynamics of non-thermal electrons, and physical conditions in the emitting plasmas. In the case of MHD oscillations, the periodicity of QPP is determined either by the presence of some resonances, e.g. standing modes of plasma structures, or by wave dispersion. Periods and other parameters of QPP are linked with properties of flaring plasmas and their morphology. Observational investigation of the QPP generation mechanisms based upon the use of spatial information, broadband spectral coverage and multi-periodicity is discussed.

Quasi-Periodic Pulsations in Solar Flares

http://www.igsnrr.cas.cn/xwzx/kydt/200608/W020090624623332810095.pdf

Cultivated land conversion and potential agricultural productivity in China

Observations of solar microwave bursts with high temporal and spectral resolution have shown interesting fine structures (FSs) of short duration and small bandwidth which are usually superimposed on the smooth continuum. These FSs are very intense (up to 1015 K) and show sometimes a high degree of circular polarization (up to 100%). They are believed to be generated by electron cyclotron maser emission (ECME) in magnetic loops. Another type are the microwave type III bursts, which are drifting microwave FSs, and are probably the signatures of travelling electron beams in the solar atmosphere. The exact emission mechanisms for these phenomena, in particular the source configuration, the plasma parameters and the distribution of radiating electrons are not clear. For a detailed study of these problems new observations of intensity and polarization with high resolution in time and in frequency in decimeter and microwave wavebands are essential. In order to investigate these features in greater detail, spectrometers with high temporal and spectral resolution are being developed by the solar radio astronomy community of China (Beijing Astronomical Observatory (BAO), Purple Mountain Observatory (PMO), Yunnan Astronomical Observatory (YAO), and Nanjing University (NJU)). The frequency range from 0.7 to about 12 GHz is covered by about five spectrometers in frequency ranges of 0.7–1.4 GHz, 1–2 GHz, 2.4–3.6 GHz, 4.9–7.3 GHz, and 8–12 GHz, respectively. The radiospectrometers will form a combined type of swept-frequency and multi-channel receivers. The main characteristics of the solar radio spectrometers are: frequency resolution: 1–10 MHz; temporal resolution: 1–10 ms; sensitivity: better than 2% of the quiet-Sun level. We pay special attention to the sensitivity and the accuracy of polarization. Now, the 1–2 GHz radiospectrometer is being set up. The full system will be set up in 3–4 years.

A broadband spectrometer for decimeter and microwave radio bursts

A new radio spectrometer, Solar Broadband Radio Spectrometer (SBRS) with characteristics of high time resolution, high-frequency resolution, high sensitivity, and wide frequency coverage in the microwave region is described. Its function is to monitor solar radio bursts in the frequency range of 0.7-7.6 GHz with time resolution of 1-10 ms. SBRS consists of five 'component spectrometers' which work in five different wave bands (0.7-1.5 GHz, 1.0-2.0 GHz, 2.6-3.8 GHz, 4.5-7.5 GHz, and 5.2-7.6 GHz, respectively). A combination of multi-channel and scanning techniques is adopted. The component spectrometers are attached to different antennas which are separately located at Beijing, Kunming, and Nanjing. Close attention was paid to solve the problems of sensitivity, dynamic range, interference-resistance, data acquisition, and handling a large amount of data. The SBRS was put into operation in the 23th solar maximum activity period, and has proved itself to be a valuable instrument for the study of solar bursts in microwaves.

New solar broadband radio spectrometer (SBRS) in China

We have observed in the microwave range (with the radio spectrometer of the Huairu station (Beijing, NAOC) around 3 GHz) the ne structure of solar radio bursts called zebra patterns and b er bursts (seen drifting on the frequency stripes in emission and in absorption on the background burst continuum emission). In all seven observed bursts we discovered a new eect: zebra stripes have a superne structure, consisting of numerous fast spikes with duration at a limit of the time resolution of the spectrometer, 8 ms. Since for zebra patterns and microwave spikes dieren t emission mechanisms were proposed, these new observations require us to revise known theories. An alternative model of microwave millisecond spikes is based on the coupling of plasma waves (l) with ion- sound waves (s) : l + s ! t. Since the main features of zebra stripes and b er bursts are similar, we consider the zebra pattern of these bursts as whistler manifestations. Whistlers (w) yield a principal contribution in the ne structure radio emission (t) by coupling with Langmuir waves at sum as well as dierence frequencies: !l !w = !t. Allowance for the conversion of ion-sound waves into whistlers (and inversely in a pulsating regime) enables us to identify the zebra pattern consisting of spikes as a simultaneous manifestation of both those processes (l + s ! t and l + w ! t ) in radio sources, related to magnetic reconnection above are regions.

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A superfine structure in solar microwave bursts

Observations of the solar radio emission in the microwave frequency range show fine structures consisting of a number of the almost parallel narrow frequency bands. We interpret these bands as the cyclotron harmonics plasma emission. This emission is generated by the anisotropic electron beam, which excites longitudinal waves on the normal Doppler effect resonance. Then the longitudinal waves convert into the radio emission on the second harmonic of the longitudinal waves frequency and sometimes into the fundamental one. Estimations of the magnetic field strength made on the basis of such a model give the values of the magnetic field in the microwave burst sources as ~ 100-200 G. The estimations of density variations are also given.

On an Estimation of the Coronal Magnetic Field Strength from Spectrographic Observations in the Microwave Range

We present results of the first simultaneous observations of zebra patterns (ZPs) with super-fine spiky structure in the microwave range made at two observatories similar to 1000 km apart (Beijing and Nanjing, China). The fine structure was recorded by a spectra polarimeter in the 5.2 - 7.6 and 2.8 - 3.6 GHz ranges at the Huairou station and by the spectrometer in the 4.5 - 7.5 GHz range at the Purple Mountain Observatory. Simultaneously, the locations of radio sources were observed by the Siberian Solar Radio Telescope (SSRT) at 5.7 GHz. For a general analysis of the April 10, 2001 event, the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) data and Transition Region and Coronal Explorer (TRACE) images in EUV 171 angstrom line were used. The circular polarization degree was very weak for the burst background radio emission and moderate to strong for the fine structure. The polarization sign in all the cases probably corresponds to the extraordinary wave mode. Estimations of the magnetic field values in the whistler model for fine structure agree well with the extrapolated values from magnetic maps. Given the possibility of wave transformation in the perpendicular magnetic field and the spiky structure of the ZP, the whistler wave model appears to be the most appropriate explanation for the zebra stripe phenomenon.

Qijun Fu

Papers

A broadband spectrometer for decimeter and microwave radio bursts

New solar broadband radio spectrometer (SBRS) in China

A superfine structure in solar microwave bursts

On an Estimation of the Coronal Magnetic Field Strength from Spectrographic Observations in the Microwave Range

Multi-site spectrographic and heliographic observations of radio fine structure on April 10, 2001