Toshifumi Shimizu

Nonthermal Radio Emission from Solar Soft X-Ray Transient Brightenings

We compare microwave total power spectral data from the Owens Valley Radio Observatory Solar Array with soft X-ray transient brightenings observed with the Yohkoh soft X-ray telescope. We find that the transient brightenings are clearly detected in microwaves in 12 of 34 events (35%), possibly detected in another 17 of 34 events (50%), and only five of 34 events (15%) had no apparent microwave counterpart. Comparing the radio and soft X-ray characteristics, we find that (1) the soft X-ray peak is delayed relative to the microwave peak in 16 of 20 events, (2) the microwave flux is correlated with the flux seen in soft X-rays, (3) when radio fluence is used instead of radio flux (24 events) the correlation increases substantially, (4) the microwave spectra in the range 1-18 GHz vary greatly from event to event, (5) the microwave spectra often peak in the range 5-10 GHz (13 of 16 events), and (6) the microwave spectra of some events show narrowband spectra with a steep low-frequency slope. We conclude that the emission from at least some events is the result of a nonthermal population of electrons, and that transient brightenings as a whole can therefore be identified as microflares, the low-energy extension of the general flare energy distribution. Soft X-ray transient brightenings, and therefore microflares, cannot heat the corona.

Temperature structure of active regions deduced from the helium-like sulphur lines

Solar active-region temperatures have been determined from the full-Sun spectra of helium-like sulphur (Sxv) observed by the Bragg Crystal Spectrometer on board theYohkoh satellite. The average temperature deduced from Sxv is demonstrated to vary with the solar activity level: A temperature of 2.5 × 106 K is derived from the spectra taken during low solar activity, similar to the general corona, while 4 × 106 K is obtained during a higher activity phase. For the latter, the high-temperature tail of the differential emission measure of active regions is found most likely due to the superposition of numerous flare-like events (micro/nano-flares).

Hinode and IRIS observations of the magnetohydrodynamic waves propagating from the photosphere to the chromosphere in a sunspot

Magnetohydrodynamic (MHD) waves have been considered as energy sources for heating the solar chromosphere and the corona. Although MHD waves have been observed in the solar atmosphere, there are a lack of quantitative estimates on the energy transfer and dissipation in the atmosphere. We performed simultaneous Hinode and IRIS observations of a sunspot umbra to derive the upward energy fluxes at two different atmospheric layers (photosphere and lower transition region) and estimate the energy dissipation. The observations revealed some properties of the observed periodic oscillations in physical quantities, such as their phase relations, temporal behaviors, and power spectra, making a conclusion that standing slow-mode waves are dominant at the photosphere with their high-frequency leakage, which is observed as upward waves at the chromosphere and the lower transition region. Our estimates of upward energy fluxes are

Japanese sounding rocket experiment with the solar XUV Doppler telescope

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Heating of Active Region Corona by Transient Brightenings (Microflares)

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Narrow-bandpass multilayer mirrors for an extreme-ultraviolet Doppler telescope

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Non-potential Field Formation in the X-shaped Quadrupole Magnetic Field Configuration

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Development of multilayer mirrors for the XUV Doppler telescope

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Instrument design of 1.5-m aperture solar optical telescope for the Solar-C Mission

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Instrument design and on-orbit performance of the solar optical telescope aboard hinode (Solar-B)

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