Shinsuke Imada

Outflows at the Edges of Active Regions: Contribution to Solar Wind Formation?

The formation of the slow solar wind has been debated for many years. In this Letter we show evidence of persistent outflow at the edges of an active region as measured by the EUV Imaging Spectrometer on board Hinode. The Doppler velocity ranged between 20 and 50 km s−1 and was consistent with a steady flow seen in the X-Ray Telescope. The latter showed steady, pulsing outflowing material and some transverse motions of the loops. We analyze the magnetic field around the active region and produce a coronal magnetic field model. We determine from the latter that the outflow speeds adjusted for line-of-sight effects can reach over 100 km s−1. We can interpret this outflow as expansion of loops that lie over the active region, which may either reconnect with neighboring large-scale loops or are likely to open to the interplanetary space. This material constitutes at least part of the slow solar wind.

CORONAL MASS EJECTION INDUCED OUTFLOWS OBSERVED WITH HINODE/EIS

We investigate the outflows associated with two halo coronal mass ejections (CMEs) that occurred on 2006 December 13 and 14 in NOAA 10930, using the Hinode/EIS observations. Each CME was accompanied by an EIT wave and coronal dimmings. Dopplergrams in the dimming regions are obtained from the spectra of seven EIS lines. The results show that strong outflows are visible in the dimming regions during the CME eruption at different heights from the lower transition region to the corona. It is found that the velocity is positively correlated with the photospheric magnetic field, as well as the magnitude of the dimming. We estimate the mass loss based on height-dependent EUV dimmings and find it to be smaller than the CME mass derived from white-light observations. The mass difference is attributed partly to the uncertain atmospheric model, and partly to the transition region outflows, which refill the coronal dimmings.

Morphology, dynamics and plasma parameters of plumes and inter-plume regions in solar coronal holes

Coronal plumes, which extend from solar coronal holes (CH) into the high corona and—possibly—into the solar wind (SW), can now continuously be studied with modern telescopes and spectrometers on spacecraft, in addition to investigations from the ground, in particular, during total eclipses. Despite the large amount of data available on these prominent features and related phenomena, many questions remained unanswered as to their generation and relative contributions to the high-speed streams emanating from CHs. An understanding of the processes of plume formation and evolution requires a better knowledge of the physical conditions at the base of CHs, in plumes and in the surrounding inter-plume regions. More specifically, information is needed on the magnetic field configuration, the electron densities and temperatures, effective ion temperatures, non-thermal motions, plume cross sections relative to the size of a CH, the plasma bulk speeds, as well as any plume signatures in the SW. In spring 2007, the authors proposed a study on ‘Structure and dynamics of coronal plumes and inter-plume regions in solar coronal holes’ to the International Space Science Institute (ISSI) in Bern to clarify some of these aspects by considering relevant observations and the extensive literature. This review summarizes the results and conclusions of the study. Stereoscopic observations allowed us to include three-dimensional reconstructions of plumes. Multi-instrument investigations carried out during several campaigns led to progress in some areas, such as plasma densities, temperatures, plume structure and the relation to other solar phenomena, but not all questions could be answered concerning the details of plume generation process(es) and interaction with the SW.

Propagating waves in polar coronal holes as seen by SUMER & EIS

Context. To study the dynamics of coronal holes and the role of waves in the acceleration of the solar wind, spectral observations were performed over polar coronal hole regions with the SUMER spectrometer on SoHO and the EIS spectrometer on Hinode. Aims. Using these observations, we aim to detect the presence of propagating waves in the corona and to study their properties. Methods. The observations analysed here consist of SUMER spectra of the Ne VIII 770 angstrom line (T = 0.6 MK) and EIS slot images in the Fe XII 195 angstrom line (T = 1.3 MK). Using the wavelet technique, we study line radiance oscillations at different heights from the limb in the polar coronal hole regions. Results. We detect the presence of long period oscillations with periods of 10 to 30 min in polar coronal holes. The oscillations have an amplitude of a few percent in radiance and are not detectable in line-of-sight velocity. From the time distance maps we find evidence for propagating velocities from 75 km s(-1) (Ne VIII) to 125 km s(-1)(Fe XII). These velocities are subsonic and roughly in the same ratio as the respective sound speeds. Conclusions. We interpret the observed propagating oscillations in terms of slow magneto-acoustic waves. These waves can be important for the acceleration of the fast solar wind.

Average profiles of energetic and thermal electrons in the magnetotail reconnection regions

[1] We study plasma heating and acceleration around magnetic reconnection region by using GEOTAIL data. We carry out the superposed analysis of thermal temperature and energetic electrons flux as a function of distance from X-type neutral line, for both the near-Earth and the distant magnetotail. It is found that the enhanced energetic flux and high temperature regions are located around reconnection outflow region downstream away from the center of the X-type neutral region. Those heated and accelerated regions are symmetric in both of the tail- and earth-ward flow regions in the distant magnetotail, while in the near-Earth magnetotail more energetic electrons are preferentially observed in the earthward flow region. In addition, we also study electron heating and acceleration during the passage of plasmoid, which may correspond to 0-type neutral line. We find the hot and energetic electrons behind the core of plasmoid but slightly away from the central plasma sheet.

STRONGLY BLUESHIFTED PHENOMENA OBSERVED WITH HINODE EIS IN THE 2006 DECEMBER 13 SOLAR FLARE

We present a detailed examination of strongly blueshifted emission lines observed with the EUV Imaging Spectrometer on board the Hinode satellite. We found two kinds of blueshifted phenomenon associated with the X3.4 flare that occurred on 2006 December 13. One was related to a plasmoid ejection seen in soft X-rays. It was very bright in all the lines used for the observations. The other was associated with the faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection is thought to be a magnetohydrodynamic (MHD) fast-mode shock wave. This is therefore the first spectroscopic observation of an MHD fast-mode shock wave associated with a flare.

MODE IDENTIFICATION OF MHD WAVES IN AN ACTIVE REGION OBSERVED WITH HINODE/EIS

In order to better understand the possibility of coronal heating by MHD waves, we analyze Fe XII 195.12A data observed with the EUV Imaging Spectrometer on board Hinode. We performed a Fourier analysis of EUV intensity and Doppler velocity time series data in the active region corona. Notable intensity and Doppler velocity oscillations were found for two moss regions out of the five studied, while only small oscillations were found for five apexes of loops. The amplitudes of the oscillations were 0.4%-5.7% for intensity and 0.2-1.2 km s–1 for Doppler velocity. In addition, oscillations of only the Doppler velocity were seen relatively less often in the data. We compared the amplitudes of intensity and those of Doppler velocity in order to identify MHD wave modes and calculated the phase delays between Fourier components of intensity and those of Doppler velocity. The results are interpreted in terms of MHD waves as follows: (1) few kink modes or torsional Alfven mode waves were seen in both moss regions and the apexes of loops, (2) upwardly propagating and standing slow mode waves were found in moss regions, and (3) consistent with previous studies, estimated values of energy flux of the waves were several orders of magnitude lower than that required for heating active regions.

Saturation of StellarWinds from Young Suns

We investigated mass losses via stellar winds from Sun-like main-sequence stars with a wide range of activity levels. We performed forward-type magnetohydrodynamical numerical experiments for Alfvwave-driven stellar winds with a wide range of input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass-loss rate rapidly at first increases, owing to suppression of the reflection of the Alfvwaves. The surface materials are lifted up by the magnetic pressure associated with the Alfvwaves, and the cool dense chromosphere is intermittently extended to 10%-20% of the stellar radius. The dense atmospheres enhance the radiative losses, and eventually most of the input Poynting energy from the stellar surface escapes by radiation. As a result, there is no more sufficient energy remaining for the kinetic energy of the wind; the stellar wind saturates in very active stars, as observed in Wood et al. (2002, ApJ, 574, 412; 2005, ApJ, 628, L143). The saturation level is positively correlated with Br;0f0, where Br;0 and f0 are the magnetic field strength and the filling factor of open flux tubes at the photosphere. If Br;0f0 is relatively large &5G, the mass-loss rate could be as high as 1000 times. If such a strong mass loss lasts for � 1 billion years, the stellar mass itself would be affected, which could be a solution to the faint young Sun paradox. We derived a Reimers- type scaling relation that estimates the mass-loss rate from an energetics consideration of our simulations. Finally, we derived the evolution of the mass-loss rates, P

Ion Temperature and Non-Thermal Velocity in a Solar Active Region: Using Emission Lines of Different Atomic Species

We have studied the characteristics of the ion thermal temperature and non-thermal velocity in an active region observed by the EUV Imaging Spectrometer onboard Hinode. We used two emission lines of different atomic species (Fe XVI 262.98 ? and S XIII 256.69??) to distinguish the ion thermal velocity from the observed full width at half-maximum. We assumed that the sources of the two emission lines are the same thermal temperature. We also assumed that they have the same non-thermal velocity. With these assumptions, we could obtain the ion thermal temperature, after noting that M sulfur ~ 0.6M iron. We have carried out the ion thermal temperature analysis in the active region where the photon counts are sufficient (>4500). What we found is as follows: (1) the common ion thermal temperatures obtained by Fe XVI and S XIII are ~2.5?MK, (2) the typical non-thermal velocities are ~13?km?s?1, (3) the highest non-thermal velocities (>20?km?s?1) are preferentially observed between the bright points in Fe XVI, while (4) the hottest material (>3?MK) is observed relatively inside the bright points compared with the highest non-thermal velocity region.

Comparison of extreme ultraviolet imaging spectrometer observations of solar coronal loops with Alfvén wave turbulence models

The observed non-thermal widths of coronal emission lines could be due to Alfven wave turbulence. To test this idea, we examine and analyze the dynamics of an active region observed on 2012 September 7. We use spectral line profiles of Fe XII, Fe XIII, Fe XV, and Fe XVI obtained by the Extreme-ultraviolet Imaging Spectrometer on the it Hinode spacecraft. The observations show non-thermal velocities, Doppler outflows, and intensities for loops in this active region. The observed non-thermal velocities are compared with predictions from models for Alfven wave turbulence in the observed coronal loops. This modeling takes into account the relationship between the width of the coronal emission lines and the orientation of the coronal loops with respect to the line-of-sight direction. We find that in order to produce the observed line widths we need to introduce a random parallel-flow component in addition to the perpendicular velocity due to Alfven waves. The observed widths are consistent with photospheric footpoint velocities in the range 0.3-1.5 km s–1. We conclude that the Alfven wave turbulence model is a strong candidate for explaining how the observed loops are heated.