A study of coronal bright points at 20 cm wavelength     

N. Nitta  M. R. Kundu 《Solar physics》1988,117(1):37-50

We present the results of a study of coronal bright points observed at 20 cm with the VLA on a day when the Sun was exceptionally quiet. Microwave maps of bright points were obtained using data for the entire observing period of 5 hours, as well as for shorter periods of a few minutes. Most bright points, especially those appearing in the full-period maps appear to be associated with small bipolar structures on the photospheric magnetogram. Overlays of bright point (B.P.) maps on the Ca⁺K picture, show that the brightest part of a B.P. tends to lie on the boundary of a supergranulation network. In general, the bright points exhibit rapid variations in intensity. There is no systematic correlation between the size of a B.P. and its intensity; the apparently slow variation of B.P. emission may have rapid fluctuations superimposed on it.  相似文献   

Solar Flare and CME Observations with STEREO/EUVI     

M. J. Aschwanden  J. P. Wuelser  N. V. Nitta  J. R. Lemen 《Solar physics》2009,256(1-2):3-40

STEREO/EUVI observed 185 flare events (detected above the GOES class C1 level or at >?25 keV with RHESSI) during the first two years of the mission (December 2006?–?November 2008), while coronal mass ejections (CMEs) were reported in about a third of these events. We compile a comprehensive catalog of these EUVI-observed events, containing the peak fluxes in soft X rays, hard X rays, and EUV, as well as a classification and statistics of prominent EUV features: 79% show impulsive EUV emission (coincident with hard X rays), 73% show delayed EUV emission from postflare loops and arcades, 24% represent occulted flares, 17% exhibit EUV dimming, 5% show loop oscillations or propagating waves, and at least 3% show erupting filaments. We analyze an example of each EUV feature by stereoscopic modeling of its 3D geometry. We find that EUV emission can be dominated by impulsive emission from a heated, highly sheared, noneruptive filament, in addition to the more common impulsive EUV emission from flare ribbons or the delayed postflare EUV emission that results from cooling of the soft-X-ray-emitting flare loops. Occulted flares allow us to determine CME-related coronal dimming uncontaminated from flare-related EUV emission. From modeling the time evolution of EUV dimming we can accurately quantify the initial expansion of CMEs and determine their masses. Further, we find evidence that coronal loop oscillations are excited by the rapid initial expansion of CMEs. These examples demonstrate that stereoscopic EUV data provide powerful new methods to model the 3D aspects in the hydrodynamics of flares and kinematics of CMEs.  相似文献   

Interpretation of the soft X-ray spectra from Hinotori     

K. Tanaka  N. Nitta  K. Akita  T. Watanabe 《Solar physics》1983,86(1-2):91-100

We present analyses of the soft X-ray iron line spectra of flares obtained from the Bragg Spectrometer on Hinotori. We first present a case of strong K emission at the impulsive phase of the hard X-ray burst, and assess net K emission due to the electron impact by eliminating the fluorescence contribution. Second we discuss on the differences in the electron temperatures and emission measures derived respectively from FeXXVI and FeXXV spectra. A pilot two-temperatures model which can explain the two spectra is presented. Finally, we compare the temporal relations between the soft X-ray and hard X-ray intensities and show two extreme classes of flares, one characterized by the efficient formation of a hot thermal plasma above 30 million degree, and the other characterized by the spiky hard X-ray component. Energetical relation of the thermal plasma to the electron beam is discussed for the two classes.  相似文献   

Accumulation features of trace elements in mass-stranded harbor seals (Phoca vitulina) in the North Sea coast in 2002: the body distribution and association with growth and nutrition status     

Agusa T  Yasugi SY  Iida A  Ikemoto T  Anan Y  Kuiken T  Osterhaus AD  Tanabe S  Iwata H 《Marine pollution bulletin》2011,62(5):963-975

Body distribution and growth- and nutritional status-dependent accumulation of 21 trace elements were investigated in harbor seals (Phoca vitulina) stranded in the North Sea coast in 2002. Higher concentrations and burdens of Mn, Se, Mo, Ag, Sn, Hg, and Bi in the liver, Cd in the kidney, As in the blubber, and Co, Sr, and Ba in the bone were observed. Significant positive correlations of hepatic Se, Mo, Ag, Cd, Sn, Hg, Tl, and Bi with standard body length were found, while significant negative relationships were detected for Mn, As, Rb, Sr, and Sb in the liver. Concentrations of Co, Se, Sr, Sn, Hg, and Bi in the liver, V, Sr, Ag, Sn, and Hg in the kidney, V, Mn, Co, Rb, Sr, Sn, Ba, and Pb in the blubber increased with decreasing blubber thickness of harbor seals, indicating enrichment of these elements in the target tissue by emaciation.  相似文献   

The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts     

Nariaki V. Nitta  Wei Liu  Nat Gopalswamy  Seiji Yashiro 《Solar physics》2014,289(12):4589-4606

Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies and high altitudes tend to accompany an extended arc-shaped feature, which probably represents the 3D structure of the CME and the shock wave around it, and not just its near-surface track, which has usually been identified with EIT waves. This feature expands and propagates toward and beyond the limb. These events may be characterized by stretching of field lines in the radial direction and may be distinct from other LCPFs, which may be explained in terms of sudden lateral expansion of the coronal volume. Neither LCPFs nor type II bursts by themselves serve as necessary conditions for coronal shock waves, but these phenomena may provide useful information on the early evolution of the shock waves in 3D when both are clearly identified in eruptive events.  相似文献   

Simultaneous imaging observations of the sun at microwaves and hard X-rays     

Nakajima  H.  Takakura  T.  Nitta  N.  Ohki  K. 《Solar physics》1987,113(1-2):63-65

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Thermal evolution of flare plasma     

Tetsuya Watanabe  Katsuo Tanaka  Kyo Akita  Nariaki Nitta 《Solar physics》1983,86(1-2):107-113

The evolution of hot thermal plasma in solar flares is analyzed by a single-temperature model applied to continuum emission in the 5 keV < E ? 13 keV spectral range. The general trend that the thermal plasma observed in soft X-rays is heated by the non-thermal electrons that emit as the hard X-ray bursts is confirmed by the observation of an electron temperature increase at the time interval of hard X-ray spikes and a quantitative comparison between thermal energy content and hard X-ray energy input. Non-thermal electrons of 10 keV < E < 30 keV energy may play an important role in pre- and post-burst phases.  相似文献   

Clear Detection of Chromospheric Evaporation Upflows with High Spatial/Temporal Resolution by Hinode XRT     

S. Nitta  S. Imada  T. T. Yamamoto 《Solar physics》2012,276(1-2):183-197

We find clear evidence for typical chromospheric evaporation associated with small transient brightenings, using the data from the X-ray Telescope (XRT) onboard Hinode. We found 13 events, each having a pair of evaporation upflows arising almost symmetrically from both foot points of a magnetic loop. These facts strongly support the standard flare model based on the magnetic reconnection. The apparent upflow velocities of three of the events are ≈?500?km?s^?1, while those of the other events are ≈?100?km?s^?1. This is the first clear direct detection of evaporating upflow motion in soft X-ray images from Hinode/XRT; such images were obtained with high cadence (≈?60?s) and high spatial resolution (1?arcsec).  相似文献   

Short-period pulsations observed simultaneously by X-ray and radio waves     

S. S. Degaonkar  T. Takakura  P. Kaufmann  J. E. R. Costa  K. Ohki  N. Nitta 《Solar physics》1983,86(1-2):237-238

From simultaneous high-time-resolution observations of solar X-rays from Hinotori and the millimeter waves at Itapetinga Radio Observatory in Brazil during a solar flare on November 4, 1981 at 1827 UT, short period ( 300 ms) pulsations have been detected in five time intervals of 2 s each. Both a cross-correlation analysis between X-rays and microwaves and a Fourier analysis were made to verify the significance of the quasi-periodic pulsations. The cross-correlation is significant but the pulsations could not be periodic oscillation.on leave of absence from Physical Res. Lab., Ahmedabad, India  相似文献   

On the reconciliation of simultaneous microwave imaging and hard X-ray observations of a solar flare     

N. Nitta  S. M. White  E. J. Schmahl  M. R. Kundu 《Solar physics》1991,132(1):125-136

We have compared microwave imaging data for a small flare with simultaneous hard X-ray spectral observations. The X-ray data suggest that the power-law index of the energy distribution of the radiating electrons is 5.3 (thick-target) which differs significantly from the estimate ( = 1.4) from a homogeneous optically-thin gyrosynchrotron model which fits the radio observations well. In order to reconcile these results, we explore a number of options. We investigate a double power-law energy spectrum for the energetic electrons in the flare, as assumed by other authors: the power law is steep at low energies and much flatter at the higher energies which produce the bulk of the microwaves. The deduced break energy is about 230 keV if we tentatively ignore the X-ray emission from the radio-emitting electrons: however, the emission of soft photons by the flat tail strongly contributes to the observed hard X-ray range and would flatten the spectrum there. A thin-target model for the X-ray emission is also inconsistent with radio data. An inhomogeneous gyrosynchrotron model with a number of free parameters and containing an electron distribution given by the thick-target X-ray model could be made to fit the radio data.  相似文献