A filament eruption and accompanying coronal field changes on November 5, 1992     

McAllister  A. H.  Kurokawa  H.  Shibata  K.  Nitta  N. 《Solar physics》1996,169(1):123-149

An H filament eruption on November 5, 1992 was fully observed in H with the Hida Flare Monitoring Telescope, while Yohkoh's Soft X-ray Telescope observed the pre- and post-eruption evolution of the coronal magnetic fields. From the H data, including the red and blue wings, we have reconstructed the rise of the filament, including trajectory, velocity, and acceleration. In combination with the Yohkoh data this reconstruction suggests that the filament had several interactions with other coronal magnetic fields during the eruption. The Yohkoh data also shows pre-eruption changes in the coronal fields and several post-eruption bright coronal structures. The pre-eruption changes are interpreted as a partial opening of the corona, indicating that it is not necessary to have a complete opening of the corona in order for a filament to erupt and we discuss the several possible contributions from emerging flux. The post-event bright coronal structures are compared with theory and with a cleaner filament eruption event on July 31, 1992. These comparisons suggest that, although there are many similarities, it is hard to completely reconcile the observations with the existing theory.  相似文献   

Volcanic hazards from Bezymianny- and Bandai-type eruptions     

Lee Siebert  Harry Glicken  Tadahide Ui 《Bulletin of Volcanology》1987,49(1):435-459

Major slope failures are a significant degradational process at volcanoes. Slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years; the historic record provides evidence for at least six of these events in the past century. Several historic debris avalanches exceed 1 km³ in volume. Holocene avalanches an order of magnitude larger have traveled 50–100 km from the source volcano and affected areas of 500–1500 km². Historic eruptions associated with major slope failures include those with a magmatic component (Bezymianny type) and those solely phreatic (Bandai type). The associated gravitational failures remove major segments of the volcanoes, creating massive horseshoe-shaped depressions commonly of caldera size. The paroxysmal phase of a Bezymianny-type eruption may include powerful lateral explosions and pumiceous pyroclastic flows; it is often followed by construction of lava dome or pyroclastic cone in the new crater. Bandai-type eruptions begin and end with the paroxysmal phase, during which slope failure removes a portion of the edifice. Massive volcanic landslides can also occur without related explosive eruptions, as at the Unzen volcano in 1792.The main potential hazards from these events derive from lateral blasts, the debris avalanche itself, and avalanche-induced tsunamis. Lateral blasts produced by sudden decompression of hydrothermal and/or magmatic systems can devastate areas in excess of 500km² at velocities exceeding 100 m s^–1. The ratio of area covered to distance traveled for the Mount St. Helens and Bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume. The potential for large-scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice, as at Mount St. Helens and Bezymianny.Debris avalanches can move faster than 100 ms^–1 and travel tens of kilometers. When not confined by valley walls, avalanches can affect wide areas beyond the volcano's flanks. Tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions. The probable travel distance (L) of avalanches can be estimated by considering the potential vertical drop (H). Data from a catalog of around 200 debris avalanches indicates that the H/L rations for avalanches with volumes of 0.1–1 km³ average 0.13 and range 0.09–0.18; for avalanches exceeding 1 km³, H/L ratios average 0.09 and range 0.5–0.13.Large-scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts. The nature and duration of precursory activity vary widely, and the timing of slope faliure greatly affects the type of associated eruption. Bandai-type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity.  相似文献   

Volcanic dry avalanche deposits — Identification and comparison with nonvolcanic debris stream deposits     

Tadahide Ui 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

A “volcanic dry avalanche deposit” is defined as a volcaniclastic deposit formed as a result of a large-scale sector collapse of a volcanic cone associated with some form of volcanic activity. Avalanche transport occurred in response to the gravitational field, in a manner similar to the transport of nonvolcanic debris streams (e.g. Hsü, 1975). Such deposits are characterized by megablock structure — deformed and fractured large blocks up to several hundreds meters in diameter. A megablock preserves original layering, intrusive contacts or weathered surfaces of the source volcanic edifice. Surface topography of the deposit is characterised with hummocky relief. Ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0.18 and 0.06. This range is similar but smaller than the value of 0.58 to 0.08 for nonvolcanic debris stream deposit. This similarity suggests similar transportation mechanisms. Excessive travel distances as defined by Hsü (1975), calculated for volcanic dry avalanche deposits, give values larger than for debris stream deposits of the same volume. The difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers, alteration around the vent, development of fractures owing to new cryptodome intrusion, and boiling of supercritical fluid contained within the collapsed mass.  相似文献   

Fine structure in the inner corona observed at the 1970 eclipse     

T. Tsubaki  H. Kurokawa  M. Kanno 《Solar physics》1971,21(2):305-313

On the slit spectrogram obtained at the 1970 eclipse in Mexico, the intensities of four coronal lines (Nixiii 5116, Fexiv 5303, Fex 6374, and Nixv 6702) and the continuum were measured as a function of distance along the slit. It is found that there exist a lot of fine fluctuations both in the lines and in the continuum intensities superposed on a large scale formation. The correspondence of such fluctuations between the continuum and the lines is good, with the exception of the line 6374 which shows a peculiar fluctuation. It is shown that the intensities of the three lines 5116, 5303, and 6702 seem to be proportional to the square of the continuum intensity while the 6374 line intensity may be proportional to the fourth power or more.  相似文献   

Precise determination of cooling times of post-flare loops from the detailed comparison between Hα and soft X-ray images     

Suguru Kamio  Hiroki Kurokawa  Takako T. Ishii 《Solar physics》2003,215(1):127-146

A detailed study of the evolution and cooling process of post-flare loops is presented for a large X9.2 solar flare of 2 November 1992 by using H images obtained with Domeless Solar Telescope at Hida Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope (SXT). The detailed analysis with a new method allows us to determine more precise values of the cooling times from 10⁷ K to 10⁴ K plasma in the post-flare loops than in previous works. The subtraction of sequential images shows that soft X-ray dimming regions are well correlated to the H brightening loop structure. The cooling times between 10⁷ K and 10⁴ K are defined as the time difference between the start of soft X-ray intensity decrease and the end of H intensity increase at a selected point, where the causal relation between H brightening and soft X-ray dimming loops is confirmed. The obtained cooling times change with time; about 10 min at the initial stage and about 40 min at the later stage. The combined conductive and radiative cooling times are also calculated by using the temperature and density obtained from SXT data. Calculated cooling times are close to observed cooling times at the beginning of the flare and longer in the later stage.  相似文献   

Relationship between chemical composition of Japanese Island-Arc volcanic rocks and gravimetric data     

Tadahide Ui  Shigeo Aramaki 《Tectonophysics》1978,45(4):249-259

1670 published chemical analyses from 137 Quaternary eruption centers of Kurile, Japan and Izu—Mariana arcs are collected and K₅₅ and K₆₀ values of individual centers are calculated. Along with the well-established trend of increase of K₅₅ and K₆₀ values across the arc towards the continent, longitudinal change is also recognizable. Interrelation between K₅₅ or K₆₀ value pattern and a map of Bouguer anomaly distribution along the volcanic front is characteristic.To develop one possible simplified model to explain the facts, we assume first that the asthenosphere has a homogeneous thermal state beneath the volcanic zone, second that the thickness of the crust is quite variable areally, and third that the mean density of the crust is constant throughout the area. Thus, the composition of the magma generated along a zone corresponding to equal depths along the Benioff zone should be identical throughout the volcanic arc, and lower values of the Bouguer anomaly should be observed where the crust is thicker. We then assume that magma generated in the asthenosphere ascends into the crust, then cools as fractional crystallization proceeds. Depths of fractional crystallization would be deeper where the crust is thicker. The ratio of the clinopyroxene phase separated from the magma to the plagioclase phase should be larger where the level of fractionation is deeper. Thus, magmatic liquid should be enriched in K where K-poor crystal fractions are subtracted at the deeper level.  相似文献   

The X10 Flare on 29 October 2003: Was It Triggered by Magnetic Reconnection between Counter-Helical Fluxes?     

Yu Liu  Hiroki Kurokawa  Chang Liu  David H. Brooks  Jingping Dun  Takako T. Ishii  Hongqi Zhang 《Solar physics》2007,240(2):253-262

Vector magnetograms taken at Huairou Solar Observing Station (HSOS) and Mees Solar Observatory (MSO) reveal that the super active region (AR) NOAA 10486 was a complex region containing current helicity flux of opposite signs. The main positive sunspots were dominated by negative helicity fields, while positive helicity patches persisted both inside and around the main positive sunspots. Based on a comparison of two days of deduced current helicity density, pronounced changes associated with the occurrence of an X10 flare that peaked at 20:49 UT on 29 October 2003 were noticed. The average current helicity density (negative) of the main sunspots decreased significantly by about 50%. Accordingly, the helicity densities of counter-helical patches (positive) were also found to decay by the same proportion or more. In addition, two hard X-ray (HXR) “footpoints” were observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the flare in the 50 – 100 keV energy range. The cores of these two HXR footpoints were adjacent to the positions of two patches with positive current helicity that disappeared after the flare. This strongly suggested that the X10 flare on 29 October 2003 resulted from reconnection between magnetic flux tubes having opposite current helicity. Finally, the global decrease of current helicity in AR 10486 by ∼50% can be understood as the helicity launched away by the halo coronal mass ejection (CME) associated with the X10 flare. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

A Multiple Flare Scenario where the Classic Long-Duration Flare Was Not the Source of a CME     

C. P. Goff  L. van Driel-Gesztelyi  P. Démoulin  J. L. Culhane  S. A. Matthews  L. K. Harra  C. H. Mandrini  K. L. Klein  H. Kurokawa 《Solar physics》2007,240(2):283-299

A series of flares (GOES class M, M and C) and a CME were observed in close succession on 20 January 2004 in NOAA 10540. Radio observations, which took the form of types II, III and N bursts, were associated with these events. We use the combined observations from TRACE, EIT, Hα images from Kwasan, MDI magnetograms and GOES to understand the complex development of this event. Contrary to a standard interpretation, we conclude that the first two impulsive flares are part of the CME launch process while the following long-duration event flare represents simply the recovery phase. Observations show that the flare ribbons not only separate but also shift along the magnetic inversion line so that magnetic reconnection progresses stepwise to neighboring flux tubes. We conclude that “tether cutting” reconnection in the sheared arcade progressively transforms it to a twisted flux tube, which becomes unstable, leading to a CME. We interpret the third flare, a long-duration event, as a combination of the classical two-ribbon flare with the relaxation process following forced reconnection between the expanding CME structure and neighboring magnetic fields. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

Application of Chlorite Geothermometry to Hydrothermal Alteration in Toyoha Geothermal System, Southwestern Hokkaido, Japan   总被引：1，自引：0，他引：1  

Atsuyuki Inoue  Kyohei Kurokawa    Tamao Hatta 《Resource Geology》2010,60(1):52-70

In this study, we applied chemical geothermometers to the estimation of formation temperatures of chlorites from various types of hydrothermally altered rocks in the Toyoha geothermal field, using core samples from six drill holes (TH-2 to TH-7) together with wasted ore samples from Toyoha vein-type ore deposit. Based on the preliminary examination of mineral assemblages by X-ray powder diffraction and optical microscopy, hydrothermal alteration observed through the drill holes was classified into four types of alteration zones: propylitic, mixed-layer minerals, kaolin minerals, and ore mineralized zones. The mineral assemblage of the ore mineralized zone observed through TH-2, TH-4, and TH-6 is similar to those of Toyoha ore veins reported previously. The Fe³⁺/ΣFe ratios of chlorites were determined by X-ray photoelectron spectroscopy (XPS), in addition to the usual microprobe analyses. The ratios ranged from 0.20–0.26 for chlorites from the propylitic alteration zone and from 0.13 to 0.17 for those from the ore mineralized zone associated with sulfide minerals. After correcting the Fe³⁺ contents in the octahedral sites of chlorite structures, we obtained acceptable temperatures of the chlorite formation by application of geothermometers, for instance, a similar range of 150–300°C for chlorites from either the propylitic zone or the ore mineralized zone developed through TH-2, TH-4, and TH-6. Chlorites from the ore mineralized zone proximal to the Toyoha deposit are characterized by high Fe and Mn contents compared to the propylitic chlorites, which is similar to the Toyoha vein-filling chlorites; the formation temperatures were close to both the homogenization temperatures of fluid inclusions and the present subsurface temperatures measured through drill holes. Chlorites from the Toyoha ore veins, however, gave slightly higher formation temperatures (180–350°C) than those of chlorites from the ore mineralized zone in the drill cores. This suggests that several types of hydrothermal alteration occurred at different stages in the Toyoha geothermal field and the composition of product chlorite was controlled not only by the temperature but also the composition of fluid related to the formation. Reliable estimation of temperature for the chlorite formation provides basic information on evaluating correctly other physicochemical conditions prevalent at the formation.  相似文献   

Mass motions in active region filaments     

Hanaoka  Yoichiro  Kurokawa  Hiroki 《Solar physics》1989,124(2):227-250

Mass motions in active region filaments of regions NOAA 4171 and McMath 16208 are analyzed. Both regions were continuously observed with the Zeiss Lyot filter for about a week at the Hida Observatory. As for NOAA 4171, Dopplergrams are made from the H filtergrams of 7 wavelengths for the qualitative study of the velocity fields in the filament, and Beckers' cloud model analysis is employed for a quantitative study of them. Dopplergrams of McMath 16208 are also constructed for qualitative analyses to determine whether the results derived from the analysis of NOAA 4171 are applicable to this region.The following results are obtained. Matter in the long-lived filaments, which lie along the magnetic neutral lines, flows generally horizontally and along the axes of the filaments. Since the matter in the filaments is considered to flow along the magnetic field, the magnetic fields in the filaments must be highly sheared. The same patterns of mass flow are found in the same filaments on successive days; some of them last for at least several days. Some filaments show long-lived symmetrical downflows to both of their ends in which the velocity is about 30 km s^-1. Such flows are seen both in NOAA 4171 and McMath 16208. We show a morphological model of such flows.Contributions from the Kwasan and Hida Observatory, Kyoto University, No. 295.  相似文献