Late phase gradual enhancements in microwaves and hard X-rays of the 6 November 1980 flare

Solar Physics - We have calculated eigenfrequencies of radial and nonradial p-mode oscillations with low harmonic index l (l = 0, 1, 2, 3, and 4) for a standard solar model with normal composition...     

Influence of crystal shapes on radiative fluxes in visible wavelength: ice crystals randomly oriented in space

Radiative properties of cirrus clouds are one of the major unsolved problems in climate studies and global radiation budget. These clouds are generally composed of various ice-crystal shapes, so we tried to evaluate effects of the ice-crystal shape on radiative fluxes. We calculated radiative fluxes of cirrus clouds with a constant geometrical depth, composed of ice crystals with different shapes (hexagonal columns, bullets, bullet-rosettes), sizes and various concentrations. We considered ice particles randomly oriented in space (3D case) and their scattering phase functions were calculated by a ray-tracing method. We calculated radiative fluxes for cirrus layers for different microphysical characteristics by using a discrete-ordinate radiative code. Results showed that the foremost effect of the ice-crystal shape on radiative properties of cirrus clouds was that on the optical thickness, while the variation of the scattering phase function with the ice shape remained less than 3% for our computations. The ice-water content may be a better choice to parameterize the optical properties of cirrus, but the shape effect must be included.     

Radio evidence for a delayed acceleration process in solar flares

Evidence for a delayed acceleration process in solar flares is presented in the form of an analysis of simultaneous observations in microwaves, decimetre and metrewaves, and hard X-rays of six delayed gradual bursts which appear 0.5–1 hr after the strong main bursts have faded. The observed characteristics of the delayed bursts are: (a) similarity of flux time profiles at all the wavelengths, (b) low turn-over frequency (4 GHz) of the microwave spectrum, (c) moderately strong circular polarization (30–40%) and low altitude of the microwave source (which is displaced toward the disk centre by a projected distance of 10–20 from that of the preceding main burst), and (d) low spectral index of the energy spectrum of hard X-rays.From these observations it is suggested that (i) electrons are accelerated up to MeV even some tens of minutes after the impulsive phase acceleration has almost ceased, (ii) the delayed acceleration occurs in a large magnetic structure extending to a height of at least 2 × 10⁵ km, and (iii) the radio source has columnar structure with the microwave source predominantly near a leg or legs and the metrewave source near the top of the magnetic structure. The present observations of the delayed bursts do not seem to be consistent with the classical second-phase acceleration mechanism proposed in the past for normal hard X-ray gradual (extended) bursts.Minamimaki-mura, Minamisaku-gun, Nagano-ken 384-13, Japan.Greenbelt, MD 20771, U.S.A., NASA/NRC Research Associate, on leave from Tokyo Astronomical Observatory.P.O. Box 76, Epping, N.S.W. 2121, Australia.Berkeley, CA 94720, U.S.A.     

Some remarks on the spectrum of rapid-changing random data in the ocean

Spectral characteristics of rapid-changing random data in the ocean are discussed. Analysis shows that, if records are approximated by saw-toothed random series ₁ and step series ₂, ₁ and ₂ generally have spectral ranges of the –4th power and –2nd power, respectively, with respect to frequency (or wave number).     

Structure of tidal mixing at the Hayasui Straits

Based on the observation at the Hayasui Straits, actual conditions of the tidal mixing, of two water masses separated by the strait, are investigated for the time scale shorter than the the tidal period. Analyses show that the tidal mixing of water masses occurs by the disintegration of mutually penetrating small masses of water, which have been produced by the reciprocating tidal motion of the water masses with some topographical effect, especially at the slack water as large tongues. The mutual penetration occurs rather horizontally, and some of these turbulent smaller masses of water keep their own properties for a rather long period of the order of three hours, without mixing even in the violent shear flows. Initial horizontal scale of these turbulent masses is estimated as of the order of three kilometers. These actual conditions reveal themselves as the macroscopic diffusion coefficient.     

Community structures of coral reefs around Peninsular Malaysia

Coral community structures at eleven fringing reef sites were investigated along the coast of Peninsular Malaysia. Estimated coverage of coral communities is examined by applying quantitative digital image analysis to the line transect method. Four coral community types were characterized by dominant genera and lifeforms: Acropora branching community, Montipora-Acropora community, Porites massive community, and Heliopora community. Live coral coverage in all study sites ranged from 17.9% to 68.6%. Most reefs were in “fair” condition while some reefs were shown to be in “poor” condition. Coral community structures among the study sites were divided into the west coast of Peninsular Malaysia with a dominant Porites massive lifeform, and the east coast with a variety of lifeform categories of Montipora and Acropora. Physical effects such as the monsoon wind regime and sedimentation are likely to influence the formation of dominant coral communities around Peninsular Malaysia.     

Parallel Visualization of Large-scale Unstructured Geophysical Data for the Earth Simulator

— A scalable and high-performance parallel visualization subsystem has been developed in GeoFEM for the Earth Simulator. As part of the Earth Simulator project in Japan, the proposed subsystem is effective for the visualization of large-scale geoscientific data, and can be concurrent with computation subsystems on the same high-performance parallel computer. Moreover, several parallel visualization methods are developed for large unstructured datasets, covering scalar, vector and tensor fields. Furthermore, a number of strategies are adopted in order to improve the parallel performance of the proposed subsystem for the Earth simulator, including the three-level hybrid parallelization and dynamic load balancing. Good visualization images and high parallel performance have been obtained on a Hitachi SR8000 for large unstructured geoscientific data sets, and thus demonstrating the feasibility and effectiveness of the proposed method for use on the Earth Simulator.     

Along-arc lateral variation of Rb−Sr and K−Ar ages of Cretaceous granitic rocks in Southwest Japan

Cretaceous granitic rocks were emplaced over a distance of 700 km along arc in Southwest Japan. Rb–Sr and K–Ar ages of a major group of these granitic rocks, with ilmenite series ore mineralogy, were examined. Rb–Sr whole rock ages of 92.8±4.0 Ma and Rb–Sr and K–Ar biotite ages of 80–88 Ma were obtained on one group of these granitic rocks from Kamo-Sera area of central Hiroshima Prefecture. The K–Ar ages of various minerals, combined with the Rb–Sr whole-rock age, give a smooth cooling curve, which suggests a 5 to 10 Ma time-lag between intrusion and cooling at 300° C for the Cretaceous granitic rocks. The Rb–Sr whole-rock and Rb–Sr/K–Ar biotite ages of these granitic rocks become younger eastward along the Southwest Japan arc, and the time-lag between the two systems remains constant at 5 to 10 Ma over the entire area. The along-arc age variation does not support the genetical relationship of the Cretaceous granitoids with steady-state subduction. The Cretaceous granitic province at the eastern margin of Eurasian continent was, at least partly, formed by an episodic event such as ridge subduction.     

Microwave Neutral Line Associated Source and a Current Sheet

Neutral Line associated Sources (NLSs) are quasi-stationary microwave sources projected onto vicinities of the neutral line of the photospheric magnetic field. NLSs are often precursors of powerful flares, but their nature is unclear. We endeavor to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact site of colliding sunspots, whose relative motion goes on, resulting in a large shear along a tangent. Then the nascent NLS becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time, the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles a usual sunspot–associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare onset. We reveal i) upward lengthening of this bar before the flare onset, ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS.