Radio,X-ray,and optical observations of the flare of June 13, 1980, at 6h22m UT

A subflare of importance Sf was observed on June 13, 1980 simultaneously by instruments aboard the Solar Maximum Mission (SMM) and various ground based observatories. We describe and compare different kinds of observations, with emphasis on the Hard X-Ray Imaging Spectrometer (HXIS) images and spectra, and on the one-dimensional microwave images with high time and spatial resolution, obtained with the Westerbork Synthesis Radio Telescope (WSRT). The fast electrons causing the X-ray and microwave impulsive bursts had a common acceleration source, but the burst were produced at the opposite footpoints of the loops involved, with microwaves emitted near to a sunspot penumbra. The flare (of a ‘compact’ type) was probably triggered by an emerging flux, and two possible interpretations of this process are briefly discussed.

     

Rapid subsidence of the Kikai Seamount inferred from drowned Pleistocene coral limestone: Implication for subduction of the Amami Plateau,northern Philippine Sea

Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau.     

Radio Emission of the Quiet Sun and Active Regions (Invited Review)

Solar radio emission provides valuable information on the structure and dynamics of the solar atmosphere above the temperature minimum. We review the background and most recent observational and theoretical results on the quiet Sun and active region studies, covering the entire radio range from millimeter to decameter wavelengths. We examine small- and large-scale structures, at short and long time scales, as well as synoptic aspects. Open questions and challenges for the future are also identified.     

Types of Microwave Quasi-Periodic Pulsations in Single Flaring Loops

Quasi-periodic pulsations (QPP) of microwave emission generated in single flaring loops observed with the Nobeyama Radioheliograph (NoRH) and Nobeyama Radio Polarimeters (NoRP) are studied. Specific features of the time profiles, i.e. the visible presence or absence of QPPs, are not accounted for in the selection. The time evolution of the periods of the QPPs is examined using wavelet and correlation analyses. In ten out of twelve considered events, at least one or more significant spectral components with periods from 5 – 60 s have been found. The quality of the oscillations is rather low: Q=π N, where N is the number of cycles, mostly varies in the range 12 to 40, with an average of 25. We suggest that the detected QPPs can be classified into four types: i) those with stable mean periods (e.g. of 15 – 20 s or 8 – 9 s, the prevailing type); ii) those with spectral drift to shorter periods (mostly in the rise phase of the microwave emission); iii) those with drift to longer periods (mostly in the decay phase); iv)  those with multiple periods showing an X-shaped drift (e.g. in the range from 20 – 40 s in the rise phase).     

Spatially Resolved Microwave Observations of Multiple Periodicities in a Flaring Loop

Quasi-periodic pulsations (QPPs) with at least three simultaneously existing spectral components with periods P≥30 s, P≈20 s, and about P≈10 s were detected during the decay phase of a solar flare on 3 July 2002, observed with the Nobeyama Radioheliograph (NoRH). A detailed study of the spatial structure of the Fourier amplitudes of QPPs along a flaring loop has revealed different spatial distributions of the three components. It is shown that the source of the QPPs with period P≥30 s has its maximum amplitude in the inner region of the loop, between the footpoints. QPPs with period P≈20 s are localized at the periphery of the loop, mainly in the outer parts of the footpoints. The spatial distribution of oscillations with period about P≈10 s contains three regions of high QPP amplitudes: two near the footpoints and one in the middle of the flaring region. It is shown that the observed properties of the spectral components are most accurately described by the fundamental, second, and third harmonics of the kink mode standing waves. This is the first identification of the kink mode in flare loops which is based on strict limitations derived from data on the spatial structure of a pulsating flare region.     

The X-Ray Telescope (XRT) for the Hinode Mission

The X-ray Telescope (XRT) of the Hinode mission provides an unprecedented combination of spatial and temporal resolution in solar coronal studies. The high sensitivity and broad dynamic range of XRT, coupled with the spacecraft’s onboard memory capacity and the planned downlink capability will permit a broad range of coronal studies over an extended period of time, for targets ranging from quiet Sun to X-flares. This paper discusses in detail the design, calibration, and measured performance of the XRT instrument up to the focal plane. The CCD camera and data handling are discussed separately in a companion paper.     

The Hinode X-Ray Telescope (XRT): Camera Design, Performance and Operations

The X-ray Telescope (XRT) aboard the Hinode satellite is a grazing incidence X-ray imager equipped with a 2048×2048 CCD. The XRT has 1 arcsec pixels with a wide field of view of 34×34 arcmin. It is sensitive to plasmas with a wide temperature range from < 1 to 30 MK, allowing us to obtain TRACE-like low-temperature images as well as Yohkoh/SXT-like high-temperature images. The spacecraft Mission Data Processor (MDP) controls the XRT through sequence tables with versatile autonomous functions such as exposure control, region-of-interest tracking, flare detection, and flare location identification. Data are compressed either with DPCM or JPEG, depending on the purpose. This results in higher cadence and/or wider field of view for a given telemetry bandwidth. With a focus adjust mechanism, a higher resolution of Gaussian focus may be available on-axis. This paper follows the first instrument paper for the XRT (Golub et al., Solar Phys. 243, 63, 2007) and discusses the design and measured performance of the X-ray CCD camera for the XRT and its control system with the MDP.     

Dissipation of diamagnetic currents and plasma heating in coronal magnetic loops

SOHO and TRACE data have shown that the coronal plasma is heated most actively near sunspots, in magnetic loops that issue from the penumbral region. The source of heating is nonuniform in height, and its power is maximum near the footpoints of the magnetic loops. The heating process is typically accompanied by the injection of dense chromospheric plasma into the coronal parts of the magnetic loops. It is important that the radiative losses cannot be compensated for via electron thermal conduction in the loops, which have temperatures of 1.0–1.5 MK; therefore, some heating source must operate throughout the entire length of the loop, balancing radiative losses and maintaining a quasi-steady state of the loop over at least several hours. As observations show, the plasma density inside the loops exceeds the density of the ambient plasma by more than an order of magnitude. It is supposed that the enhanced plasma density inside the loops results from the development of the ballooning mode of a flute-type instability in the sunspot penumbra, where the plasma of the inner sunspot region, with β _i ? 1, comes into contact with the dense chromospheric plasma, which has β _e ? β _i (β is the gas-to-magnetic pressure ratio). As the chromospheric plasma penetrates into the potential field of the sunspot, the generated diamagnetic currents balance the excess gas pressure. These currents efficiently decay due to the Cowling conductivity. Even if neutrals are few in number in the plasma (accounting for less than 10^?5 of the total mass density), this conductivity ensures a heating rate that exceeds the rate of the normal Joule dissipation of diamagnetic currents by 7–8 orders of magnitude. Helium is an important factor in the context of plasma heating in magnetic loops. Its relatively high ionization potential, while not forbidding dielectronic recombination, ensures a sufficiently high number of neutrals in the coronal plasma and maintains a high heating rate due to the Cowling conductivity, even at coronal temperatures. The heating results from the “burning-out” of the nonpotential component of the magnetic field of the coronal magnetic loops. This mechanism provides the necessary heating rate for the plasma inside the loops if the loops are thin enough (with thickness of the order of 10⁵–10⁶ cm). This may imply that the observed (1–5) × 10⁸-cm-thick loops consist of numerous hot, thin threads. For magnetic loops in hydrostatic equilibrium, the calculated heating function exponentially decreases with height on characteristic scales a factor of 1.8 smaller than the total-pressure scale height, since the scale heights for the total pressure and for the ⁴He partial pressure are different. The heating rate is proportional to the square of the plasma pressure in the loop, in agreement with observational data.

     

Growth history and formation environments of ferromanganese deposits on the Philippine Sea Plate, northwest Pacific Ocean

Abstract   Hydrogenetic ferromanganese crusts are widespread on the floor of the northwestern Pacific Ocean, south and east of the Japanese Islands, despite vigorous tectonic activity, such as subduction and back-arc spreading, since at least the Mid-Paleogene over the Philippine Sea Plate region and nearby. The crusts occur mainly at water depths shallower than 3000 m, but also at greater depths of up to 6000 m. Fine-scale ¹⁰Be/⁹Be dating was undertaken on several 5–10 cm thick hydrogenetic ferromanganese crusts sampled from different geological environments, including inactive submarine volcanoes, tectonic escarpments and abandoned rifts. The results indicate that the crusts have grown at relatively constant rates of 4–7 mm/my without any significant time breaks. These uniform and constant growth rates suggest that the basins have been exposed constantly to oxygenated bottom waters since their formation in the Middle Miocene ( ca 15 Ma) or earlier. Local geological or oceanographic environmental changes might have slowed or increased some of the growth rates resulting in correlation of some internal structures. The Philippine Sea Plate region could have economic potential in areas of thick hydrogenetic ferromanganese crusts over a wide range of water depths.     

Detection of Periodic Oscillations in Sunspot-Associated Radio Sources

Using microwave observations made with the Nobeyama radioheliograph (=1.76 cm), we have studied temporal variations of sunspot-associated sources in the circularly polarized component. For all three cases of well-developed and rather stable sunspots we found nearly harmonic oscillations with periods in a range of 120–220 s. In one case of an unstable and quickly devolving active region, the fluctuations appear to be irregular with no dominant period. Sunspot-associated solar radio sources are known to be generated by cyclotron radiation of thermal electrons in magnetic tubes of sunspots at the level of the lower solar corona or chromosphere–corona transition region (CCTR). At the wavelength of 1.76 cm, the polarized emission arises in a layer where the magnetic field is B=2000 G (assuming the emission generated at the third harmonic of electron gyrofrequency). We suggest that the observed effect is a manifestation of the well-known 3-min oscillations observed in the chromosphere and photosphere above sunspots. The observed effects are believed to be a result of resonance oscillation of MHD waves inside a magnetic tube. Radio observations of this phenomenon open a new tool for studying regions of reflection of MHD waves near CCTR level. The method is very sensitive both to the height of the CCTR and magnetic fields above sunspots. Thus, detection of oscillations of the height of the transition region even with an amplitude of a few km are possible. The use of a spectrum of one of the observed sources obtained with the radio telescope RATAN-600 allows us to conclude that oscillations in magnetic field strength of about 4 G could be responsible for the effect and are reliably registered. The appearance of the famous 5-min oscillations in the solar atmosphere was also registered in some spectra of radio oscillations.