Acceleration of electrons and solar flares due to quasi-static electric field

The storage of flare energy, efficient acceleration of electrons and the trigger of the flares are suggested to be attributed to a quasi-static electric field caused by a gas motion near the photosphere without satisfying the frozen condition. The primary cause of the onset of flares would be the acceleration of electrons due to the electric field above a critical strength. The electrons excite plasma waves which make the conductivity lower by several orders in the lower corona, so that the electro-magnetic energy I ² L stored before the onset of the flare would be rapidly converted into the heat due to the ohmic loss in about 10 s.     

Time variation of the spectrum of Gyro-synchrotron emission from the Sun

The emission spectra and their time variations of gyro-synchrotron emission from an ensemble of energetic electrons are computed for some initial power-law distributions of the electron energies N()d= ^– with =2 or 4. The spectra and decay curves of the emission are compared with solar microwave bursts in order to separately estimate the magnetic field H and . From a limited number of observations, we have 3 and H 10³ gauss for the microwave impulsive bursts, and 2 and H (500–1000) gauss for the microwave type-IV bursts.     

Simulation for electron acceleration by DC electric field in the presence of ion sound waves and associated hard X-ray emission

Time-dependent Fokker-Planck equation was numerically solved to demonstrate the dynamics of electrons in a uniform coronal loop with an applied axial DC electric field in the presence of ion-sound waves. This electric field is attributed to an anomalous resistivity due to the ion-sound turbulence caused by an initially given critical current density.The electron momentum distribution becomes a steady state in the whole turbulent region in a short time for which some electrons can be accelerated to the maximum electric potential K _c. The steady energy distribution of electrons flowing out the end of the turbulent region has a very hard power-law-like spectrum with an index of about 0.75. The associated hard X-rays from a thick target also show a hard spectrum with a photon spectral index of 1.3. In order for to be much greater as observed in impulsive X-ray bursts, it is required that the source is a sum of many elementary loops with a power-law-like distribution in K _c with an index = – + 2.5.     

Degradation ofn-paraffin mixture by marine microorganisms in enriched seawater medium

The ability to degraden-paraffin mixture of two bacterial strains,Caulobacter sp. andFlavobacterium sp., isolated from sea water of Tokyo Bay was studied experimentally in the enriched seawater (ESW) medium. These bacteria degraded actively the mixture ofn-tridecane,n-tetradecane,n-pentadecane andn-hexadecane. The maximum rate of degradation was observed after a lag period of 2 to 8 day and these bacteria were found to degrade then-paraffin mixture at rates calculated to be in a range from 3.3×10^?12 to 3.4×10^?11 mg-oil cell^?1 h^?1 at 20°C. The maximum degradation rate,r _m mg-oil l^?1 h^?1, was correlated with the amount of the initial totaln-paraffin,S mg-oil l^?1, as expressed by the following equation: $$rm = (rm)\max \left( {\frac{S}{{S + Km}}} \right)$$ where (r _m )_max denotes the largest value ofr _m whenn-paraffin exists in large excess andK _m is a constant and represents the amount ofn-paraffin at which the degradation rate,r _m , reaches 1/2 of its largest value, (r _m )_max. The values of (r _m )_max andK _m were calculated to be as follows: In the case ofCaulobacter sp. (strain KM-1), (r _m )_max=6.0 mg-oil l^?1 h^?1 andK _m =191 mg-oillesw ^?1; in the case ofFlavobacterium sp., (r _m )_max=5.47 mg-oil l^?1 h^?1 andK _m =152 mg-oillesw ^?1.     

Identification of typical synoptic patterns causing heavy rainfall in the rainy season in Japan by a Self-Organizing Map

In order to systematically and visually understand well-known but qualitative and complex relationships between synoptic fields and heavy rainfall events in Kyushu Islands, southwestern Japan, during the BAIU season, these synoptic fields were classified using the Self-Organizing Map (SOM), which can convert complex non-linear features into simple two-dimensional relationships. It was assumed that the synoptic field patterns could be simply expressed by the spatial distribution of (1) wind components at the 850 hPa level and (2) precipitable water (PW) defined by the water vapor amount contained in a vertical column of the atmosphere. By the SOM algorithm and the clustering techniques of the U-matrix and the K-means, the synoptic fields could be divided into eight kinds of patterns (clusters). One of the clusters has the notable spatial features represented by a large PW content accompanied by strong wind components known as low-level jet (LLJ). The features of this cluster indicate a typical synoptic field pattern that frequently causes heavy rainfall in Kyushu during the rainy season.In addition, an independent data set was used for validating the performance of the trained SOM. The results indicated that the SOM could successfully extract heavy rainfall events related to typical synoptic field patterns of the BAIU season. Interestingly, one specific SOM unit was closely related to the occurrence of disastrous heavy rainfall events observed during both training and validation periods. From these results, the trained SOM showed good performance for identifying synoptic fields causing heavy rainfall also in the validation period. We conclude that the SOM technique may be an effective tool for classifying complicated non-linear synoptic fields and identifying heavy rainfall events to some degree.     

Magnetotelluric resistivity modeling for 3D characterization of geothermal reservoirs in the Western side of Mt. Aso, SW Japan

Geothermal reservoirs are usually located at a depth range of 2 to 5 km, so to efficiently utilize such resources an advanced prospecting method is needed to detect these deep geologic structures. This study aimed to three-dimensionally characterize geothermal reservoirs by a combination of Magnetotelluric (MT) survey, inversion analysis of apparent resistivity, and interpolation of the resistivity data obtained. The western side of Mt. Aso crater, southwest Japan, was chosen as the case study area. Three hot springs exist there and a fault is assumed to go in the direction connecting them. A MT survey was carried out at 26 sites and the data processed by a remote reference method to reduce artificial noises. Based on skewness and Mohr circle analyses of the impedance tensor, the local geologic structure at each site could be approximated as horizontally layered and therefore, a one-dimensional inversion analysis was applied to the MT raw data. The resultant resistivity column data were then interpolated by the three-dimensional optimization principle method. The resistivity distributions obtained clarified continuous conductors with especially low resistivity (less than 10 Ω·m) at the hot springs along the fault. Because the resistivity decreases largely with an abundance of clay minerals, the conductors could be considered to correspond with the cap rocks. Thus, two geothermal reservoirs, whose shapes were estimated to be pillar, were detected under the cap rocks in an elevation range of − 1000 to − 3000 m. By comparing the resistivity distributions with the temperature distributions based on fluid-flow calculations at a steady state using FEM, the validity of the location and dimension of the estimated reservoirs were confirmed.     

Soft X-Ray and White-Light Coronal Observations of the Post-Flare Arch on 2 November 1991

A giant post-flare arch observed on 2-3 November 1991 was analyzed using the soft X-ray telescope (SXT) on board Yohkoh and the Mark III (MK3) K-coronameter at the High Altitude Observatory/Mauna Loa Solar Observatory. The rising arch was observed in both soft X-ray and K-corona observations. The estimated rising speed from the MK3 observation was approximately 4 km s^-1. A V-shaped depression area was observed on the south side of the giant arch. Change in the K-corona observations was faint while the arch was rising. According to the solar wind observations by the Pioneer Venus Orbiter and the Interplanetary Cometary Explorer, this giant arch event may have been associated with an interplanetary shock.     

Thermal expansion of single-crystal tephroite

The thermal expansion of tephroite (Mn₂SiO₄) at temperatures between 25 and 850°C has been determined by a dilatometric technique. The analysis of data in terms of Grüneisen's theory yields the Grüneisen's parameter γ=1.04, and the pressure derivative of rigidity (?G/?P)=0.7.     

A preparation zone for volcanic explosions beneath Naka-dake crater,Aso volcano,as inferred from magnetotelluric surveys

The 1st crater of Naka-dake, Aso volcano, is one of the most active craters in Japan, and known to have a characteristic cycle of activity that consists of the formation of a crater lake, drying-up of the lake water, and finally a Strombolian-type eruption. Recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water, mud eruptions, and red hot glows on the crater wall. Temporal variations in the geomagnetic field observed around the craters of Naka-dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater. Volcanic explosions act to release the energy transferred from magma or volcanic fluids. Measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices, where energy from various sources accumulates, and in investigating the behaviors of magma and volcanic fluids. We carried out audio-frequency magnetotelluric surveys around the craters of Naka-dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km. The main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption. Two-dimensional inversions were applied to four profiles across the craters, revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area. In contrast, we found no such remarkable conductor at shallow depths beneath the 4th crater, which has been inactive for 70 years, finding instead a relatively resistive body. The distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results. This unusual shallow structure probably reflects the existence of a supply path of high-temperature volcanic gases to the crater bottom. We propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep-level magma and as a floor to infiltrating fluid from the crater lake. The relatively resistive body found beneath the 4th crater represents consolidated magma. These results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within Naka-dake.