Vertical structure of hard X-ray flare

This paper presents studies of the vertical structure of hard X-ray flares for two contrasting examples. The 1981 May 13 flare contained a coronal hard X-ray source which was located above 50000 km above the photosphere. On the other hand, the 1981 July 20 flare had a chromospheric double source structure in the initial phase. Electrons in this case were able to stream freely from the corona to the chromosphere.     

Separation of periodic, chaotic, and random components in solar activity

Two new techniques were applied to search for chaotic behavior in solar activity. A mixture of periodic and chaotic components in a time series makes it difficult to find chaotic behavior. The singular spectrum analysis (SSA) method (Broomhead and King, 1986) was used to separate periodic and irregular components in solar activity (e.g., sunspot number and 10.7 cm flux). The nonlinear prediction method (Sugihara and May, 1990) was applied for each component to examine whether it has a chaotic characteristic. The result suggests that are are dominant periodic components and highly irregular (random) components in solar activity.     

Evolution of emerging force-free flux tube to be a flare loop

Solar Physics - Evolution of a filamentary magnetic flux tube emerging from the photosphere is investigated in the assumption that the magnetic field is force-free and unchanged during the...     

Field-aligned electric field caused by the decay of force-free magnetic field and particle acceleration

Numerical simulation for the dynamics of a coronal filamentary magnetic loop has been made under the assumption that the field is initially force-free and an electric resistivity suddenly increases at a given moment due to an appearance of ion sound waves, which can be excited due to a high current density if a characteristic radius r ₀ of the magnetic loop is about 3 km or less in a magnetic field B ₀ of 1000 G. During the resistive decay of the magnetic field a strong field-aligned electric field is created and maintained for a sufficient time to acceleratie both electrons and protons to a high energy, which is proportional to B ₀/r ₀ and can be 100 MeV if r ₀ = 10 km and B ₀ = 1000 G. If the coronal magnetic tube is composed of many such filamentary loops, the total number of accelerated electrons is consistent with the observations.     

X-ray imaging of a solar limb flare on 1982 January 22

Simultaneous X-ray images in hard (20–40 keV) and softer (6.5–15 keV) energy ranges were obtained with the hard X-ray telescope aboard the Hinotori spacecraft of an impulsive solar X-ray burst associated with a flare near the solar west limb.The burst was composed of an impulsive component with a hard spectrum and a thermal component with a peak temperature of 2.8 × 10⁷ K. For about one minute, the impulsive component was predominant even in the softer energy range.The hard X-ray image for the impulsive component is an extended single source elongated along the solar limb, rather steady and extends from the two-ribbon H flare up to 10⁴ km above the limb. The centroid of this source image is located about 10 (7 × 10³ km) ± 5 above the neutral line. The corresponding image observed at the softer X-rays is compact and located near the centroid of the hard X-ray image.The source for the thermal component observed in the later phase at the softer X-rays is a compact single source, and it shows a gradual rising motion towards the later phase.     

Experimental degradation of crude oil by marine bacteria

The ability of biodegradation for crude oil was examined for ten strains of marine bacteria. With regard to their degradation ability forn-alkanes the microorganisms tested could be divided into four groups, although the same result was not observed for microbial degradation of aromatic hydrocarbons obtained by the UV measurements.     

On “A model of impulsive loop flares revisited” by Smith and Brecht

A criticism of my papers was recently presented by Smith and Brecht, that the electron distribution resulting from anomalous heat conduction is not unstable for electron plasma waves. The aim of the present letter is to show that their criticism is irrelevant.     

Numerical simulation of type III solar radio bursts on meter- and hectometer-waves

Numerical simulation of type III bursts is made by the use of fully numerical scheme showing a general rule for obtaining a numerically stable difference scheme. Although the electron distribution function is one-dimensional in velocity space, the plasma waves is cylindrically symmetric two-dimensional in K-space.It is confirmed that the previous simulation made by the use of semi-analytical method assuming the plateau distribution of electron distribution is qualitatively correct, but the number density of electron beam to have a typical type III burst was overestimated by a factor of about 3.It is demonstrated that a tentative neglection of a term for the induced scattering of plasma waves into nonresonant K-range gives no remarkable effect on the energy loss of the electron beam, though the scattering is strong. The reason is that the scattering reduces the saturation level of plasma waves resulting in a reduction of the energy loss, while a part of the energy of electron beam is indirectly lost by the scattering.     

Dynamics of a cloud of fast electrons travelling through the plasma

Numerical analysis of quasi-linear relaxation has been made for four models of electron beam with a finite length travelling through the plasma. In Model 4, a model atmosphere of the corona is adopted and also an increase in the cross-section of the electron beam is taken into account. The electron velocity distribution generally becomes a quasi-plateau form in limited velocity and time ranges. If, however, collisional decay of the fast electrons is too strong and the initial beam density is not high enough, the plateau does not appear. Collisional damping of plasma waves cannot be neglected, since the growth rate of the waves is strongly suppressed by the appearance of the quasi-plateau.An approximate formula for the velocity distribution of the solar electrons passing through the corona has been derived analytically taking into account not only the interaction with plasma waves, but also the collisional damping of the plasma waves and collisions with thermal particles. By the use of this formula, we can easily compute the time profile of the plasma waves caused by these solar electrons at any given place in the interplanetary space. The validity of this semi-analytical approach is checked by the numerical analysis of Model 4, showing a satisfactory fit between the numerical and semi-analytical results.The direct application of this method to the problems of type III radio bursts is left to a later paper.     

A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSRE and the vertical amplification correction function

Under hypothetical and idealized conditions, the horizontal site amplification factor (HSAF) is defined as the ratio of the horizontal Fourier amplitude spectrum (FAS) at a point on the Earth's surface with respect to the horizontal FAS at the identical location but on the outcropping seismological bedrock. The HSAF reflects the profile of local sedimentary soils and weathered rock formations, indicating site effects. In most cases, such an idealized HSAF is difficult to measure directly. Thus, quantitatively estimating a HSAF value is a crucial task in strong-motion prediction over the last century. Fortunately, many strong-motion stations have been constructed throughout Japan, facilitating the characterization of HSAFs down to seismological bedrock at more than 1600 observational sites by the generalized inversion technique (GIT). First, this study reported the similarity distribution of the HSAF and the horizontal-to-vertical spectral ratio of earthquakes (HVSR_E). Subsequently, we proposed a hybrid method from a novel aspect for estimating HSAF in terms of the observed similarity distribution and the vertical amplification correction function (VACF) proposed previously. Compared with the direct use of HVSR_E for substituting HSAF, the hybrid method proposed herein demonstrated an improvement of greater than 30% in terms of the residuals between estimated HSAFs and those separated from observations.