Effects of solar wind parameters on the development of magnetospheric substorms

Effects of solar wind parameters on the development of substorms during the events of southward interplanetary magnetic field (IMF) lasting more than one hour were studied. Analysis on 175 events with average magnitude of the southward component of IMF larger than l·5γ as observed in July–December 1965 lead to the following results: (1) The total auroral electrojet (AEJ) current associated with the southward IMF event is approximately proportional to the time integral of the magnitude of the southward component. (2) The azimuthal component of IMF also affects the AEJ development. AEJ about twice as intense were observed when IMF was directed duskward than when IMF was directed dawnward. (3) AEJ intensity is strongly affected by the solar wind velocity during the southward IMF events, the intensity being approximately proportional to the square of the velocity. (4) No indication was found that the angle between the Sun-Earth line and the Earth's dipole axis plays any role on the development of substorms if effects of the solar wind parameters as described above are eliminated.     

Güttler scattering analogues for dust aggregates

We show that suitably defined Güttler (core-mantle) analogues can satisfactorily represent the optical cross-sections of aggregates of very small particles that result from mutual collisions and sticking. Earlier calculations using the discrete dipole approximation are seen to be in good agreement with Güttler analogue calculations, particularly in the case of the so-called Ballistic Particle-Cluster Aggregates (BPCA).     

Stray-Light Effect on Magnetograph Observations

To examine the stray-light effect in magnetograph observations, we have determined the point spread functions of the vector magnetograph mounted on the Japanese Solar Flare Telescope based on two indirect methods, one analyzing the solar limb intensity profile, and the other using the Fourier power spectra of photospheric intensity distributions. Point spread functions consist of two parts: a blurring part which describes seeing and small-spread-angle stray light, and a scattering part which describes large-spread-angle stray light. The FWHM spatial resolution is typically 3.0, and the amount of scattered light is about 15% on clear days. We find that the blurring part is well described by a Moffat function whose Fourier transform is given by an exponential function. Our results indicate that polarization measurements of low-intensity magnetic elements like sunspots may be significantly underestimated due to the large-spread-angle stray light, and polarization measurements of magnetic elements which are smaller than 5–7 appear to be disturbed by small-spread-angle stray light.     

Impact of road‐generated storm runoff on a small catchment response

The impact of road‐generated runoff on the hydrological response of a zero‐order basin was monitored for a sequence of 24 storm events. The study was conducted in a zero‐order basin (C1; 0·5ha) with an unpaved mountain road; an adjacent unroaded zero‐order basin (C2; 0·2 ha) with similar topography and lithology was used to evaluate the hydrological behaviour of the affected zero‐order basin prior to construction of the road. The impact of the road at the zero‐order basin scale was highly dependent on the antecedent soil‐moisture conditions, total storm precipitation, and to some extent rainfall intensity. At the beginning of the monitoring period, during dry antecedent conditions, road runoff contributed 50% of the total runoff and 70% of the peak flow from the affected catchment (C1). The response from the unroaded catchment was almost insignificant during dry antecedent conditions. As soil moisture increased, the road exerted less influence on the total runoff from the roaded catchment. For very wet conditions, the influence of road‐generated runoff on total outflow from the roaded catchment diminished to only 5·4%. Both catchments, roaded and unroaded, produced equivalent amount of outflow during very wet antecedent conditions on a unit area basis. The lag time between the rainfall and runoff peaks observed in the unroaded catchment during the monitoring period ranged from 0 to 4 h depending on the amount of precipitation and antecedent conditions, owing mainly to much slower subsurface flow pathways in the unroaded zero‐order basin. In contrast, the lag time in the roaded zero‐order basin was virtually nil during all storms. Copyright © 2009 John Wiley & Sons, Ltd.     

Fine‐structures of planar deformation features in shocked olivine: A comparison between Martian meteorites and experimentally shocked basalts as an indicator for shock pressure

We performed shock recovery experiments on an olivine‐phyric basalt at shock pressures of 22.2–48.5 GPa to compare with shock features in Martian meteorites (RBT 04261 and NWA 1950). Highly shocked olivine in the recovered basalt at 39.5 and 48.5 GPa shows shock‐induced planar deformation features (PDFs) composed of abundant streaks of defects. Similar PDFs were observed in olivine in RBT 04261 and NWA 1950 while those in NWA 1950 were composed of amorphous lamellae. Based on the present results and previous studies, the width and the abundance of lamellar fine‐structures increased with raising shock pressure. Therefore, these features could be used as shock pressure indicators while the estimated pressures may be lower limits due to no information of temperature dependence. For Martian meteorites that experienced heavy shocks, the minimum peak shock pressures of RBT 04261 and NWA 1950 are estimated to be 39.5–48.5 GPa and 48.5–56 GPa, respectively, which are found consistent with those estimated by postshock temperatures expected by the presence of brown olivine. We also investigated shock‐recovered basalts preheated at 750 and 800 °C in order to check the temperature effects on shock features. The results indicate a reduction in vitrifying pressure of plagioclase and a pressure increase for PDFs formation in olivine. Further temperature‐controlled shock recovery experiments will provide us better constraints to understand and to characterize various features found in natural shock events.     

Petrological,petrofabric, and oxygen isotopic study of five ungrouped meteorites related to brachinites

Northwest Africa (NWA) 6112, Miller Range (MIL) 090206 (plus its pairs: MIL 090340 and MIL 090405), and Divnoe are olivine‐rich ungrouped achondrites. We investigated and compared their petrography, mineralogy, and olivine fabrics. We additionally measured the oxygen isotopic compositions of NWA 6112. They show similar petrography, mineralogy, and oxygen isotopic compositions and we concluded that these five meteorites are brachinite clan meteorites. We found that NWA 6112 and Divnoe had a c axis concentration pattern of olivine fabrics using electron backscattered diffraction (EBSD). NWA 6112 and Divnoe are suggested to have been exposed to magmatic melt flows during their crystallization on their parent body. On the other hand, the three MIL meteorites have b axis concentration patterns of olivine fabrics. This indicates that the three MIL meteorites may be cumulates where compaction of olivine grains was dominant. Alternatively, they formed as residues and were exposed to olivine compaction. The presence of two different olivine fabric patterns implies that the parent body(s) of brachinite clan meteorites experienced diverse igneous processes.     

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2

We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.