Magnetosphere–Ionosphere Convection as a Compound System

Convection is the most fundamental process in understanding the structure of geospace and disturbances observed in the magnetosphere–ionosphere (M–I) system. In this paper, a self-consistent configuration of the global convection system is considered under the real topology as a compound system. Investigations are made based on the M–I coupling scheme by analyzing numerical results obtained from magnetohydrodynamic (MHD) simulations which guarantee the self-consistency in the whole system under the Bv (magnetic field and velocity) paradigm. It is emphasized in the M–I coupling scheme that convection and field-aligned current (FAC) are different aspects of same physical process characterizing the open magnetosphere. Special attention is given in this paper to the energy supplying (dynamo) process that drives the FAC system. In the convection system, the dynamo must be constructed from shear motion together with plasma population regimes to steadily drive the convection. Convection patterns observed in the ionosphere are also the manifestation of achievement in global self-consistency. A primary approach to apply these concepts to the study of geospace is to consider how the M–I system adjusts the relative motion between the compressible magnetosphere and the incompressible ionosphere when responding to given solar-wind conditions. The above principle is also applicable for the study of disturbance phenomena such as the substorm as well as for the study of apparently unique processes such as the flux transfer event (FTE), the sudden commencement (SC), and the theta aurora. Finally, an attempt is made to understand the substorm as the extension of enhanced convection under the southward interplanetary magnetic field (IMF) condition.     

Surface error estimation and correction of a space antenna based on antenna gainanalyses

Novel methods for the estimation and correction of antenna surface deformations are developed and investigated. Surface adjustment mechanisms, which are used for a reconfigurable antenna system, are used to estimate and correct surface errors. Relations between antenna surface errors and changes in antenna gains caused by intentional deformations are derived from the Ruze equation. In these methods, an antenna surface is deformed using the surface adjustment mechanisms, and the changes in the gains caused by the intentional deformations are measured. On the basis of the information regarding the intentional deformations and the resultant changes in the antenna gains, original deformation of the antenna surface is estimated. The deformation is corrected using the surface adjustment mechanisms. Some numerical simulations are carried out to investigate the feasibility of these methods. The results of these simulations show that the antenna deformations are estimated and corrected adequately using these methods.     

Estimating the High-Resolution Mean Sea-Surface Velocity Field by Combined Use of Altimeter and Drifter Data for Geoid Model Improvement

The mean sea-surface height obtained from satellite altimeters is different from the geoid by the amount of mean sea-surface dynamic topography associated with ocean currents. Assuming geostrophy at the sea surface, the mean sea-surface dynamic topography can be obtained from the mean sea-surface velocity field. This field is derived by combining anomalies (i.e., deviations from the mean) of sea-surface velocity obtained from altimeter data and in situ surface velocities estimated from trajectories of surface drifting-buoys (hereafter, drifters). Where a drifter measured the surface velocity, the temporal mean velocity can be estimated by subtracting the altimeter-derived velocity anomaly at that time from the drifter-measured surface velocity. The method is applied to the surface flow field of the North Pacific, using TOPEX/POSEIDON and ERS-1/2 altimeter data, and WOCE-TOGA surface drifter data obtained from October 1992 through December 2000. The temporal mean velocity field is estimated with a resolution of quarter degrees in both latitude and longitude. The obtained mean velocity field clearly shows the Kuroshio and Kuroshio Extension, which are narrower and stronger than the climatological mean features derived from historical hydrographic data averaged over several decades. Instantaneous velocities are estimated by summing up these temporal mean velocities and anomalies, every ten days during the eight years. They compare well with in situ velocities measured by the surface drifters. The instantaneous velocity field shows energetic fluctuation of the Kuroshio Extension vividly. This revised version was published online in August 2006 with corrections to the Cover Date.     

A numerical study of the charge diameter effect on unsteady detonation

A numerical study for the unsteady detonation of an unconfined tetryl charge of small diameter, which is assumed to be homogeneous, was performed by using the two-dimensional Lagrangian hydrodynamic computer code, 2 DL, with the first order Arrhenius equation of reaction rate. Becker-Kistiakowsky-Wilson (BKW) and Kihara-Hikita (KH) equations of state have been applied to the detonation products.In the case of BKW, it is shown that the rarefaction waves propagating inward from the lateral surface make the reaction rate slow and give a curvature to the front. Then after an induction time, a strong initiation occurs in the reaction zone near the lateral surface and higher pressure zone moves to the axis. This higher pressure accelerates the detonation propagation near the lateral surface and the curvature of detonation front is reduced. Then, the reaction at the lateral surface again begins to decay by the rarefaction waves. Such a sequence of process is repeated periodically.The possibility of the occurrence of the strong initiation depends on the pressure and temperature in the shocked zone near the surface. In a small diameter charge, the delayed explosion becomes weaker near the surface, while its frequency increases. No shock interaction occurs because the direction of the particle flow is always divergent.In the case of KH equation of state, the temperature of detonation is higher than that obtained by BKW and the behaviour of instability becomes rather different from the previous result, i.e. in the axis the pressure oscillates repeating the overdriven and underdriven detonation similar with the case of BKW.     

Characterization of a novel gravitropic mutant of morning glory, weeping2

In higher plants, gravity is a major environmental cue that governs growth orientation, a phenomenon termed gravitropism. It has been suggested that gravity also affects other aspects of morphogenesis, such as circumnutation and winding movements. Previously, we showed that these aspects of plant growth morphology require amyloplast sedimentation inside gravisensing endodermal cells. However, the molecular mechanism of the graviresponse and its relationship to circumnutation and winding remains obscure. Here, we have characterized a novel shoot gravitropic mutant of morning glory, weeping2 (we2). In the we2 mutant, the gravitropic response of the stem was absent, and hypocotyls exhibited a severely reduced gravitropic response, whereas roots showed normal gravitropism. In agreement with our previous studies, we found that we2 mutant has defects in shoot circumnutation and winding. Histological analysis showed that we2 mutant forms abnormal endodermal cells. We identified a mutation in the morning glory homolog of SHORT-ROOT (PnSHR1) that was genetically linked to the agravitropic phenotype of we2 mutant, and which may underlie the abnormal differentiation of endodermal cells in this plant. These results suggest that the phenotype of we2 mutant is due to a mutation of PnSHR1, and that PnSHR1 regulates gravimorphogenesis, including circumnutation and winding movements, in morning glory.     

A Simple Method for Evaluating the System Observability in Satellite Orbit Determination

A method is described for evaluating the system observability in satellite orbit determination. The method is simple and rapid in computation time, because it uses the calculation of the mutual orthogonality between the observation partial vectors rather than the calculation of eigenvalues of the Grammian matrix.     

Application of an MHD simulation to the study of substorms

The substorm mechanism is studied by the numerical solutions obtained from a resistive magnetohydrodynamic (MHD) simulation. After a southward turning of the interplanetary magnetic field (IMF), the simulation results reproduce observed features of the growth phase. The numerical solutions show that the plasma sheet thinning during the growth phase is formed under the dynamic balance between the flux pileup from the midtail and the flux removal toward the dayside controlled by the convection in the magnetosphere-ionosphere (M-I) coupling system. After the growth phase, dipolarization is generated in the near-earth tail accompanied by a plasma injection into the inner magnetosphere, the formation of plasmoid in the midtail, and the enhancement of the nightside field-aligned currents (FACs). The direct cause of this onset is the state (phase space) transition of the convection system from a thinned state to a dipolarized state associated with a self-organization in the nonlinear system.     

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and Vstar (Ouna), and the radio signals were observed by the Japanese VERA (VLBI Exploration of Radio Astrometry) network, and an international VLBI network. Multi-frequency and same-beam VLBI techniques were utilized and were essential aspects of the successful observing program. Multi-frequency VLBI was employed in order to improve the accuracy of the orbit determination obtained from the phase delay from the narrow-band satellite signals, while the same-beam VLBI method was used to resolve the cycle ambiguity which is inherent in the multi-frequency VLBI method. The observations were made at three S-band frequencies (2212, 2218 and 2287 MHz), and one X-band frequency (8456 MHz). We have succeeded in correlating the recorded signals from Okina/Ouna, and we obtained phase delays with an accuracy of several pico-seconds at S-band.     

In-flight Performance and Initial Results of Plasma Energy Angle and Composition Experiment (PACE) on SELENE (Kaguya)

MAP-PACE (MAgnetic field and Plasma experiment—Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its ～1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV–9 keV and 9 eV–16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q–28 keV/q and 7 eV/q–29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the dayside of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.