Fundamental properties of substorm time energetic electrons in the inner magnetosphere

We studied fundamental properties of spatial-temporal evolution of energetic electrons trapped in the inner magnetosphere (L ≤ 7.4) during an isolated substorm by using a four-dimensional drift kinetic simulation under the time-dependent electric and magnetic fields provided by a global magnetohydrodynamics (MHD) simulation. When the interplanetary magnetic field turns southward, both the potential and induction electric fields start to increase in the inner magnetosphere, resulting in a gradual injection of low-energy electrons (≤51.9 keV) and deceleration of high-energy electrons (≥114 keV). The deceleration of high-energy electrons results in a decrease in the phase space density of the high-energy electrons during the growth phase. After a while, an abrupt transition of phase state (a substorm onset) occurs in the magnetosphere, which triggers abrupt changes in the magnetosphere and ionosphere. The AL index decreases rapidly, and magnetic field lines become dipole-like. The dipolarization does not proceed smoothly in the inner magnetosphere because of significant force imbalance between the J × B force and the grad P force. As a consequence, the electric field oscillates with a period of 2–3 min, resulting in multiple injections of the low-energy electrons. The low- and high-energy electrons are accelerated under the strong influence of the drift betatron and gyro betatron, so that the acceleration process is essentially nonlinear. Our simulation results suggest that the force-induced processes play an essential role in the substorm-associated redistribution of energetic particles in the inner magnetosphere

Counter equatorial electrojet and overshielding after substorm onset: Global MHD simulation study

By performing a global magnetohydrodynamic (MHD) simulation, we have demonstrated for the first time that an electrojet at the dayside magnetic equator can be reversed and an overshielding condition can be established in the inner magnetosphere after substorm onset without northward turning of the interplanetary magnetic field. Near the substorm onset, the plasma pressure is highly enhanced in the inner magnetosphere on the nightside. The Region 2 field-aligned current diverges from the diamagnetic current on the surface of the dayside extension of the high-pressure region, which is connected to the ionosphere in the relatively low-conductivity region a few degrees equatorward of the main auroral oval that is formed as the projection of the plasma sheet. The separation of the equatorward boundary of the auroral region and the equatorward boundary of the Region 2 current results in dusk-dawn electric fields that generate a counter electrojet (CEJ) at the dayside magnetic equator. Poleward electric fields in a narrow latitudinal width, which may be regarded as subauroral ion drift and subauroral polarization stream, are simultaneously intensified. The dusk-dawn electric fields may propagate to the inner magnetosphere along a field line as shear Alfvén waves. Then, the inner magnetosphere is completely constrained by the overshielding condition. The intensity and polarity of the CEJ depend largely on at least the ionospheric conductivity that is related to the plasma pressure (probably associated with diffuse aurora). This may explain the observational fact that overshielding does not always occur after onset

Field dependent effective masses in YbAl3_{3}

We show for the intermediate valence compound YbAl$_{3}$ that the high field (40 $\lesssim B \lesssim$ 60T) effective masses measured by the de Haas-van Alphen experiment for field along the $$ direction are smaller by approximately a factor of two than the low field masses. The field $B^{*} \sim$ 40T for this reduction is much smaller than the Kondo field $B_{K} \sim k_{B}T_{K}/\mu_{B}$ ($T_{K}\sim$ 670K) but is comparable to the field $k_{B}T_{coh}/\mu_{B}$ where $T_{coh}\sim$ 40K is the temperature for the onset of Fermi liquid coherence. This suggests that the field scale $B^{*}$ does not arise from 4$f$ polarization but is connected with the removal of the anomalies that are known to occur in the Fermi liquid state of this compound.Comment: 7 pages plus 3 figures Submitted to PRL 9/12/0

Absolute instabilities of travelling wave solutions in a Keller-Segel model

We investigate the spectral stability of travelling wave solutions in a Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity function and a constant, sublinear, and linear consumption rate. Linearising around the travelling wave solutions, we locate the essential and absolute spectrum of the associated linear operators and find that all travelling wave solutions have essential spectrum in the right half plane. However, we show that in the case of constant or sublinear consumption there exists a range of parameters such that the absolute spectrum is contained in the open left half plane and the essential spectrum can thus be weighted into the open left half plane. For the constant and sublinear consumption rate models we also determine critical parameter values for which the absolute spectrum crosses into the right half plane, indicating the onset of an absolute instability of the travelling wave solution. We observe that this crossing always occurs off of the real axis

Occurrence Distribution of Polar Cap Patches: Dependences on UT, Season and Hemisphere

Polar cap patches are islands of enhanced electron density in the polar cap F region ionosphere, which sometimes affect the propagation of trans-ionospheric radio waves. Considering the intake of daytime sunlit plasma by the high-latitude convection as the primary cause of patches, the spatial overlap between the convection and the daytime sunlit plasma should be one of the critical factors controlling the generation of patches. To confirm this hypothesis, we statistically investigated the UT and seasonal distributions of patch occurrence frequency in both the hemispheres by using in situ plasma density data from the Swarm satellite. As a result, it was found that the occurrence distribution of patches is a complex function of UT, season and hemisphere, but it can be mostly interpreted by the spatial overlap between the high-latitude convection and the solar terminator. This suggests that polar cap patches are not necessarily phenomena that occur only during winter months. That is, patches can often be observed even in periods away from the winter solstice if the location of solar terminator in the magnetic coordinate system is appropriate for the generation of patches. For example, in the southern hemisphere, where the offset between the geographic and magnetic poles is larger than that in the northern hemisphere, the highest patch occurrence rate is obtained around the equinoctial periods. These results indicate that it is needed to take these dependences into account when we discuss and predict the space weather impacts of patches on the trans-ionospheric radio propagation

Attempts for Simultaneous Observation of Image and Elemental Component in a Pottery Sample using Neutrons

AbstractIn the pottery sample which is the replica of the archeological sample, we attempted to get simultaneously not only the image by neutron radiography but also the information about elemental components by prompt gamma-ray analysis (PGA) at the B-4 beam hole that is usually used for the neutron radiography facility in Kyoto University Research Reactor Institute. It was confirmed that qualitative analysis of elements in the pottery sample was successfully performed by PGA at the B-4 beam hole and that PGA is applicable to the large sample analysis for inhomogeneous bulk archeological samples in the future

A detailed case study of dayside diffuse aurora using GEOTAIL, FAST, and South pole all sky imager

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン

Metallic partial melting processes on the acapulcoite-lodranite parent body.

第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月29日（木） 国立国語研究所 2階講