Geomagnetic Conjugacy between the Antarctic and the Arctic

Along a tube of force of the geomagnetic field, charged particles such as electrons, electric field and hydromagnetic waves propagate simultaneously from the equatorial region in the magnetosphere to the mutually conjugate areas of the earth\u27s surface. The auroral electrojets, SSC\u27s, SI\u27s and pc-5 pulsations show remarkable simultaneity and similarity between the conjugate areas. Their time-dependent parameters such as the form of frequency spectra, the dominant period of pulsations, the rise-time of SSC\u27s, etc., are almost exactly the same in the conjugate stations. However, the correlation between amplitudes or magnitudes of these phenomena at the conjugate points is considerably smaller than that for the time-dependent parameters. The horizontal polarizations of SSC\u27s, SI\u27s and pulsations are the left-hand mode in the morning and right-hand one in the afternoon with an absolutely high statistical significance. These discussions are mostly based on the data from the conjugate pair of Syowa Station and Reykjavik and that of Macquarie Island and Alaskan stations

Magnetic analysis of Antarctic chondrites on the basis of a magnetic binary system model

Ordinary chondrites often have extremely large values of their remanence coercive force (H_) while their coercive force (H_C) is not particularly large, H_/H_C often amounting to a magnitude larger than 30. Since H_/H_C of ferromagnetic materials is generally smaller than 5,the observed large values of chondrites are considered anomalous. A magnetic binary system model consisting of (a)-component having large H_C and H_ values and (b)-component having small H_C and H_ values can approximates the anomalously large value of H_/H_C. Using the magnetic binary system model, Antarctic chondrites having anomalously large values of H_/H_C are analyzed; metallic constituents in these chondrites are decomposed into (a)-component with H_C≳1000Oe and (b)-component with H_C≲30Oe. Interest from a viewpoint of meteoritics may be concerned with following results of the analysis. (i) With the aid of thermomagnetic analysis and other methods, the high coercivity component (a) is identified to tetrataenite which has an extremely large value of H_C, while the absolute majority of (b)-component comprises relatively large grains of kamacite of multi-domain structure. (ii) Metallic fine grains in both chondrules and matrix of ALH-769 (L6) chondrite are composed of statistically same tetrataenite and kamacite. This result suggests that both chondrules and matrix were extremely slowly cooled down together through 320℃ in the final process of the thermal history of this chondrite

Magnetic analysis of Antactic ordinary chondrites and achondrites on the basis of a magnetic binary system model

Magnetic hysteresis cycles of 9 ordinary chondrites and 10 achondrites, collected mainly from Antarctica, are analyzed on the basis of a newly proposed model of a non-interactive magnetic binary system, by taking into account their thermomagnetic characteristics for identifying ferromagnetic phases involved. All the chondrites and achondrites examined consist of a high-coercivity (a) component and a low-coercivity (b) component. In ordinary chondrites, the (a) component is often identified to be tetrataenite (tetragonal-ordered crystal of FeNi) having an apparent coercive force H^_C≳10^3 Oe (TT-type phase), while in other chondrites the (a) component comprises fine grains of shape-anisotropic single-domain structure (A. SD-type phase) having H^_C=(2∿5)×10^2 Oe. The (b) component consists of mostly multi-domain grains of kamacite and/or taenite of H^_C≲20 Oe. In most achondrites, the (a) component comprises A. SD-type phase of H^_C=(2∿5)×10^2 Oe except a special case consisting of a small amount of tetrataenite. The structure of the (b) component in achondrites is the same as in ordinary chondrites. An anomalous hump-shape rise in saturation magnetization (I_s) between 330℃ and Curie point of taenite (540∿590℃) during the initial heating process is found in diogenites and a eucrite. The thermomagnetic hump is considered here to be due to an increase of A. SD-type phase of taenite associated with a relatively smaller increase of the (b) component multi-domain phase. However, a possible metallographical interpretation of the hump phenomenon has not yet been obtained

Magnetic Characteristics of Some Yamato Meteorites─Magnetic Classification of Stone Meteorites─

13 Yamato stone meteorites have been magnetically examined. They are one enstatite chondrite (E), 6 olivine-bronzite chondrites (H), 2 olivine-hypersthene chondrites (L), one carbonaceous chondrite (C) and 3 achondrites (aC). The intrinsic magnetic parameters of these stone meteorites obtained from their magnetic hysteresis curves and thermomagnetic curves, together with those of other 7 known chondritic meteorites, are specifically examined in terms of the compositional and petrographical classification of stone meteorites. The saturation magnetization (I_s) and major magnetic transition temperature (Θ_c) in the cooling process can be taken as the representative magnetic parameters in the proposed magnetic classification of stone meteorites. In the I_s versus Θ_c diagram, those examined stone meteorites, 25 in total, are separated into groups ; namely, I_s (E) > I_s (H) > I_s (L) > I_s (aC), Θ_c (H and L) < Θ_c (E and aC) &sime; 770℃, I_s (C) &sime; I_s (L) but Θ_c (C) < 600℃ < Θ_c (L). Although the boundary between the L-group and the H-group is not sharp enough in the I_s-Θ_c diagram, the L-group chondrites contain a distinctly larger amount of plessite phase which can be magnetically identified

Experimental demonstration of formation of iron-sulfide grains withFe-S coalescence technique and iron-sulfide grains in carbonaceouschondrite

The coalescence growth process of a joint cloud of fine smoke particles evaporated from Fe and those from S produces fine grains of pyrrhotite, in addition to stoichiometric troilite and marcasite. Pyrrhotite grains exhibited a typical DDSS (diffusion-dependence shell structure) shape produced by diffusion of iron atoms to the surface layer. Various superstructures of pyrrhotites were observed by changing the heater temperature. An outline of the experimental procedures of coalescence growth formation of iron sulfide and the main experimental results are described. Magnetic properties of some carbonaceous chondrites have been summarized and discussed in comparison with the characteristics of the coalescence product

Constitution of Polar Substorm and Associated Phenomena in the Southern Polar Region (AERONOMY)

A meridian scanning photometer was designed for investigating the time and space variations of auroral luminosity. With the aid of the quick-scan auroral photometer data of more than 300 clear night hours recorded at Syowa Station, Antarctica (geomagnetic lat. 69.6°S, long. 77.1°E), the following problems are studied: (1) space and time variation of auroral displays, (2) magnetic field variations associated with the space-time auroral displays, (3) relationships among auroras, magnetic field disturbance, magnetic pulsations, VLF hiss, VLF chorus and GNA during the course of substorms. Various kinds of morphological evidence obtained through the above investigations show that a polar substorm consists of the breakup phase and the post-breakup phase. The breakup phase is characterized by a sudden intensification of auroral arc(s) or band(s) and a rapid poleward movement of the intensified aurora(s) with speed of about 1 km/s (Breakup type aurora). The post-breakup phase is defined as diffused auroras or rays which still remain after the intense breakup type aurora(s) have passed away polewards (Post-breakup type aurora). Generally, the post-breakup aurora(s) move towards the equator side. A breakup type aurora is accompanied by a sharp pulsative geomagnetic disturbance (Breakup magnetic disturbance), while a post-breakup type aurora by a gradual negative bay-shape disturbance (Post-breakup magnetic disturbance). It seems that the sharp pulsative disturbance moves polewards together with the moving breakup aurora, while the gradual negative bay stays with the associated post-breakup aurora(s). Thus, the auroral electrojet can also be classified into AEJ-1, which is an intense and narrow electrojet moving together with the breakup aurora, and AEJ-2, which is a comparatively broad and weak electrojet associated with the post-breakup aurora(s). The auroral breakup phase is accompanied not only by a sharp pulsative geomagnetic disturbance but also by VLF hiss emissions, ULF emissions of PiB type and a sharp CNA phenomenon, while the post-breakup aurora is accompanied by a gradual geo-magnetic bay, a gradual, weak CNA, VLF chorus emissions and ULF emissions of PiC type. With reference to \u27the space-time variations in auroras associated with geomagnetic perturbations at Syowa Station, an overall physical picture of dynamic auroral behaviors over the entire polar region is given, as a conclusion

ナンキョク タイリク シュウヘン ニ オケル チキュウ ジバ エイネン ヘンカ

南極大陸近辺における地球磁場の永年変化は著しくはげしいことが,IGY南極観測の結果明らかになった.特に,昭和基地近傍はその変化量がはげしく,鉛直磁力の変化量は約2×10γ/年にも達する.第4図と第5図とを比較すれば,南半球,特に南極大陸近辺の地球磁場永年変化が北半球のそれに比していかに著しいものであるか一見して明らかであろう.特に昭和基地とHeard島の間は2800kmの距離であるにかかわらず,前者ではZ=181γ/年,後者ではZ=-98γ/年である.このきわめて顕著な永年変化局部異常は第6図に示す如く,地核表面附近の磁気双極子対の変動によって代表せしめ得るが,物理的に見て,このような磁気双極子対を実現する電流渦対は極めて強烈なものであって,未だその発生機構について物理的に合理的な解釈は得られていない

Magnetic properties and natural remanent magnetization of carbonaceous chondrites containing pyrrhotite

Magnetic properties, NRM characteristics and magnetic minerals of four carbonaceous chondrites, the Allende, the Leoville, Y-74662 and Y-81020,are examined. These C-chondrites contain ferrimagnetic pyrrhotite grains in addition to magnetite, kamacite and/or taenite as magnetic minerals possessing NRM. The low temperature NRM component which is possessed by ferrimagnetic pyrrhotite at temperatures below 300℃, indicates that the corresponding paleointensity (F_p) is around 1 Oe in order of magnitude. The high temperature NRM component possessed by magnetite and/or taenite is magnetic at temperatures below about 600℃, giving rise to F_p&lsim;0.1 Oe. The kamacite magnetization contributes very little at temperatures below 770℃