Dynamo-electric field-aligned currents in the plasmasphere

The dynamo-theory has been used to interpret antisymmetric S_q-variations. The following results have been found analytically: 1. The antisymmetric electric field is important only for driving field-aligned coupling currents between both hemispheres. 2. The antisymmetric part of the observed S_q-variations can be explained best by the dynamo-action of seasonally depending (1, 1)-,(1, −2)-, and (2, 2)-tidal modes. 3. At all seasons the field-aligned currents are strongest near noon where they have at north-summer in the northern hemisphere a source near 50° and a sink near 30° latitude.     

Topside and intelhemispheric ion flows in the mid-latitude plasmasphere

A modelling study has been carried out of field-aligned ion flows in the topside ionospheres of conjugate hemispheres under solstice conditions at mid to low latitudes. In the model calculations coupled time-dependent O⁺, H⁺ and electron continuity, momentum and heat balance equations are solved along dipole magnetic field lines at L = 1.5 and 3.0 Sunspot medium and sunspot minimum atmospheric conditions are considered.It has been found that thermal coupling between conjugate hemispheres gives rise to strong flows of O⁺ in the topside ionosphere of the summer hemisphere that are directed upwards at conjugate sunrise and directed downwards at conjugate sunset. At conjugate sunrise in the winter hemisphere there is a small upward-directed signature in the O⁺ field-aligned flux; there is no observable signature in the O⁺ field-aligned flux in the winter hemisphere at conjugate sunset. There are strong upward and downward flows of O⁺ at local sunrise and local sunset, respectively, in both the summer and winter hemispheres.At both L = 1.5 and 3.0 the 24 h time-integrated interhemispheric H⁺ flux is in the direction summer hemisphere to winter hemisphere. At L = 1.5 its magnitude is in good agreement with the magnitude of the 24 h time-integrated plasma (O⁺ + H⁺) field-aligned flux at 1000 km altitude; there are no such agreements at L = 3.0.A study of the roles played by the individual terms of the O⁺ momentum equation has demonstrated the complex structure of momentum balance. Certain of the terms may be orders of magnitude greater than the combined total of the individual terms, i.e. the O⁺ field-aligned flux.     

Temperatures in the plasmasphere determined from VLF observations

Satellite and ground-based VLF recordings were made at SANAE, Antarctica from 1976 to 1979. In this paper we combine ground and satellite observations to determine temperatures in the plasmasphere. Scale heights in the plasmasphere are determined at high altitudes using a diffusive equilibrium model and measurements of equatorial electron densities and densities at about 3000 km. The temperatures corresponding to these scale heights show a gradual increase with increasing L-value and sharp increases of about 2000 K just inside the plasmapause.     

Diffusion equations for the major ions in the mid-latitude ionosphere and plasmasphere

Diffusion equations for O⁺ and H⁺ ions for ionosphere-plasmasphere interaction are derived from the transport equations formulated by Schunk. Low speed geomagnetic field aligned flow was assumed and the interaction between different kinds of ions, between ions and electrons and between ions and neutrals taken into account. The appropriate terms of the equations have been derived and the transport coefficients calculated using parameters typical for the mid-latitude ionosphere and the ionospheric main trough. It is found that interaction of ions with neutral particles influences to some extent the ion thermal diffusion. Diffusion equations retaining only terms not smaller than one-tenth of the largest are given in the paper.     

Post-midnight equatorial scintillation activity in relation to geomagnetic disturbances

VHF amplitude scintillation measurements made during the period April 1978 through December 1982 at Calcutta (23°N, 88.5°E; 32°N dip), situated near the northern crest of the Appleton Anomaly in the Indian sector, have been used to study the association of post-midnight (as well as post-sunrise) scintillations with the occurrences of the maximum negative excursion in the variation of the Earth's horizontal magnetic intensity. The post-midnight scintillation has been found to be related to the maximum negative excursion occurring in the 0000–0600 LT interval. No such relation is observed with the pre-midnight excursions. Scintillation with onset between 0000 and 0300 LT shows remarkable correspondence with the occurrence of negative excursion (18 out of 20 available cases). Magnetic conditions with Dst < −150 nT have been found to be most effective in producing the above scintillation activity. From the present observations, a threshold value of the maximum negative excursion of Dst for producing scintillation may be obtained, Dst < −75 nT being significantly associated with the post-midnight scintillation occurrences. The results are interpreted in terms of the reversal of the equatorial horizontal electric field, under magnetically disturbed conditions, due to a coupling of the high latitude and magnetospheric current systems with the equatorial electric field.     

NDVI variation and its relation to climate in Canadian ecozones

Parks Canada began the Northern Satellite Monitoring Program in 1997, with the objective of tracking large‐scale vegetation variation in Canadian ecosystems and helping land managers to develop appropriate management practices in response to climate change. Under this program, a sequence of 10‐day composite Advanced Very High Resolution Radiometer (AVHRR)‐derived Normalized Difference Vegetation Index (NDVI) data from 1985 to 2007 was examined to study seasonal and inter‐annual relationships between vegetation and climate data over Canadian ecosystems using statistical and wavelet analysis. Statistical analysis showed that temperature was the principal driver for seasonal variability in greenness, explaining more than 70 percent of seasonal variation in vegetation for most Canadian ecozones. In comparison with temperature, the relationships between NDVI and precipitation were weaker but still significant. Maximum annual NDVI showed increasing trends in Canadian ecozones during the study period, although increasing rates were spatially heterogeneous. Wavelet analysis confirmed that inter‐annual variation in NDVI was different at two ecozones in Canada. NDVI variation in the Northern Arctic was significant at scales of 3–4 years from 1997 to 2001, which was associated with temperature and precipitation variation. Comparatively, NDVI variation in the Boreal Shield was significant at scales of 5–8 years from 1991 to 1999, but did not correspond with climate variation.     

Electric field sources in the quiet plasmasphere from whistler observations

Existing evidence for the ionospheric dynamo being the source of quiet time electric fields in the plasmasphere is reviewed. Part of a 24 h set of whistler data recorded continuously at Sanae, Antarctica (L = 4), during quiet magnetic (average K_p = 1) is analysed to obtain westward electric fields in the equatorial plane. These electric fields are examined as a function of L-value in order to infer their source. It is found that for periods of outward flow of plasma during the noon-midnight local time period, the electric fields are consistent with the dominant source being the ionospheric dynamo. There is some evidence that during the evening period of inward flow the electric fields are magnetospheric in origin, although this could also be consistent with a refined dynamo model. The observed whistler duct convection patterns do not fit either of two theoretical models, which invoke a magnetospheric field but not a dynamo field.     

The late prehistory of xinjiang in relation to its neighbors

Recent research by Chinese archaeologists has identified many late prehistoric (2000-400 B.C.) oases, pastoral settlements, and cemeteries in eastern Central Asia (Xinjiang province of China). The synthesis presented here organizes the data into 10 archaeological cultures, defined on the basis of ceramics, burials, small finds, and architecture. The archaeological cultures reveal two periods, corresponding to the Bronze Age and the Iron Age. The oases cultures formed a core area before the Chinese Han period and maintained close contacts with nearby highland pastoralists in Siberia and western Central Asia. The evidence for interaction between Xinjiang and the complex cultures in China and western Central Asia is evaluated with regard to the origins of the early Xinjiang cultures.     

Determination of the latitude of Sq focus and its relation to the electrojet variations

The latitude of the Sq focus is determined analytically using the method of natural orthogonal components. Geomagnetic data along the 75°E meridian have been used. The day-to-day variations of the latitude of the Sq focus thus determined are very highly correlated with the electrojet enhancements. The strength of the normal Sq field and the electrojet field are not correlated. It appears that as the Sq focus moves towards the equator the entire current pattern bodily moves equatorwards with an increased current concentration in the electrojet region.     

Substorm activity precursors in the dayside magnetic perturbations

Magnetic data from a meridional chain of stations in Greenland and AL-indices of magnetic activity have been used to study the relationship between magnetic perturbations in the dayside cleft region and substorm activity in the night-time auroral zone. The analysis of 14 substorms, isolated and prolonged, has shown that intensification of westward currents in the postnoon sector of the cleft precedes or accompanies substorm development in the night-time auroral zone. Westward currents appear in the northern cleft as substorm precursors even under the adverse influence of the IMF positive B_y component. These currents trend to extend in the prenoon sector. To explain the relationship between the cleft currents and auroral electrojet the connection between neutral layer currents and noon Birkeland currents is proposed. This connection can be realized by means of the source region acting just inside the daytime magnetopause owing to stationary reconnection of geomagnetic field and IMF, the source region flowing downstream to the tail magnetopause.     

Wooly mammoth mass accumulation next to the Paleolithic Yana RHS site,Arctic Siberia: its geology,age, and relation to past human activity

In 2001, the Yana RHS archaeological site was discovered in the lower Yana river valley, Arctic Siberia. Its radiocarbon age is about 28 000 BP. While enormous amount of Pleistocene mammal bones was excavated from the site, the mammoth bones occurred at an unexpectedly low frequency. That was interpreted as an indication of the limited role of mammoths in the subsistence economy of the Pleistocene Yana people. In 2008, next to the excavation local ivory miners opened a mass accumulation of mammoth accompanied by the artifacts. About one thousand mammoth bones from at least 26 individuals, and few wooly rhinoceros, bison, horse, reindeer, and bear bones have been unearthed there. Stratigraphy and radiocarbon dating provide evidence for cultural layer of Yana RHS and the mass accumulation of mammoth to be coeval. The geology and taphonomy of Yana mass accumulation of mammoth indicate its anthropogenic nature. Discovery of the anthropogenic mass accumulation of mammoth next to the Yana site suggests a greater role of mammoth in the subsistence practices of the Pleistocene Yana people than previously thought.     

Pi(c) magnetic pulsations: their relation to ionospheric currents

The association of the phase of the H and D components of the Pi(c) pulsations with the phase of the broadscale H component magnetic bays confirms that Pi(c) pulsations result from auroral electron precipitation induced conductivity enhancements of existing current systems. Statistically determined relationships between the time delays and phases of the H and D components of magnetic Pi(c) pulsations with respect to the optical pulsations are used to infer a delay between the E-region Hall and Pedersen current fluctuations associated with the pulsating electron fluxes. Theoretical modelling of an auroral pulsation patch, as per Oguti and Hayashi, is used to show that the polarization of the Pi(c) pulsations is controlled principally by the delay between the Hall and Pedersen currents and the direction of the background E-region electric field.     

Average electron density profiles in the plasmasphere between L = 1.4 and 3.2 deduced from whistlers

985 whistlers recorded at Tihany, Hungary (L = 1.9) between December 1970 and May 1975 have been processed for equatorial crossing radius L, equatorial electron density n_eq and tube electron content N_T. The obtained L values lie in the range L = 1.4-3.2. The median values of n_eq and N_T as a function of L fit well to the density profiles published by Park et al. The results also indicate that at lower L values the whistlers are ducted by stronger density enhancements.     

明清以来徽州的演戏娱神与信仰活动

明清以来,徽州各地的演戏活动极为频繁,成为宗族或会内的重要活动,现存的大量徽州文书不仅证明了这一点,而且更深刻揭示了徽州演戏和游神的紧密关系、演戏活动与信仰和娱乐的关系.演戏活动已经成为徽州民众日常生活的一部分,甚至由此导致官府的干涉和民间的竞争与矛盾,当然这并不排除有特别重大的原因所作推迟或停演的举措.     

The equatorial ring-current energy during magnetic storms as related to Dst activity indices

On the basis of geomagnetic activity indices Dst and solar wind parameters (velocity and density), we calculate the kinetic energy of the equatorial ring-current during the development of a magnetic storm, following the hypothesis of Sckopke's theorem.Supposing that the relaxation mechanisms of the plasmaspheric drift current which lead to the pre-storm state are always present and depend solely on the kinetic energy, it is found that the major part of the energy gain is lost, except during the main phase, when the interplanetary magnetic field permits it to be stored.     

A theoretical study of the distribution of ionization in the high-latitude ionosphere and the plasmasphere: first results on the mid-latitude trough and the light-ion trough

A model of the O⁺ and H⁺ distributions in the plasmasphere and high-latitude ionosphere is described and first results are presented. The O⁺ and H⁺ continuity and momentum equations are solved from the F-region to the equatorial plane in the inner plasmasphere, and to an altitude of 1400 km in the outer plasmasphere and high-latitude ionosphere. Account is taken of high-latitude convection, departure from corotation inside the plasmasphere, and neutral air winds. The neutral air winds are consistent with the assumed convection pattern. For equinox and magnetically quiet conditions the calculations show that a mid-latitude trough in F-layer electron concentration is present from 1600 to 0600 LT and the trough may occur either inside or outside the plasmasphere. The movement of the trough in this period is from higher to lower latitudes and is in qualitative agreement with AE-C and ESRO-4 data. A light-ion trough feature is apparent in the H⁺ distribution in the topside ionosphere at all local times. During the day the upward H⁺ flow increases with latitude to produce the light-ion trough. At night the H⁺ trough may be directly produced by the occurrence of the mid-latitude O⁺ trough. The relationships between the position of the plasmapause and the trough are discussed. Also discussed are the influence of particle ionization in the auroral zone and the effect of the neutral air wind.     

The influence of sunspot number and magnetic activity on the diurnal variation of the geomagnetic field at mid to high latitudes

The variations of the diurnal range of the geomagnetic field with sunspot number and with magnetic activity was studied at mid and high latitude stations in the northern hemisphere at different seasons. The effect of increasing sunspot number is small at lower latitudes and increases with geomagnetic latitude, while the effect of increasing magnetic activity is to increase the range at all latitudes, very greatly at the higher geomagnetic latitudes.