Deuteron whistlers in the outer ionosphere

Summary Upgoing and downgoing deuteron whistlers were found on VLF records made by Interkosmos 5, 14 and 19 satellites even at heights below 1000 km. To account for them, a slight admixture ofD ⁺ ions has been introduced into the ionospheric plasma model with the usual content of only three ion speciesH ⁺,He ⁺ andO ⁺. Relations derived for the calculation of characteristic frequencies in a five-component plasma (e,H ⁺,D ⁺,He ⁺,O ⁺) are given as well as the values of characteristic frequencies calculated on this basis. The observed features of upgoing and downgoing deuteron whistlers could be explained by the calculation results, and it is also possible to formulate some conclusions for the purposes of plasma diagnostics.

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mu um, anmau a ma u u, u a a nmua m 5, 14 u 19 a ma ¶rt;a 1000 . u u a ¶rt;a ¶rt; u na ¶rt;au uH ⁺,He ⁺,O ⁺ aa nuD ⁺ u. m mm ua nma ¶rt;a ¶rt; aamumuu amm ¶rt;a ¶rt;u na. uu aamumuu amm nuu um a¶rt;a mu ¶rt;mu um. a m ¶rt; unam aamumuu ¶rt;mu um ¶rt; u¶rt;au naam na.

     

Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P     

Critical frequency foF2 as an indicator of trends in thermospheric dynamics

Variations with time during recent decades of three parameters are considered. R(foF2) is the correlation coefficient between the nighttime and daytime values of foF2 within the same day. Stable trends are found for minimal (R(foF2)(min)) and maximal (R(foF2)(max)) values of R(foF2) over the year. The foF2(day)/foF2(night) ratio demonstrates both negative and positive trends; the sign of the trend being governed by the inclination I and declination D of the magnetic field. The correlation coefficient r(h,fo) between foF2 and the 100-hPa level in the stratosphere demonstrates a decrease (both, for the years of maximum and minimum solar activity) from the 1980s to the 1990s. The trends in all three groups of data are considered in the scope of an assumption that there is a long-term change in the circulation in the upper atmosphere. The data considered in the paper provide an indirect confirmation of the existence of this change and show the possibility that further studies of the thermospheric dynamics can be undertaken using ground-based ionospheric observations.     

Variations in the horizontal correlation radius of the ionosphere during a magnetospheric substorm

A change in the correlation radius of the ionosphere during the magnetospheric substorm of February 14, 2011, which is considered to be 500 km at midlatitudes, has been estimated. The vertical sounding (VS) data from the St. Petersburg and Sodankyla (Finland) observatories, as well as the data of oblique incidence sounding (OIS) at the Sodankyla-St. Petersburg path with a length of 790 km, have been analyzed. A specific feature of the experiment consisted in that the signals of a VS transmitter from Sodankyla were synchronously received at the receiving point on the OIS path in St. Petersburg. The OIS path reflection point is located at a distance of ～400 km from the VS reflection point. Ionograms typical of the VS and OIS signal reflection points in the ionosphere, the distance between which was slightly smaller than the correlation radius of the ionosphere (500 km), and the data of the Sodankyla and St. Petersburg ionosondes have been compared. It has been indicated that a horizontal correlation radius of 400 km can only be considered acceptable during three disturbance phases: the initial phase before the reconfiguration of the ionosphere; the explosion phase (the disturbance maximum), when only the sporadic Es layer is the reflecting ionospheric layer; and the recovery phase, when a disturbance already ceases and the ionosphere returns to its initial undisturbed state. During other disturbance phases, the correlation radius (if it exists) is much smaller than 400 km.     

Galactic cosmic ray fluctuation parameter as an indicator of the degree of magnetic field inhomogeneity

The parameter of cosmic ray fluctuations, which indicates the degree of IMF inhomogeneity, was introduced in order to quantitatively describe the dynamics of the galactic cosmic ray (GCR) intensity fluctuations during the geoeffective phases of the 11-year cycle. The 5-min data of the high-latitude neutron monitor at Oulu station (Finland) during cycles 20–23 was used in the calculations. The nonrandom non-Gaussian character of the GCR fluctuation parameter is caused by the nonstationary semiannual variation reflecting the transient nonstationary oscillatory process of sign reversal of the general solar magnetic field. This transient oscillatory process is responsible for the maximal geoeffectiveness and duration of the phase of polarity reversal, which manifests itself in a sharp and deep GCR intensity minimum during the final stage of the field sign reversal. The invariant of the 11-year “amplitude-duration” cycle was confirmed on a new basis: the LF drift of the “low” cycle period was detected, which was observed in an increase in the duration of cycle 23 we anticipated.     

Intensity of vlf and elf phenomena in the outer ionosphere

Summary Spatial and temporal variability of natural ELF-VLF phenomena field intensity has been studied using data from Interkosmos satellites with apogees below 2000 km. The results show a distinct dependence of the diurnal variation and latitudinal intensity distribution on the magnetic activity. The L-value at which the maximum of plasmaspheric noise occurs, e.g., correlates better with the Dst-index than with other indicies.

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mama u a auau anmu n mm - u a ua a uu ¶rt;a uu m an u 2000 . mam naam m auum m ¶rt;a u um an¶rt;u uu m aum amumu. uua L-naama, a m nm au naa uu, um Dst-u¶rt; ¶rt;uu u¶rt;auaum amumu.

     

Features of poleward expansion of the outer radiation belt during magnetospheric substorms

Cases in which the outer boundary of the electron belt shifts to high latitudes are studied. The cases evidence that the zone of quasi-trapping of the night magnetosphere expands to the pole. These events are shown to be caused by substorm activity which, shifting to high latitudes, can lead to the development of so-called polar-cap substorms. It is shown that high-latitude bursts of energetic electrons can be generated in such substorms by analogy with their generation in classical substorms of the auroral zone.     

CUTLASS HF radar observations of high-latitude azimuthally propagating vortical currents in the nightside ionosphere during magnetospheric substorms

High-time resolution CUTLASS observations and ground-based magnetometers have been employed to study the occurrence of vortical flow structures propagating through the high-latitude ionosphere during magnetospheric substorms. Fast-moving flow vortices (800 m s^–1) associated with Hall currents flowing around upward directed field-aligned currents are frequently observed propagating at high speed (1 km s^–1) azimuthally away from the region of the ionosphere associated with the location of the substorm expansion phase onset. Furthermore, a statistical analysis drawn from over 1000 h of high-time resolution, nightside radar data has enabled the characterisation of the bulk properties of these vortical flow systems. Their occurrence with respect to substorm phase has been investigated and a possible generation mechanism has been suggested.     

Yeasts as an indicator of pollution

A survey of yeast populations at various points along the St Lawrence River indicates that certain yeast blooms occur after bacteria have degraded the easily metabolizable constituents of the raw sewage and that their numbers could be used as an indicator of pollution.     

Low-frequency noise at altitudes of the outer ionosphere and solar activity

The results of recording the intensity of low-frequency electromagnetic emissions at altitudes of the outer ionosphere based on satellite data at various levels of solar activity have been investigated. The intensity of low-frequency emissions has been found to depend on the solar activity, i.e., the spatial noise characteristics vary. Mean values of the noise amplitude variations at various phases of the solar activity cycle are presented. The low-frequency emissions are shown to serve as a source of information about the processes in the surface plasma; in particular, the state of the radiation belts is judged from them. The noise carries information about the variations in the particle fluxes intruding into the Earth’s plasmasphere under various solar activity conditions and about the magnetospheric plasma variations related to the growth of solar activity. In other words, the electromagnetic low-frequency noise can be a peculiar kind of indicator of the solar activity and the state of the magnetosphere.     

Response of the outer ionosphere to a magnetic storm at equinox

Summary The observations of the ACTIVE Project satellites in the interval of March 17–23, 1990 were analyzed for the purpose of studying the response of the outer ionosphere to the magnetic storm with SSC on March 20 at 22.43 UT. In particular, measurements of thermal plasma parameters were used, but VLF broadband measurements and data on energetic ion and electron fluxes in the range of 17.7–272 keV were also available. The results of this case study show that the observations in the morning sector at altitudes around 2000 km reflect well the state of the plasmasphere during enhanced activity, namely the depth to which the plasmasphere has been affected by enhanced magnetospheric convection. They also provide the possibility of monitoring the initial phase of recovery. The early evening observations of the plasma parameters in the outer ionosphere at altitudes of 500–1000 km indicate a distinct trough in electron concentration. In the dusk sector, the equatorward edge of this trough can be assumed to be the projection of the equatorial plasmapause. This, combined with the occurrence of electron temperature peaks and with the morning plasmapause position, enables one to judge whether the plasmaspheric bulge has formed and whether an inner plasmapause has occurred.     

The ionosphere as an Alfven resonator in the Pc1 micropulsation range

Summary A local planar approximation of a stratified, inhomogeneous, anisotropic and dissipative ionosphere is presented as an Alfven quarter-wave plate resonator in the Pc1 micropulsation range. The frequency-amplitude structure of the resonance response of an isotropic Alfven wave on the Earth's surface and at a given altitude in the ionosphere is studied in comparison to standing waves in vacuum above an ideal conductor for a particular model of the ionosphere. An asymmetry in the response was found at both boundary of the resonator, at the Earth's surface and at the given altitude z₀. The results are related to the vertical changes of frequency dispersion in the dissipative medium of the ionosphere and to the vertical profile of the inhomogeneities of the resonator being considered.     

Pyroclast textural variation as an indicator of eruption column steadiness in andesitic Plinian eruptions at Mt. Ruapehu

Hudson is one of the most active volcanoes in the Southern Andes—it had one of the largest eruptions of the 20th century in 1991 (VEI?=?5) and smaller eruptions in 1971 (VEI?=?3), maybe 1973, and 2011 (VEI of 1-2). We use satellite-based interferometric synthetic aperture radar (InSAR) and thermal imagery to characterize the activity of Hudson between 2004 and 2011 and during the 2011 eruption. InSAR data show that the volcano inflated between 2004 and 2010 with a maximum change rate of between 2 and 3 cm/yr—about half of the deformation rate observed during a previous deformation episode from 1993–1999. Inversion for an inflating point source suggests magma accumulation beneath the SW part of the caldera at an average depth of 10 km. This inferred source is deeper than both the sources estimated for the magma chamber of the 1991 eruption (from petrology) and for the 1993–1999 deformation event. Also, the deformation from 2004–2010 is centered at a slightly different location and has a smaller volume change than that between 1993–1999—further indicating that there is either a large magma reservoir or several separate ones. While the deformation center is a few km from the eruption location near the caldera rim, the two are possibly linked since the predicted static Coloumb stress changes due to the inferred inflation source would encourage unclamping on potential faults in the caldera rim. We also analize nighttime satellite thermal images from MODIS and ASTER. While MODIS did not show any unambiguous evidence for hot spots, ASTER thermal imagery show that at least four months before the eruption there were locations with temperatures 7–8ºK above background. Lahars observed by helicopter overflights on 4 March 2011 and October 2011 suggest that the hotspots may have been caused by lakes or subglacial melting. There is no InSAR data available for the months immediately preceding the eruption, but the ASTER thermal imagery results may indicate an increase in geothermal activity that could have been used to forecast the eruption.     

Posidonia as an indicator of mercury contamination

The mercury content in the marine phanerogam Posidonia oceanica, sampled in an area near a chloralkali complex, has been measured and compared with that of the samples collected in a non-impacted region.Plants growing in the seawater facing the chlor-alkali complex showed mercury content of 0.19 μg g⁻¹ f.w., compared with 0.02 μg g⁻¹ f.w. in the samples from the control area. Sediments of the industrial area have mercury levels 20–30 times higher than those from the control area. As the mercury concentration in seawater of both areas is comparable, the mercury content in the plant appears to be correlated with mercury levels in the sediment; probably the metal uptake in Posidonia oceanica takes place mainly through the root system.     

Plasma disturbance sources in the postsunset low-latitude outer ionosphere according to the Intercosmos-Bulgaria-1300 satellite

The satellite low-latitude and midlatitude measurements of the disturbed postsunset plasma density and electron temperature at altitudes of ～900 km have been compared with the data of incoherent scattering and high-altitude rocket launching at the corresponding local time. It has been found that plasma density disturbances are independently caused by the turbulent interaction between atmospheric masses of gas and plasma ascending from heated and not yet cooled ionospheric regions and cooling masses descending from protonospheric altitudes. Plasma regions with an energetically nonequilibrium vertical density distribution of the mixture of heavy ion impurity (O⁺) and major light ions (H⁺) can simultaneously appear, as a result of which the gradient-drift impurity instability is generated. If this instability is sufficiently developed, there appears an anomalous ion drift with the formation of real plasma regions of decreased density. All these phenomena generate different irregularities in a wide range of scales: from several tens or hundreds of meters to several hundreds of kilometers.     

Weathering of quartz as an Archean climatic indicator

Chert and other hard monomineralic quartz grains weather mostly by mechanical processes in modern environments. Their clasts are overrepresented in conglomerates and sands relative to their sources regions. Conversely, macroscopic dissolution features, including quartzite karst, are rare but not nonexistent. The similar rarity of quartz dissolution in Archean deposits provides a paleothermometer for climate on the early Earth. For example, chert is overrepresented in conglomerates and sands of the ∼3.2 Ga Moodies Group (South Africa) relative to the source region. Features related to the far-from-equilibrium dissolution rate are particularly diagnostic as it increases an order of magnitude over 25 °C, much more than solubility. Extrapolating from observed dissolution rates in modern environments that weather at ∼25 °C, we expect obvious dissolution features in ancient climates above ∼50 °C. Polycrystalline quartz and chert would readily disaggregate by solution along grain boundaries, yielding silt and clay. Quartz grains within slowly weathering granite would become friable, yielding silt and clay, rather than sand. At still higher temperatures, Al₂O₃-rich clays from weathered granite would stand above solution-weathered chert on low-relief surfaces. The observed lack of these features is evidence that the Archean climate was not especially hot.     

Uranium as an indicator of the origin of the Tethyan ophiolites

The distribution of uranium in minerals and rocks of the ophiolitic sequences from the Northern Apennines (Italy) and the Hellenides (Greece) of the Tethyan mountain belt has been investigated by fission-track mapping. Whole-rock U abundances, ranging from 11 to 74 ppb in ultramafic rocks, from 13 to 54 ppb in gabbroic rocks, from 73 to 281 ppb in basalts and from 279 to 900 ppb in spilites, partially reflect the post-crystallization history of the rocks. Among the fresh relics of primary rock-forming minerals, clinopyroxene has the highest U content. The estimated original U concentration of ultramafic rocks is about 1 – 10 ppb. These rocks do not appear to represent the primary undepleted mantle material. U distribution in the analyzed suites of ophiolites is consistent with a model for alpine-type ophiolites, where harzburgites and lherzolites of the basal ultramafic zone represent the residuum after extraction of oceanic tholeiitic magma. The segregated basaltic liquid either extruded rapidly as basalts or underwent magmatic differentiation in a quiet environment producing mineral accumulates as troctolites and gabbros.     

汶川大地震前电离层参量的变化特征与分析

利用重庆,兰州,曲靖和拉萨的电离层测高仪数据和IGS全球TEC数据,分析2008年5月12日汶川大地震前电离层参量的变化特征,发现震前2～3天多个电离层参量均出现异常增强现象,且主要出现于震中以南区域.其中foF1和foE于震前2天的正午在重庆出现最大约4.5%和9%的相对增加.foEs,h′F和hmF2出现多次异常增加,无明显规律性,h′F的异常增加主要出现在夜间.foF2和TEC在震前2～3天的午后至日落时段出现显著的异常增强.TEC在南半球磁共轭区也出现异常增强,且随时间推移具有向磁赤道漂移的趋势.foF2和TEC的震前异常现象很明显且具有独特规律性,作为地震电离层异常前兆参数是合适的.根据经验公式由电离层参量估算的可能与地震过程有关的F区异常电场的量级与Pulinets基于异常电场假说的理论模拟值一致.     

The structure of extremely low frequency field reflected by the ionosphere

The amplitudes of variations in the magnetic and electric fields at extremely low frequencies were studied on the Kola Peninsula during a five-day-long experiment under different geophysical conditions. These studies demonstrated that the influence of the ionosphere is distinguishable at frequencies of <10 Hz and the structure of field variations reflected by the ionosphere is similar to that of the transverse wave. It is established that the ratio between semimajor axes of polarization ellipses of the electric and magnetic fields is independent of the state of the ionosphere and is likely determined by the deep structure of the crust beneath the site of the experiment.