Altitude variation of the plasmapause signature in the main ionospheric trough

The projection of the plasmapause magnetic-field lines to low altitudes, where the light-ion chemistry is dominated by O⁺, tends to occur near the minimum electron density in the main (midlatitude) electron density trough at night. With increasing altitude in the trough, where H⁺ emerges as the dominant ion on the low-latitude boundary, we have found cases where the plasmapause field lines are located on the sharp low-latitude side of the trough as expected if this topside ionosphere H⁺ distribution varies in step with the plasmapause gradient in the distant plasmasphere. These conclusions are based on near-equatorial crossings of the plasmapause (corresponding to the steep gradient in the dominant species H⁺) by the Explorer-45 satellite as determined from electric-field measurements by Maynard and Cauffman in the early 1970s and ISIS-2 ionospheric topside-sounder measurements. The former data have now been converted to digital form and made available at http://nssdcftp.gsfc.nasa.gov. The latter provide samples of nearly coincident observations of ionospheric main trough crossings near the same magnetic-field lines of the Explorer 45-determined equatorial plasmapause. The ISIS-2 vertical electron density profiles are used to infer where the F-region transitions from an O⁺ to a H⁺ dominated plasma through the main trough boundaries.     

Comparison between two theoretical mechanisms for the formation of the plasmapause and relevant observations

The plasmapause formation physical mechanisms are recalled: (i) the MHD convection mechanism, based on the original idea that the plasmapause coincides with the last closed equipotential (LCE) of the magnetospheric convection electric field or with the last closed streamline (LCS) of the equatorial plasma, and (ii) the interchange mechanism, which is based on peeling off the plasmasphere as a result of substorm associated enhancements of the night side convection velocity, leading to an enhanced centrifugal acceleration in the outermost layers of the plasmasphere. The plasmapause positions, predicted by these alternative theories, were numerically determined for two different magnetospheric empirical electric field models: (i) the Volland-Stern-Maynard-Chen (VSMC) and (ii) McIlwain E5D models, both of which are Kp-dependent. The predicted positions and overall shape of the equatorial plasmapause cross-sections are confronted to those derived from decades of whistler and satellite observations including the EUV observations during the substorm of June 27, 2001. It is found that the VSMC electric field model and the LCS plasmapause formation theory less correspond to whistler measurements and in-situ satellite observations than the E5D model and the interchange plasmapause formation mechanism. Published in Russian in Geomagnetizm i Aeronomiya, 2008, Vol. 48, No. 5, pp. 579–597. The article was translated by the authors.     

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.     

Modeling of properties of the plasmasphere under quiet and disturbed conditions

Based on theoretical models of the ionosphere and the plasmasphere, the ion composition variations in the plasmasphere and the plasmapause structure were studied depending on the choice of the distribution model of the magnetospheric convection electric field at low and high geomagnetic activity at the equinox and the December solstice. Based on the model calculations performed, the plasmapause shape and size during an increase and decrease in geomagnetic activity were studied. It was revealed that the size of the plasmasphere mainly depends on the magnetic local time (MLT) sector and the level of geomagnetic activity, and it greatly depends on the maximum universal time during the equinox. The Earth’s plasmasphere asymmetry is manifested in the noon-midnight and morning-evening directions. The analysis results of daily and seasonal variations in the ionic composition of the Earth’s plasmasphere at a moderate solar activity level show that there is a certain increase in the ion concentrations of H⁺ and He⁺ in the winter period probably due to an increase in the exospheric density at the summer to winter transition. The data obtained are in good agreement with satellite observations which makes it possible to use the model proposed to study the plasmasphere under different geophysical conditions.     

Proposal for an ionosphere/plasmasphere monitoring system

A space-based satellite system suited for long-term monitoring of the Earth’s ionosphere/plasmasphere systems is proposed. The monitoring system consists of a network of radio beacon satellites capable of measuring the ionospheric and plasmaspheric electron content on a continuous base with high time resolution. It takes advantage of the geometrical relationship between the orbit of geostationary satellites and the position of the plasmapause region characterized by a steep electron density gradient. A combination of geostationary and nongeostationary satellites may explore the three-dimensional structure of the plasmasphere. Taking into account plasmaspheric characteristics some criteria for an effective arrangement of the satellites are derived and discussed. Since the plasmapause position is very sensitive to changes or distortions in the solar wind and the related geomagnetic activity, a continuous monitoring of the position of the plasmapause would be helpful in understanding solar-terrestrial relationships.     

A quantitative model for cyclotron wave-particle interactions at the plasmapause

The formation of a zone of energetic electron precipitation by the plasmapause, a region of enhanced plasma density, following energetic particle injection during a magnetic storm, is analyzed. Such a region can also be formed by detached cold plasma clouds appearing in the outer magnetosphere by restructuring of the plasmasphere during a magnetic storm. As a mechanism of precipitation, wave-particle interactions by the cyclotron instability between whistler-mode waves and electrons are considered. In the framework of the self-consistent equations of quasi-linear plasma theory, the distribution function of trapped electrons and the electron precipitation pattern are found. The theoretical results are compared with experimental data obtained from NOAA satellites.     

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     

Restoration of the proton density distribution in the Earth’s plasmasphere from measurements along the INTERBALL-1 satellite orbit

Based on experimental data obtained in 1995?C2000 on board the INTERBALL-1 spacecraft using the ALPHA-3 instrument, a semi-empirical two-dimensional model of the Earth plasmasphere is developed, which allows for the plasma distribution in the entire meridional plane to be restored from the temperature and proton density measurements along the satellite orbit. The model has also been tested using the data of the IMAGE spacecraft. The model uses theoretical expressions (Lemaire and Schere, 1974) that describe the plasma distribution in the plasmasphere for the cases of thermal equilibrium and collisionless initial partial filling of plasmaspheric shells; therefore, the parameters of the constructed model have a clear physical meaning and make it possible, in particular, to estimate the degree of plasmasphere filling.     

On the relationship of SAPS to storm-enhanced density

We use magnetic field-aligned mapping between the ionosphere and the magnetosphere to intercompare ground-based observations of storm enhanced density (SED), and plasmasphere drainage plumes imaged from space by the IMAGE EUV imager, with the enhanced inner-magnetosphere/ionosphere SAPS electric field which develops during large storms. We find that the inner edge of the SAPS electric field overlaps the erosion plume and that plume material is carried sunward in the SAPS overlap region. The two phenomena, SED in the ionosphere and the erosion plume at magnetospheric heights, define a common trajectory for sunward-propagating cold plasma fluxes in the midnight—dusk–postnoon sector. The SAPS channel at ionospheric heights and its projection into the equatorial plane serve to define the sharp outer boundary of the erosion plume. The SAPS electric field abuts and overlaps both the plasmasphere boundary layer and the plasmasphere erosion plume from pre-midnight through post-noon local times.     

Nonlinear phenomena related to the solar shock motion in the Earth’s magnetosphere

The motion of the MHD nonlinear shock in the Earth’s magnetosphere is considered in the scope of magnetic hydrodynamics. This wave comes from the solar wind and is refracted into the magnetosphere, generating a fast return rarefaction wave. It has been indicated that a wave refracted into the magnetosphere is a weak fast dissipative shock, propagating in magnetospheric plasma at a velocity higher than its propagation velocity in a solar wind stream. The wave motion near the Earth-Sun line with regard to the effect of the geomagnetic field transverse component is described. In this case, shock damping follows the generalized Crussard-Landau law and a wave retains its shock character up to the plasmapause, interacting with this region when an arbitrary MHD discontinuity is disintegrated. It is stated that an MHD shock loses its shock character when moving in a strongly inhomogeneous plasma within the plasmasphere and a weak shock reflected from the plasmapause can combine with a return secondary shock in the magnetosheath, promoting the experimentally observed backward motion of the bow shock front.     

Kalman filter-based algorithms for monitoring the ionosphere and plasmasphere with GPS in near-real time

Data collected from a GPS receiver located at low latitudes in the American sector are used to investigate the performance of the WinTEC algorithm [Anghel et al., 2008a, Kalman filter-based algorithm for near realtime monitoring of the ionosphere using dual frequency GPS data. GPS Solutions, accepted for publication; for different ionospheric modeling techniques: the single-shell linear, quadratic, and cubic approaches, and the multi-shell linear approach. Our results indicate that the quadratic and cubic approaches perform much better than the single-shell and multi-shell linear approaches in terms of post-fit residuals. The performance of the algorithm for the cubic approach is then further tested by comparing the vertical TEC predicted by WinTEC and USTEC [Spencer et al., 2004. Ionospheric data assimilation methods for geodetic applications. In: Proceedings of IEEE PLANS, Monterey, CA, 26–29 April, pp. 510–517] at five North American stations. In addition, since the GPS-derived total electron content (TEC) contains contributions from both ionospheric and plasmaspheric sections of the GPS ray paths, in an effort to improve the accuracy of the TEC retrievals, a new data assimilation module that uses background information from an empirical plasmaspheric model [Gallagher et al., 1988. An empirical model of the Earth's plasmasphere. Advances in Space Research 8, (8)15–(8)24] has been incorporated into the WinTEC algorithm. The new Kalman filter-based algorithm estimates both the ionospheric and plasmaspheric electron contents, the combined satellite and receiver biases, and the estimation error covariance matrix, in a single-site or network solution. To evaluate the effect of the plasmaspheric component on the estimated biases and total TEC and to assess the performance of the newly developed algorithm, we compare the WinTEC results, with and without the plasmaspheric term included, at three GPS receivers located at different latitudes in the American sector, during a solar minimum period characterized by quiet and moderate geomagnetic conditions. We also investigate the consistency of our plasmaspheric results by taking advantage of the specific donut-shaped geometry of the plasmasphere and applying the technique at 12 stations distributed roughly over four geomagnetic latitudes and three longitude sectors.     

Asymmetric mantle dynamics in the MELT region of the East Pacific Rise

The mantle electromagnetic and tomography (MELT) experiment found a surprising degree of asymmetry in the mantle beneath the fast-spreading, southern East Pacific Rise (MELT Seismic Team, Science 280 (1998) 1215–1218; Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Wolfe and Solomon, Science 280 (1998) 1230–1232; Scheirer et al., Science 280 (1998) 1221–1224; Evans et al., Science 286 (1999) 752–756). Pressure-release melting of the upwelling mantle produces magma that migrates to the surface to form a layer of new crust at the spreading center about 6 km thick (Canales et al., Science 280 (1998) 1218–1221). Seismic and electromagnetic measurements demonstrated that the distribution of this melt in the mantle is asymmetric (Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Evans et al., Science 286 (1999) 752–756) at depths of several tens of kilometers, melt is more abundant beneath the Pacific plate to the west of the axis than beneath the Nazca plate to the east. MELT investigators attributed the asymmetry in melt and geophysical properties to several possible factors: asymmetric flow passively driven by coupling to the faster moving Pacific plate; interactions between the spreading center and hotspots of the south Pacific; an off-axis center of dynamic upwelling; and/or anomalous melting of an embedded compositional heterogeneity (MELT Seismic Team, Science 280 (1998) 1215–1218; Forsyth et al., Science 280 (1998) 1235–1238; Toomey et al., Science 280 (1998) 1224–1227; Wolfe and Solomon, Science 280 (1998) 1230–1232; Evans et al., Science 286 (1999) 752–756). Here we demonstrate that passive flow driven by asymmetric plate motion alone is not a sufficient explanation of the anomalies. Asthenospheric flow from hotspots in the Pacific superswell region back to the migrating ridge axis in conjunction with the asymmetric plate motion can create many of the observed anomalies.     

The “fan” instability as a possible generating mechanism of vlf quarter-gyrofrequency emissions during the recovery phase of a magnetospheric storm

Summary VLF quarter-gyrofrequency emissions, whose experimental characteristics differ from those of discrete plasmaspheric emissions usual during active times, have been observed by low-altitude Intercosmos 24 and Magion 2 satellites within the plasmasphere during periods of quieting geomagnetic activity. A new kind of instability is proposed which could lead to the production of these emissions. It is shown that quasi-electrostatic whistler waves can be generated in the eqquatorial region due to the fan instability, with maximum growth rate and spectral energy density in a frequency band below one half of the equatorial electron gyrofrequency. The observations of low-energy electrons and plasma waves in the equatorial region within or in the vicinity of the plasmapause, which could support our hypothesis experimentally, are discussed.     

Anomalous polarization features of the cyclotron radiation source in the NOAA 7123 active region: The structure, dynamics, and reasons of occurrence

The research results of the unique NOAA 7123 active region (April 1992) are presented; its anomalous polarization features (long-term predominance of O-mode radiation above the central part of the main sunspot) were previously revealed by VLA observations with a resolution of (2–4)” at wavelengths of 3.6 and 6.4 cm (Vourlidas et al., 1997). Additional observations in a wider band of electromagnetic radiation, including, in particular, spectrum-polarization observations performed with the RATAN-600 and SSRT radio telescopes, are considered. The analysis of these data allowed for the conclusion that the anomaly was caused by the presence of a cold substance in the upper coronal layers, starting from the height where (6–7) cm radiation was generated. A possible transportation agent of this substance—Hα filament—one of the bases of which fell on the sunspot’s umbra-penumbra boundary, was found.     

Seismotectonic Model and CN Earthquake Prediction in Italy

—The choice of the regions is essential in the application of the algorithm CN, therefore a seismotectonic criterion for their definition is tested. In order to take into account the geodynamic complexity characterising the Italian peninsula, we established to strictly follow the seismotectonic zones, including in each region only zones with similar seismogenic behaviour and the transitional zones connected to them. Three regions have been successfully defined in this way, corresponding approximately to the North, Centre and South of Italy. The reduction of the space-time uncertainty and the increase of the stability of prediction results obtained with this regionalisation, with respect to the previous applications of CN in Italy (Keilis-Borok et al., 1990; Costa et al., 1995, 1996), can be interpreted as a validation of the seismotectonic model.     

磁宁静期核心等离子体层电子密度分布的统计研究

等离子体层已有数十年研究历史,但对其核心等离子体区域却一直没有一个相对准确的界限和模型定义.基于范阿伦辐射带卫星RBSP-A在2012年9月18日至2014年10月13日约两年的观测,我们统计研究了磁宁静期间核心等离子体层电子密度随磁地方时（MLT）及磁壳指数（L-value）的分布特征.发现了核心等离子体层电子密度在不同MLT条件下随L值的变化趋势几乎一致,但与以前的等离子体层经验模式计算的电子密度存在较大的偏差.在不同L值下电子密度随MLT的变化趋势也相差不大,而且随MLT存在明显的逐日和半日变化.最后我们获得了等离子体层电子密度随L值和MLT变化的经验公式.研究结果对空间等离子体层建模及研究具有重要的意义.

     

Ionospheric space weather effects monitored by simultaneous ground and space based GNSS signals

Ionospheric space weather effects can degrade the performance of global navigation satellite systems (GNSS), i.e. their accuracy, reliability and availability. However, well established ground based and innovative space based GNSS measurements offer the unique chance for a permanent monitoring of the electron density structure of the global ionosphere–plasmasphere system. In this paper we review various types of perturbations in the ionospheric plasma density and distribution. In order to analyze these space weather effects we use 30 s sampled measurements provided by the global GPS ground tracking network of the IGS. Furthermore, to get a more comprehensive view on the perturbations analyzed also are simultaneously obtained GPS measurements onboard the LEO satellite CHAMP (challenging minisatellite payload). Whereas the ground based measurements show strong horizontal redistribution of plasma during ionospheric storms, the space-borne measurements indicate a severe vertical redistribution of the ionospheric plasma during the selected events. The role of the various dynamical forces such as meridional winds and electric fields is also discussed.     

SIMS U-Pb zircon age of a tuff layer in the Meishucun section,Yunnan, southwest China: Constraint on the age of the Precambrian-Cambrian boundary

Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out closely following the guidance of cathodoluminescence images, and the majority of analyses were conducted on the oscillatory zircon grains. Thirteen measurements yield a highly reliable Concordia U-Pb age of 536.7 ± 3.9 Ma for the Bed 5 horizon. A grand mean of 206Pb/238U age of 535.2± 1.7 Ma (...