Magnetotail response during a strong substorm as observed by GEOTAIL in the distant tail

Simultaneous energetic particle and magnetic field observations from the GEOTAIL spacecraft in the distant tail (X_GSM -150 Re) have been analysed to study the response of the Earths magnetotail during a strong substorm (AE 680 nT). At geosynchronous altitude, LANL spacecraft recorded three electron injections between 0030 UT and 0130 UT, which correspond to onsets observed on the ground at Kiruna Ground Observatory. The Earths magnetotail responded to this substorm with the ejection of five plasmoids, whose size decreases from one plasmoid to the next. Since the type of magnetic structure detected by a spacecraft residing the lobes, depends on the Z extent of the structure passing underneath the spacecraft, GEOTAIL is first engulfed by a plasmoid structure; six minutes later it detects a boundary layer plasmoid (BLP) and finally at the recovery phase of the substorm GEOTAIL observes three travelling compression regions (TCRs). The time-of-flight (TOF) speed of these magnetic structures was estimated to range between 510 km/s and 620 km/s. The length of these individual plasmoids was calculated to be between 28 Re and 56 Re. The principal axis analysis performed on the magnetic field during the TCR encountered, has confirmed that GEOTAIL observed a 2-D perturbation in the X-Z plane due to the passage of a plasmoid underneath. The first large plasmoid that engulfed GEOTAIL was much more complicated in nature probably due to the external, variable draped field lines associated with high beta plasma sheet and the PSBL flux tubes surrounding the plasmoid. From the analysis of the energetic particle angular distribution, evidence was found that ions were accelerated from the distant X-line at the onset of the burst associated with the first magnetic structure.     

Nonlinear geodynamics of the Baikal rift system: An evolution scenario with triple equilibrium bifurcation

This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 M_LH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.     

The evolving concept of a magnetospheric substorm

A magnetospheric substorm is an episode of energy transport and dissipation in the Earth|s ionosphere and mag- netosphere which takes place in response to a time limited increase in energy input from the solar wind to the magnetosphere. For the past few decades, scientists have tried to understand the physical processes which take place that are responsible for the substorm disturbances of the geospace environment. In this paper, The development of the substorm concept is reviewed from its origins at the beginning of the 20th century to the present time. The theoretical framework in which substorm physics is normally presented is then discussed, and an outline is given of how that framework has changed in recent times. This paper concludes by posing two questions which need to be answered if further progress is to be made in solving the substorm problem.     

Active phase of a substorm as a chain of two types of reconnection: In the closed plasma sheet and in the open tail lobes

The maps of the field-aligned current (FAC) density distribution in the ionosphere obtained by the TIM-2 magnetogram inversion technique are used to investigate the August 27, 2001 substorm. The open magnetic flux Ψ and intensity J of the substorm current wedge (SCW) have been determined with a step of 1–5 min. The substorm onsets are divided into two types, PSR (plasma sheet reconnection) and TLR (tail lobe reconnection). The fast expansion tailward of the PSR region is described as the transition from PSR to PSR+TLR. Assuming that the SCW FACs flow down into the ionosphere from the edges of the disruption region of the cross-tail dawn-dusk current, several parameters of the disruption region have been estimated. The disrupted magnetic field has been found to be ∼5% of the undisrupted one for PSR and ∼95% for PSR+TLR. The disturbance power Q for PSR is an order of magnitude lower than that for PSR+TLR. The abrupt growth of Q during the transition from PSR to PSR+TLR is observed over the entire SCW area from its near-Earth part to the midtail and distant tail.     

Guided waves in the plasma sheet and triggering of a substorm

A guided propagation of magnetoacoustic wave in the plasma sheet located between two lobes of the magnetotail is investigated. The dispersion equation for the wave and equation connecting a disturbance of plasma pressure inside the plasma sheet and amplitude of the plasma sheet boundary oscillations are obtained. For some value of plasma pressure disturbance, the displacement of the plasma sheet boundaries becomes of order of the half-thickness of the plasma sheet. In the case of symmetrical oscillations of the boundaries (“sausage-like” mode), it creates the favorable conditions for reconnection of the magnetic field lines in the magnetotail and may lead to triggering of a substorm. The magnetoacoustic wave may be generated by sudden impulse of the solar wind plasma pressure.     

Response of a Magnetospheric Storm in the Atmospheric Electric Field of the Midlatitudes

Geomagnetism and Aeronomy - The response of strong magnetic storms in variations of the electric field of the near-ground atmosphere of the midlatitudes are studied according to data from long-term...     

A review of: “Magnetospheric plasma physics”

Abstract

Edited by A. Nishida. D. Reidel Publishing Company, xii+348 pp. Cloth Dfl. 130,-/US $49.50 (ISBN 0 8130 0601 5) 1982.     

The magnetosphere as a nonlinear system

Summary In order to study the nonlinear physical processes connected with substorm activity we analyse time series of local geomagnetic field variations. The concepts of deterministic chaos and magnetospheric chaotic attractors are examined. The general objective of this article is to detect low dimensional magnetosphere chaos and to properly interpret it as a consequence of magnetosphere — ionosphere informational — energetic coupling.     

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.     

Magnetospheric Effects during the Approach of the Chelyabinsk Meteoroid

We have analyzed the observational results for variations in the main geomagnetic field and its fluctuations in the range of periods 1–1000 s that accompanied the approach of the Chelyabinsk space body to the magnetosphere and ionosphere of the Earth. The measurements were conducted with a magnetometerfluxmeter near the city of Kharkiv, as well as with the network of magnetometers located at the observatories of Novosibirsk, Kyiv, Lviv, Almaty, Khabarovsk, Arti, Borok, and Yakutsk. Variations in the main geomagnetic field and its fluctuations approximately 33–47 min prior to the explosion of the Chelyabinsk meteoroid have been discovered; they persisted for 25–35 min and were probably associated with meteoroid passage through the magnetosphere. The amplitude of variations reached 1–6 nT. We have proposed a model of the generation of aperiodic, quasi-periodic, and noise-like variations in the geomagnetic field induced by the approach of a space body.     

Radar observations of auroral zone flows during a multiple-onset substorm

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s⁻¹ or less during the first few minutes, before surging equatorward at 0.5-1.0 km s⁻¹ during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.     

Observation of a double-onset substorm during northward interplanetary magnetic field

For the first time, a substorm event with double onsets is shown observationally under northward IMF condition in this study. Magnetic field data from ground stations and from geosynchronous satellite, and aurora data from IMAGE satellite are examined to study the substorm activity. The results show that the intensity and the spatial extent of the event are as large as those of typical substorms. Another interesting finding is that two expansion onsets seem to occur during the event. A possible mechanism for the two onsets was proposed. The energy source for the event was also discussed.     

Specific features in the countermotion of substorm auroral intensifications

The dynamics of northern auroral structures drifting equatorward and bright auroral forms of substorm intensifications in the south, simultaneously moving northward, is analyzed based on data from the Lovozero, Loparskaya, and Tumanny auroral stations and using effective methods for filtering TV images. A fundamentally new fact that the structures of northern intensifications drifting southward cross the structures of southern intensifications propagating northward has been discovered. The effect is detected statistically and is only clearly defined on filtered keograms. The presence of this effect possibly means that northern structures and intense breakup auroras in the south have radically different sources and are caused by different mechanisms by which electrons accelerate and precipitate.     

Application of the methods of dynamical systems theory to solve nonlinear inverse problems in geophysics

Izvestiya, Physics of the Solid Earth - A method for the solution of inverse geophysical problems for finding the shape of an anomalous body by analyzing the dispersionless Toda hierarchy chain is...     

2008年1月5日磁层亚暴期间磁尾近地重联事件的THEMIS观测与分析

本文主要应用THEMIS卫星的磁场和等离子体流观测数据,分析了2008年1月5日08∶51~08∶57 UT亚暴膨胀相期间磁尾的一个近地重联事件.在亚暴膨胀相期间,地面的全天空成像仪清楚地记录到了极光的极向扩展,THEMIS的P5卫星在地球同步轨道附近观测到了磁场的偶极化现象.在亚暴膨胀相末期的08∶51~08∶57 UT期间,P3(X_GSM~-9.12R_E) 和P4 (X_GSM ~-9.40R_E) 同时观测到了一对方向相反的高速等离子体流.这对方向相反的高速等离子体流是由磁尾的重联现象所引起.重联的位置被估计位于X_GSM ~-9.12R_E 和X_GSM~-9.40R_E之间较小的空间范围内.并且,在重联位置的两侧,重联的Hall效应被P3和P4两颗卫星观测到.因此,这一磁尾重联事件发生在距离地球非常近的空间范围内.     

Testing the anelastic nonhydrostatic model EULAG as a prospective dynamical core of a numerical weather prediction model Part I: Dry benchmarks

In this paper, a feasibility of anelastic approach for numerical weather prediction (NWP) is examined. The study concerns the anelastic nonhydrostatic model EULAG as a prospective candidate for the new dynamical core of a high-resolution NWP model. Such an application requires a series of benchmark tests to be performed. The study presents the results of dry idealized two-dimensional linear and non-linear tests. They include evolution of cold and warm density currents in neutrally stratified atmosphere, inertia-gravity waves in short and long channels, as well as mountain gravity waves for a set of different flow regimes. Detailed comparison of the results with the reference solutions, based mainly on the results of compressible models, indicates a high level of conformity for all of the experiments. It verifies the anelastic approach as strongly consistent with the compressible one for a broad class of atmospheric problems. It also corroborates the robustness of EULAG numerics, an essential requirement of dynamical core of NWP model.     

Study of the longitudinal expansion velocity of the substorm current wedge

In this work we examine simultaneous observations from the two geosynchronous satellites GOES-5 and GOES-6 located at 282°E and 265°E respectively, and from middle and low latitude ground observatories located within 250°E and 294°E geographic longitude, during isolated substorms of moderate activity. The spatial distribution of our observation points allows us to make a detailed study of the azimuthal expansion of the substorm current wedge. The data analysis shows evidence that the substorm initiation and development mechanism include the cross-tail current diversion/disruption, the substorm current wedge formation and the azimuthal expansion of the inner plasma sheet. The triggering mechanism is initially confined in a longitudinally narrow sector, estimated to be less than 15° and located very close to local midnight to the east or to the west. The current disruption region expands both eastward and westward in the magnetotail, so that the location of major field-aligned currents flowing into the ionosphere shifts successively eastward, and the location of the currents flowing out of the ionosphere shifts successively westward. Evidence was found that the perturbation travels toward the west with velocities greater than those expanding the wedge eastward. The drastic decrease of the velocity with the azimuthal distance from the location of the disturbance initiation, i.e., the onset sector, indicates that the energy release is a very localized phenomenon. Finally, the transient D perturbation observed by the geosynchronous satellites suggests that the field-aligned currents forming the wedge have a longitudunally limited extent.     

Testing the anelastic nonhydrostatic model EULAG as a prospective dynamical core of a numerical weather prediction model Part II: Simulations of supercell

The anelastic nonhydrostatic model EULAG is a candidate for the future dynamical core of a numerical weather prediction model. Achieving such an objective requires a number of experiments focused on testing correctness of the solutions and robustness of the solver. In the spirit of this idea, a set of tests related to standard atmospheric problems was performed, of which the two regarding development and evolution of a supercell were employed as benchmarks of moist dynamics of the model. Their results are discussed in this paper. Development and evolution of a stormsystem with a set of characteristic features such as stormsplitting along with the generation of horizontal vorticity and cold pool formation is investigated. In addition, the influence of domain geometry, boundary conditions and subgrid-scale mixing is examined.     

Interhemispheric contrasts in the ionospheric convection response to changes in the interplanetary magnetic field and substorm activity: a case-study

Interhemispheric contrasts in the ionospheric convection response to variations of the interplanetary magnetic field (IMF) and substorm activity are examined, for an interval observed by the Polar Anglo-American Conjugate Experiment (PACE) radar system between 1600 and 2100 MLT on 4 March 1992. Representations of the ionospheric convection pattern associated with different orientations and magnitudes of the IMF and nightside driven enhancements of the auroral electrojet are employed to illustrate a possible explanation for the contrast in convection flow response observed in radar data at nominally conjugate points. Ion drift measurements from the Defence Meteorological Satellite Program (DMSP) confirm these ionospheric convection flows to be representative for the prevailing IMF orientation and magnitude. The location of the fields of view of the PACE radars with respect to these patterns suggest that the radar backscatter observed in each hemisphere is critically influenced by the position of the ionospheric convection reversal boundary (CRB) within the radar field of view and the influence it has on the generation of the irregularities required as scattering targets by high-frequency coherent radar systems. The position of the CRB in each hemisphere is strongly controlled by the relative magnitudes of the IMF B_z and B_y components, and hence so is the interhemispheric contrast in the radar observations.