Effects of the Lipetsk Meteoroid in the Geomagnetic Field

Geomagnetism and Aeronomy - Observational data from the Kiev (Ukraine), Borok, St. Petersburg, Hel (Poland), Arti, Novosibirsk, Almaty (Kazakhstan), and Irkutsk magnetic observatories are used to...     

Magnetic and Ionospheric Effects of a Meteoroid Plume

This paper is concerned with the study of the possibility of products of a meteoroid explosion in the atmosphere (meteoroid plume) to reach ionospheric altitudes. It has been shown that, in the case of meter-sized or larger space bodies entering the atmosphere, the plume is able to reach the lower ionosphere. The plume can be one of the sources of the formation of nacreous and noctilucent clouds. The aerosols ejected by the plume to lower ionospheric altitudes can lead to the formation of dust plasma, significantly changing the electrodynamic properties of the medium. The motion of the plume with a velocity of ~1 km/s is accompanied by the generation of a ballistic shock with a radius of 1–10 km. The relative excess pressure in the shock front can cause relative disturbances in the electron content at the altitudes of D, E, and F1 layers by ~10–100%. The geomagnetic effect of the plume and ballistic shock can reach ~1–10 nT.     

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.     

Magnetospheric and Ionospheric Effects Accompanying the Strongest Technogenic Catastrophe

The results of observations of quasi-periodic variations of horizontal components of the geomagnetic field, the Doppler frequency shift of the radio waves reflected from the ionosphere, and observations of anomalous traces in ionograms during a catastrophe at the largest European ammunition depot on March 23, 2017, are presented. It is shown that the catastrophe was accompanied by oscillations of the geomagnetic field level (with periods from 5–6 to 13–14 min and an amplitude of 2–3 nT) and the ionospheric electron density (with periods from 14–16 to 50–60 min and a relative amplitude of ～1–10%). A mechanism for the transfer of disturbances from the catastrophe site to the ionosphere altitudes is proposed. A key role in this mechanism is played by the acoustic gravity waves generated by widespread explosions and large-scale fire events.     

Investigating Ionospheric Scintillation Effects on Multifrequency GPS Signals

Surveys in Geophysics - Over the last 15 years, the satellite constellation of the global positioning system (GPS) has been modernized for more precise applications, with the introduction...     

Meteoroid ablation spheres from deep-sea sediments

We present analyses of spheres magnetically extracted from mid-Pacific abyssal clays 0–500,000 years old. The concentration of spheres >200 μm is a few times 10 ppb. The spheres were divided into three groups using their dominant mineralogy, and are named iron, glassy, and silicate. Most spheres were formed from particles that completely melted as they separated from their parent meteoroids during the ablation process. However, some of the silicate spheres contain relict grains of the parent meteoroids that did not experience any melting. Typically, these relict grains are olivine crystals whose cores are Mg-rich (Fo_89–99). Commonly the outer rims of these grains were altered during heating. Other relict mineral grains include enstatite, ferrous spinel, chromite, and pentlandite.The three groups of spheres may possibly indicate some genetic significance. It seems reasonable to expect iron-rich spheres to be produced during ablation of iron and metal-rich silicate meteoroids. Metal spheres are probably not produced by ablation of predominantly silicate meteoroids because studies of fusion crusts and laboratory ablated silicate materials have never yielded separate metal spheres, but rather have produced spheres with intergrown iron oxide and silicate phases. The iron spheres possess identical mineralogy with the fusion crusts of Boguslavka, Norfork, and N'Kandhla iron meteorites as well as with the ablation debris created in the laboratory using iron and nickel-iron samples.The glassy spheres are considerably more Fe-rich than the silicate spheres. They consist of magnetite and a Fe-rich glass which is relatively low in Si. Some of these spheres may have experienced pronounced volatile depletion during the ablation process and could have been derived from silicate or metal-rich silicate meteoroids.The silicate spheres are undoubtedly derived from ablation of stony meteoroids. Two of the mineral assemblages occurring in these spheres (olivine-magnetite-glass and sulfide) are identical to those described in the natural fusion crusts of Allende, Orgueil, and Murchison meteorites, laboratory-made ablation debris, and melted interplanetary dust collected from the stratosphere. Bulk compositions and relict grains are useful for determining the parent meteoroid types for the silicate spheres. Bulk analyses of spheres have non-volatile elemental abundances similar to chondritic abundances. Analyses of relict grains identified high-temperature minerals which often occur as larger crystals in a fine-grained matrix that is characterized by voids. These voids were caused by escaping volatiles as minerals decomposed during ablation. Because larger crystals of higher-temperature minerals are associated with fine-grained, low-temperature, volatile-rich matrix, the obvious candidates for parent meteoroids of the silicate spheres containing relict grains are carbonaceous chondrites.     

Local Ionospheric Modeling Using the Localized Global Ionospheric Map and Terrestrial GPS

global ionosphere maps are generated on a daily basis at CODE using data from about 200 GPS/GLONASS sites of the IGS and other institutions. The vertical total electron content is modeled in a solargeomagnetic reference frame using a spherical harmonics expansion up to degree and order 15. The spherical Slepian basis is a set of bandlimited functions which have the majority of their energy concentrated by optimization inside an arbitrarily defined region, yet remain orthogonal within the spatial region of interest. Hence, they are suitable for decomposing the spherical harmonic models into the portions that have significant strength only in the selected areas. In this study, the converted spherical harmonics to the Slepian bases were updated by the terrestrial GPS observations by use of the least-squares estimation with weighted parameters for local ionospheric modeling. Validations show that the approach adopted in this study is highly capable of yielding reliable results.     

Estimation of the Ionospheric Effects of Geomagnetic Disturbances Based on Data from Wakkanai Station

Geomagnetism and Aeronomy - Ionosonde measurements of the critical frequency of the ionospheric F2 layer (foF2) at Wakkanai station (Japan) are analyzed with the method of superposed epochs. The...     

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.     

Recording the Response of the Chelyabinsk Meteoroid Fall by Dual-Frequency and Single-Frequency GPS Equipment

The Chelyabinsk meteoroid fall has been used to show that an appropriate ionospheric response can be recorded from signals of satellite radar systems. This can be done using dual-frequency or single-frequency equipment. The recording time of the response commencement has been used to estimate the propagation rate of primary disturbance in the atmosphere.     

Empirical Model of the Location of the Main Ionospheric Trough

The empirical model of the location of the main ionospheric trough (MIT) is developed based on an analysis of data from CHAMP satellite measured at the altitudes of ~350–450 km during 2000–2007; the model is presented in the form of the analytical dependence of the invariant latitude of the trough minimum Φ_m on the magnetic local time (MLT), the geomagnetic activity, and the geographical longitude for the Northern and Southern Hemispheres. The time-weighted average index Kp(τ), the coefficient of which τ = 0.6 is determined by the requirement of the model minimum deviation from experimental data, is used as an indicator of geomagnetic activity. The model has no limitations, either in local time or geomagnetic activity. However, the initial set of MIT minima mainly contains data dealing with an interval of 16–08 MLT for Kp(τ) < 6; therefore, the model is rather qualitative outside this interval. It is also established that (a) the use of solar local time (SLT) instead of MLT increases the model error no more than by 5–10%; (b) the amplitude of the longitudinal effect at the latitude of MIT minimum in geomagnetic (invariant) coordinates is ten times lower than that in geographical coordinates.     

Ionospheric imaging of the northern crest of the Equatorial Anomaly

The dominant structure in free electron concentration in the tropical ionosphere is the Equatorial Anomaly, where the largest values of TEC are found. This structure follows the geomagnetic equator and extends some 40° in latitude. The edges of the structure (crests) are characterised by steep, latitudinal gradients in TEC, which are temporally as well as spatially variable.This phenomenology is traditionally explained in terms of the theory of “fountain effect”, which is shortly reviewed in this work before presenting our results.Here we study the northern crest of the Equatorial Anomaly using a program that can perform multi-instrument two- or three-dimensional time-evolving mathematical inversions. This program is designed to unify a number of different measurement techniques, thus allowing the spatial and temporal study of the ionospheric features at hand. The paper reports on experimental results from winter 2000/2001. This is a highly significant period to study the ionospheric anomalies because it is around the maximum of the 11-year solar cycle and TEC is at a maximum.     

Ionospheric correction of space radar data

Radar is a critical tool for maintaining knowledge of the many objects in low Earth orbit and thus for maintaining confidence that societies around the world are secure against a variety of space-based threats. It is therefore important to raise awareness that LEO objects are embedded in the envelope of relatively dense plasma that co-rotates with the Earth (ionosphere-plasmasphere system) and thus accurate tracking must correct for the group delay and refraction caused by that system. This paper seeks to promote that awareness by reviewing those effects and high-lighting key issues: the need to customise correction to the altitude of the tracked object and prevailing space weather conditions, that ionospheric correction may be particularly important as an object approaches reentry. The paper outlines research approaches that should lead to better techniques for ionospheric correction and shows how these might be pursued in the context of the EURIPOS initiative.     

Ionospheric Response to the Acoustic Gravity Wave Singularity

An original model of atmospheric wave propagation from ground sources to the ionosphere in the atmosphere with a realistic high-altitude temperature profile is analyzed. Shaping of a narrow domain with elevated pressure in the resonance region where the horizontal phase wave velocity is equal to the sound velocity is examined theoretically within the framework of linearized Eq.s. Numerical simulations for the model profiles of atmospheric temperature and viscosity confirm analytical result for the special feature of wave fields. The formation of the narrow domain with plasma irregularities in the D and low E ionospheric layers caused by the acoustic gravity wave singularity is discussed.     

中国电离层TEC现报系统

作为最重要的电离层参量之一,电离层电子浓度总含量(TEC)可以通过当前广泛使用的全球定位系统(GPS)的信标进行观测.我们在我国北起漠河、经北京和武汉、南到三亚四个观测站建立了GPS接收站,经单站数据处理后将原始的单站GPS TEC观测数据上载到北京数据处理中心;采用我们发展的经验基函数模式算法,用实测数据估算格点TEC并提供给用户,同时生成覆盖中国疆域的TEC地图并在因特网上实时发布.这一电离层TEC现报系统是我国首个类似的技术系统,在观测站布局和TEC地图算法上有所创新.该系统已用于实时监测我国电离层环境,并可为我国卫星定位导航和测控等技术系统的电波修正提供实测电离层数据.     

Ionospheric signatures of magnetospheric boundaries in the post-noon sector

Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary.On leave from Artic Geophysics, University Course on Svalbard (UNIS), N-9170 Longyearbyen, Norway