Development of high latitude phase fluctuationsduring the January 10, April 10–11, and May 15, 1997magnetic storms

GPS satellite transmissions have been used to study the development of moderateionospheric phase irregularities. The use of the multi-station, multi-path observations of the GPSbeacons has allowed the study of the time development of irregularities as a function of latitudeand longitude of individual storms. The basic storms studied were those of January 10, April10–11, and May 15, 1997. The results from studying these storms showed the unique nature ofeach storm. For the three storms, data were available from four stations near 65° CorrectedGeomagnetic Latitude (CGL); the stations ranged from Fairbanks to Tromso. In addition, datafrom higher latitude stations are analysed. For the January storm, irregularity development startedat Fairbanks. Then as magnetic midnight approached longitudes to the west, the storm effectsreached the Tromso–Kiruna longitudes. For the April magnetic storm, at 65° CGL, irregularitydevelopment maximized at approximately the same UT at stations ranging in longitude fromFairbanks to Kiruna. For this storm, the development of irregularities was dominated by stormtime. The May storm irregularities were dominated by magnetic local time once the stormcommenced.With both total electron content and rate of change of total electron content (phasefluctuations) available, it was noted that over periods of minutes, clumps of irregularities wereaccompanied by increases in TEC. In addition total electron content increased over large areasduring maximum magnetic activity in the auroral oval. During the storms, ionograms showed thatthe altitude of maximum electron density fluctuated; at times the dominant maximum frequencywas noted in the E layer and at other times in the F layer. This fluctuation of electron density ineach layer during storms led to the conclusion that the turbulent activity within the auroral regiondominated the development of irregularities. The irregularities that are noted on trans-ionosphericpaths are therefore thought to be in both the E and the F layers with a combination of structuredhard and soft electron precipitation and coupling initiating the turbulent activity. The generalpositive correlation of one periods phase scintillation data with the Ultra Violet Imagerobservations as shown on POLAR indicates the importance of 100–200 km precipitation.However the very high occurrence of spread F at high latitudes as shown by both ground andsatellite ionosondes indicates the considerable contributions of F layer irregularities.     

Role of atmospheric circulation in the baric field response to the Earth’s crossing of the interplanetary magnetic field sector boundaries

The Earth’s crossings of the magnetic sector boundaries are accompanied by changes in the magnetosphere, ionosphere, and troposphere. We considered the baric field’s response to the crossing of the inter-planetary magnetic field (IMF) sector boundaries during a geomagnetically quiet period. The IMF sign is shown to affect atmospheric pressure in high-latitude regions. The efficiency and sign of the relationship vary during the year. The baric field response to the Earth’s crossing of the IMF sector boundaries is most distinct during equinoxes. It is shown that, during a geomagnetically quiet period, the circulation processes in the atmosphere drive the changes in the atmospheric pressure when the Earth passes from one IMF sector into another.     

Intensity of geomagnetic field in the Precambrian and evolution of the Earth’s deep interior

Reliable data on the paleointensity of the geomagnetic field can become an important source of information both about the mechanisms of generation of the field at present and in the past, and about the internal structure of the Earth, especially the structure and evolution of its core. Unfortunately, the reliability of these data remains a serious problem of paleomagnetic research because of the limitations of experimental methods, and the complexity and diversity of rocks and their magnetic carriers. This is true even for relatively “young” Phanerozoic rocks, but investigation of Precambrian rocks is associated with many additional difficulties. As a consequence, our current knowledge of paleointensity, especially in the Precambrian period, is still very limited. The data limitations do not preclude attempts to use the currently available paleointensity results to analyze the evolution and characteristics of the Earth’s internal structure, such as the age of the Earth’s solid inner core or thermal conductivity in the liquid core. However, such attempts require considerable caution in handling data. In particular, it has now been reliably established that some results on the Precambrian paleointensity overestimate the true paleofield strength. When the paleointensity overestimates are excluded from consideration, the range of the field strength changes in the Precambrian does not exceed the range of its variation in the Phanerozoic. This result calls into question recent assertions that the Earth’s inner core formed in the Mesoproterozoic, about 1.3 billion years ago, triggering a statistically significant increase in the long-term average field strength. Instead, our analysis has shown that the quantity and quality of the currently available data on the Precambrian paleointensity are insufficient to estimate the age of the solid inner core and, therefore, cannot be useful for solving the problem of the thermal conductivity of the Earth’s core. The data are consistent with very young or very “old” inner core ages and, correspondingly, with high or low values of core thermal conductivity.     

Harmonic sources of the main geomagnetic field in the Earth’s core

The large-scale harmonic magnetic-convective sources of the main geomagnetic field in the Earth’s core have been determined for the first time. The determination is based on a complete system of eigenfunctions of the magnetic diffusion equation in a homogeneously conducting sphere, which is surrounded by an insulator. The sources of the main geomagnetic field observed, which is responsible for the distribution of the electric currents generating this field in the core, are expressed in terms of large-scale eigenfunctions. In this case, the dipole sources are directly related to the observed geomagnetic dipole, whereas the quadrupole sources are related to the quadrupole, etc. The time variations in the obtained sources are responsible for individual spatiotemporal features in the generation or suppression of each Gaussian component of the observed geomagnetic field. When the commonly accepted observational international geomagnetic reference field (IGRF) models were used to partially reveal these time variations, it became possible to specify the estimate of the Earth’s core conductivity and determine the minimum period that can separate us from the commencement of further inversion or excursion.     

Asymmetry of geomagnetic polarity: Equatorial dipole,Pangaea, and the Earth’s core

The paper presents the results of analyzing the set of dual-polarity paleomagnetic results the Global Paleomagnetic Database (GPMDB). The dataset was expanded by the results from the Paleomagnetic Data Catalogue for the USSR and with new data published after 2005. Some results were rejected to avoid the influence of overprints of ancient and recent magnetization. Overall, 59 dual-polarity results for the lithospheric plates of Baltica, Laurentia, and Siberia with their immediate framing were selected for the analysis in the interval of ages 207–359 Ma. The new data confirmed the model of the paleomagnetic field, according to which the field contains a long-lived component corresponding to the equatorial dipole which is responsible for the non-antipodal paleomagnetic directions in the zones of normal and reverse polarity in sedimentary and volcanic rock sequences. Retaining its value of 5–8% of the central axial dipole, the equatorial dipole changed its polarity a few times during the interval 359–207 Ma. The northern poles of the dipole formed two antipodal groups on the Earth’s surface, which lie within or near the subduction zones on the periphery of the Pangaea Supercontinent. Such localization of the equatorial dipole is suggested to be related to the ascending branches of the mantle convection and to the topography of both boundaries of the outer Earth’s core.     

The relation between solar activity and orientation of the solar wind electric field relative to the Earth’s magnetic moment

The relation of the Kp index of geomagnetic activity to the solar wind electric field (E _SW) and the projection of this field onto the geomagnetic dipole has been estimated. An analysis indicated that the southward component of the IMF vector (B _z < 0) is the main geoeffective parameter, as was repeatedly indicated by many researchers. The presence of this component in any combinations of the interplanetary medium parameters is responsible for a high correlation between such combinations and geomagnetic activity referred to by the authors of different studies. Precisely this field component also plays the main role in the relation between the Kp index and the relative orientation of E _SW and the Earth’ magnetic moment.     

Possible impact of interplanetary and interstellar dust fluxes on the Earth’s climate

This article considers the process of entry of cosmic substance into the Earth’s atmosphere and the further evolution of the formed extraterrestrial aerosol. It is shown that meteorite-derived aerosol generated in the atmosphere may affect the Earth’s climate in two ways: (a) particles of meteoric haze may serve as condensation nuclei in the troposphere and stratosphere; (b) charged meteor particles residing in the mesosphere may markedly change (by a few percent) the total atmospheric resistance and, thereby, affect the global current circuit. Changes in the global electric circuit, in turn, may influence cloud formation processes. The obtained results argue for the fact that the meteoric dust in the Earth’s atmosphere is potentially one of the important climate-forming agents. It is shown that the amount of interstellar dust in the Earth’s atmosphere is too small to have a considerable affect on atmospheric processes.     

Comparison of Earth’s magnetospheric magnetic field models in the context of cosmic ray physics

Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000. For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages and drawbacks of the different models in the context of space weather.     

Effect of the magnetic field on measurements of the electron density and temperature by cylindrical probes in the Earth’s ionosphere

In the 1960s and 1970s, quite simply produced cylindrical Langmuir probes were used in the USSR both on satellites (Kosmos-378, Intercosmos-2, -4, -8, -10, -19) and to measure the electron density and temperature on vertical launched rockets (Vertical’-4, -6, -10) within the Intercosmos program. These measurements were first made at middle latitudes. With increasing inclination of the orbits of launched satellites (satellites had no stabilization), falling sections were sometimes observed on probe characteristics in the electron saturation region. The Intercosmos-Bulgaria-1300 satellite, which was stabilized along three axes and was equipped with a cylindrical probe whose longitudinal axis was always directed downward to the Earth, was launched in 1981. This satellite allowed definite conclusions on the effect of the geomagnetic field on the form of the probe characteristic and, hence, on the determination of the electron density and temperature. Probe characteristics with falling sections are presented. These measurements are compared with those performed in a laboratory plasma. The appearance of negative sections on the probe characteristics is shown to be due to the effect of the geomagnetic field. The degree of this effect depends both on the electron density and temperature and on the probe voltage.     

Variation of the intensity of the Earth’s magnetic field in Portugal in the 1st millennium BC

The study of magnetization of the ceramic material from 21 archeological monuments of Portugal (the Evora province), dated archeologically from the Bronze Age to the end of the Iron Age has been carried out. For the purpose of more detailed timing of the material from the monuments the method of ceramic age dating on the basis of its porosity has been used. In order to take into account the distorted factors in the determination of the parameters of the ancient geomagnetic field with the aim of the maximal approximation to the actual values the diagnostic features of magnetite weathering have been considered and the level of weathering of the magnetic fraction in the ceramics from archeological monuments has been determined. The data of geomagnetic field-strength variation in the time interval of the 12th century BC to the beginning of the Common Era have been obtained. The field-strength at this time interval varied in the range of 60–90 micro Tesla with the maximal values in the 9th, 8th, and the second half of the 5th to the beginning of the 4th century BC. In addition, the timing of the ceramic material from the urns of the megalithic complex Monte de Tera of the Evora province has been clarified.     

Accuracy estimates for some global analytical models of the Earth’s main magnetic field on the basis of data on gradient magnetic surveys at stratospheric balloons

Two global analytical models of the main magnetic field of the Earth (MFE) have been used to determine their potential in deriving an anomalous MFE from balloon magnetic surveys conducted at altitudes of ～30 km. The daily mean spherical harmonic model (DMSHM) constructed from satellite data on the day of balloon magnetic surveys was analyzed. This model for the day of magnetic surveys was shown to be almost free of errors associated with secular variations and can be recommended for deriving an anomalous MFE. The error of the enhanced magnetic model (EMM) was estimated depending on the number of harmonics used in the model. The model limited by the first 13 harmonics was shown to be able to lead to errors in the main MFE of around 15 nT. The EMM developed to n = m = 720 and constructed on the basis of satellite and ground-based magnetic data fails to adequately simulate the anomalous MFE at altitudes of 30 km. To construct a representative model developed to m = n = 720, ground-based magnetic data should be replaced by data of balloon magnetic surveys for altitudes of ～30 km. The results of investigations were confirmed by a balloon experiment conducted by Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation of the Russian Academy of Sciences and the Moscow Aviation Institute.     

Daytime geomagnetic disturbances at high latitudes during a strong magnetic storm of June 21–23, 2015: The storm initial phase

The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm (SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm^–3) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations (ipcl and vlp) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.     

Holocene Earth’s magnetic field variations recorded in marine sediments of the NW African continental margin

Holocene records documenting variations in direction and intensity of the geomagnetic field during the last about seven and a half millennia are presented for Northwest Africa. High resolution paleomagnetic analyses of two marine sediment sequences recovered from around 900 meter water depth on the upper continental slope off Cape Ghir (30°51′N, 10°16′W) were supplemented by magnetic measurements characterizing composition, concentration, grain size and coercivity of the magnetic mineral assemblage. Age control for the high sedimentation rate deposits (∼60 cm/kyr) was established by AMS radiocarbon dates. The natural remanent magnetization (NRM) is very predominantly carried by a fine grained, mostly single domain (titano-)magnetite fraction allowing the reliable definition of stable NRM inclinations and declinations from alternating field demagnetization and principal component analysis. Predictions of the Korte and Constable (2005) geomagnetic field model CALS7K.2 for the study area are in fair agreement with the Holocene directional records for the most parts, yet noticeable differences exist in some intervals. The magnetic mineral inventory of the sediments reveals various climate controlled variations, specifically in concentration and grain size. A very strong impact had the mid-Holocene environmental change from humid to arid conditions on the African continent which also clearly affects relative paleointensity (RPI) estimates based on different remanence normalizers. To overcome this problem the pseudo-Thellier RPI technique has been applied. The results represent the first Holocene record of Earth’s magnetic field intensity variations in the NW Africa region. It displays long term trends similar to those of model predictions, but also conspicuous millennium scale differences.     

Perturbation of the magnetic field in the Earth’s magnetosphere due to plateau creation in the radial distribution of plasma pressure

The nonlinear perturbation of a dipole field by a system of transverse currents, which arises due to the radial pressure distribution when the pressure is almost independent of the radial distance, is analyzed. This distribution of pressure was observed in the experiment. The radial dependences of the magnetic field depression, transverse current density, and volumes of magnetic flux tubes have been obtained at different values of the plasma parameter via nonlinear simulation. It is shown that a dependence of the volume of magnetic flux tube on the radial distance can change and a region of the negative gradient of volume can appear at some plasma-parameter values.     

On the gradient of curvature of the plumblines of the Earth’s normal gravity field and its isocurvature lines

This paper presents an approach to determine the gradient of curvature of the normal plumblines at a point P above the ellipsoid and introduces a new geometrical object which is the isocurvature line. The assumed facts are the coordinates of the point P and the formula for the normal gravity potential U. For the determination of the gradient of the normal plumbline curvature k at the point P we define a small circle on the meridian plane of P whose center is at the point P. The circle has the radius of one meter and interior D. In this circle we construct a curvature replacement function to approximate the curvature function k. This replacement function is a quotient of polynomials hence it is easy to find its partial derivatives at the point P. For the construction of replacement function we make the assumption that in the interior of the circle D the first order partial derivatives of U behave linearly and the second order partial derivatives have constant values which equal their value at the point P. Then we set the gradient of the curvature function to be equal with the gradient of the aforementioned replacement function at P. An isocurvature line of the normal gravity field passing through a point P is a curve such that the value of the function of the plumblines’ curvature k is constant and equals k(P). We give a formula to find the direction of the isocurvature line on the meridian plane and we prove that there are infinitely many isocurvature lines passing through the point P and they all lie on a special surface, the isocurvature surface.     

The Effects of the Earth’s Curvature on Gravity and Geoid Calculations

While it is obvious that large-scale gravity studies should account for the sphericity of the Earth, each case should be examined. If a geometry model is very large for the 3D-gravity calculation, it cannot be correctly defined in Cartesian coordinates. Because of the Earth’s curvature it is necessary to use spherical coordinates, the importance of which is shown in this paper. The calculation of the gravity for a cylinder reveals, 1 m above the center of the cylinder, a relative difference of 13% between the models with Cartesian and spherical coordinates.     

Interdependent perturbations of the Earth’s surface, atmosphere, and ionosphere

The results of original experiments performed with a ground-based geophysical laser interferometer and a GPS-based satellite ionospheric profilometer are given. Synchronous growth was recorded for deformations of the Earth’s surface and variations in the atmospheric pressure and in the level of spatiotemporal modifications of the electron content within the ionospheric F2 layer with characteristic space scales of 10²–10³ km and periods of 10²–10³ s. The relationship between the revealed phenomena and the Earth’s seismic activity is analyzed.     

The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6–12 April 1990

We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6–12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earths ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O⁺(⁴S) ions as a result of new high-temperature flowing afterglow measurements of the rate coefficients K₁ and K₂ for the reactions of O⁺(⁴S) with N₂ and O₂. The deviations from the Boltzmann distribution for the first five vibrational levels of O₂(v) were calculated, and the present study suggests that these deviations are not significant. It was found that the difference between the non-Boltzmann and Boltzmann distribution assumptions of O₂(v) and the difference between ion and neutral temperature can lead to an increase of up to about 3% or a decrease of up to about 4% of the calculated NmF2 as a result of a respective increase or a decrease in K₂. The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N₂(v > 0) and O₂(v > 0) in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N₂(v > 0) and O₂(v > 0). This could be due to possible uncertainties in model neutral temperature and densities, EUV fluxes, rate coefficients, and the flow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the flux of ionization above the station. Our calculations show that the increase in the O⁺ + N₂ rate factor due to N₂(v > 0) produces a 5–36% decrease in the calculated daytime peak density. The increase in the O⁺ + O₂ loss rate due to vibrationally excited O₂ produces 8–46% reductions in NmF2. The effects of vibrationally excited O₂ and N₂ on N_e and T_e are most pronounced during the daytime.     

Assessment of the possibility of using E. A. Ponomarev’s magnetospheric substorm model to analyze geomagnetic disturbances during the magnetic storms of December 14 and 15, 2006

Spatial distributions of pressure and fluxes of precipitating magnetospheric plasma particles were constructed for the strong magnetic storm of December 14 and 15, 2006. The calculations were performed using a model developed by E.A. Ponomarev. Geotail and ACE satellite data were used to specify realistic initial and boundary conditions. The model results were compared with the spatial distribution of the field of geomagnetic disturbances recorded by ground-based magnetic observatories during the storm. The results show that the model (in its current form) provides good agreement between latitudinal displacements of electron precipitations and auroral electrojets but fails to reflect their longitudinal structure. The model fails to yield the strong westward electrojet observed by all auroral zone observatories during the main phase of the magnetic storm.     

Effect of substorms in the Earth’s nightside sector on variations in the surface atmospheric electric field at polar and equatorial latitudes

We performed an analysis of mean daily variations in the ΔEz atmospheric electric field at the Hornsund (located near the polar cap boundary) and Kakioka (located at near-equatorial latitudes) observatories under magnetically quiet and weakly disturbed conditions. At both observatories, the mean daily variations in ΔEz were found to be mainly controlled by the location of the observation point with respect to the focuses of the convective vortices of the DP ₀ system. The substorm evolution in the nightside of the magnetosphere (a sharp burst in the AE index) was shown to lead to negative variations in ΔEz in the dayside sector at polar latitudes (the Hornsund observatory) and positive deviations in ΔEz at premidnight time at equatorial latitudes (the Kakioka observatory). It is concluded that variations in ΔEz at the Kakioka observatory are largely controlled by the equatorial electrojet, which is maximal during day-time hours, and at the Hornsund observatory these variations are controlled by the auroral electrojet, which is maximal at night-time and early morning hours of local time.