Geomagnetism and Aeronomy

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Future Inversion of the Magnetic Field and Possible Changes in the Structure of the Magnetosphere

Wed, 05/01/2019 - 00:00
Abstract

IGRF-12 model data have been used to analyze the change in the global structure of internal sources of the Earth’s magnetic field. A decrease in the dipole magnetic moment is accompanied by a rapid growth of multipole moments. This justifies the theoretical model of the magnetic field inversion as a gradual decrease in the dipole field with general conservation of its direction and amplification of multipole moments. Paleo- and archeomagnetic data indicate that this process has already been taking place for almost 2.5 thousand years and has occurred repeatedly many times in the past. A decrease in the dipole magnetic moment leads the magnetopause to approach the Earth to disappear completely in almost 1.5 thousand years.

Regression Derivatives and Their Application to the Study of Geomagnetic Jerks

Wed, 05/01/2019 - 00:00
Abstract

New mathematical constructions are developed for the regression smoothing of discrete time series defined on an irregular grid. The new method is used to study secular trends for the period 1991–2015 and relies on observations of three components of the magnetic field at five geomagnetic observatories of the INTERMAGNET network. The detected changes in the trend coincided in time with the jerk properties calculated by conventional methods, which indicates the applicability of the method of regression derivatives to geophysical problems.

Influence of Substorm Activity on the Formation of Ultra Low Frequency Noise Emissions in the Frequency Range of 0–7 Hz

Wed, 05/01/2019 - 00:00
Abstract

The results of the study of simultaneous observations of midlatitude ultra low frequency (ULF) noise emissions in the frequency range of 0–7 Hz and disturbances in the night sector of an auroral oval are presented. Data from observations of the magnetic field at the midlatitude Borok Observatory (L = 2.8) and 1-min data of the AL index are used for the analysis. It is shown that two kinds of ULF noise emission are observed simultaneously in the hertz range primarily in the summer season: one looks like a diffuse spot, and the other one is characterized by the occurrence of spectral resonance structures determined by the influence of the ionospheric Alfvén resonator. Diffuse spots are recorded mostly in the evening sector of the magnetosphere, and they precede the observation of spectral resonance structures, which are detected primarily at about midnight. Comparison of the observation intervals for diffuse spots with the dynamics of the AL index showed that diffuse spots form during substorm activity on the night side of the Earth in 80% of cases. It is established that the interval between the onset of substorm disturbances and the onset of the observation of diffuse spots is ∼60 min in most cases. It is assumed that the formation of diffuse spots is related to characteristics of the dynamics of protons injected from the magnetospheric tail in substorms and to the appearance of plasmaspheric plumes in the evening sector.

Dynamics of the Plasma Bunch at the Initial and Following Stages of Motion in a Rarefied Gas

Wed, 05/01/2019 - 00:00
Abstract

Physical and comprehensive numerical studies of the generation of plasma bunches with a high specific energy have been carried out with the use of a plasma gun. The parameters of the plasma bunch upon exit from the plasma accelerator and during propagation in the ionosphere (h > 200 km) to considerable distances (≈100 km) have been calculated. A special numerical algorithm is presented to determine the results of the impact of a rarefied high-velocity gas flow ( \({v}\) ∼ 5 × 107 cm/s) on the surface of crystalline and amorphous solid bodies.

Unusual Рс 1 Geomagnetic Pulsations in September 2017

Wed, 05/01/2019 - 00:00
Abstract

The results of analysis an unusual event in the frequency range of Pc1 geomagnetic pulsations discovered at the end of solar cycle 24 are presented. This event was recorded on September 11, 2017, at the late phase of the strong magnetic storm recovery that occurred on September 7‒8, 2017. The dynamic spectrum of pulsations was a cascade of short “jumping” series of “pearls” with decreasing central frequency. On the Earth’s surface, 1 pulsations were observed in the early morning sector with similar complex dynamic spectra simultaneously in a wide range of latitudes, from middle to auroral. In the Scandinavian profile of induction magnetometers, the greatest amplitude of Рс1 pulsations was recorded at the lowest-latitude observatory of the profile at NUR (L = 3.3). The analytical expressions enabling an explanation of the changes in central frequency and width of spectrum of Рс1 pulsations are presented. It is shown that the decrease in central spectrum frequency of Рс1 pulsations from 2.5 Hz to 1.1 Hz can be a result of linear displacement of the plasmapause from L ~ 3.3 to L ~ 4.2. An interpretation based on the linear process of EMIC-wave decomposition into a lower frequency EMIC wave and an ion sound is proposed.

Atmospheric Emission Layers according to Photographic Observations from the International Space Station

Wed, 05/01/2019 - 00:00
Abstract

Photographic and video observations made by astronaut Thomas Pesquet (European Space Agency) during the 51st expedition to the International Space Station (ISS) contain a series of color images of the emission and scattering layers of the Earth’s atmosphere under night and twilight conditions. The stars of various constellations can be clearly seen in the atmosphere images above the limb of the Earth. This makes it possible to accurately determine the geometric parameters of the emission layers and the conditions of their illumination by the Sun. A model is proposed to explain the blue glow of the thin atmospheric layer near the horizon resulting from the Rayleigh scattering of sunlight in the lower layers of the atmosphere.

Bursts of Auroral-Hiss VLF Emissions on the Earth’s Surface at L ~ 5.5 and Geomagnetic Disturbances

Wed, 05/01/2019 - 00:00
Abstract

We have studied the geomagnetic conditions during the occurrence of auroral-hiss VLF emissions on the Earth’s surface in the form of noise bursts at frequencies above 5–6 kHz. The study is based on an analysis of auroral-hiss observations at auroral latitudes in northern Finland at Kannuslehto station (KAN, L ~ 5.5) during the winter campaigns of 2013–2018. It is shown that auroral-hiss bursts are most often observed in the interval of 20–01 MLT under low geomagnetic activity (Kp < 3). It has been found that the bursts are typical for the growth phase of a magnetospheric substorm; the bursts cease abruptly at the onset of the substorm (the break-up of auroras), which is apparently due to a drastic increase in the absorption of VLF waves in the ionosphere. The bursts are often accompanied by the generation of geomagnetic Pi2 pulsations. VLF observations have shown that auroral-hiss bursts are not observed on the Earth’s surface in the main phase of magnetic storms; however, they are typical of the recovery phase. It has been found from model data that, during the occurrence of auroral hiss, KAN station is usually projected to the near-equatorial region of the auroral oval or to the zone of diffuse precipitation of more energetic electrons, i.e., to lower latitudes than the typical position of visible auroras during that time.

Effect of Anisotropy of Ionospheric Inhomogeneities in the Detection of Faults in Phase GNSS Measurements

Wed, 05/01/2019 - 00:00
Abstract

Phase and amplitude fluctuations (scintillations) are recorded when a signal of the global navigation satellite system (GNSS) passes through the anisotropic, randomly inhomogeneous ionosphere. In this case, the Earth’s magnetic field exerts a double effect, not only on the refractive index of the ionospheric plasma but also on the shape of ionospheric inhomogeneities, which determines their “elongation” along the lines of force. This is observed in the spatiotemporal distribution of measurement faults related to the phase scintillations. It was shown earlier that the density of faults in tracking the GPS carrier phase depends on the angle between the satellite-receiver beam and magnetic field direction at the altitude of the ionosphere under disturbed conditions. In this work, these studies are also compared to measurements in calm environments and research on the aspect dependences of GPS fault densities. In addition, the performed numerical simulation of the effect of anisotropy of ionospheric inhomogeneities showed good agreement with the experimental data and made it possible to determine the factors masking the effects of anisotropy.

Possible Generation of Quasi-Periodic Magnetic Precursors of Earthquakes

Wed, 05/01/2019 - 00:00
Abstract

A mechanism for the generation of quasi-periodic magnetic precursors of earthquakes is proposed on the basis of air heating above an impending earthquake, the rise of heated “bubbles,” the generation of acoustic–gravity waves (AGWs), the modulation of AGWs of the ionospheric current jet, and the generation of quasi-periodic oscillations of the geomagnetic field. According to estimates, the amplitude of a magnetic precursor can vary from 0.1 to 1 nT in the range of oscillation periods of ~10–1000 s.

Hertz Range Pulsations during Recovery Phase of the Magnetic Storm on September 7–8, 2017, and Relation between their Dynamics and Changes in the Parameters of the Interplanetary Medium

Wed, 05/01/2019 - 00:00
Abstract

The shape and dynamics of an unusual disturbance in the Pc1 geomagnetic pulsation range recorded by ground-based induction magnetometers during the morning hours (03–06 MLT) on September 11, 2017, in the late recovery phase of a strong magnetic storm were analyzed in the context of changes in the parameters of the interplanetary medium. Pulsations were observed in the auroral and subauroral zones, as well as at midlatitudes, and had a complex structure in the form of multiplet “pearls” (1–1.5 Hz range) and two series of narrow-band bursts (2–3 Hz range) with a repetition period of ~5 and ~20 min. Pulsations in the form of a series of bursts are a rare event and are recorded mainly during the daytime hours. Comparison of the dynamics of Pc1 pulsations with the parameters of the interplanetary medium was carried out with data from the DSCOVR and THEMIS satellites. A change in the carrier frequency and intensity of multiplet pearls was a response to a jump in the plasma density of the solar wind. A series of bursts with a period of ~5 min could be initiated by a simultaneous increase in the solar-wind velocity and the By-component of the interplanetary magnetic field, which was observed ~40 min after the density jump. We associate bursts with a period of ~20 min either with the response of the magnetosphere to the short-term excursion of the daytime magnetopause to the Earth or with oscillations of a close period in the transition region ahead of the front of the density perturbation. The frequency, period, and amplitude of the pulsations are estimated.

A Model of Fluxes of Solar Extreme Ultraviolet Irradiance

Wed, 05/01/2019 - 00:00
Abstract

We develop an approach to create a model of the solar extreme ultraviolet spectrum in the wavelength range responsible for dissociation of molecular oxygen (115−242 nm). The model is based on the concept of the linear dependence of irradiance fluxes in intervals 1 nm in width on the intensity in the Lyman-alpha hydrogen line (this line is supposed to be measured by photometers of the extreme ultraviolet irradiance onboard space probes). The linear dependence coefficients were obtained for each of these intervals. Comparison of the model calculation results with observations showed that the model inaccuracy does not exceed 1−2%, which is sufficient for calculations of the thermospheric state.

Influence of Total Solar Irradiance on the Earth’s Climate

Wed, 05/01/2019 - 00:00
Abstract

The results of analysis of variations in the total solar irradiance in the 17–24th solar activity cycles and their relation to the climate global warming are presented. The influence of galactic cosmic rays and volcanic activity on the climate is considered. It is shown that the Earth’s temperature varied in the 17–20th cycles according to the behavior of solar activity without any observed trend: the temperature increased with an increase in solar activity and decreased in solar minima. Global warming began in 1976 in the 21st solar activity cycle. In light of the observed trend, the changes in the Earth’s global temperature in the 21–24th solar activity cycles were related to the cyclical variation of the total solar irradiance in the same way as in the 17–20th cycles. By changing the atmospheric transparency on the background of reductions of the total solar irradiance, galactic cosmic rays also contributed to the increase in the temperature minima. Strong volcanic eruptions were accompanied by 1- to 2-year annual decreases in the temperature, which did not disturb the cyclical process of changes in the Earth’s climate. In the absence of trends in the cosmophysical factors influencing the climate, the process of the gradual increase in the global mean temperature of the Earth in the 21–24th solar activity cycles is explained by the anthropogenic factor.

Wind Preparation of the Generation of Equatorial Plasma “Bubbles”

Wed, 05/01/2019 - 00:00
Abstract

According to theoretical conclusions, zonal western thermospheric winds are the key influence on the generation of equatorial plasma “bubbles.” To verify this assumption, a comparative analysis of the longitudinal distribution of equatorial plasma bubbles and the longitudinal profile of deviations of the zonal western thermospheric wind velocity has been carried out. The data on plasma bubbles (from the ISS-b satellite, ~1100 km) averaged over two hemispheres during the spring equinox were analyzed. The wind characteristics used in the study (the CHAMP satellite, ~400 km) were taken as the median values over the equinox period in the interval (15–21 LT) covering the preparation time and the generation period of equatorial plasma bubbles. It was found that these characteristics are very similar with a high degree of correlation (R ≅ 0.76). It has been newly confirmed that the theoretical statement (Kudeki model) on the key influence of zonal western thermospheric winds on the generation of equatorial plasma bubbles.

Role of Averaging in Statistical Analysis of Solar Wind Data from the DSCOVR Spacecraft for the First Year of Operation

Wed, 05/01/2019 - 00:00
Abstract

The results from a statistical analysis of solar wind data obtained near the Earth’s orbit by the DSCOVR spacecraft for the period of one year starting August 2016 are discussed. The distribution of the solar wind temperature T for this period was bimodal and exhibited two maxima at 15 × 103 and 190 × 103 K (with a standard deviation of the same order of magnitude, respectively). This distribution can be represented as the sum of two lognormal distributions. The first peak of the T distribution is caused by the slow-cold wind component, the distributions of which over speed V and density n (varying in wide ranges) are also close to lognormal. This component covers slightly more than a quarter of the entire time period. A fast hot wind (the distribution maximum is at 310 × 103 K) can be distinguished from the remainder; this component covers slightly less than a quarter of the period. Its T, V, and n distributions are also close to lognormal. The rest the wind, nearly half, exhibits a complex “jagged” distribution over speed and a double-peak distribution over density. The conclusion is that data averaging is of key importance in the classification of solar wind at the quantitative level. This is shown by the results of data averaging over a minute, hour, day, and week.

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