Search

Made available in DSpace on 2022-05-01T09:47:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-01 We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente (Brazil, magnetic latitude 12.8°S). The investigated ionospheric sector is ideal to study small-scale irregularities, being located close to the expected position of the southern crest of the equatorial ionospheric anomaly. The measurement campaign took place between September 2013 and February 2014, i.e. equinox and summer solstice seasons under solar maximum, during which the probability of formation of small-scale irregularities is expected to maximize. We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours. Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory (magnetic latitude 0.1°N), by the Boa Vista Ionosonde (magnetic latitude 12.0°N), and by applying a recently-developed empirical regional short-term forecasting model. Additionally, we investigated the relationship with the percentage occurrence of amplitude scintillation; we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it. Istituto Nazionale di Geofisica e Vulcanologia SpacEarth Technology Space Research Centre of the Polish Academy of Sciences Instituto Federal de Educação Ciência e Tecnologia de São Paulo Universidade Estadual Paulista “Júlio de Mesquita Filho” University of Salento Universidade Estadual Paulista “Júlio de Mesquita Filho”

The regular behavior of the electrodynamics of the low latitude ionosphere makes the scintillation on GNSS signals a daily phenomenon, occurring after the local sunset. The solar activity changes ionospheric conditions. In the specific, a solar storm hitting the Earth may change the ExB drift, leading to a suppression or to an intensification of the Equatorial Fountain. This result into a change in the mechanism regulating the formation of the plasma bubbles, and has strong dependence on the local time of the storm development. The regular and irregular behavior of the low latitude ionosphere in producing scintillation-effective irregularities pose then a challenge to model and predict the disruption of GNSS signals [1]. Mitigation of the degradation of the GNSS performance due to presence of ionospheric irregularities, i.e. the equatorial plasma bubbles, is of paramount importance for high-precision applications, such as precision agriculture.

Magnetospheric cusps are regions which are characterized by highly turbulent plasma. We have used Polar magnetic field data to study the structure of turbulence in the cusp region. The wavelet transform modulus maxima method (WTMM) has been applied to estimate the scaling exponent of the partition function and singularity spectra. Their features are similar to those found in the nonlinear multifractal systems. We have found that the scaling exponent does not allow one to conclude which intermittency model fits the experiment better. However, the singularity spectra reveal that different models can be ascribed to turbulence observed under various IMF conditions. For northward IMF conditions the turbulence is consistent with the multifractal p-model of fully developed fluid turbulence. For southward IMF experimental data agree with the model of non-fully developed Kolmogorov-like fluid turbulence.

We discuss mechanisms of the generation of ultralow frequency (ULF) upstream waves in the terrestrial foreshock that are essential for the acceleration of ions in space plasmas. The analysis is based on global hybrid kinetic simulations of the magnetosphere that provide realistic environment for the growth of the ULF waves in a quasi-radial configuration of the interplanetary magnetic field. We focus on a long-debated problem of the generation mechanism of oblique and parallel ULF waves and provide quantitative arguments in favor of the ion/ion cyclotron resonant instability. We also show that parallel propagating waves are predominantly generated in this configuration, but geometrical effects related to the phase space density in wave vector space lead to apparent predominance of obliquely propagating waves. Correspondence between the results outlined above and previously published experimental claims is thoroughly discussed and our results are shown to be consistent with spacecraft measurements.

We present a case study of ionospheric wave activity during solar terminator crossing using GPS TEC measurements. As a basic tool, the spatial gradient of total electron content (TEC) has been used. We tested with positive result the hypothesis on anisotropic response to assumed one-dimensional solar terminator forcing. The approximate drift velocity of irregularities has been computed. The wavelet analysis gave an interesting insight into variable frequency content of TEC gradient time series. We also proposed a filtering with respect to spatial scale allowing for resolving the spatio-temporal ambiguity.

We present a dispersion analysis of the phase of GPS signals received at high latitude. Basic theoretical aspects for spectral analysis of two-point measurement are given. To account for nonstationarity and statistical robustness a power distribution of the windowed Fourier transform cross-spectra as a function of frequency and phase is analysed using the Radon transform.

As a partial contribution to the International Polar Year, the Space Research Centre of the Polish Academy of Sciences has installed on the Polish Polar Station, located in the region of the Hornsund Bay in southern Spitsbergen, the equipment intended to monitor ionospheric scintillation and total electron content. We describe the equipment setup and the aims of the experiment. As an illustration of data analysis, we present the reconstruction of irregular structure of the ionosphere from the complex amplitude data, and the estimate of the form and drift of diffraction pattern based on the spaced receiver measurements.

Sharp increase of the Alfven speed above the ionosphere is expected to create a resonant cavity for the Alfven waves traveling along the geomagnetic field lines (so-called Ionospheric Alfven Resonator). The wavelet transform has been used to analyze magnetic and electric fields recorded on Freja satellite. Cross-phase spectra between field components in the frequency range 0.5–10 Hz reveal a pattern similar to that predicted theoretically for the resonator. The Fourier cross-phase spectra fail to show any characteristic features. We conclude that this is due to the spatial structure of the resonator which can be examined only with local analysis techniques.