Long-lasting disturbances in the mid-latitude sub-ionospheric VLF radio signals due to the super geomagnetic storm of 17 March 2015
TL;DR: In this article, the authors reported disturbance in the mid-latitude sub-ionospheric VLF radio signals due to the super geomagnetic storm which began on 17 March 2015.
Abstract: This paper reports disturbance in the mid-latitude sub-ionospheric VLF radio signals due to the super geomagnetic storm which began on 17 March 2015. Narrow-band signals from the NAA transmitter are studied for the storm period recorded at eight mid-latitude receiving stations spread over the Europe and USA. Daytime signals amplitude at all places showed a disturbing pattern after 17 March. Fluctuation in the nighttime signals significantly increased in the succeeding nights. As a primary effect of the storm, the entire diurnal signals in the transoceanic west to east long propagation paths enhanced by 3–5 dB, which gradually decreased over the period of ~ 10 days following the storm recovery. A different behavior was observed in the east to west short propagation paths over the landmass, where during the peak storm the daily variations of the VLF amplitude reduced to 20–25% of a normal day and, after ~ 10 days the signals returned to the pre-storm condition. Modeling of the radio waves in the west to east paths shows that the D-region electron density was increased by ~ 8-fold and varied up to 10 days. Electron density variations in the D-region closely follows the variations of precipitated electron flux as observed by the POES satellite over the region. The elevated electron density in the D-region ionosphere caused by the extension of the auroral precipitation to the mid-latitudes along with interference among the various waveguide modes in the earth-ionosphere waveguide during the storm is suggested for the cause of observed VLF signals behaviors.
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24 Jun 2022
TL;DR: In this paper , the rate of total electron content index (ROTI) parameter was incorporated into the EAS model to mitigate severe storm effects on GNSS PPP, which improved the PPP accuracy in 3D direction by approximately 12.9% to 14.7%.
Abstract: For global navigation satellite system (GNSS), ionospheric disturbances caused by the geomagnetic storm can reduce the accuracy and reliability of precision point positioning (PPP). At present, common stochastic models in GNSS PPP, such as the elevation angle stochastic (EAS) model or carrier‐to‐noise power‐density ratio ( C/N0 $C/{N}_{\mathit{0}}$ ) based SIGMA‐ ε $\varepsilon $ model, do not properly consider storm effects on GNSS measurements. To mitigate severe storm effects on GNSS PPP, this study further implements the rate of total electron content index (ROTI) parameter into the EAS model referred to as the EAS‐ROTI model. This model contains two operations. The first one is to adjust variance of GNSS measurements using ROTI observations on EAS model. The second one is to determine the ratio of the priori variance factor between pseudorange and carrier phase measurements during severe storm conditions. The performance of EAS‐ROTI model is verified by using a large number of international GNSS service stations datasets on 17 March and 23 June in 2015. Experimental results indicate that on a global scale, the EAS‐ROTI model improves the PPP accuracy in 3D direction by approximately 12.9%–14.7% compared with the EAS model, and by about 24.8%–45.9% compared with the SIGMA‐ ε $\varepsilon $ model.
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TL;DR: In this paper , the first report of global ionospheric disturbances due to the most powerful Gamma Ray Burst GRB221009A occurred on 9 October 2022, and both daytime and nighttime effects were analyzed in VLF and LF bands.
Abstract: We present the first report of global ionospheric disturbances due to the most powerful Gamma Ray Burst GRB221009A occurred on 9 October 2022. Very Low Frequency (VLF) and Low Frequency (LF) sub-ionospheric radio signals are used to diagnose the effect of the GRB on the lower ionosphere. Both daytime and nighttime effects are analyzed in VLF and LF bands. The magnitude of VLF signal perturbations varied with the propagation condition (day/night), path length, and frequency of the signal. The recovery times for the VLF/LF signals to get back to their pre-GRB levels varied from 2–60 min. Radio signals reflected from the E-region ionosphere for nighttime VLF signals and daytime LF signals showed greater effects compared to the daytime VLF signals reflected from the lower parts of the D-region.
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TL;DR: In this paper, the proper interpretation of irregular motions in the upper atmosphere has been investigated by a variety of techniques, but their proper interpretation has yet to be established. But their proper meaning has not yet been established.
Abstract: Irregularities and irregular motions in the upper atmosphere have been detected and studied by a variety of techniques during recent years, but their proper interpretation has yet to be established...
1,886 citations
TL;DR: A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented in this paper.
Abstract: A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented. Some recent experimental studies of AGW's using the Chatanika incoherent scatter radar and other geophysical sensors are reported. Specifically, the following features are described in detail: (1) cause/effect relations between aurorally generated AGW's and TID's detected at mid-latitudes, including probable ‘source signature’ identification, (2) AGW source phenomenology, particularly a semiquantitative assessment of the relative importance of Joule heating, Lorentz forces, intense particle precipitation, and other mechanisms in generating AGW's, and (3) detection of TID's in the auroral ionosphere. Several instances of F region electron density, temperature, and plasma periodicities accompanied by horizontal plasma velocities which were consistent with theoretical AGW/TID models are documented.
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06 Oct 2018
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TL;DR: In this article, a brief overview of effects on the ionosphere of upward propagating waves from lower-lying regions is given, separately for the lower ionosphere, for the E-region ionosphere.
Abstract: Meteorological processes in the lower-lying layers, particularly in the troposphere, affect the ionosphere predominantly through the upward propagating waves and their modifications and modulations. Those waves are planetary waves, tidal waves, gravity waves, and almost forgotten infrasonic waves. A part of wave activity can be created in situ at ionospheric heights as primary (e.g., diurnal tide, gravity waves) or secondary waves (e.g., some gravity or planetary waves), but this paper is focused on the upward propagating waves from below the ionosphere. They propagate into the ionosphere mostly directly but the planetary waves can propagate upwards to the F region heights only indirectly, via various potential ways like modulation of the upward propagating tides. The waves may be altered during upward propagation via non-linear interactions, particularly in the MLT region. A brief overview of effects on the ionosphere of upward propagating waves from lower-lying regions is given, separately for the lower ionosphere, for the E-region ionosphere, and for the F-region ionosphere. The upward propagating waves of the neutral atmosphere origin are important both from the point of view of vertical coupling in the atmosphere–ionosphere system, and for applications in radio propagation/telecommunications, as they are responsible for a significant part of uncertainty of the radio wave propagation condition predictions.
333 citations
TL;DR: In this paper, the authors examined large-scale gravity waves in the thermosphere and their ability to transfer energy from high to low latitudes during magnetic disturbances, assuming that the gravity wave source is either the Lorentz force of auroral electrojet currents or a heat input due to energetic particle precipitation or to Joule heating.
Abstract: This is the first in a series of papers examining large-scale gravity waves in the thermosphere and their ability to transfer energy from high to low latitudes during magnetic disturbances. The gravity wave source is assumed to be either the Lorentz force of auroral electrojet currents or else a heat input due to energetic particle precipitation or to Joule heating. It is pointed out that the characteristic vertical width of the gravity wave source should usually lie between 2 and 4 pressure scale heights, placing constraints on the vertical wavelengths and horizontal velocities of the generated waves. A simplified analytic model of small-amplitude wave generation by a current source shows how wave energy production depends on the temporal and spatial dimensions of the source, on the electric field strength, and on the electron density enhancement. The steep thermospheric temperature gradient in the vicinity of the source altitude strongly influences the properties of upward and downward propagating waves compared with waves generated in an isothermal atmosphere. Waves produced by the Lorentz force of Hall currents, by the Lorentz force of Pedersen currents, and by Joule heating are influenced quite differently by this temperature gradient. Because upgoing waves above the source are combinations of waves originally launched upward and waves originally launched downward but reflected around 110 km altitude, the mean effective source altitude is about 110 km for the far field response in the thermosphere. Large-scale traveling ionospheric disturbances observable at middle latitudes are most likely produced primarily by Pedersen, rather than Hall, currents. The temperature structure of the thermosphere generally causes gravity wave packets to refract upward; waves traveling with a horizontal component of velocity faster than 250 m/s and with an initial downward component of group velocity will always be reflected upward in the lower thermosphere. The effects of viscosity, heat conduction, and Joule dissipation tend to filter out shorter-period and slower moving waves from observation points at some distance from the source, so that only long-period fast moving waves can reach low latitudes from an auroral source. For example, a wave with a 94-min period moving horizontally at 605 m/s is largely dissipated by the time it has traveled 4000 km from a typical auroral source. A numerical simulation using a fairly realistic thermospheric model illustrates many of the points described from analytic considerations.
261 citations