Analysis of the Variability of Diurnal Profiles of Critical foF2 Frequencies in the Light of Solar Radiation

Effect of geomagnetic storms on the daytime low-latitude thermospheric wave dynamics

The paper discusses on the variations of the atmospheric vertical electric field measured at sub-auroral station Maitri (70∘75′S, 11∘75′E), and polar station Vostok (78.5∘S, 107∘E) during the geomagnetic disturbances on 25–26 January 2006. Diurnal variation of surface electric field measured at Maitri shows a similar variation with worldwide thunderstorm activity, whereas the departure of the field is observed during disturbed periods. This part of the field corresponds to the magnetospheric/ionospheric (an additional generator in the polar regions) voltage generators. Solar wind parameters and planetary indices represent the temporal variation of the disturbances, and digital fluxgate magnetometer variation continuously monitored to trace the auroral movement at Maitri. We have observed that the electrojet movement leaves its signature on vertical and horizontal components of the DFM in addition; the study infers the position of auroral current wedge with respect to Maitri. To exhibit the auroral oval, OVATION model is obtained with the aid of DMSP satellite and UV measurements. It is noted that the Maitri is almost within the auroral oval during the periods of disturbances. To examine the simultaneous changes in the vertical electric field associated with this magnetic disturbance, the dawn–dusk potential is studied for every UT hours; the potential was obtained from Weimer model and SuperDARN radar. The comparison reveals the plausible situation for the superposition of dawn–dusk potential on surface electric field over Maitri. This observation also shows that the superposition may not be consistent with the phase of the electrojet. Comparison of surface electric field at Maitri and Vostok shows that the parallel variation exhibits with each other, but during the period of geomagnetic disturbances, the influence is not much discerned at Vostok.

The article recommended the method of protection of power transformer from the influence of geomagnetically induced currents, by launching the resistive grounding mode at the period of geomagnetic disturbances and reversion to the solid-grounded mode on completing of geomagnetic disturbances. The article shows that for the identification of single-side saturation of the magnetic system of power transformer at the periods of geomagnetic disturbances could be used registration of simultaneous appearance of 6th harmonic and DC component of the magnetizing current in the neutral of power transformer.

[1] The vertical component of the ion velocity measured with the European Incoherent Scatter (EISCAT) Tromsø UHF radar (69.6°N, 19.2°E) in the lower ionosphere (from 95 to 130 km) was found to be characterized by notably large variances at oscillation periods of 2–8 min. Of particular interest was the geomagnetic activity dependence above ∼106 km, which showed larger variances (100–500 m2 s−2) during periods of geomagnetic disturbance than during quiet periods. Below 106 km, the variance was less sensitive to the geomagnetic activity. Height profiles of the variance during the disturbed period showed steep increases with heights above 106 km, then reaching a peak at 120 km, where the ion gyrofrequency is equal to the modeled ion-neutral collision frequency. A theoretical prediction well reproduced the height profile for the geomagnetically disturbed period by assuming oscillations in the meridional component of the electric field. The theoretical study suggested that the electric field oscillation is a possible cause of large variances of the vertical ion speed in the polar lower ionosphere. However, below 106 km, other mechanisms were necessary.

We present first results from a study of the plasma instability mechanism responsible for the small-scale (∼10 m) ionospheric density irregularities commonly observed by the Super Dual Auroral Radar Network (SuperDARN) HF radars in the vicinity of Sub Auroral Polarization Streams (SAPS) during periods of geomagnetic disturbance. A focus is placed on the mid-latitude region of the ionosphere over North America where recent expansion of the SuperDARN network allows for extensive direct comparisons with total electron content (TEC) measurements from a dense network of ground-based GPS receivers. The TEC observations indicate that high-speed SAPS channels and the associated small-scale irregularities are typically located within the mid-latitude ionospheric trough. The Millstone Hill Incoherent Scatter Radar (ISR), operating in campaign mode in support of the NASA Van Allen Probes mission, provided measurements of F region ion/electron density, velocity, and temperature suitable for identifying potential mechanisms of plasma instability during a SAPS event that extended over 12 hours of magnetic local time (MLT) on 2 February 2013. Previous work has indicated that the density gradients associated with the poleward wall of the mid-latitude trough can produce small-scale irregularities due to the gradient drift instability during quiet periods by cascade from larger-scale structures. In this study we demonstrate that the gradient drift instability is a viable source for the direct generation of the small-scale irregularities observed by SuperDARN radars in the mid-latitude ionosphere during geomagnetically disturbed conditions.

Es layer and dynamics of neutral atmosphere during the periods of geomagnetic disturbances

[1] Results of the experimental studies of features of HF signals propagation during the period of geomagnetic disturbances at oblique sounding paths in the Eurasian longitudinal sector from England to Magadan are presented. Joint analysis of the vertical and oblique sounding of the ionosphere and satellite data showed that appearance of additional signals during magnetic disturbances can be due to the refraction of radio waves in the region of the auroral oval and the main ionosphere trough and also to the scatter on small-scale field-aligned irregularities in the vicinity of the equatorial boundary of the auroral oval. On the basis of calculations and comparison to the experimental data of the oblique sounding of the midlatitude ionosphere, the side spread signals recorded at Inskip (England) to Rostov on Don path are identified as signals scattered at small-scale field-aligned irregularities, their location positioning to the southern boundary of the auroral oval. The perspective of use of the Russian and global network of linearly frequency modulated ionosondes for studying the dynamics of the midlatitude ionospheric trough and auroral oval in the Eurasian longitudinal sector poorly equipped by observational means during magnetic disturbances is described.

In this paper, the correlation of the Earth’s Radiation Belts electron doses in low near-Earth orbit behind a small shield with the average indicators of the Earth’s magnetosphere state during periods of geomagnetic disturbances is shown and analyzed. The results of the “Expose-R2” experiment on the ISS and “DEPRON” on the “Lomonosov” satellite (SINP MSU) are considered. In the “Expose-R2” experiment on the ISS, the absorbed dose behind the shield at 0.6 g cm was measured every 10 seconds. In the “DEPRON” experiment, the absorbed dose behind the shield at 0.45 g cm and 0.81 g cm was measured every second. Due to a large number of measurement gaps in the “DEPRON” experiment, a procedure for restoring the experimental data is proposed. Based on the data obtained, correlations between the average daily absorbed dose rate and various cosmophysical indices in fixed ranges of -coordinate variations (the McIlwain parameter, at the geomagnetic equator equal to the distance to the Earth’s center in Earth radii) are considered. It is shown that after geomagnetic disturbances, the linear regression coefficients between the absorbed dose rate and the considered geophysical indices have a uniform dependence on the -coordinate. For magnetic storms with < 100 nT, the dependences of the linear regression coefficients on the -coordinate are well approximated by a normal distribution up to = 4.7. The average value of the maximum position = 4.10 ± 0.15, standard deviation σ = 0.40 ± 0.07. For magnetic storms with > 100 nT, the distribution maximum shifts to = 3.0 and σ = 0.22.

Observations of the reduction in the available HF band on four high latitude paths during periods of geomagnetic disturbance

We present observations from the Falkland Islands Super Dual Auroral Radar Network radar of the propagation of HF radio waves via the Weddell Sea Ionospheric Anomaly (WSA), a region of enhanced austral summer nighttime ionospheric electron densities covering the southern Pacific and South Americas region. This anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorward thermospheric winds. Of particular interest are perturbations of the WSA‐supported propagation, which suggest that during periods of geomagnetic disturbance, the ionospheric layer can be lowered by several tens of kilometers and subsequently recover over a period of 1 to 2 h. Perturbations can appear singly or as a train of two to three events. We discuss possible causes of the perturbations and conclude that they are associated with equatorward propagating large‐scale atmospheric waves produced by magnetospheric energy deposition in the auroral or subauroral ionosphere. Changes in high/middle latitude electrodynamics during geomagnetic storms may also account for the perturbations, but further modeling is required to fully understand their cause.

Since 2022, the Institute of Cosmophysical Research and Aeronomy (SB RAS) for the first time has been continuously monitoring the forecast of terrestrial winds of space weather based on data from neutron monitors in Yakutsk and Tiksi. Preliminary studies during periods of geomagnetic disturbances in 2022. The peculiarity is that the results of this may provide an additional opportunity for their use for the purpose of forecasting large geomagnetic storms.

A bistatic 50‐MHz CW radar was used to simultaneously observe the horizontal components of E region auroral drift motions and the underlying D region meteor trail drift motions over northern Saskatchewan (L ∼ 6.5). About 1800 meteor trail echoes were analyzed over 5 separate days, 3 of which were geomagnetically quiet and 2 of which were disturbed. For the quiet days, the observed meteor trail drifts were consistent with the normal D region motions observed at these latitudes. For the disturbed days, however, the meteor trail drifts near local midnight were much larger than normal, were predominantly southward and were well correlated with the E region auroral drifts measured at some 10 km higher altitude. This suggests that meteor trail drift motions may not be representative of the neutral medium motions at auroral latitudes during periods of geomagnetic disturbance.

The paper presents results of experimental estimation of space-time correlation radii of absolute errors in determination of rectangular geocentric coordinates of users of satellite radio-navigation systems under various geophysical conditions. During magnetic storms, the radius of spatial correlation of errors of coordinates’ determination decreases roughly by a factor of 1.3 against the calm (non-perturbed) conditions. The radius of time correlation of errors under calm conditions is roughly 1.5 times larger than in the periods of geomagnetic disturbance. The paper illustrates a possibility for implementation of wide-area augmentation systems of satellite navigation based on the already existing worldwide network of GPS stations.

The present study demonstrates the feasibility of using plasma and magnetic field data from Defense Meteorological Satellite Program (DMSP) satellites to estimate the Alfvénic reflectances (α) in the polar cap ionosphere during periods of geomagnetic disturbance. Quantitative values of α are then used to support calculations of field‐aligned Poynting flux (S||i) transmitted along open field lines from magnetosheath generators to the conjugate polar ionospheres. Analyzed data were acquired during high‐latitude passes of DMSP F16 during the 17 March 2013 magnetic storm. Between the main phase onset and the day's end, plasma velocity and magnetic field perturbations manifest the phase relations predicted by Alfvén and Fälthammar (1963) for electromagnetic coupling. The most reliable (sunward‐antisunward) components of measured plasma velocities and magnetic perturbations are consistent with that α ranging between 0.65 and 0.97, with a mean of ~0.8. Subsequent calculations indicate that incident S||i varied between 0.2 and 0.02 W/m2 with a mean of 0.085. We suggest that these reported ranges of α and S||i reflect both large variations in IMF BZ and the growth of antisunward neutral winds in the polar caps during the storm's main phase.

Abstract. Ionospheric storms showing a strong depression in daytime foF2 values were sought which penetrated to low-latitudes, as identified by vertical ionosondes operating at Darwin and Townsville over the period 1992-1998. The 32 storms thus identified showed a seasonal occurrence peaking near the equinoxes with a bias to the summer side. Of these storms, three (27 March 1995, 25 October 1997, 8 November 1997) combined Australian and South East Asian ionosonde observations with local afternoon TOPEX/Poseidon measurements of TEC. The equatorial anomaly is usually well developed at this time of day and consequently these storms were chosen for detailed study. The TOPEX/Poseidon satellite provided vertical profiles of the ionosphere across both hemispheres, thus allowing the totality of storm behaviour to be observed for the first time at low-latitudes and related directly to the ionosonde observations. The three storms were remarkably consistent in their behaviour, the negative ionospheric storm day followed some 24-36h after the beginning of a magnetic storm and the development of the equatorial anomaly was suppressed. However, the suppression of the equatorial anomaly was not the main cause of the strong depression in foF2 observed by the Southern Hemisphere ionosondes. The latter was associated with an additional bite-out in both TEC and foF2 that occurred on the southern side of the magnetic equator. None of the three storms produced any major negative disturbance outside the range of normal variability of TEC and foF2 at the northern latitude sites for which data was available, despite the absence of the anomaly. The satellite measurements show the strength of the anomaly to be highly variable from day-to-day and anomaly peaks are frequently not present even on magnetically quiet days. Thus, an absence of anomaly peaks is contained within the normal variability of non-storm days. The north-south asymmetry and seasonal occurrence are consistent with an enhancement of the normal summer-to-winter system carrying compositional changes induced by energy inputs at auroral latitudes to equatorial latitudes not usually reached. The ability of associated atmospheric and/or electric field changes to coincidentally switch off the equatorial E region electrojet remains to be explained, as indeed does the large range of variability in equatorial anomaly development from day-to-day evident in the TEC measurements outside periods of geomagnetic disturbance. Some possible positive storm effects occurring on the day preceding the negative storm phase are also noted.