Weak Magnetic Storm Research Articles

Investigation of the influence of space weather on the occurrence of geoinduction currents in the middle latitudes

The study of physical processes based on geomagnetic induction currents among the geophysical problems of the last decade is one of the main problems of fundamental research. Consideration of geomagnetic-induced current as a threatening "shock" aspect originally took place in the NASA project "life with a star", and one of the main results of this working group was that the problems of geomagnetic-induced current must be solved in combination with science and methods. In the proposed work, calculations were carried out using a model of the same type, the model of which is based on the fundamental laws. The retrospective analysis of the geophysical situation for 2016-2021 was carried out on the basis of the data of the Alma-Ata geomagnetic observatory. For all the considered events, the GIC values were calculated and the peculiarities of the occurrence of GIC at middle latitudes were studied. Of all the events studied for 2016-2021, 25 events were identified. Among these events: 1 large geomatnetic storm, 1 medium geomagnetic storm, 5 substorms and 18 weak geomagnetic storms. For these events, the following was identified. During a large geomagnetic storm, the GIC amplitude value was I=0.4mA. During an average magnetic storm I=0.14mA. During a storm with a sudden onset induced current amplitude I=0.75mA. During weak magnetic storms, the amplitude values varied within (0.06 - 0.15)mA. In general, it can be seen, that the GIC amplitude values depend on the intensity of the geomagnetic storm. However, there are some exceptions. For example, a storm with a sudden onset according to the planetary index refers to weak geomagnetic storms, however, the GIC value turned out to be greater than the GIC induced during a large geomagnetic storm. At the same time, we also considered substorms. During substorms, currents of the order of 0.07-0.13mA were induced.

Observation of Scintillation Enhancements and Large‐Scale Structures Within the Equatorial Ionization Anomaly During a Sudden Stratospheric Warming Event

AbstractTotal electron content (TEC) and L‐band scintillations measured by several networks of GPS and GNSS receivers that operate in South and Central America and the Caribbean region are used to observe the morphology of the equatorial ionization anomaly (EIA), examine the evolution of plasma bubbles, and investigate the enhancement of L‐band scintillations that occurred on February 12 and 13, 2016. A few weak and short magnetic storms developed these days, and a minor sudden stratospheric warming (SSW) event was initiated a few days before. During these unusual conditions, TEC maps reported a split of the otherwise continuous crests of the EIA and the formation of a large‐scale (thousands of kilometers) almost‐circular structure. The western part of the southern crest faded, and a north‐south aligned segment developed near the center of the South American continent, joining the north and south crests of the EIA, forming an anomaly that resembled a closed loop on the eastern side of the continent. Concurrently with the anomaly events, several GPS stations reported increases in the L‐band scintillation index from 0.4 to values greater than 1. We analyzed TEC values from receivers between ±6° from the magnetic equator to identify and follow TEC depletions associated with plasma bubbles when they reach different stations. Although the magnetic activity was moderate (Kp = 3°), we believe that the anomaly redistribution and the scintillation enhancements are not related to a prompt penetration electric field but to enhancing the semidiurnal lunar tide propitiated by the onset of the minor SSW event. We found that depending on the lunar tide phase cycle, the neutral wind's meridional component can augment sub‐km scale irregularities and enhance L‐band scintillations through the wind gradient instability when U·n < 0 or the action of wind gradients (U) within the bubbles. Our observations imply that the SSW event enables prominent changes in the thermosphere wind system at F‐region altitudes.

Physical effects of geocosmic storms. Part 3

A review of the results of observing the effects of the most interesting ionospheric and magnetic storms that took place in 2018–2019 is presented. Ionospheric and magnetic storms are considered as components of geocosmic storms. In accordance with the systemic paradigm of L.F. Chernogor, a geocosmic storm is a complex of processes caused by a solar storm, reduced to synergistically interacting storms in a magnetic field (magnetic storm), ionosphere (ionospheric storm), atmosphere (atmospheric storm) and electric field atmospheric-ionospheric-magnetospheric origin (electric storm). Using the analysis of specific magnetic and ionospheric storms as an example, it is shown that, in addition to general patterns, each storm has its own individual characteristics. The expediency of a comprehensive study of the manifestations of each new geocosmic storm has been confirmed. A wide variety of ionospheric and magnetic storms have been confirmed. A weak magnetic storm is not necessarily accompanied by a weak ionospheric storm, while a strong one is accompanied by a strong one. An ionospheric storm can be single-phase (positive or negative) or multi-phase, when the phases alternate. Storms can last from several hours to many days. Storms are accompanied by both aperiodic and quasi-periodic variations. The latter are caused by atmospheric gravity waves (periods 10–180 min) and infrasound (period less than 5 min). Of all the components of a geocosmic storm, except for academic ones, ionospheric storms are of the greatest practical interest. It is these storms that limit the potential characteristics of radio systems for various purposes (telecommunications, radio navigation, radar, remote radio sounding, radio astronomy). It is shown that ionospheric storms are accompanied by the appearance of multipath, broadening of the Doppler spectra (and even their collapse), significant aperiodic and quasi-periodic variations in the Doppler frequency shift, the amplitude of radio signals, and the trajectories of radio waves in the decameter range. In particular, the height of reflection of radio waves changed during ionospheric storms by 50–180 km. The electron concentration during moderate negative ionospheric storms decreased up to 2 times, and during moderate positive ionospheric storms it increased up to 3 times. Under the action of atmospheric gravity waves, the relative amplitude of quasi-periodic variations in the electron concentration reached 50%, and due to low-frequency infrasound, it did not exceed 0.7%.

Physical effects of geocosmic storms

A review of the results of observing the effects of the most interesting ionospheric and magnetic storms that took place in 2018–2019 is presented. Ionospheric and magnetic storms are considered as components of geocosmic storms. In accordance with the systemic paradigm of L.F. Chernogor, a geocosmic storm is a complex of processes caused by a solar storm, reduced to synergistically interacting storms in a magnetic field (magnetic storm), ionosphere (ionospheric storm), atmosphere (atmospheric storm) and electric field atmospheric-ionospheric-magnetospheric origin (electric storm). Using the analysis of specific magnetic and ionospheric storms as an example, it is shown that, in addition to general patterns, each storm has its own individual characteristics. The expediency of a comprehensive study of the manifestations of each new geocosmic storm has been confirmed. A wide variety of ionospheric and magnetic storms have been confirmed. A weak magnetic storm is not necessarily accompanied by a weak ionospheric storm, while a strong one is accompanied by a strong one. An ionospheric storm can be single-phase (positive or negative) or multi-phase, when the phases alternate. Storms can last from several hours to many days. Storms are accompanied by both aperiodic and quasi-periodic variations. The latter are caused by atmospheric gravity waves (periods ~10–180 min) and infrasound (period less than 5 min). Of all the components of a geocosmic storm, except for academic ones, ionospheric storms are of the greatest practical interest. It is these storms that limit the potential characteristics of radio systems for various purposes (telecommunications, radio navigation, radar, remote radio sounding, radio astronomy). It is shown that ionospheric storms are accompanied by the appearance of multipath, broadening of the Doppler spectra (and even their collapse), significant aperiodic and quasi-periodic variations in the Doppler frequency shift, the amplitude of radio signals, and the trajectories of radio waves in the decameter range. In particular, the height of reflection of radio waves changed during ionospheric storms by 50–180 km. The electron concentration during moderate negative ionospheric storms decreased up to 2 times, and during moderate positive ionospheric storms it increased up to 3 times. Under the action of atmospheric gravity waves, the relative amplitude of quasi-periodic variations in the electron concentration reached 50%, and due to low-frequency infrasound, it did not exceed 0.7%.

Effect of Weak Magnetic Storms on the Propagation of HF Radio Waves

Effect of Weak Magnetic Storms on the Propagation of HF Radio Waves

Estimation of the Electric Field Zonal Component Value and Particle Transfer Velocity Due To Electromagnetic Drift in the Ionosphere during Magnetic Storm on September 25, 2016 over Kharkiv

Background. Dynamic processes in plasma play a significant role in the formation of the spatial structure of the ionosphere at altitudes above the main ionization maximum. During geomagnetic disturbances, the dynamic mode of the ionospheric plasma noticeably changes, and these changes in the variations in the physical process parameters directly affect the spatial-temporal distribution of the main parameters of the ionosphere. One of the mechanisms affecting the behavior of the dynamic process parameters in the ionosphere is the penetration of electric fields of magnetospheric origin into the mid-latitude ionosphere during magnetic storms. The effects of the electric field, which are practically absent in quiet conditions, during geomagnetic storms lead to an additional transfer of charged particles due to electromagnetic drift. Accounting for these effects in variations in the dynamic process parameters and, as a consequence, in variations in the parameters of the ionosphere, is necessary for a more adequate prediction of the behavior of geospace parameters during geomagnetic disturbances. Development of ionospheric models of the disturbed ionosphere for solving applied problems in the field of radio communication, radio navigation and uninterrupted operation of telecommunication systems for various purposes. The aim of this work is to estimate the magnitude of the zonal component of the electric field in the ionosphere over Kharkiv during a weak magnetic storm on September 25, 2016, as well as to calculate the neutral wind velocity taking into account plasma transport in crossed electric and magnetic fields. Materials and methods. To calculate the parameters of dynamic processes in the ionosphere, the experimental data of the Kharkiv incoherent scatter radar were used. Results. The value of the zonal component of the electric field Ey was calculated during a weak magnetic storm on September 25, 2016. The maximum value of Ey took place around 23:00 EEST on September 25, 2016 and was equal to 5.9 mV/m. Calculated values of particle transfer velocity due to electromagnetic drift vEB during the September 25, 2016 magnetic storm are obtained. Variations in vEB correlate with variations in Ey, and the maximum velocity was –52 m/s. The calculation results showed that during weak magnetic storms (Kp = 4) it is necessary to take into account the plasma transfer due to electromagnetic drift. The contribution of the velocity vEB to the total velocity of charged particle transfer is significant. The neutral (thermospheric) wind velocity vnx is calculated without and taking into account the particle transfer velocity in crossed electric and magnetic fields. Conclusions. As shown by the results of the comparative analysis, taking into account the influence of the electric field made it possible to refine the values of the velocities vnx during a magnetic storm, which, in turn, makes it possible to explain the behavior of the main parameters of the F2 layer of the ionosphere under disturbed conditions.

F Region Electric Field Effects on the Intermediate Layer Dynamics During the Evening Prereversal Enhancement at Equatorial Region Over Brazil

AbstractUsing ionograms from the Brazilian equatorial site of São Luís (SL, 2° S; 44° W, I = −3.8°), the relationship between the uplift of the intermediate layers (ILs) at sunset and the prereversal enhancement of the zonal electric field (PRE) is investigated. The ILs were studied during the solar maximum (2003) and minimum activity (2009) periods. The presence of the ILs during the PRE occurrence time was very low during both years. In 2003, six ILs’ events were observed, being four of them in the summer solstice and one in the March equinox. In 2009, only a single event was registered and occurred during the December month. The results show that depending on the height at which the ILs are located, their upward movement at sunset can be in some way related to the normal F layer rise at sunset due to the PRE. The initial altitude at which such ascending ILs were observed was higher than their normal height near sunset. Additionally, the eastward prompt penetration electric fields (PPEFs) during weak magnetic storms can also contribute to the IL’s rise. An interesting case of uplift of a sporadic‐E layer from ∼120 to 290 km probably due to the PPEF is also investigated.

Radio and optical investigations of storm time evolution of post-midnight equatorial plasma bubbles (EPBs) and their drifts over Indian sector

We investigated the spatio-temporal evolution of disturbed time post mid-night Equatorial Plasma Bubbles (EPBs) using Canadian Advanced Digital Ionosonde (CADI) located at dip equatorial station, Tirunelveli (8.73°N, 77.7°E, 0.23°N Dip. Lat.), an all-sky imager (ASI) observations at low latitude station Panhala (16.48°N, 74.6°E, 11.1°N Dip. Lat.) and Gadanki Ionospheric Radar Interferometer (GIRI) at Gadanki (13.5°N, 79.2°E; 6.5°N Dip. Lat.) which is situated at few degrees towards east and south of Panhala on 02–03 February 2017 night. During this night, IMF Bz showed its periodic variation starting from 16:00 UT to 23:00 UT accompanied by decrease in SYM-H to as low as −35 nT indicating the onset of weak magnetic storm. The analyzed results suggested that cause of post-midnight EPBs could be due to manifestation of fluctuating eastward/westward electric field due to combined under-shielding/over-shielding Electric Fields and disturbance dynamo electric fields that led to rise and fall of the F-layer over dip equator. Interestingly, the EPBs over Panhala showed eastward motion initially that quickly reversed to westward later. Along with westward motion they also started growing until 21:30 UT. However, most of these EPBs disappeared with time except the one that started descending/shrinking towards southern side (i.e. towards equator). The rising and shrinking of EPBs is found to be fairly correlated with the equatorial vertical drifts. The westward drift of EPBs at Panhala and its anti-correlation with vertical drifts has been confirmed from CADI zonal/vertical drifts. Accordingly, the study also investigated the role of storm induced vertical Hall electric field as a possible cause for westward drifts and its anti-correlation with vertical drifts. However, GIRI observations do not show any significant westward drift on this night at Gadanki suggesting that there is a longitudinal gradient in the zonal drift of these EPBs. In addition to longitudinal drift reversal, the latitudinal gradient in zonal drifts also has been noticed. The present work highlights the role of storm induced disturbances in the generation and evolution of post-midnight EPBs which is believed to be triggered by weak magnetic disturbances in the deep low solar minimum.

Long-term variability in occurrence frequencies of magnetic storms with sudden and gradual commencements

Long-term variations in annual frequencies of occurrence of magnetic storms with sudden and gradual commencements were studied on the base of the data from IZMIRAN and Slutsk (Pavlovsk) magnetic observatories for the period 1878–2015. It was found that occurrences of strong and moderate magnetic storms with gradual commencements are characterized by a pronounced variability on the multidecadal time scale. Their wavelet spectra reveal strong periodicities of ~36 years (close to the climatic Brückner cycle), as well as less pronounced ~60-year and ~90-year ones throughout the entire time interval under study. The occurrences of strong, moderate and weak magnetic storms with sudden commencements are characterized by dominating ~11-year periodicities, whereas long-term variations are substantially weaker. The obtained results provide evidence for a different temporal evolution of local and global solar magnetic fields responsible for solar agents (CMEs and high-speed solar wind streams from coronal holes) contributing to the development of these types of magnetic storms. The obtained results allow suggesting a possible contribution of solar/geomagnetic activity to the formation of climatic oscillations on the multidecadal time scale.

Weak Magnetic Storms Can Modulate Ionosphere‐Plasmasphere Interaction Significantly: Mechanisms and Manifestations at Mid‐Latitudes

AbstractA comprehensive study of the response of the ionosphere‐plasmasphere system at mid‐latitudes to weak (Dstmin > −50 nT) magnetic storms is presented. For the first time, it is shown that weak magnetic disturbances can lead to significant modulation of ionosphere‐plasmasphere H+ ion fluxes. It is found that this modulation is caused by the enhancements/reductions of the topside O+ ion density, which is induced by F2‐layer peak height rise and fall during the storms. The F2‐layer motion is caused by thermospheric wind changes and by a penetration electric field. Both drivers are closely related to the changes in the Bz component of interplanetary magnetic field. The most prominent manifestation of the H+ ion flux modulation is strong changes in H+ ion fraction in the topside ionosphere. This study also indicates that the NRLMSISE‐00 model provides the correct relative changes of neutral H density during weak magnetic storms and also that there is a compelling need to include geomagnetic activity indices, in addition to solar activity (F10.7), as input parameters to empirical topside ionosphere models.

Highly Relativistic Electron Flux Enhancement During the Weak Geomagnetic Storm of April–May 2017

AbstractWe report observations of energetic electron flux and phase space density to show that a relatively weak magnetic storm with Sym‐Hmin≈−50 nT, resulted in a relativistic and ultrarelativistic electron enhancement of two orders of magnitude similar to the St. Patrick's event of 2015, an extreme storm with Sym‐Hmin≈−235 nT. This enhancement appeared at energies up to ≈10 MeV, lasted for at least 24 days, and was not recorded in geosynchronous orbit where most space weather alert data are collected. By combined analysis of phase space density radial profiles and Fokker‐Planck simulation, we show that the enhancement of relativistic and ultrarelativistic electrons is caused by different mechanisms: first, chorus waves during the intense substorm injections of 21–25 April accelerate the seed electron population to relativistic energies and redistribute them while inward diffusion driven by Pc5 Ultra‐Low Frequency (ULF) waves further accelerates them to ultrarelativistic energies.

ВЛИЯНИЕ ГЕЛИОГЕОФИЗИЧЕСКИХ ФАКТОРОВ НА СВЕРТЫВАЮЩУЮ СИСТЕМУ КРОВИ БЕРЕМЕННЫХ С ПЛАЦЕНТАРНЫМИ НАРУШЕНИЯМИ

Geomagnetic storms are one of the natural abiotic risk factors for human health. The response of the organism to their impact depends on the individual adaptive abilities, which were formed during the evolution, but can change in the conditions of pathological processes. Evaluation of the effect of a weak magnetic storm (G4v (22 < Ar < 39 nTl) on hemorheological parameters of blood of pregnant women with placental insufficiency compared to healthy pregnant women showed an increase in platelet count (p = 0.05), fibrinogen content (p = 0.02), thrombocyte (p = 0.03), erythrocyte sedimentation rate (p = 0.004). At the same time, a decrease in the number of red blood cells (p = 0.04), hemoglobin concentration (p = 0.001), hematocrit value (p = 0.0009) was registered. We found a strong direct correlation between subpopulations of platelets, which are characterized by different functional activity. Heterogeneity of platelets, their multidirectional correlations with indicators of blood coagulation system of healthy pregnant women can be considered as a response to the change in the disturbance of the earth's magnetic field. For pregnant women with placental disorders, the magnetic storm was associated with increased activity of the blood coagulation system and a significant increase in its components in the blood of patients. Despite the fact that changes in the blood coagulation system occur from the beginning of pregnancy and are often adaptive, in pregnant women with placental disorders, the additional impact of a weak magnetic storm can be a risk of hemostasis disorders and the development of platelet thrombosis, timely diagnosis and therapy of which is important.

Investigating the polar ionosphere during the development of neutral density enhancements on 24–25 September 2000

AbstractWe focus on the well‐known northern daytime neutral density spikes detected by CHAMP on 25 September 2000 and related coupled magnetospheric‐ionospheric‐thermospheric processes. We investigate the underlying magnetic events and resultant thermospheric variations plus the state of the ionospheric polar region by employing multi‐instrument CHAMP and DMSP data. Results show the unfolding of a weak (SYM‐HMin ≈ −27 nT; ~0345 UT) magnetic storm during which these northern density spikes occurred. Some smaller southern daytime density spikes were also detected prior to this storm on the previous day. All these density spikes were detected in or near polar convection flow channels (FCs). Each FC was characterized by strong antisunward zonal ion drifts that excited the zonal and meridional neutral winds leaving the signature of FC in the CHAMP neutral wind measurements and thus providing direct observational evidence of FC underlying the density spike. Additional to the small‐scale field‐aligned current (SS‐FAC) filaments, the sudden intensifications of ionospheric closure current in the FC fueled the thermosphere and contributed to the development of upwelling and density spike. Some smaller density increases occurred due to the weak intensification of ionospheric closure currents. Equatorward (poleward) directed meridional neutral winds strengthened (weakened) the density spike by moving the neutral density up and along (down and against) the upwelling fueled by the ionospheric closure current and SS‐FAC filaments.

Conditions in solar wind and magnetosphere during the nontypical VLF hiss burst on December 8, 2013

The features of the dynamics of solar wind and IMF parameters were studied during the initial phase of the weak magnetic storm of December 8, 2013, where a nontypical two hour lasting wide-band (∼4–10 kHz) hiss burst was recorded during VLF observations in auroral latitudes near Sodankyla observatory (L ∼ 5.5), which differed from classical auroral hiss. A similar VLF hiss burst was recorded at Russian Lovozero observatory, which is located ∼400 km to the east. In contrast to a typical auroral hiss, the VLF emissions at both points were left-polarized and arrived at the observation point from the southeast. Although the VLF hiss burst coincided in time with the development of a substorm and the appearance of zenithal bright auroras near the stations traveling north-south, the excitation of the VLF hiss apparently has no relation to the auroras. It is suggested that the VLF emissions were generated due to cyclotron instability far to the east of Scandinavia in the region of plasmapause at L ∼ 3.5, where the equatorial gyrofrequency (f He) is about 20 kHz. The generated VLF waves could be ducted in the plasmapause at frequencies lower than a half of f He, i.e., below ∼10 kHz, they arrive at the Earth’s surface near the projection of their source and propagate in the Earth-ionosphere waveguide to large distances, as left-polarized waves. A sharp increase in the solar wind dynamic pressure was noted during the hiss burst under study, which resulted in a significant contraction of the daytime magnetosphere, a shift of the plasmapause and radiation belt to lower L shells, and the development of a substorm and southward travel of auroral arcs. The VLF hiss may have been generated in the region where energetic particles of the radiation belt crossed the plasmapause. The fact that the hiss under study was generated not in the early morning sector (Scandinavian meridian), but much further to the east, could be indirectly confirmed by quasiperiodic modulation of the VLF noise intensity in the range of Pc5 geomagnetic pulsations, which were observed in this period at eastern stations but not at the Scandinavian meridian.

Significant loss of energetic electrons at the heart of the outer radiation belt during weak magnetic storms

AbstractFor various reasons, the Earth's outer radiation belt often exhibits dramatic and sudden increases or decreases in the observed particle flux. In this paper, we report three dropout events of energetic electrons observed by multiple spacecraft while traveling across the outer radiation belt. The three events were first identified based on observations of a significant dropout in the &gt;2 MeV electron flux at geosynchronous orbit. Subsequently, for each event, we analyzed the energetic electron data obtained near the magnetic equator by THEMIS spacecraft to determine the responses of the entire outer radiation belt. Our analysis is mainly based on the electron fluxes measured at energies of 52 keV, 203 keV, and 719 keV, and on the phase space densities estimated for the first adiabatic invariant μ values of 100 MeV/G, 200 MeV/G, and 300 MeV/G. The main shared feature among the three events is that while, for the lowest energy, sources from the convection and/or particle injections of plasma sheet electrons dominate over losses, the higher energies exhibit a dramatic dropout effect that penetrates deeply into L ~ 4.5 – 5. In terms of the phase space density, a similar dropout effect is clearly seen for the μ values of 200 MeV/G and 300 MeV/G, while the convection effect and/or injections dominates for μ = 100 MeV/G. What is astonishing about this dropout phenomenon is that the three events are all associated with only very weak magnetic storms with a SYM‐H minimum of ‐40 nT or larger. This implies that a significant loss of electrons deep inside the outer radiation belt can occur even during a very weak magnetic storm. Low‐altitude observations of electrons by NOAA POES satellites indicate no significant atmospheric precipitation due to strong diffusion. Our simulations with various conditions suggest that radial diffusion effect in combination with the magnetopause shadowing are responsible for the observed dropouts to a large extent for all of the three events, although the contribution by the weak atmospheric precipitation that might have been missed by the NOAA POES observations can be non‐negligible.

Multi-instrumental observation of weak magnetic storms occurred during the period, 18–21 March 2002

Multi-instrumental observation of ionospheric responses to two weak magnetic storms occurred during the period, 18–21 March 2002, was conducted using GPS network, MU radar, and ionosondes, over the mid-latitude sector, and compared with the output generated by FLIP model. Latitudinal and temporal variations of GPS–TEC exhibit poleward expansion up to 35°N, during day time hours (around 1000–1300 JST), of 19 and 21 March after the SSCs. It is interesting to note that, although the second storm considered here is very weak, on 20 March after the SSC around mid-night, MU radar observed that neutral wind increases rapidly up to 200 m/s, towards equator and simultaneously, a perturbation component of about 2 TECU is observed by GPS network, around 0100 JST of 21 March, which propagate from north to equator. Ionosondes also revealed that, after the second SSC, around 0200 JST on 21 March, F-layer height increases at Wakkanai, and Kokubunji which propagates to Okinawa, exhibiting a latitudinal dispersion feature, showing the influence of equatorward neutral wind/propagating nature of a powerful wind surge. The equivalent neutral wind derived from FLIP model by including vibrationally excited nitrogen, N 2 ⁎ and without its inclusion are almost identical and in good agreement with the MU radar neutral wind. The interplanetary–magnetosphere scenario of the initial and main phase of the two weak geomagnetic storms considered in the present study are quite different, which is reflected in the ionospheric responses to these events.

Experimental evidence for direct penetration of ULF waves from the solar wind and their possible effect on acceleration of radiation belt electrons

The event of March 12–19, 2009, when a moderately high-speed solar wind stream flew around the Earth’s magnetosphere and carried millihertz ultralow-frequency (ULF) waves, has been analyzed. The stream caused a weak magnetic storm (D st min = −28 nT). Since March 13, fluxes of energetic (up to relativistic) electrons started increasing in the magnetosphere. Comparison of the spectra of ULF oscillations observed in the solar wind and magnetosphere and on the Earth’s surface indicated that a stable common spectral peak was present at frequencies of 3–4 mHz. This fact is interpreted as evidence that waves penetrated directly from the solar wind into the magnetosphere. Possible scenarios describing the participation of oscillations in the acceleration of medium-energy (E > 0.6 MeV) and high-energy (E > 2.0 MeV) electrons in the radiation belt are discussed. Based on comparing the event with the moderate magnetic storm of January 21–22, 2005, we concluded that favorable conditions for analyzing the interaction between the solar wind and the magnetosphere are formed during a deep minimum of solar activity.

First results of Coherent Ionospheric Doppler Receiver measurements over Egypt

[1] This paper presents the first results of total electron content (TEC) measurements over Egypt taken by UHF/VHF receivers. Such ionospheric measurements over the Middle East and north Africa have been previously unable to the scientific community but are now available for ionospheric studies. In particular, these receivers are well situated to study the northern peak of the equatorial anomaly. This initial study examines the behavior of the equatorial anomaly during a weak magnetic storm of 12 July 2008. The response of the northern equatorial anomaly crest is examined during the storm time, using the TEC measurements from the Coherent Ionospheric Doppler Receivers (CIDR) at Helwan, Egypt (29.8641°N, 31.3172°E). Particular attention is shown to diurnal changes in the crest structure and its response to the minor magnetic storm.

Latitudinal profile of the ionospheric disturbance dynamo magnetic signature: comparison with the DP2 magnetic disturbance

Abstract. During magnetic storms, the auroral electrojets intensification affects the thermospheric circulation on a global scale. This process which leads to electric field and current disturbance at middle and low latitudes, on the quiet day after the end of a storm, has been attributed to the ionospheric disturbance dynamo (Ddyn). The magnetic field disturbance observed as a result of this process is the reduction of the H component amplitude in the equatorial region which constitutes the main characteristic of the ionospheric disturbance dynamo process, associated with a westward electric current flow. The latitudinal profile of the Ddyn disturbance dynamo magnetic signature exhibits an eastward current at mid latitudes and a westward one at low latitudes with a substantial amplification at the magnetic equator. Such current flow reveals an "anti-Sq" system established between the mid latitudes and the equatorial region and opposes the normal Sq current vortex. However, the localization of the eastward current and consequently the position and the extent of the "anti-Sq" current vortex changes from one storm to another. Indeed, for a strong magnetic storm, the eastward current is well established at mid latitudes about 45° N and for a weak magnetic storm, the eastward current is established toward the high latitudes (about 60° N), near the Joule heating region, resulting in a large "anti-Sq" current cell. The latitudinal profile of the Ddyn disturbance as well as the magnetic disturbance DP2 generated by the mechanism of prompt penetration of the magnetospheric convection electric field in general, show a weak disturbance at the low latitudes with a substantial amplification at the magnetic equator. Due to the intensity of the storm, the magnitude of the DP2 appears higher than the Ddyn over the American and Asian sector contrary to the African sector.

THEMIS observations of penetration of the plasma sheet into the ring current region during a magnetic storm

Observations from the THEMIS spacecraft during a weak magnetic storm clearly show that the inner edge of the ion plasma sheet near dusk moved from r ∼ 6 RE during the pre‐storm quiet time to r ∼ 3.5 RE during the main phase, and then moved outward during the recovery phase. The plasma sheet particles from the tail reached the inner magnetosphere during the main phase through open drift paths, which extended earthward with increasing convection, and were energized to ring current energies, resulting in an increase in ring current population. During the recovery phase, the plasma sheet region retreated to outside the inner magnetosphere as the region of open drift paths moved outward with decreasing convection, leaving the ring current particles within the expended closed drift path region. With no new particles from the plasma sheet, ring current population gradually decreased due to losses as the recovery phase proceeded.