Ionospheric disturbances during the severe magnetic storm of November 7–10, 2004

Results of the study of the behavior of the F ₂ region and topside ionosphere during the magnetic storm on November 7–10, 2004, which was a superposition of two sequent Severe magnetic disturbances (Kp = 9–) are presented. The observations were conducted by the incoherent scatter radar at Kharkov. Considerable effects of a negative ionospheric disturbance are registered, including a decrease in the electron density in the F ₂-layer maximum by a factor of 6–7 and of the total electron content up to a height of 1000 km by a factor of 2, a lifting up of the ionospheric F ₂ layer by 300 km at night and by 150–180 km in the daytime, unusual nighttime heating of the plasma with an increase of the ion and electron temperatures up to 2000 and 3000 K, respectively, and a decrease in the relative density of hydrogen ions N(H⁺)/N _e by a factor of up to 3.5 because of the emptying of the magnetic flux tube passing over Kharkov. The effects usually observed in the high-latitude ionosphere, including the coherent echoes, are detected during the main phase of the storm. The results obtained manifest a shift of the large-scale structures of the high-latitude ionosphere (the auroral oval, main ionospheric trough, hot zone, etc.) down to latitudes close to the latitude of the Kharkov radar.     

Effect of auroral electrojets and solar wind parameters on variations in the intensity of low-latitude geomagnetic disturbances and Dst during the extremely large magnetic storm of November 20–21, 2003

The effect of auroral electrojets on the variations in the low-latitude geomagnetic disturbances and Dst during a strong magnetic storm of November 20–21, 2003, with Dst ≈ ?472 nT has been studied based on the global magnetic observations. It has been indicated that the magnetospheric storm expansive phase with Δt ≈ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 30–100 nT in the premidnight-dawn sector. A growth of negative low-latitude ΔH values and Dst is mainly caused by regular convection electrojets with Δt ≥ 10 h, the centers of which shift to latitudes of ～ 50°–55° during the storm development. It has been established that the maximal low-latitude values of the field ΔH component at 1800–2400 MLT are observed when the auroral luminosity equatorward boundary shifts maximally southward during an increase in the negative values of the IMF B _z component. It has been assumed that, during this storm, a magnetic field depression at low latitudes was mainly caused by an enhancement of the partially-ring current which closes through field-aligned currents into the ionosphere at the equatorward boundary of the auroral luminosity zone.     

The recovery phase of the superstrong magnetic storm of July 15–17, 2000: Substorms and ULF pulsations

The geomagnetic observations, performed at the global network of ground-based observatories during the recovery phase of the superstrong magnetic storm of July 15–17, 2000 (Bastille Day Event, Dst = ?301 nT), have been analyzed. It has been indicated that magnetic activity did not cease at the beginning of the storm recovery phase but abruptly shifted to polar latitudes. Polar cap substorms were accompanied by the development of intense geomagnetic pulsations in the morning sector of auroral latitudes. In this case oscillations at frequencies of 1–2 and 3–4 mHz were observed at geomagnetic latitudes higher and lower than ～62°, respectively. It has been detected that the spectra of variations in the solar wind dynamic pressure and the amplitude spectra of geomagnetic pulsations on the Earth’s surface were similar. Wave activity unexpectedly appeared in the evening sector of auroral latitudes after the development of near-midnight polar substorms. It has been established that the generation of Pc5 pulsations (in this case at frequencies of 3–4 mHz) was spatially asymmetric about noon during the late stage of the recovery phase of the discussed storm as took place during the recovery phase of the superstrong storms of October and November 2003. Intense oscillations were generated in the morning sector at the auroral latitudes and in the postnoon sector at the subauroral and middle latitudes. The cause of such an asymmetry, typical of the recovery phase of superstrong magnetic storms, remains unknown.     

Extremely strong geomagnetic storm of September 2–3, 1859, according to the archived data of observations at the Russian network

A retrospective analysis of the Russian magnetic observations of the Carrington event that occurred on September 2–3, 1859, has been performed. The conclusion has been made that this event was caused by the series of three recurrent eruptive solar flares during ～40 h. The characteristics of the geomagnetic crochet, related to a considerable flux of the ionizing electromagnetic radiation during this flare, have been studied. The value and direction of a magnetic field disturbance, registered during the maximum of the geomagnetic storm of September 2, unambiguously indicate that all Russian stations were in the auroral oval zone, which was strongly expanded southward from its average position. The disturbance dependence on the station longitude—the absence of magnetometer pinning in Nerchinsk—is interpreted as the possible manifestation of a strong asymmetry in the effective contour of the current system, which was connected to the heliosphere and covered the disturbed magnetosphere and ionosphere during the short period that lasted only 1–3 h.     

Signatures of storm sudden commencements in geomagnetic H, Y and Z fields at Indian observatories during 1958–1992

The work describes an intensive study of storm sudden commencement (SSC) impulses in horizontal (H), eastward (Y) and vertical (Z) fields at four Indian geomagnetic observatories between 1958–1992. The midday maximum of δH has been shown to exist even at the low-latitude station Alibag which is outside the equatorial electrojet belt, suggesting that SSC is associated with an eastward electric field at equatorial and low latitudes. The impulses in Y field are shown to be linearly and inversely related to δH at Annamalainagar and Alibag. The average SC disturbance vector is shown to be about 10–20°W of the geomagnetic meridian. The local time variation of the angle is more westerly during dusk hours in summer and around dawn in the winter months. This clearly suggests an effect of the orientation of shock front plane of the solar plasma with respect to the geomagnetic meridian. The δZ at δC have a positive impulse as in δH. The ratio of δZ/δH are abnormally large exceeding 1.0 in most of the cases at Trivandrum. The latitudinal variation of δZ shows a tendency towards a minimum over the equator during the nighttime hours. These effects are explained as (1) resulting from the electromagnetic induction effects due to the equatorial electrojet current in the subsurface conducting layers between India and Sri Lanka, due to channelling of ocean currents through the Palk Strait and (2) due to the concentration of induced currents over extended latitude zones towards the conducting graben between India and Sri Lanka just south of Trivandrum.     

The day-to-day effects of strong geomagnetic disturbances on the North Atlantic Oscillation in the winter periods of years 1951–2003

The day-to-day effects of the strong geomagnetic disturbances on geopotential heights (GPH) in the winter lower atmosphere were described in many papers in the beginning of 1970s. These works focused on the North-East Pacific, while the North Atlantic was until now omitted. Our aim is therefore to investigate the possible effect of strong geomagnetic disturbances on the lower atmosphere GPH changes over the winter North Atlantic on the day-to-day time scale, represented by the daily index of the North Atlantic Oscillation (NAO). The investigated intervals are winter periods (December-March) of 1951–2003. The daily NAO average values in 3-day intervals before and after the disturbance onsets are compared. The graphs of NAO differences are complemented by the maps of GPH differences. The NAO response to geomagnetic disturbance, as registered on the day-to-day time scale, also shows a change in its behaviour around the year 1970. This response reaches its highest values in the years 1951–1969, usually 2–5 days following the onset of geomagnetic disturbances. Intensity of the response depends on the disturbance intensity (the largest differences were associated with extremely strong disturbances).

     

The Earth’s passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L’Aquila, Italy) station during the Earth’s passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth’s magnetosphere.     

Variations in the critical frequency of the ionospheric F-region during magnetic storms in 2008–2012 at auroral latitudes

Fifty-one magnetic storms occurred during the last solar half-cycle of transition from the epoch minimum to the epoch maximum are considered. Ionospheric (foF2) and magnetic (X component) data from Sodankyla observatory, Finland, were used for the analysis, as well as values of the ΣKp indices of magnetic activity. The dependence of variations in the critical frequency foF2 was studied before, during, and after each storm. It has been revealed that a major effect (ME) takes place for all of the storms analyzed. It consists in the following: the first maximum in foF2 values occurs several days before the onset of the active phase of a storm, then foF2 attains its minimum during the active phase, and the second maximum occurred after the active phase. Five principals, the most frequent types of variation in foF2 during a storm, have been revealed. However, special cases (30%) in which an ME exists but shifts rightward several days along the time axis are observable. Ionospheric “memory” (inertia) from 8–9 h to 2 days has been revealed. It has been ascertained that the occurrence of the first ME maximum can be considered a magnetic storm precursor. Such a precursor potentially can be used for forecasting the beginning of magnetic storm development, which is important for space weather problems.     

MHD structure of interplanetary disturbances observed near the earth during the solar-terrestrial storm of November 7–13, 2004

This paper considers the MHD structure and configuration of near-Earth interplanetary disturbances during the heliospheric extrastorm of November 2004, taking into account the effect of the IMF sector structure and using the measurements of near-Earth satellites. During three successive disturbance intervals, the Earth entered, remained and left a relative narrow positive sector with flare-active region 10696, which generated a series of shocks and an active transequatorial filament. It has been indicated that the MHD structure and configuration of near-Earth disturbances substantially and specifically (for each position) depend on the IMF sector structure and interactions between shocks and sector boundaries, filaments, and magnetic clouds in these three different positions. Specifically, this manifested itself in multiple crossings of sector boundaries and considerable deformations of magnetic clouds. It has been indicated that the models of circular clouds are applied with limitations under the considered conditions.     

Role of magnetospheric convection and precipitation in the formation of the “dusk effect” during the main phase of a magnetic storm

This paper studies the role of magnetospheric factors, such as convection and energetic electron precipitation during the formation of positive disturbances in the total electron content under the conditions of the summer evening ionosphere. à numerical model of the ionosphere and plasmasphere, where time variations in the magnetospheric convection velocity and electron precipitation parameters correspond to the main phase of a magnetic storm, has been used for this purpose. It has been indicated that the total electron content sharply increases (the “dusk effect”) in the eastern and western sectors at approximately the same geomagnetic latitudes corresponding to the subauroral zone provided that a sudden storm commencement is registered in the morning hours. local time. This peak of the total electron content is formed as a result of joint reconstruction of the magnetospheric convection pattern and energetic electron precipitation during the main phase of a storm. In this case, magnetospheric convection plays the main role, raising the F2 layer by 40–80 km into the region with a lower recombination rate.     

The “twin” storm surges during 21st–24th December, 1954. A case of resonance

Summary The actual sea level disturbances at Hoek van Holland during the two storms of 21^st–24^th December, 1954 are compared to disturbance heights that are computed on the assumption that the sea level disturbances at any place behave like the deviations of a damped harmonic oscillator from its equilibrium position. From this comparison the parameters of the model and, hence, the eigen-period and the resonance period of oscillation have been computed.Moreover, it is shown that in the present case, we can speak of resonance and, finally, that an assumed third storm of the same force and occurring after the same time interval would have given about the same maximum disturbance height.

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Die Sturmfluten der Nordsee vom 21. bis 24. Dezember 1954. Ein Fall von Resonanz

Zusammenfassung Die beobachteten Erhöhungen des Meeresspiegels in Hoek van Holland während zweier Stürme vom 21. bis 24. Dezember 1954 wurden mit Erhöhungen verglichen, die auf Grund der Voraussetzung berechnet wurden, daß die Wasserstandserhöhungen an einem beliebigen Ort sich wie die Ausschläge eines gedämpften harmonischen Oszillators verhalten. Aus diesem Vergleich ergeben sich Werte für die Parameter dieses mathematischen Modells, aus denen sich dann die Eigenschwingungsdauer und die Resonanzschwingungsdauer berechnen lassen.Außerdem ergibt sich, daß man es hier mit einem Fall von Resonanz zu tun hat.Schließlich wird gezeigt, daß ein hypothetischer, nach gleichem Zeitintervall folgender dritter Sturm derselben Stärke schon keine wesentlich größeren Erhöhungen mehr hervorgerufen haben würde.

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Les ondes des tempêtes du 21 au 24 décembre 1954 dans la mer du Nord. Un cas de résonance

Résumé On compare les élévations actuelles du niveau de la mer observées à Hoek van Holland pendant les deux tempêtes du 21 au 24 décembre 1954 avec des élévations calculées en supposant que l'élévation à une place quelconque peut être «expliquée» à l'aide du modèle mathématique d'un oscillateur harmonique amorti. On déduit de cette comparaison les paramètres du modèle et, conséquemment, la période propre et la période de résonance.En outre, on montre que dans le cas considéré il s'agit d'une résonance et, enfin, qu'une troisième tempête hypothétique de la même force qui se serait produite après un même interval de temps aurait causé environ la même élévation maximale.

     

The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6–12 April 1990

We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6–12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earths ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O⁺(⁴S) ions as a result of new high-temperature flowing afterglow measurements of the rate coefficients K₁ and K₂ for the reactions of O⁺(⁴S) with N₂ and O₂. The deviations from the Boltzmann distribution for the first five vibrational levels of O₂(v) were calculated, and the present study suggests that these deviations are not significant. It was found that the difference between the non-Boltzmann and Boltzmann distribution assumptions of O₂(v) and the difference between ion and neutral temperature can lead to an increase of up to about 3% or a decrease of up to about 4% of the calculated NmF2 as a result of a respective increase or a decrease in K₂. The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N₂(v > 0) and O₂(v > 0) in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N₂(v > 0) and O₂(v > 0). This could be due to possible uncertainties in model neutral temperature and densities, EUV fluxes, rate coefficients, and the flow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the flux of ionization above the station. Our calculations show that the increase in the O⁺ + N₂ rate factor due to N₂(v > 0) produces a 5–36% decrease in the calculated daytime peak density. The increase in the O⁺ + O₂ loss rate due to vibrationally excited O₂ produces 8–46% reductions in NmF2. The effects of vibrationally excited O₂ and N₂ on N_e and T_e are most pronounced during the daytime.     

Development of high latitude phase fluctuationsduring the January 10, April 10–11, and May 15, 1997magnetic storms

GPS satellite transmissions have been used to study the development of moderateionospheric phase irregularities. The use of the multi-station, multi-path observations of the GPSbeacons has allowed the study of the time development of irregularities as a function of latitudeand longitude of individual storms. The basic storms studied were those of January 10, April10–11, and May 15, 1997. The results from studying these storms showed the unique nature ofeach storm. For the three storms, data were available from four stations near 65° CorrectedGeomagnetic Latitude (CGL); the stations ranged from Fairbanks to Tromso. In addition, datafrom higher latitude stations are analysed. For the January storm, irregularity development startedat Fairbanks. Then as magnetic midnight approached longitudes to the west, the storm effectsreached the Tromso–Kiruna longitudes. For the April magnetic storm, at 65° CGL, irregularitydevelopment maximized at approximately the same UT at stations ranging in longitude fromFairbanks to Kiruna. For this storm, the development of irregularities was dominated by stormtime. The May storm irregularities were dominated by magnetic local time once the stormcommenced.With both total electron content and rate of change of total electron content (phasefluctuations) available, it was noted that over periods of minutes, clumps of irregularities wereaccompanied by increases in TEC. In addition total electron content increased over large areasduring maximum magnetic activity in the auroral oval. During the storms, ionograms showed thatthe altitude of maximum electron density fluctuated; at times the dominant maximum frequencywas noted in the E layer and at other times in the F layer. This fluctuation of electron density ineach layer during storms led to the conclusion that the turbulent activity within the auroral regiondominated the development of irregularities. The irregularities that are noted on trans-ionosphericpaths are therefore thought to be in both the E and the F layers with a combination of structuredhard and soft electron precipitation and coupling initiating the turbulent activity. The generalpositive correlation of one periods phase scintillation data with the Ultra Violet Imagerobservations as shown on POLAR indicates the importance of 100–200 km precipitation.However the very high occurrence of spread F at high latitudes as shown by both ground andsatellite ionosondes indicates the considerable contributions of F layer irregularities.     

Assessment of the possibility of using E. A. Ponomarev’s magnetospheric substorm model to analyze geomagnetic disturbances during the magnetic storms of December 14 and 15, 2006

Spatial distributions of pressure and fluxes of precipitating magnetospheric plasma particles were constructed for the strong magnetic storm of December 14 and 15, 2006. The calculations were performed using a model developed by E.A. Ponomarev. Geotail and ACE satellite data were used to specify realistic initial and boundary conditions. The model results were compared with the spatial distribution of the field of geomagnetic disturbances recorded by ground-based magnetic observatories during the storm. The results show that the model (in its current form) provides good agreement between latitudinal displacements of electron precipitations and auroral electrojets but fails to reflect their longitudinal structure. The model fails to yield the strong westward electrojet observed by all auroral zone observatories during the main phase of the magnetic storm.     

Sun–Earth geometry,geomagnetic activity,and planetary F2 layer ion density: Part I: Signatures of magnetic reconnection

Our previous quantitative analyses have shown that geomagnetic activity and planetary ion density of the F2 layer of the ionosphere seem to share the same parent cause, the solar wind, whose entry into geospace is controlled by the Sun–Earth geometry. The thrust of this paper is four fold: (a) to establish the reality of this not clearly recognized connection, (b) to demonstrate that geomagnetic activity varies seasonally with three separate and independent components, viz. a semiannual, an annual and a Sun–Earth-distance determined component, all of which can be accurately derived from solar–terrestrial geometry alone, (c) to evaluate the contribution of each of these components which, taken together, appear to represent the steady-state signatures of the mechanism of magnetopause reconnection, and (d) to highlight the fact that the currently used planetary geomagnetic indices are deficient and therefore need to be revised. Since detailed understanding of the precise mechanism of the entry of solar wind energy into geospace is still lacking, no mechanism is suggested to show how solar wind energy is transported to the F2 layer (including low and equatorial latitudes). Magnetospheric electric fields, precipitation of energetic neutrals produced through charge exchange reactions with ions in the ring current and radiation belt particles, Joule heating, etc., may all be involved, but the energy for all such processes still comes from the solar wind. Apart from the three components of the reconnection mechanism mentioned above, a steady component due to the viscous interaction mechanism should also be present.     

The ECORS-Truc Vert’08 nearshore field experiment: presentation of a three-dimensional morphologic system in a macro-tidal environment during consecutive extreme storm conditions

A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results.     

HCl emissions at Soufrière Hills Volcano,Montserrat, West Indies,during a second phase of dome building: November 1999 to October 2000

HCl:SO₂ mass ratios measured by open path Fourier transform spectroscopy (OP-FTIR) in the volcanic plume at Soufrière Hills Volcano, Montserrat, are presented for the second phase of dome building between November 1999 and November 2000. HCl:SO₂ mass ratios of greater than 1 and HCl emission rates of greater than 400 t day^–1 characterise periods of dome building for this volcano. The data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent. This is substantiated by a correlation between chlorine and water content in the melt (derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase I and II of dome growth). The matrix glass from the November 1999 and March 2000 domes indicate an open system degassing regime with a fluid-melt partition coefficient for chlorine of the order of 250–300. September 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in September and October 1997. The OP-FTIR HCl time series suggests that HCl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13.5 kt day^–1 HCl during a period of high extrusion rate in September 2000. A calculation of the HCl emission rate expected for varying extrusion rates from the open-system degassing model suggests a HCl emission rate of the order of 1–4 kt day^–1 is indicative of an extrusion rate of between 2 and 8 m³ s^–1. Monitoring of HCl at Soufrière Hills Volcano provide a proxy for extrusion rate, with changes in ratio between HCl and SO₂ occurring rapidly in the plume. Order of magnitude changes occur in HCl emission rates over the time-scale of hours to days, making these changes easy to detect during the day-to-day monitoring of the volcano. Mean water emission rates are calculated to range from 9–24 kt day^–1 during dome building activity, calculated from the predicted mass ratio of H₂O:HCl in the fluid at the surface and FTIR-derived HCl emission rates.     

Neutron generation and geomagnetic disturbances in connection with the Chilean earthquake of February 27, 2010 and a volcanic eruption in Iceland in March–April 2010

The relationship between solar and geomagnetic activities in connection with seismicity and volcanic eruptions on the globe during the period 1680–2010 is studied. The centennial cycles of terrestrial endogenous activity, related to solar and geomagnetic activity, are revealed; at the beginning of these cycles, solar cycles with small Wolf numbers were detected, while intensive seismic and volcanic activity was observed for several decades. A stable negative correlation between seismicity and volcanism, on the one hand, and solar and geomagnetic activity, on the other hand, were found. Experiments, which were simultaneously carried out at the Pushkov Institute of Geomagnetism, Ionosphere, and Radiowave Propagation, Russian Academy of Sciences (IZMIRAN), Troitsk, Moscow oblast, and the Karymshina Complex Geophysical Observatory, Kamchatka Branch, Geophysical Survey, Russian Academy of Sciences, have verified the suggestion that disturbances in the geomagnetic field and neutron generation occur during the early stages of strong earthquakes. It is supposed that the mechanism of primary generation of terrestrial neutrons is related to nuclear reactions in the Earth’s interior.     

High-latitude ionosphere during magnetic storms of October 26, 2003–November 1, 2003: Tomographic reconstructions and numerical modeling

The height-latitude distributions of the electron density in the European Arctic sector of the subauroral and high-latitude ionosphere have been reconstructed based on the data of satellite radio tomography. The reconstructions have been compared with the results of the numerical modeling obtained using the UAM global numerical model and the IRI-2001 empirical ionospheric model. The goal of the paper was to find the degree of adequacy of these models to the observational data during geomagnetic disturbances. The UAM theoretical model adequately reproduces the dynamics of the main ionospheric trough, in particular, the position of its equatorward wall, and to a certain degree better describes the behavior of the high-latitude ion-osphere than the IRI empirical model. The discrepancies are observed in the regions of increased electron density poleward of the trough. To eliminate such disagreements, it was proposed to correct the model input distributions of precipitating high-energy electron fluxes with an energy of about 0.5 keV; i.e., the inverse problem of determining these distributions has been solved for extremely strong geomagnetic disturbances.