Quiet Geomagnetic Conditions Research Articles

Magnetospheric electron‐velocity‐distribution function information from wave observations

The electron‐velocity‐distribution function was determined to be highly non‐Maxwellian and more appropriate to a kappa distribution, with κ ≈ 2.0, near magnetic midnight in the low‐latitude magnetosphere just outside a stable plasmasphere during extremely quiet geomagnetic conditions. The kappa results were based on sounder‐stimulated Qn plasma resonances using the Radio Plasma Imager (RPI) on the IMAGE satellite; the state of the plasmasphere was determined from IMAGE/EUV observations. The Qn resonances correspond to the maximum frequencies of Bernstein‐mode waves that are observed between the harmonics of the electron cyclotron frequency in the frequency domain above the upper‐hybrid frequency. Here we present the results of a parametric investigation that included suprathermal electrons in the electron‐velocity‐distribution function used in the plasma‐wave dispersion equation to calculate the Qn frequencies for a range of kappa and fpe/fce values for Qn resonances from Q1 to Q9. The Qn frequencies were also calculated using a Maxwellian distribution, and they were found to be greater than those calculated using a kappa distribution with the frequency differences increasing with increasing n for a fixed κ and with decreasing κ for a fixed n. The calculated fQn values have been incorporated into the RPI BinBrowser software providing a powerful tool for rapidly obtaining information on the nature of the magnetospheric electron‐velocity‐distribution function and the electron number density Ne. This capability enabled accurate (within a few percent) in situ Ne determinations to be made along the outbound orbital track as IMAGE moved away from the plasmapause. The extremely quiet geomagnetic conditions allowed IMAGE/EUV‐extracted counts to be compared with the RPI‐determined orbital‐track Ne profile. The comparisons revealed remarkably similar Ne structures.

Comparative analysis of TEC disturbances over tropical cyclone zones in the North–West Pacific Ocean

In this paper, we study ionospheric total electron content (TEC) disturbances associated with tropical cyclones (TCs). The study relies on the statistical analysis of six cyclones of different intensity which occurred in the North–West Pacific Ocean in September–November 2005. We have used TEC data from the international network of two-frequency ground-based GPS receivers and NCEP/NCAR meteorological archive. TEC variations of different period ranges (02–20 and 20–60min) are shown to be more intense during TC peaks under quiet geomagnetic conditions. The highest TEC variation amplitudes are registered when the wind speed in the cyclone and the TC area are maximum. The intensification of TEC disturbances is more pronounced when several cyclones occur simultaneously. We have revealed that the ionospheric response to TC can be observed only after the cyclone has reached typhoon intensity. The ionospheric response is more pronounced at low satellite elevation angles.

Detection of a plasmaspheric wind in the Earth's magnetosphere by the Cluster spacecraft

Abstract. Plumes, forming at the plasmapause and released outwards, constitute a well-established mode for plasmaspheric material release to the Earth's magnetosphere. They are associated to active periods and the related electric field change. In 1992, Lemaire and Shunk proposed the existence of an additional mode for plasmaspheric material release to the Earth's magnetosphere: a plasmaspheric wind, steadily transporting cold plasmaspheric plasma outwards across the geomagnetic field lines, even during prolonged periods of quiet geomagnetic conditions. This has been proposed on a theoretical basis. Direct detection of this wind has, however, eluded observation in the past. Analysis of ion measurements, acquired in the outer plasmasphere by the CIS experiment onboard the four Cluster spacecraft, provide now an experimental confirmation of the plasmaspheric wind. This wind has been systematically detected in the outer plasmasphere during quiet and moderately active conditions, and calculations show that it could provide a substantial contribution to the magnetospheric plasma populations outside the Earth's plasmasphere. Similar winds should also exist on other planets, or astrophysical objects, quickly rotating and having an atmosphere and a magnetic field.

Simultaneous observations of quasi‐periodic ELF/VLF wave emissions and electron precipitation by DEMETER satellite: A case study

We present results of case studies of quasi‐periodic (QP) ELF/VLF hiss emissions detected onboard the DEMETER satellite. Three events with simultaneous periodic modulation in VLF wave intensity and energetic electron precipitation are found. In each event we observe exact coincidence of one or two busts of VLF wave intensity with energetic electron precipitation peaks. To our knowledge, such observations made onboard satellites have not been reported earlier. All events are observed at fairly quiet geomagnetic conditions (Kp <3). The dynamic spectrum of the VLF waves in these QP events was characterized by a regular frequency increase in each burst, and the repetition period was less than or about 20 s. These features allow us to suggest that the observed events belong to the QP2‐class, i.e., events which are not associated with geomagnetic pulsations. We also analyze energetic electron data from NOAA‐17 spacecraft which has helio‐synchronous circular orbit similar to DEMETER spacecraft and measured in the same region of the magnetosphere within 30 min for the analyzed events. NOAA‐17 data confirm that the QP emissions were detected by DEMETER in the region of isotropization of energetic electrons, which is typically associated with the development of the cyclotron instability. Modulation of electron flux with a period close to the QP emission period is observed in two events. Based on the observed correlation between bursts of wave intensity and energetic particle flux, we estimate the location and spatial extent of the source region for QP emissions.

Longitudinal and day‐to‐day variability in the ionosphere from lower atmosphere tidal forcing

AbstractSimulations with the global ionosphere plasmasphere model driven by whole atmosphere model winds show significant longitudinal and day‐to‐day variations in the ionospheric parameters. Under fixed solar and geomagnetic activity levels, the contributions of lower atmosphere tides to the longitudinal and day‐to‐day variability in the upper atmosphere are estimated. Larger relative variability is found in the nighttime than in the daytime, which is consistent with observations. The perturbations from the lower atmosphere contribute about half of the observed variability in the ionospheric F2 peak plasma density under moderate solar activity and geomagnetic quiet conditions. The daily variability of the equatorial vertical plasma drifts is primarily driven by the day‐to‐day amplitude changes of the migrating semidiurnal tide, while the wave‐4 and wave‐3 longitudinal variations during September are dominated by the nonmigrating diurnal eastward propagating tides with zonal wave numbers 3 and 2, respectively.

Constructing the frequency and wave normal distribution of whistler‐mode wave power

We introduce a new methodology that allows the construction of wave frequency distributions due to growing incoherent whistler‐mode waves in the magnetosphere. The technique combines the equations of geometric optics (i.e., raytracing) with the equation of transfer of radiation in an anisotropic lossy medium to obtain spectral energy density as a function of frequency and wavenormal angle. We describe the method in detail and then demonstrate how it could be used in an idealized magnetosphere during quiet geomagnetic conditions. For a specific set of plasma conditions, we predict that the wave power peaks off the equator at ∼15° magnetic latitude. The new calculations predict that wave power as a function of frequency can be adequately described using a Gaussian function, but as a function of wavenormal angle, it more closely resembles a skew normal distribution. The technique described in this paper is the first known estimate of the parallel and oblique incoherent wave spectrum as a result of growing whistler‐mode waves and provides a means to incorporate self‐consistent wave‐particle interactions in a kinetic model of the magnetosphere over a large volume.

Geomagnetic storm decreases the coherence of electric oscillations in the human brain during work on computer

A study was made of the influence of geomagnetic storms at the latitude of Moscow on the electric activity of the human cerebral cortex. By electroencephalographic measurements it was shown that when volunteers aged 18–23 were performing tasks on a computer during moderate magnetic storm or within 24 h after it, the values of the coherence function for electric oscillations in the frontal-polar and occipital areas of the brain in the 4.0–7.9 Hz range (theta rhythm) decreased by a factor of two or more (relative to quiet geomagnetic conditions), whereas the arterial blood pressure, respiratory rate and the electrocardiogram registered in parallel did not deviate from the norm.

Morphology of the G condition occurrence over Irkutsk

Using Irkutsk digisonde data obtained in 2003–2011, a morphological analysis of the G condition occurrence has been made. The G condition was found to occur during daylight hours in summer; in winter, it is extremely rare, and its appearance is associated with intense magnetic storms. In the years of moderate solar activity, the G condition is most frequently registered at Kp⩾4, in the forenoon. During low solar activity, it can be observed under quiet geomagnetic conditions; in most cases, local time of its appearance shifts to afternoon hours. The highest percentage of the G condition occurrence (7.7–6.4%) was recorded in June and July 2008 when the levels of solar and geomagnetic activity were abnormally low.

Electron temperature enhancements in nighttime equatorial ionosphere under the occurrence of plasma bubbles

Simultaneous in-situ measurements of electron density and temperature in the nighttime equatorial region were performed by a rocket experiment launched under solar minimum and geomagnetic quiet conditions from the station of Alcântara (2.24°S; 44.24°W), Brazil, on Dec. 18, 1995, 21:17 LT. These measurements detected during the upleg flight a large overheated area around the base of density profile. The presence of plasma bubbles was revealed during the downleg phase, as well as temperature enhancements detected preferentially at altitudes where plasma depletions are found. It was assumed that the region traversed by the rocket during the downleg was preceded before the bubble's onset by a large overheating as observed during the upleg flight. Analyzing this framework under the light of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), as well as a 2D numerical code that simulate the growth of an instability and the evolution of thermal energy inside a bubble, we found that despite an overheated area in the F-region bottomside can disturb the electron density profile around the altitude interval where such heat is deposited, it seems not have a direct influence over parameters responsible for the bubble onset. Additionally, the phenomenon of the intra-bubble thermal enhancement could be formed due to the convection of hot-electron fluid transported from the overheated region surrounding the base of the F-region to upper altitudes by the underlying mechanism of bubble generation.

Modeling the plasmasphere with SAMI3

The study of the plasmasphere is extremely important to understanding space weather phenomena; for example, it plays a critical role in the regulation of radiation belt dynamics. In this paper, the first 3D simulation of the plasmasphere based on the first‐principles physics model SAMI3 is presented. We include the co‐rotation potential, the neutral wind dynamo potential, and a time‐dependent Volland‐Stern‐Maynard‐Chen potential to model the response of the convection potential to an idealized magnetic storm. We find that prior to the storm the plasmasphere is largely toroidal and symmetric in magnetic local time with He+/H+ ~ 5–10%. After the storm, the plasmasphere substantially contracts because plasma is convected away from the outer plasmasphere by the enhanced convection velocity. Moreover, a plume‐like structure forms in the mid‐afternoon sector because of the modified convection pattern associated with the storm. Additionally good agreement is found between the simulation results and data for the L‐shell dependence of the equatorial electron density as well as the electron density along the field line at a given L‐shell under quiet geomagnetic conditions.

Novelty detection in time series of ULF magnetic and electric components obtained from DEMETER satellite experiments above Samoa (29 September 2009) earthquake region

Abstract. Using ULF (ultra low frequency) measurements of magnetometer and ICE (Instrument Champ Electrique) experiments on board the DEMETER satellite, possible irregularities in ULF magnetic and electric components have been surveyed in the vicinity of Samoa (29 September 2009) earthquake region. The data used in this paper cover the period from 1 August 2009 to 11 October 2009. The anomalous variations in magnetic components (Bx, By and Bz) were clearly observed on 1 and 3 days before the event. It is seen that the periodic patterns of the magnetic components obviously changed prior to the earthquake. These unusual variations have been also observed in the variations of polarization index obtained from the magnetic components during the whole period at ~10:30 and ~22:30 LT. It is concluded that the polarization exhibits an apparent increase on 1 and 3 days preceding the earthquake. These observed unusual disturbances in ULF magnetic components were acknowledged using the detected perturbations in ULF electric components (Ex, Ey and Ez) in the geomagnetic coordinate system. Finally, the results reported in this paper were compared with previous results for this Samoa earthquake. Hence, the detected anomalies resulting from the magnetometer and ICE ULF waveforms in quiet geomagnetic conditions could be regarded as seismo-ionospheric precursors.

Peculiarities of low-latitude and equatorial ionosphere prior to strong earthquakes

The brief review of a number of recent publications regarding pre-earthquake anomalies of ionosphere electron density is presented. It is shown that the effects of earthquakes with their epicentres located at different latitudes are observable in the low-latitude ionosphere. The paper analyses the retrospective plasma frequency data obtained by a topside ionosonde onboard the satellite Alouette 1 at the peak height of the ionospheric F region prior to several strong earthquakes. These are the earthquakes of magnitudes M ≥6 that have occurred in the American longitudinal zone with their epicentres located within the ±20° range of magnetic inclination. Bottomside ionograms of nearby ionospheric stations Huancayo, La Paz, Talara and Bogota are also used. Only the data for quiet geomagnetic conditions are considered. The main peculiarities of the F peak electron density modification at low latitudes are summarized. Their possible explanation within the framework of already existing approaches is proposed.

PENGUIn/AGO and THEMIS conjugate observations of whistler mode chorus waves in the dayside uniform zone under steady solar wind and quiet geomagnetic conditions

We perform a case study of conjugate observations of whistler mode chorus waves on the dayside made on 26 July 2008 by three THEMIS spacecraft and ground‐based ELF/VLF receivers at the Automatic Geophysical Observatories (AGO) in Antarctica supported by the U.S. Polar Experiment Network for Geospace Upper‐atmosphere Investigations (PENGUIn) project. The dayside chorus waves were excited during a period of no substorm activity with geomagnetic indices indicating quiet conditions (Dst ∼ −10 nT; AE < 200 nT). The solar wind dynamic pressure was almost constant during the chorus wave intensification. Conjugate observations in the outer magnetosphere confirm that the chorus intensification was localized within the radial distance R = 7–10 RE near noon (12.5 < MLT < 13.5 h). The waves persisted for at least 1.5 h in the same location, where field lines are not accompanied by off‐equatorial minimum‐B pockets but rather exhibit nearly zero dB/ds, the field‐aligned gradient in B‐magnitude, over a wide range of magnetic latitudes (∼±20°). The location did not seem to corotate with the Earth or drift with the energetic electrons. The chorus waves consisted of discrete, rising tone elements, propagating away from the magnetic equator, quasi‐parallel to the ambient magnetic field (wave‐normal angles < 20°). We conclude that the long‐lasting, localized, quiet time dayside chorus amplification was due to the nearly zero dB/ds conditions that occur naturally in the dayside uniform zone (DUZ), the transition region between the near‐Earth dipole and the compressed, off‐equatorial double‐minimum field configuration found closer to the magnetopause. We thus suggest that the magnetic field configuration in the dayside outer magnetosphere plays a key role in the generation of dayside chorus waves under quiet geomagnetic conditions.

Very large array observations of disturbed ion flow from the plasmasphere to the nighttime ionosphere

We present the results of a multiscale analysis of TEC fluctuations using a roughly five‐hour observation of the bright radio source Virgo A with the Very Large Array (VLA) at 74 MHz in its B configuration. Our analysis combines data sensitive to fine‐scale structure (∼10 km and <0.001 TECU in amplitude) along the line of sight to Virgo A as well as larger structures (hundreds of km) observed using several (∼30) moderately bright sources in the field of view. The observations span a time period from midnight to dawn local time during 1 March 2001. Several groups of magnetic eastward directed (MED), wavelike disturbances were identified and determined to be located within the plasmasphere (2.1 < L < 2.9). We have also detected evidence of non‐wavelike structures associated with these disturbances which are propagating roughly toward magnetic north. These likely represent a non‐uniform density flow from the plasmasphere toward the nighttime ionosphere. AE andKp indices and GPS TEC data indicate that during the observations, there were low levels of geomagnetic activity accompanied by somewhat localized depletions in ionospheric density. Thus, the observed plasmaspheric disturbance may be part of a flow triggered by these ionospheric depletions, likely associated with forcing from the lower atmosphere which is typically more prominent during quiet geomagnetic conditions. In addition, we have also observed several roughly westward directed and southeast directed waves located within the ionosphere. They are coincident in time with the plasmaspheric disturbances and may be related to the deposition of material onto the nighttime ionosphere.

Auroral forms that extend equatorward from the persistent midday aurora during geomagnetically quiet periods

Auroral forms (“crewcuts”) that extend equatorward from the geomagnetically east–west aligned persistent midday aurora have been characterized based on a survey of Svalbard 630.0-nm all-sky images from eight December solstice seasons. The 630.0-nm forms are directly related to a mix of precipitating magnetosheath and plasma sheet electrons embedded in a population of boundary layer ions, as observed by NOAA 6. The associated midday aurora lies at the equatorward edge of poleward velocity-dispersed cusp ‘ion plumes’ observed by DMSP F7 at 1000 magnetic local time. In this survey, crewcuts are found to occur for Kp≤3. Distinct in many salient ways (including dynamics, orientation and associated IMF polarity) from the poleward-moving auroral forms (PMAFs) associated with transient dayside merging, crewcuts represent a solar wind-magnetosphere interaction that is more characteristic of quiet geomagnetic conditions. Crewcuts are present on 44% of the days for which all-sky images are complete and observing conditions are clear ±1.5h around geomagnetic noon. During these periods, crewcuts are observed during 10.6% of the minutes for which IMF data from ISEE 2 or IMP 8 are available. We derive from the data a simple set of IMF “search criteria” that maximize the likelihood of observing crewcuts around the December solstice. The IMF magnitude range for which crewcuts are most commonly observed is 3.5±0.5nT (36%). The IMF GSM component ranges in which crewcuts are most commonly observed are: Bx=−3.5±0.5nT (27%), By=−1.5±0.5nT (25%), and Bz=0.5±0.5nT (26%). The IMF clock angular ranges for which crewcuts are most commonly observed are −70°±10° and 90°±10° (both 21%). The IMF cone angular range for which crewcuts are most commonly observed is 12.5°±2.5° (28%). Considering these observations in the context of magnetic merging topologies, we suggest crewcuts observed at Svalbard are most likely to lie at the foot of overdraped field lines recently opened by spatially patchy, quasi-steady merging in the southern hemisphere.

Enhanced energetic electron fluxes at the region of the auroral oval during quiet geomagnetic conditions November 2009

Enhanced fluxes of subrelativistic electrons were studied using the CORONAS-PHOTON satellite data during November 2009. During this time interval quiet geomagnetic conditions were unusually quiet. It was found that for more than 50% of all events, the enhanced fluxes with very similar characteristics were observed at two or more consecutive orbits, i.e. have a life time of a few hours. The analysis of relative location of enhanced fluxes and auroral particle precipitations, measured simultaneously by the low orbiting METEOR-M and DMSP satellites, showed that the enhanced fluxes are located inside the auroral oval, i.e. poleward from the external boundary of the outer electron radiation belt. This fact was also confirmed comparing these fluxes with the auroral oval boundaries provided by the OVATION model of auroral precipitations. The nature of the observed events is discussed.

Non-typical ground-based quasi-periodic VLF emissions observed at L∼5.3 under quiet geomagnetic conditions at night

Non-typical long lasting quasi-periodic (QP) VLF emissions have been recorded in Northern Finland at L∼5.3 during the recent Finnish VLF campaign held in December 2011. Contrary to the typical daytime QP emissions, the night-time and early morning (00–05UT) event reported here for the first time is a sequence of 1.5–3.5kHz noise bursts lasting for several tens of seconds with an unusually long repetition period which gradually decreases from ∼700s to ∼50s. These QP emissions were observed under conditions of very quiet geomagnetic activity (Kp=0). In spite of that, the interplanetary magnetic field generally had a small southward component, and a high-latitude substorm occurred on the night-side. After this substorm, the repetition period of the VLF bursts suddenly dropped from ∼200s to∼60s and the spectral structure of QP wave changed. We attribute these QP emissions to auto-oscillations of the cyclotron instability of the Earth's radiation belts. According to the theory, the repetition period of the QP should be inversely proportional to the flux of the gyroresonant energetic electrons. Thus the increased flux of energetic electrons injected by the substorm probably led to the decreasing QP repetition periods.

Mechanisms of stratification of the F2 layer and formation of the F3 and G layers in the equatorial ionosphere

The paper is dedicated to the studies of formation mechanisms of additional layers in the equatorial ionosphere carried out using numerical simulations with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) modified in the part of the solution of the electric field equation in the Earth’s ionosphere. Calculations were preformed for quiet geomagnetic conditions using the MSIS-90 model for the calculation of thermospheric parameters. The obtained spatio-temporal pattern of thermospheric circulation and the variations in the dynamo electric field obtained on its basis make it possible to reproduce the stratification effect of the F2 layer and the appearance of the F3 layer in the equatorial ionosphere due to the action of the nonuniform in height zonal electric field at the geomagnetic equator. On the basis of the earlier presented results of calculations using the modified GSM TIP model, the appearance of a maximum in the vertical profile of the electron density at a height of ∼1000 km formed by H+ ions, which we called the G layer, has been predicted. Numerical simulations showed that this layer is formed by the meridional component of the thermospheric wind and is related to the formation of the nighttime midlatitude maximum at heights of the ionospheric F region.

Variations in statistical parameters of the NmF2 winter anomaly with latitude and solar activity

The maximal R ratios of the winter-to-summer NmF2 values of each ionosonde are calculated for a specified UT under daytime quiet geomagnetic conditions and at approximately equal levels of solar activity, based on foF2 measurement data of 98 ionosondes at mid- and low geomagnetic latitudes of the Northern and Southern hemispheres for 1957–2009. The P(R > 1) conditional probability of NmF2 winter anomaly observations, as well as the most probable RMP and average of R values are calculated for low, moderate, and high solar activity on the base of foF2 measurements during the periods December 22 ± 30 days and June 21 ± 30 days. Variations in P(R > 1), RMP, and 〈R〉 with latitude and solar activity are analyzed.

Ionospheric disturbances on 8 September, 2010: Was it connected with the incoming moderate Chongqing earthquake?

Earthquake prediction stimulates the searches for a correlation between seismic activity and ionospheric anomalies. Contrary to common focuses on strong earthquakes, we report the ionospheric disturbances, 2days before a moderate Ms=4.7 Chongqing earthquake (29.4°N, 105.5°E, depth=7.0km, occurred at 21:21LT, 10 September, 2010) with the data of ground-based ionosondes and IGS receivers. The data covering the period under the quiet geomagnetic conditions and a geomagnetic storm was analyzed with upper and lower bounds. It is found that there were significant enhancements of foF2 and total electron content (TEC) on the afternoon of 8 September, 2010, with a limited area close to the epicentre, which was different from the feature of ionospheric perturbations triggered by the geomagnetic storm on 15 September. Taking into account the heliogeomagnetical condition, we conclude that the observed ionospheric enhancements were very likely associated with the forthcoming moderate Chongqing earthquake, which implies that the relationship between the amplitudes of ionospheric disturbances and earthquakes is very complicated.