Equatorial Density Research Articles

Reconstruction of Plasmaspheric Density Distributions by Applying a Tomography Technique to Jason‐1 Plasmaspheric TEC Measurements

AbstractWe have developed a tomography algorithm and applied it to a plasmaspheric total electron content data set from Jason‐1 satellite (~1,336 km), which has a Global Positioning System receiver onboard. To invert the measured plasmaspheric total electron content into vertical distribution of electron density, we adopted a multiplicative algebraic reconstruction technique with an assumed initial density distribution. The reconstruction of the plasmaspheric density distribution was performed on Indian (70°E − 90°E), Pacific (200°E − 220°E), and Atlantic (320°E − 340°E) longitudinal planes during the periods of high solar activity (F10.7 > 100) and low geomagnetic activity (Ap < 12) from 2002 to 2005. The reconstructed density distribution displays general climatological characteristics of the plasmasphere. For all three longitudinal sectors, the reconstructed density distributions show weak diurnal variations being greater during daytime (09–15 LT) than nighttime (21–03 LT). In Atlantic sector, the reconstructed plasmaspheric density exhibits an annual anomaly (higher density in December than in June), which was not apparent in other longitude sectors. By fitting the reconstructed density profiles, we derived empirical functions of equatorial plasmaspheric density profiles for 4 months (March, June, September, and December) in the three longitude sectors. The parameters associated with these functions were found to exhibit diurnal variation and annual anomaly characteristics.

Development and Validation of the Whole Atmosphere Community Climate Model With Thermosphere and Ionosphere Extension (WACCM‐X 2.0)

AbstractKey developments have been made to the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). Among them, the most important are the self‐consistent solution of global electrodynamics, and transport of O+ in the F‐region. Other ionosphere developments include time‐dependent solution of electron/ion temperatures, metastable O+ chemistry, and high‐cadence solar EUV capability. Additional developments of the thermospheric components are improvements to the momentum and energy equation solvers to account for variable mean molecular mass and specific heat, a new divergence damping scheme, and cooling by O(3P) fine structure. Simulations using this new version of WACCM‐X (2.0) have been carried out for solar maximum and minimum conditions. Thermospheric composition, density, and temperatures are in general agreement with measurements and empirical models, including the equatorial mass density anomaly and the midnight density maximum. The amplitudes and seasonal variations of atmospheric tides in the mesosphere and lower thermosphere are in good agreement with observations. Although global mean thermospheric densities are comparable with observations of the annual variation, they lack a clear semiannual variation. In the ionosphere, the low‐latitude E × B drifts agree well with observations in their magnitudes, local time dependence, seasonal, and solar activity variations. The prereversal enhancement in the equatorial region, which is associated with ionospheric irregularities, displays patterns of longitudinal and seasonal variation that are similar to observations. Ionospheric density from the model simulations reproduces the equatorial ionosphere anomaly structures and is in general agreement with observations. The model simulations also capture important ionospheric features during storms.

Seasonal Atmospheric Argon Variability Measured in the Equatorial Region of Mars by the Mars Exploration Rover Alpha Particle X‐Ray Spectrometers: Evidence for an Annual Argon‐Enriched Front

AbstractThe Mars Exploration Rover Opportunity (MER‐B) has been exploring the surface of Mars since landing in 2004. Its Alpha Particle X‐ray Spectrometer (APXS) is primarily used to interrogate the chemical composition of rocks and soil samples in situ. Additionally, the APXS has measured the atmosphere of Mars with a regular cadence, monitoring the change in relative atmospheric argon density. Atmospheric measurements with the MER‐B APXS span over six Mars years providing an unprecedented level of statistics for careful study of the ubiquitous APXS spectral background. Several models were applied to high‐frequency long‐duration Spirit rover atmospheric APXS measurements. The most stable model with the least uncertainty was applied to the MER‐B data set. Seasonal variation of 10–15% in equatorial atmospheric argon density was observed ‐ in agreement with existing literature and global climate models. Unseen in previous work and global climate models, an abrupt deviation from the model‐predicted annual mixing ratio was measured by the MER‐B APXS around Ls 150. The sharp change, ~10% over 10° Ls, provides strong evidence for a northward migrating front, enriched in argon, sourced from the south pole at the end of southern winter. A similar weaker front is possibly observed around Ls 325, sourced from the northern polar region.

Four-peak longitudinal distribution of the equatorial plasma bubbles observed in the topside ionosphere: Possible troposphere tide influence

In this paper we consider an idea of the troposphere tide influence on the character of the longitudinal variations in the distribution of the equatorial plasma bubbles (EPBs) observed in the topside ionosphere. For this purpose, the obtained EPB longitudinal patterns were compared with the thermosphere and ionosphere characteristics having the prominent “wave-like” longitudinal structures with wave number 4, which are uniquely associated with the influence of the troposphere DE3 tides. The characteristics of the equatorial mass density anomaly (EMA), equatorial ionization anomaly (EIA), zonal wind and pre-reversal E × B drift enhancement (PRE) were used for comparison. The equinox seasons during high solar activity were under consideration. It was obtained that the longitudinal patterns of the EMA and zonal wind show the surprising similarity with the EPB distributions (R ≅ 0.8, R ≅ 0.72). On the other hand, the resemblance with the ionosphere characteristics (EIA, PRE) is rather faint (R ≅ 0.37, R ≅ 0.12). It was shown that the thermosphere zonal winds are the most possible transfer mediator of the troposphere DE3 tide influence. The most successful moment for the transfer of the troposphere DE3 tide energy takes place in the beginning of the EPB production, namely, during the seed perturbation development.

Modeling the Jovian magnetosphere under an antiparallel interplanetary magnetic field from a global MHD simulation

We present preliminary results of a new global Magnetohydrodynamics (MHD) simulation model of the Jovian magnetosphere. The model incorporates mass loading from Jupiter's satellite Io, the planet's fast corotation, and electrostatic coupling between its magnetosphere and ionosphere (M-I coupling). The basic configuration of the Jovian magnetosphere including the equatorial plasma flow pattern, the corotation enforcement current system, and the field aligned currents (FACs) in the ionosphere are presented under an antiparallel interplanetary magnetic field (IMF) condition. The simulation model results for equatorial density and pressure profiles are consistent with results from data-based empirical models. It is also found that there are similarities between the FACs distribution in the ionosphere and the observed aurora features, showing the potential application of the simple ionospheric model to the complicated M-I coupling. This model will help deepen our understanding of the global dynamics of the Jovian magnetosphere.

Swept Forward Magnetic Field Variability in High‐Latitude Regions of Saturn's Magnetosphere

AbstractSwept forward field is the term given to configurations of magnetic field wherein the field lines deviate from the meridional planes of a planet in the direction of its rotation. Evidence is presented for swept‐forward field configurations on Cassini orbits around Saturn from the first half of 2008. These orbits were selected on the basis of high inclination, spatial proximity, and temporal proximity, allowing for the observation of swept‐forward field and resolution of dynamic effects using data from the Cassini magnetometer. Nine orbits are surveyed; all show evidence of swept‐forward field, with typical sweep angle found to be 23°. Evidence is found for transient events that lead to temporary dramatic increases in sweep‐forward angle. The Michigan Solar Wind Model is employed to investigate temporal correlation between the arrivals of solar wind shocks at Saturn with these transient events, with two shown to include instances corresponding with solar wind shock arrivals. Measurements of equatorial electron number density from anode 5 of the Cassini Plasma Spectrometer instrument are investigated for evidence of magnetospheric compression, corresponding with predicted shock arrivals. Potential mechanisms for the transfer of momentum from the solar wind to the magnetosphere are discussed.

Comprehensive Analysis of the Geoeffective Solar Event of 21 June 2015: Effects on the Magnetosphere, Plasmasphere, and Ionosphere Systems

A full-halo coronal mass ejection (CME) left the Sun on 21 June 2015 from active region (AR) NOAA 12371. It encountered Earth on 22 June 2015 and generated a strong geomagnetic storm whose minimum Dst value was −204 nT. The CME was associated with an M2-class flare observed at 01:42 UT, located near disk center (N12 E16). Using satellite data from solar, heliospheric, and magnetospheric missions and ground-based instruments, we performed a comprehensive Sun-to-Earth analysis. In particular, we analyzed the active region evolution using ground-based and satellite instruments (Big Bear Solar Observatory (BBSO), Interface Region Imaging Spectrograph (IRIS), Hinode, Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), covering H $\upalpha$ , EUV, UV, and X-ray data); the AR magnetograms, using data from SDO/Helioseismic and Magnetic Imager (HMI); the high-energy particle data, using the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument; and the Rome neutron monitor measurements to assess the effects of the interplanetary perturbation on cosmic-ray intensity. We also evaluated the 1 – 8 A soft X-ray data and the ${\sim}\, 1$ MHz type III radio burst time-integrated intensity (or fluence) of the flare in order to predict the associated solar energetic particle (SEP) event using the model developed by Laurenza et al. (Space Weather 7(4), 2009). In addition, using ground-based observations from lower to higher latitudes (International Real-time Magnetic Observatory Network (INTERMAGNET) and European Quasi-Meridional Magnetometer Array (EMMA)), we reconstructed the ionospheric current system associated with the geomagnetic sudden impulse (SI). Furthermore, Super Dual Auroral Radar Network (SuperDARN) measurements were used to image the global ionospheric polar convection during the SI and during the principal phases of the geomagnetic storm. In addition, to investigate the influence of the disturbed electric field on the low-latitude ionosphere induced by geomagnetic storms, we focused on the morphology of the crests of the equatorial ionospheric anomaly by the simultaneous use of the Global Navigation Satellite System (GNSS) receivers, ionosondes, and Langmuir probes onboard the Swarm constellation satellites. Moreover, we investigated the dynamics of the plasmasphere during the different phases of the geomagnetic storm by examining the time evolution of the radial profiles of the equatorial plasma mass density derived from field line resonances detected at the EMMA network ( $1.5 < \mathrm{L} < 6.5$ ). Finally, we present the general features of the geomagnetic response to the CME by applying innovative data analysis tools that allow us to investigate the time variation of ground-based observations of the Earth’s magnetic field during the associated geomagnetic storm.

Ω-slow Solutions and Be Star Disks

Abstract As the disk formation mechanism(s) in Be stars is(are) as yet unknown, we investigate the role of rapidly rotating radiation-driven winds in this process. We implemented the effects of high stellar rotation on m-CAK models accounting for the shape of the star, the oblate finite disk correction factor, and gravity darkening. For a fast rotating star, we obtain a two-component wind model, i.e., a fast, thin wind in the polar latitudes and an Ω-slow, dense wind in the equatorial regions. We use the equatorial mass densities to explore Hα emission profiles for the following scenarios: (1) a spherically symmetric star, (2) an oblate star with constant temperature, and (3) an oblate star with gravity darkening. One result of this work is that we have developed a novel method for solving the gravity-darkened, oblate m-CAK equation of motion. Furthermore, from our modeling we find that (a) the oblate finite disk correction factor, for the scenario considering the gravity darkening, can vary by at least a factor of two between the equatorial and polar directions, influencing the velocity profile and mass-loss rate accordingly, (b) the Hα profiles predicted by our model are in agreement with those predicted by a standard power-law model for following values of the line-force parameters: , and , and (c) the contribution of the fast wind component to the Hα emission line profile is negligible; therefore, the line profiles arise mainly from the equatorial disks of Be stars.

Erosion and refilling of the plasmasphere during a geomagnetic storm modeled by a neural network

AbstractWe present a history‐dependent model of the equatorial plasma density of the inner magnetosphere using a feedforward neural network with two hidden layers. As the model inputs, we take locations and time series of SYM‐H, AL, and F10.7 indices. By considering not only the instantaneous values but also the past values of geomagnetic and solar indices, the model is history dependent on levels of geomagnetic and solar activity. The modeled electron density is continuous both spatially and temporally so that the evolution of the density can be studied (such as plasmaspheric refilling). The model is trained using the electron density inferred from the spacecraft potential from three THEMIS probes. The equatorial electron density is shown to be accurately reconstructed with a correlation coefficient of r ~ 0.953 between data and model target. Since the model is history dependent, it succeeds in reconstructing various density features and dynamic behaviors, such as the quiet time plasmasphere, erosion and recovery of the plasmasphere, as well as the plume formation during a storm on 4 February 2011. Our model may provide unprecedented insight into the behavior of the equatorial density at any time and location; as an example we show the inferred refilling rate from our model and compare it to previous estimates.

Spatial distribution of the demodulated low-frequency field in the low-latitude perturbed ionosphere

Features of propagation of low-frequency electromagnetic waves in the low-latitude ionosphere are considered in the case when such waves are generated by means of demodulation of the radiation of a high-power short-wave ground transmitter in the lower ionosphere. Calculations are performed in the ray approximation based on a simplified model (developed specially for the case under study) of the anomaly of the low-latitude equatorial electron density. It is demonstrated that latitude gradients of the equatorial anomaly may result in both additional focusing and defocusing of the beam of demodulated low-frequency waves.

Solar wind, F10.7, and geomagnetic activity relationship to the equatorial plasma mass density at geosynchronous orbit

AbstractWe consider two types of events, identified by decreases in Dst below a threshold value and increases in the equatorial mass density at geosynchronous altitudes, ρeq, above a threshold value using the Takahashi et al. (2010) data set. From the Dst events and 1 day averages, we find that there is a statistically weak and small‐amplitude difference between ρeq on the day of the event and the days before and after. When hourly averages are considered, a significant peak is found to occur 6 h after event onset, and the primary factor that determines the postonset peak amplitude in ρeq is elevated F10.7. In addition, for hourly averages, ρeq following the onset of a Dst event depends on the north‐south component of the interplanetary magnetic field, Bz, after the time of onset, with higher average Bz 4 h after the event onset corresponding to larger ρeq values 7–11 h after onset. From the ρeq events, we find a weak dependence on Bz after the onset of an event, with higher average Bz 4 h after the event onset corresponding to larger ρeq values 24–36 h after onset.

Simplified models of circumstellar morphologies for interpreting high-resolution data

Equatorial density enhancements (EDEs) are a very common astronomical phenomenon. Studies of the circumstellar environments (CSE) of young stellar objects and of evolved stars have shown that these objects often possess these features. These are believed to originate from different mechanisms, ranging from binary interactions to the gravitational collapse of interstellar material. Quantifying the effect of the presence of this type of EDE on the observables is essential for a correct interpretation of high-resolution data. We seek to investigate the manifestation in the observables of a circumstellar EDE, to assess which properties can be constrained, and to provide an intuitive bedrock on which to compare and interpret upcoming high-resolution data (e.g. \emph{ALMA} data) using 3D models. We develop a simplified analytical parametrised description of a 3D EDE, with a possible substructure such as warps, gaps, and spiral instabilities. In addition, different velocity fields (Keplerian, radial, super-Keplerian, sub-Keplerian and rigid rotation) are considered. The effect of a bipolar outflow is also investigated. The geometrical models are fed into the 3D radiative transfer code {\tt LIME}, that produces 3D intensity maps throughout velocity space. We investigate the spectral signature of the $J$=3$-$2 up to $J$=7$-$6 rotational transitions of CO in the models, as well as the spatial aspect of this emission by means of channel maps, wide-slit position-velocity (PV) diagrams, stereograms, and spectral lines. Additionally, we discuss methods of constraining the geometry of the EDE, the inclination, the mass-contrast between the EDE and the bipolar outflow, and the global velocity field. Finally, we simulated \emph{ALMA} observations...

Statistical study of Saturn's auroral electron properties with Cassini/UVIS FUV spectral images

About 2000 FUV spectra of different regions of Saturn's aurora, obtained with Cassini/UVIS from December 2007 to October 2014 have been examined. Two methods have been employed to determine the mean energy 〈E〉 of the precipitating electrons. The first is based on the absorption of the auroral emission by hydrocarbons and the second uses the ratio between the brightness of the Lyman-α line and the H2 total UV emission (Lyα/H2), which is directly related to 〈E〉 via a radiative transfer formalism. In addition, two atmospheric models obtained recently from UVIS polar occultations have been employed for the first time. It is found that the atmospheric model related to North observations near 70° latitude provides the results most consistent with constraints previously published.On a global point of view, the two methods provide comparable results, with 〈E〉 mostly in the 7–17keV range with the hydrocarbon method and 〈E〉 in the 1–11keV range with the Lyα/H2 method. Since hydrocarbons have been detected on ∼20% of the auroral spectra, the Lyα/H2 technique is more effective to describe the primary auroral electrons, as it is applicable to all spectra and allows an access to the lowest range of energies (≤5keV), unreachable by the hydrocarbon method. The distribution of 〈E〉 is found fully compatible with independent HST/ACS constraints (emission peak in the 840–1450km range) and FUSE findings (emission peaking at pressure level ≤0.2µbar). In addition, 〈E〉 exhibits enhancements in the 3LT–10LT sector, consistent with SKR intensity measurements.An energy flux–electron energy diagram built from all the data points strongly suggests that acceleration by field-aligned potentials as described by Knight's theory is a main mechanism responsible for electron precipitation creating the aurora. Assuming a fixed electron temperature of 0.1keV, a best-fit equatorial electron source population density of 3 ×103m−3 is derived, which matches very well to the plasma properties observed with Cassini MAG and CAPS/ELS instruments. However, several auroral regions are characterized by relatively high 〈E〉 and low energy flux, suggesting that additional processes such as plasma injections or magnetic reconnections must be accounted for to explain the emission in these regions.The Lyα/H2 ratio technique can be used to build maps of 〈E〉 from single spectral images. As expected, preliminary results show that the spatial distribution of 〈E〉 is not uniform, as seen on Jupiter.Our study reveals that a fraction of the aurora is due to very low energy electrons (<1keV). Even in this case, comparisons between observed and modeled spectra show that 100eV is a suitable value to represent the average energy of the secondary electrons.

New modes and mechanisms of thermospheric mass density variations from GRACE accelerometers

AbstractMonitoring and understanding the upper atmosphere processes is important for orbital decay and space physics. Nowadays, Low Earth Orbit (LEO) accelerometers provide a unique opportunity to study thermospheric density variations with unprecedented details. In this paper, thermospheric mass densities variations from Gravity Recovery and Climate Experiment (GRACE) accelerometers are investigated for the period 2003–2016 using the principal component analysis (PCA). The resulting modes are analyzed and parameterized in terms of solar and magnetospheric forcing, local solar time (LST), and annual variations. A better understanding of global thermospheric air density variations is presented, which validates the suitability of our technique and model. The parameterization of the subsolar‐point annual variation shows two maxima around June and only one in December. The LST parameterization shows a new fluctuation controlling a middle latitude four‐wave pattern, with two maxima at 12 h and 21 h LST and two minima at 1 h and 17 h LST. Our parameterizations are suitable to represent small‐scale variations including, e.g., the equatorial mass density anomaly (EMA) and the midnight density maximum (MDM). Finally, the residuals are analyzed in the spectral domain, and additional contributions are found at the frequencies of the radiational tides and at the periods of 83, 93, 152, and 431 days.

Origin of asymmetries in X-ray emission lines from the blast wave of the 2014 outburst of nova V745 Sco

The symbiotic nova V745 Sco was observed in outburst on 2014 February 6. Its observations by the Chandra X-ray Observatory at days 16 and 17 have revealed a spectrum characterized by asymmetric and blue-shifted emission lines. Here we investigate the origin of these asymmetries through three-dimensional hydrodynamic simulations describing the outburst during the first 20 days of evolution. The model takes into account thermal conduction and radiative cooling and assumes a blast wave propagates through an equatorial density enhancement. From the simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra. We find that both the blast wave and the ejecta distribution are efficiently collimated in polar directions due to the presence of the equatorial density enhancement. The majority of the X-ray emission originates from the interaction of the blast with the equatorial density enhancement and is concentrated on the equatorial plane as a ring-like structure. Our "best-fit" model requires a mass of ejecta in the outburst $M_{ej} \approx 3\times 10^{-7}\,M_{\odot}$ and an explosion energy $E_b \approx 3 \times 10^{43}$ erg and reproduces the distribution of emission measure vs temperature and the evolution of shock velocity and temperature inferred from the observations. The model predicts asymmetric and blue-shifted line profiles similar to those observed and explains their origin as due to substantial X-ray absorption of red-shifted emission by ejecta material. The comparison of predicted and observed Ne and O spectral line ratios reveals no signs of strong Ne enhancement and suggests the progenitor is a CO white dwarf.

Mass loading at the magnetopause through the plasmaspheric plume

AbstractAn investigation of the transport of the plasmaspheric plasma to the dayside magnetopause under disturbed geomagnetic conditions associated with plasmaspheric plumes is conducted by numerical simulations using the Dynamic Fluid‐Kinetic (DyFK) model. The simulations present the field‐aligned density distributions and kinetic features of multiple ion species (H+/He+/O+) in a plasmaspheric flux tube that corotates while convecting toward the dayside magnetopause. The simulations show that the plasmaspheric plume can provide an equatorial magnetopause plasma density which is up to 3 orders of magnitude higher than that under the typical conditions. With the effects of wave‐particle interaction included, such mass loading through the plasmaspheric plume is even stronger. The local reconnection rate at the location where the plasmaspheric plume mass loads at the dayside magnetopause may decrease by 90%, depending on the geomagnetic activities, the outer plasmaspheric density, and the level and spatial span of the wave‐particle interaction.

Estimating some parameters of the equatorial ionosphere electrodynamics from ionosonde data in West Africa

During the International Equatorial Electrojet Year (IEEY), an IPS-42 ionosonde located at Korhogo (9.33°N, 5.42°W, −1.88° dip-lat) and a meridian chain of 10 magnetic stations were setup in West Africa (5°West longitude). In this work, some characteristic parameters of the equatorial electrojet were estimated on the basis of the IPS-42 ionosonde data at Korhogo during the years 1993 and 1994. The study consisted of determining the zonal electric field through an estimate of the plasma vertical drift velocity. The daytime plasma vertical drift velocity was estimated from the time rates of change of the F-layer virtual height variations and a correction term that takes into account the ionization production and recombination effects. This method resulted in an improved vertical drift velocity, which was found to be comparable to the results of previous studies. The estimated vertical drift velocity was used in a semi-empirical approach which involved the IRI-2012 model for the Pedersen and Hall conductivities and the IGRF-10 model for the geomagnetic main field intensity. Thus the zonal and polarization electric fields on one hand, and the eastward Pedersen, Hall and the equatorial electrojet current densities on the other hand, were estimated. Furthermore the integrated peak current density at the EEJ center was estimated from ionosonde observations and compared with that inferred from magnetometer data. The integrated EEJ peak current densities obtained from both experiments were found to be in the same order and their seasonal variations exhibit the same trends as well.

No signatures of black hole spin in the X-ray spectrum of the Seyfert 1 galaxy Fairall 9

Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$\alpha$ emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K$\alpha$ line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall 9 and show that a face-on toroidal X-ray reprocessor model involving only nonrelativistic and mundane physics provides an excellent fit to the data. The Fe K$\alpha$ line emission and Compton reflection continuum are calculated self-consistently, the iron abundance is solar, and an equatorial column density of $\sim 10^{24} \ \rm cm^{-2}$ is inferred. In this scenario, neither the Fe K$\alpha$ line, nor the Compton-reflection continuum provide any information on the black-hole spin. Whereas previous analyses have assumed an infinite column density for the distant-matter reprocessor, the shape of the reflection spectrum from matter with a finite column density eliminates the need for a relativistically broadened Fe K$\alpha$ line. We find a 90 per cent confidence range in the Fe K$\alpha$ line FWHM of $1895$-$6205 \ \rm km \ s^{-1}$, corresponding to a distance of $\sim 3100$ to $33,380$ gravitational radii from the black hole, or $0.015$-$0.49$ pc for a black-hole mass of $\sim 1-3 \times 10^{8} \ M_{\odot}$.

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

AbstractThe response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground‐based multiinstrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP 2 current system. The quasiperiodic DP 2 current system, which fluctuates coherently with fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high‐latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

GPS and in situ Swarm observations of the equatorial plasma density irregularities in the topside ionosphere

Here we study the global distribution of the plasma density irregularities in the topside ionosphere by using the concurrent GPS and Langmuir probe measurements onboard the Swarm satellites. We analyze 18 months (from August 2014 till January 2016) of data from Swarm A and B satellites that flew at 460 and 510 km altitude, respectively. To identify the occurrence of the ionospheric irregularities, we have analyzed behavior of two indices ROTI and RODI based on the change rate of total electron content and electron density, respectively. The obtained results demonstrate a high degree of similarities in the occurrence pattern of the seasonal and longitudinal distribution of the topside ionospheric irregularities derived from both types of the satellite observations. Among the seasons with good data coverage, the maximal occurrence rates for the post-sunset equatorial irregularities reached 35–50 % for the September 2014 and March 2015 equinoxes and only 10–15 % for the June 2015 solstice. For the equinox seasons the intense plasma density irregularities were more frequently observed in the Atlantic sector, for the December solstice in the South American–Atlantic sector. The highest occurrence rates for the post-midnight irregularities were observed in African longitudinal sector during the September 2014 equinox and June 2015 solstice. The observed differences in SWA and SWB results could be explained by the longitude/LT separation between satellites, as SWB crossed the same post-sunset sector increasingly later than the SWA did.