Structure Of Plasmasphere Research Articles

A new perspective and explanation for the formation of plasmaspheric shoulder structures

Abstract. Over the hours of 05:00–09:00 UT on 8 June 2001, the extreme ultraviolet (EUV) instrument on board the IMAGE satellite observed a shoulder-like formation in the morning sector and a post-noon plume-like structure. The plasmapause formation is simulated using the test particle model (TPM), based on a drift motion theory, which reproduces various plasmapause structures and evolution of the shoulder feature. The analysis indicates that the shoulder is created by sharp reduction and spatial non-uniformity in the dawn–dusk convection electric field intensity. The TPM-modeled event is found to develop an initial pre-dawn asymmetric bulge that becomes a shoulder as a result of increased “corotation” rate with an increasing L-shell that is preceded by localized outward convection. The shoulder structure rotates sunward and develops into a single- or double-plume structure during an active time period in simulation.

A model providing long‐term data sets of energetic electron precipitation during geomagnetic storms

AbstractThe influence of solar variability on the polar atmosphere and climate due to energetic electron precipitation (EEP) has remained an open question largely due to lack of a long‐term EEP forcing data set that could be used in chemistry‐climate models. Motivated by this, we have developed a model for 30–1000 keV radiation belt driven EEP. The model is based on precipitation data from low Earth orbiting POES satellites in the period 2002–2012 and empirically described plasmasphere structure, which are both scaled to a geomagnetic index. This geomagnetic index is the only input of the model and can be either Dst or Ap. Because of this, the model can be used to calculate the energy‐flux spectrum of precipitating electrons from 1957 (Dst) or 1932 (Ap) onward, with a time resolution of 1 day. Results from the model compare well with EEP observations over the period of 2002–2012. Using the model avoids the challenges found in measured data sets concerning proton contamination. As demonstrated, the model results can be used to produce the first ever >80 year long atmospheric ionization rate data set for radiation belt EEP. The impact of precipitation in this energy range is mainly seen at altitudes 70–110 km. The ionization rate data set, which is available for the scientific community, will enable simulations of EEP impacts on the atmosphere and climate with realistic EEP variability. Due to limitations in this first version of the model, the results most likely represent an underestimation of the total EEP effect.

Geocentric position preliminary detection from the extreme ultraviolet images of Chang’E-3

An Extreme ultraviolet (EUV) Camera was installed onboard the Chinese lunar surface landing mission, the Chang’E-3 lander, as a useful method to observe the Earth plasmasphere. This EUV optical payload obtained more than 600 moon-based Earth plasmasphere images since December 14, 2013. However, due to errors of unknown size and origin in the platform attitude control of the lander and in the EUV telescope pointing control during the mission operating periods, the geocentric coordinates in these EUV images are not fixed in the same position of CCD pixel. Before adequately calibrating, these positioning offsets will introduce extra errors into the analysis of the plasmaspheric structure. With only a little insufficient telemetry information, an effective calibrating method of circle-based differential algorithm is suggested and demonstrated, for automatically and precisely detecting the geocentric position in each EUV image of Chang’E-3 mission. In each EUV image, the tested method uses the outline of a circle as the basic unit to capture the contour for the bright region based on the spectral characteristic. Then, the center of the extracted circle is adopted as the geocentric position for the image. The preliminary analysis shows that this method can effectively detect the geocentric position being always consistent with the recognition result by the basic hand labor method. It is found that the radius of the circles varies from month to month from December, 2013 to May, 2014. The monthly averages of radius show relative notable positive correlation and negative correlation with the changes of both Zenith angle of the Earth at the landing area of Chang’E-3 lander, and the Earth-moon distance, respectively. This method and results here will benefit the Chang’E-3 EUV study.

Data processing and initial results from the CE-3 Extreme Ultraviolet Camera

The Extreme Ultraviolet Camera (EUVC) onboard the Chang'e-3 (CE-3) lander is used to observe the structure and dynamics of Earth's plasmasphere from the Moon. By detecting the resonance line emission of helium ions (He+) at 30.4 nm, the EUVC images the entire plasmasphere with a time resolution of 10 min and a spatial resolution of about 0.1 Earth radius (RE) in a single frame. We first present details about the data processing from EUVC and the data acquisition in the commissioning phase, and then report some initial results, which reflect the basic features of the plasmasphere well. The photon count and emission intensity of EUVC are consistent with previous observations and models, which indicate that the EUVC works normally and can provide high quality data for future studies.

Moon‐based EUV imaging of the Earth's Plasmasphere: Model simulations

The EUV imager on board the Chang'E‐3 lunar lander will image the Earth's plasmasphere from a lunar perspective to focus on some of the open questions in plasmaspheric researches (i.e., global structures, erosion, and refilling of plasmasphere). In order to achieve the understanding of the plasmaspheric dynamics in relation to these EUV images in lunar perspective, the He+ 30.4 nm emission intensities and global structures of the plasmasphere viewed from the moon are investigated using a dynamic global core plasma model embedded with TS07 magnetic field model and W05 electric field model. Two typical storms observed by the IMAGE EUV imager are systematically simulated from the perspectives of the moon. It is found from the simulations that the maximum emission intensity of the plasmasphere is ~12.3 R which is greater than that detected from polar orbit, and the global shapes and temporal evolutions of large‐scale plasmaspheric structures (plasmapause, shoulder, and plume) also have different patterns in moon‐based simulated images. It is also shown that the plasmaspheric structures extracted from moon‐based EUV images are in agreement with those from IMAGE EUV images. Systematic simulations demonstrate that specific latitudinal distribution of the plasmaspheric structures can only be imaged at specific positions in lunar orbit. It is expected that this investigation provides us with an overall understanding on moon‐based EUV images and helps to identify the plasmaspheric structures and evolution patterns in future moon‐based EUV imaging.

Dynamical processes in space: Cluster results

Abstract. After 12 years of operations, the Cluster mission continues to successfully fulfil its scientific objectives. The main goal of the Cluster mission, comprised of four identical spacecraft, is to study in three dimensions small-scale plasma structures in key plasma regions of the Earth's environment: solar wind and bow shock, magnetopause, polar cusps, magnetotail, plasmasphere and auroral zone. During the course of the mission, the relative distance between the four spacecraft has been varied from 20 km to 36 000 km to study the scientific regions of interest at different scales. Since summer 2005, new multi-scale constellations have been implemented, wherein three spacecraft (C1, C2, C3) are separated by 10 000 km, while the fourth one (C4) is at a variable distance ranging between 20 km and 10 000 km from C3. Recent observations were conducted in the auroral acceleration region with the spacecraft separated by 1000s km. We present highlights of the results obtained during the last 12 years on collisionless shocks, magnetopause waves, magnetotail dynamics, plasmaspheric structures, and the auroral acceleration region. In addition, we highlight Cluster results on understanding the impact of Coronal Mass Ejections (CME) on the Earth environment. We will also present Cluster data accessibility through the Cluster Science Data System (CSDS), and the Cluster Active Archive (CAA), which was implemented to provide a permanent and public archive of high resolution Cluster data from all instruments.

Reconstruction of the plasmasphere from Moon-based EUV images

[1] A two-step algorithm for plasmasphere reconstruction from images obtained from the Moon-based extreme ultraviolet (EUV) imager on the Chang'e-3 mission is described and illustrated using simulation data obtained from a dynamic global core plasma model (DGCPM). According to the line of sight (LOS) integration patterns in Moon-based EUV imaging and the outline characteristics of the images, the equatorial plane plasmapause is reconstructed with the Minimum L Algorithm by adopting a magnetic dipole approximation. Having obtained the plasmapause locations, the quasi three-dimensional (3-D) plasmasphere, which is put into the Genetic Algorithm (GA) as an initial guess, is constructed with a statistical model assuming that the density along a field line is a constant. In this way, the plasmaspheric structure and the quasi 3-D plasmaspheric density are extracted from the Moon-based EUV images. This work provides a feasible and applicable method for data analysis of Moon-based EUV imaging, which is to be realized on the Chang'e-3 mission in the Second Phase of Chinese Lunar Exploration Program.

The influence of ionic temperature on plasmasphere structure formation

The formation of the three-dimensional structure of the plasmasphere-ionosphere system under the action of ionization/recombination, charge exchange, and field-aligned (along geomagnetic field lines) diffusion of the O+ and H+ ions was studied by numerical simulation with the use of the global theoretical model of the upper atmosphere of the Earth (UAM). These processes were shown to form a spatially inhomogeneous and nonstationary plasma sheath of the Earth with several large-scale structural total plasma density and ionic composition singularities. A substantial contribution to their formation was made not only by the magnetic field geometry but also by ionic temperature spatial nonuniformity mainly determined by nonlocal heating with photoelectrons. The mechanism of this influence was studied.

IMAGE and DMSP observations of a density trough inside the plasmasphere

We report coordinated observations of a density trough within the plasmasphere using the measurements from the radio plasma imager (RPI) and extreme ultraviolet imager (EUV) on the IMAGE satellite and the measurements from DMSP F‐15. The density trough inside the plasmasphere with a width of ∼0.7 RE in terms of L shell (from L ∼ 2.3 to L ∼ 3.0) was observed in situ by RPI when IMAGE traversed the plasmasphere in ∼2130 magnetic local time (MLT) sector. The plasmasphere images taken by the IMAGE EUV instrument confirm that the density trough is inside the plasmasphere. A 2‐D electron density image constructed from the RPI active sounding measurements reveals that the density trough extends along the magnetic field from the IMAGE orbit to at least 41° magnetic latitude. Meanwhile, the DMSP‐F15 satellite, circling the Earth at about 850 km altitude, detected a light ion density trough at the same time on the same L shells and similar MLT sector. The coordinated observations with the IMAGE and DMSP‐F15 satellite demonstrate, for the first time, that the density trough is a low‐density plasmaspheric structure extending from the plasmasphere to the topside ionosphere along the geomagnetic field lines.

Frost, Goldstein, and Korenaga awarded 2006 James B. Macelwane Medal

Daniel J. Frost, Jerry Goldstein, and Jun Korenaga received the James B. Macelwane Medal at the AGU Fall Meeting honors ceremony, which was held on 13 December 2006 in San Francisco, Calif. The medal is given for significant contributions to the geophysical sciences by an outstanding young scientist.Jerry Goldstein is one of the most exciting young researchers in space physics today, and his work has significantly advanced understanding of the Earth's magnetosphere. In particular, Jerry is widely recognized as the leading authority on the structure and dynamics of the Earth's plasmasphere, the region of cold plasma of ionospheric origin that is trapped in the inner portion of the magnetosphere.

Thermal structure of dayside plasmasphere according to the data of Tail and Auroral Probes, and Magion-5 satellite

We consider the results of measurements of density and temperature of cold plasma in the dayside sector of the plasmasphere. The measurements were made by Interball-1 (Tail Probe) in November 1995, by Interball-2 (Auroral Probe) in August 1996 (the periods close to the solar cycle minimum), and by the Magion-5 satellite in June 2000 (this period is close to the solar cycle maximum). It was shown by the measurements in the dayside sector of the plasmasphere that, contrary to expectations of model distributions of temperature in the plasmasphere [1, 2], under quiet geomagnetic conditions the temperature of hydrogen ions of the cold plasma filling the plasmasphere was observed to increase at altitudes 5000 km < H < 10000 km. Its altitude gradient was equal to ∼0.5 deg/km, the geomagnetic latitude being variable within the limits 10° < λ < 40°. The maximum values of temperature of protons, as measured by Tail Probe and Auroral Probe deep in the plasma-sphere, were equal to ∼4000–6000 K. According to the data obtained by the Magion-5 satellite in the depth of the plasmasphere, these temperatures varied within the limits 7500–8500 K. These results can be considered as some indication of a dependence of the plasmasphere thermal structure on the phase of the solar cycle. In the region 2.5 < L < 5 and at geomagnetic latitudes λ < 40°, drops of the ion temperature were regularly observed with values reaching ∼2000 K.

Magnetically controlled circumstellar plasma in the helium-weak stars

We report the discovery of variable line profiles in the magnetic helium-weak stars HD 142301, HD 142990, and HD 144334, all of which are members of the Sco-Cen association, and the hot helium-weak star HD 175362. These stars display behavior that is similar to HD 5737 and HD 79158, two helium-weak stars for which magnetically confined plasma has previously been reported. The present study thus extends the survey to all of the stars for which strong radio emission has been detected. No absorption has been detected for two other Sco-Cen chemically peculiar stars, HD 144844 and 146001, nor has it been detected from archival spectra of HD 28843, HD 49333, or HD 124224. The reported detections are the first helium-weak stars that do not belong to the sn subclass that have been found to display such UV line profile variations. It appears that the restriction of this phenomenon to the extreme helium-weak subgroup was a selection effect and that the occurrence of magnetically trapped corotating plasma is more widespread among the upper main sequence magnetic spectrum variables. We show model calculations for the variability that clarify the plasmaspheric structure. Supporting Hα observations show no evidence of line profile variability for HD 142301 and HD 144334, while HD 142990 appears to have extremely weak emission at certain phases, and the profile of HD 124224 shows some changing asymmetry.

Plasmaspheric plumes: CRRES observations of enhanced density beyond the plasmapause

CRRES plasma wave receiver density data were used to study the distribution and properties of dense plasmaspheric‐like plasma observed outside the plasmapause. Our study indicates that outer plasmaspheric structure, often called plasmaspheric plumes, blobs, tails, or detached plasma regions, can exist at all local times under all levels of geomagnetic activity. Of the 558 CRRES orbits that had at least one clearly defined plasmapause, 169 (or 30%) had plasmaspheric‐like density structures at higher L shells than the plasmapause. Most of the occurrences of plasmaspheric‐like plasma observed by CRRES were in the noon‐to‐dusk sector in the aftermath of enhanced geomagnetic activity consistent with plasmaspheric plume models.

Association of kilometric continuum radiation with plasmaspheric structures

A year's worth of observations of kilometric continuum (KC) from the plasma wave instrument (PWI) on GEOTAIL and extreme ultraviolet (EUV) images of the plasmasphere from IMAGE are compared. In the vast majority (∼94%) of the 87 cases when simultaneous data from both spacecraft were available, KC was observed to be associated with density depletions or notch structures in the plasmasphere. From a careful analysis of 1 month of EUV data comprising 13 notch structures, only one notch structure was found in which no accompanying KC was observed when GEOTAIL was in a low‐latitude position and therefore should have observed the emission if it were generated. IMAGE observations from the radio plasma imager (RPI) during passage through a plasmaspheric notch structure found that KC was generated in or very near the magnetic equator at steep gradients in density and associated with emissions in the upper hybrid resonance band as previously reported by others at lower frequencies. Statistical analysis of the KC events associated with plasmaspheric notch structures shows that the typical source region is at an equatorial radial distance of ∼2.4 RE (Earth radii) in the magnetic equator and produces an emission cone that is ∼40° in longitude and ∼20° in latitude. These results show that a density depletion or notch structure in the plasmasphere is typically a critical condition for the generation of KC but that the notch structures do not always provide the conditions necessary for the generation of the emission.

In situ and ground‐based intercalibration measurements of plasma density at L = 2.5

Two independent ground‐based experiments and two satellite‐borne experiments are used to interpret the changes in plasmaspheric composition at the same point in space during moderate geomagnetic activity on 22 January and 14 February 2001. Mass density at L = 2.5 was determined from an array of magnetometers on the Antarctic Peninsula, while the electron number density along the same flux tube was determined from analysis of the group delay of man‐made VLF transmissions from north‐east America. The IMAGE satellite RPI experiment provided in situ measurements of the electron number density in passing the equatorial region of the same field line, while the EUV Imager experiment was able to resolve the He+ abundance by looking back toward the same place a few hours later. On 22 January 2001 all measurements were consistent with a moderately disturbed plasmasphere. On 14 February 2001 there appeared to be a significant response of the plasmasphere to the moderate (Kp = 5) activity levels. Both the electron number density and the mass density determined from the ground‐based experiments were markedly higher than on 22 January 2001. Also, the IMAGE RPI gave a markedly lower electron number density than did the ground‐based data; this is explained by differences in the longitude at which the measurements were made and the presence of localized plasmaspheric structures. At Antarctic Peninsula longitudes a He+ column abundance value of 6 × 1010 cm−2 is found to be equivalent to plasmaspheric electron density levels of 3000 cm−3 at L = 2.5. For these conditions the He+ mass abundance was about 12–16% compared with H+. Both decreases and increases in the He+ column abundance measured by the EUV Imager appear to be linearly correlated to changes in the percentage occurrence of He+ as determined from a combination of ground‐based VLF and ULF observations.

Analytical representation of the plasmasphere electron temperature distribution based on Akebono data

A new approach is used to reveal the average thermal structure of plasmasphere at altitudes between 1000 and 10,000 km. This paper only considers the plasmasphere inside L = 3, and this region of space is sliced at L = 2 to one internal (denoted as equatorial) and one external (denoted as midlatitude) part. Each of these parts is divided into four altitude/local time zones: northern and southern daytime and northern and southern nighttime. Electron temperature (Te) distribution measured along every individual orbit within each zone is approximated by simple expressions that are functions of the geomagnetic latitude or L. The fitting is performed independently to each zone, and two coefficients are extracted from the individual fits: Te value at the equatorward border and the coefficient scaling the latitudinal shape. These coefficients are accumulated in each zone in order to obtain its average Te structure as a function of altitude. The fitting coefficients exhibit large scatter, which reflects the large day‐to‐day variability of plasmasphere Te. The fitting error is estimated at 6% and 12% for the equatorial and midlatitude zones, respectively. The average fit coefficients are used to check for seasonal variations in each zone and for a possible hemispheric asymmetry. It is determined that the winter sunlit plasmasphere is hotter than the summer one; the case for nighttime is reverse. The day/night amplitude is larger in the winter than in the summer, and the seasonal differences are more pronounced in the Southern Hemisphere. The latitude gradients of Te reveal a hemispheric asymmetry, which is largest during northern daytime winter. Solar activity is found to affect the plasmasphere Te. During the day at 3000 km and L = 2, Te increases by ∼2000°K when F10.7 changes from 70 to 300. The nighttime increase is ∼1000°K. At the equator, Te shows weaker dependence on solar activity. The average heat flux through 3000 km altitude is estimated at 3.7 × 109 (eV cm−2 s−1) during the day and 1.6 × 108 (eV cm−2 s−1) during the night.

The Earth's Plasmasphere with Contributions from D. L. Carpenter and V. Bassolo

The plasmasphere is a region of enduring scientific interest and considerable practical importance. A number of communications, navigation, and military satellites that are becoming indispensable to routine human activities are stationed in this region.To ensure the reliability of these assets, it is important to understand the plasmaspheric environment comprehensively Recently, there has been renewed interest in the plasmasphere as evidenced by a number of imaging missions, such as the NASA/Imager for Magnetopauseto‐Aurora Global Exploration (IMAGE), the U.S. Department of Defense/Advanced Research &amp; Global Observation Satellite (ARGOS), and the proposed Magnetospheric Imager (MI), whose objectives include imaging the plasmasphere. To fully use the information obtained by remote sensing, we must develop more accurate models of the plasmaspheric structure than are currently available. Hence, an emphasis on plasmaspheric research is particularly timely.

Relationship between the Pi2 pulsations and the localized impulsive current associated with the current disruption in the magnetosphere

Behavior of fast-magnetosonic-mode MHD signals in the inner magnetosphere that are driven by the impulsive eastward current is investigated as a model of the Pi2 signal at midnight. The magnetosphere is treated as an axisymmetric cold MHD regime with dipole magnetic fields and has the plasmaspheric structure of the Alfven speed distribution. MHD perturbation is assumed to be axisymmetric. Numerical calculation revealed the following: 1) The impulsive current induces the plasmasphere virtual resonance oscillation; 2) The compressional magnetic field perturbation is confined near the equator; 3) The waveform of the compressional magnetic perturbation in the plasmasphere depends on the spatial extent of the source current, its temporal variation, as well as its location; 4) The typical Pi2 waveform in the plasmasphere is obtained when the source current is located near the plasmapause (L ≤10); 5) When the source current is not located on the equator, the compressional component and the poloidal component have different waveforms.

Premidnight plasmaspheric “plumes”

To explain observations of brief intervals of cold, dense plasma by geosynchronous satellites in the midnight sector prior to or during substorm onset, it has recently been proposed that dense plasmaspheric plasma is drawn out to geosynchronous orbit in the premidnight region by inductive electric fields during the growth phase of a geomagnetic substorm. We present here the results of a statistical study of such intervals observed with the Los Alamos magnetospheric plasma analyzer (MPA) on geosynchronous satellite 1989‐046 between March and December 1993. We find that these premidnight cold plasma intervals occur only after extended periods of low magnetospheric activity identified by Kp and the midnight boundary index (MBI). We also find that the satellite typically enters the cold plasma region from the trough region and exits it into the plasma sheet. Finally, while measurements of the flow velocity of the cold plasma are rendered uncertain by the asymmetric spacecraft charge or photoelectron sheath, such measurements show no evidence of the outward flow that would be expected from the extrusion hypothesis. Rather, there are some indications that these cold plasma regions flow sunward in the (corotation) satellite frame. These results suggest an alternative explanation for the premidnight cold plasma: corotation‐dominated transport of day side plasmaspheric structures into the premidnight sector. The implications of our observations for the extrusion hypothesis and for the alternative explanation are discussed.

Electrodynamics of rotating planetary plasmaspheres in a dipole magnetic field

As a model of the actual structure of the planetary plasmasphere, we consider the electrodynamical problem of electric field and current generation by a planet with a dipole magnetic field corotating with the plasma envelope. The plasma envelope is characterized by the conductivity and angular velocity of the magnetospheric plasma as functions of the distance τ from the planet center and the angle ϑ measured from the rotation axis. The exact solutions of the Maxwell equations are obtained in the axially symmetric case within the framework of unipole electrodynamics when the rotational and magnetic axes coincide. These solutions describe the possible distributions of electric fields, currents, and charges in the rotating plasma envelope surrounding the magnetized planet. As an exmple, we constructed, using the theory proposed, the exact solution corresponding to the following structure of the plasmasphere: Analysis of the multipole expansion of the electrostatic potential showed that the electric field potential is equal to zero in the external region (L>L*+L0), independently of the number of the boundary L-shell. This solution can serve as a basis for simulation of the plasmasphere formation processes, taking into account the actual conditions in the near-planetary plasma envelopes.