Earth's Plasmasphere Research Articles

Role of Earth's plasmasphere in coupling of upper atmosphere

The near-Earth space environment is a complex, ever changing system of magnetized plasmas whose behaviour has a profound impact upon our technology dependent society. The exploration of the cold, relatively dense, inner region of upper atmosphere (the plasmasphere) and its unexpectedly sharp outer boundary (the plasma pause) has proceeded through a combination of in-situ observations and ground based whistler observations. Studies have shown that plasmasphere is highly variable both spatially and temporally responding to changes in geomagnetic indices, ring current, penetration and shielding electric fields and subauroral electric fields. Consequently the plasmasphere exhibits erosion, emptying and refilling during active times. Infact, it is the electric field that plays one of the most important roles in coupling of upper atmosphere. The atmospheric dynamo is the main generator of the large-scale electric field in the upper atmosphere. It arises because of a special situation which electrons and ions move with different velocities across the magnetic field because of different collisions between electrons and neutral particles and ions with neutral particles. This process leads to charge separation and consequently to an electric field. In the present paper, storm/ quiet period VLF whistler data recorded at lower latitudes/mid latitudes are analyzed and attempt has been made to look at plasmasphere response on coupling of ionosphere and magnetosphere.

An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions

A long-standing problem in the field of space physics has been the origin of plasmaspheric hiss, a naturally occurring electromagnetic wave in the high-density plasmasphere (roughly within 20,000 kilometers of Earth) that is known to remove the high-energy Van Allen Belt electrons that pose a threat to satellites and astronauts. A recent theory tied the origin of plasmaspheric hiss to a seemingly different wave in the outer magnetosphere, but this theory was difficult to test because of a challenging set of observational requirements. Here we report on the experimental verification of the theory, made with a five-satellite NASA mission. This confirmation will allow modeling of plasmaspheric hiss and its effects on the high-energy radiation environment.

Kalman filter-based algorithms for monitoring the ionosphere and plasmasphere with GPS in near-real time

Data collected from a GPS receiver located at low latitudes in the American sector are used to investigate the performance of the WinTEC algorithm [Anghel et al., 2008a, Kalman filter-based algorithm for near realtime monitoring of the ionosphere using dual frequency GPS data. GPS Solutions, accepted for publication; for different ionospheric modeling techniques: the single-shell linear, quadratic, and cubic approaches, and the multi-shell linear approach. Our results indicate that the quadratic and cubic approaches perform much better than the single-shell and multi-shell linear approaches in terms of post-fit residuals. The performance of the algorithm for the cubic approach is then further tested by comparing the vertical TEC predicted by WinTEC and USTEC [Spencer et al., 2004. Ionospheric data assimilation methods for geodetic applications. In: Proceedings of IEEE PLANS, Monterey, CA, 26–29 April, pp. 510–517] at five North American stations. In addition, since the GPS-derived total electron content (TEC) contains contributions from both ionospheric and plasmaspheric sections of the GPS ray paths, in an effort to improve the accuracy of the TEC retrievals, a new data assimilation module that uses background information from an empirical plasmaspheric model [Gallagher et al., 1988. An empirical model of the Earth's plasmasphere. Advances in Space Research 8, (8)15–(8)24] has been incorporated into the WinTEC algorithm. The new Kalman filter-based algorithm estimates both the ionospheric and plasmaspheric electron contents, the combined satellite and receiver biases, and the estimation error covariance matrix, in a single-site or network solution. To evaluate the effect of the plasmaspheric component on the estimated biases and total TEC and to assess the performance of the newly developed algorithm, we compare the WinTEC results, with and without the plasmaspheric term included, at three GPS receivers located at different latitudes in the American sector, during a solar minimum period characterized by quiet and moderate geomagnetic conditions. We also investigate the consistency of our plasmaspheric results by taking advantage of the specific donut-shaped geometry of the plasmasphere and applying the technique at 12 stations distributed roughly over four geomagnetic latitudes and three longitude sectors.

A new perspective on the Earth's plasmasphere

Sixty years ago, Owen Storey concluded that “whistler” radio waves propagate along the geomagnetic field lines through a dispersive medium, which is now known as the plasmasphere. This was confirmed by Gringauz's plasma measurements on Lunik 2 in 1962. In recent years, satellites such as NASA's Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) and the European Space Agency's Cluster probes have offered what previous spacecraft could not: a nonlocal perspective.As IMAGE and Cluster have accumulated more than 6 years of observations, researchers from both communities judged the time was ripe for a review at a workshop organized last September by the Belgian Institute for Space Aeronomy (http.7/ www.aeronomy.be/en/workshop/ plasmasphere/overview.htm). This meeting report summarizes some highlights of the meeting.

New aspects in plasmaspheric ion temperature variations from INTERBALL 2 and MAGION 5 measurements

INTERBALL 2 (1996) and MAGION 5 (1999–2001) cold plasma measurements provided the possibility to deduce new aspects of ion temperature distributions in the Earth's plasmasphere during magnetically quiet and moderately disturbed times. Proton temperatures in the plasmasphere were compared along the magnetic field lines to electron and ion temperatures measured by DMSP satellites in the upper (∼840 km) ionosphere. On the nightside for 1.4< L<2.8, plasmaspheric temperatures were found to be quite close to ionospheric electron temperatures. At L=2.5–2.8, ion temperatures in the plasmasphere were close to electron temperatures in the upper ionosphere everywhere except for the noon-to-dusk MLT sector. At higher L ( L>3), the plasmasphere-to-ionosphere temperature ratio was greater than 1, and there was also an increase in the 12–20 MLT sector. Apparently there is a heating source at high L that is strongest in the noon-to-dusk MLT sector. It was revealed that during moderate magnetic storm development, nighttime ion temperature was depressed in the storm main phase, but exceeded quiet time values in the storm recovery phase. Possible reasons of such temperature behavior are briefly discussed.

Study for dual-function EUV multilayer mirror

Studying the distribution of He + in Earth's plasmasphere by detecting its resonantly scattered emission at 304 Å will record the structure and dynamics of the cold plasma in Earth's plasmasphere on a global scale. EUV imaging systems usually utilizes near-normal incidence optics including multilayer mirror and filter. In this paper, the space condition of the Earth's plasmasphere to confirm the expected performance of mirror were analyzed. In order to achieve higher response at 304 Å and reduce 584 Å radiation for the optical system, a new multilayer coating of Mo/Si with UO 2 was developed. Based on optical constants of Mo, Si and UO 2, we used a simplest method to compute the reflectance of this new multilayer mirror range from 100 to 584 Å. The results show the desirable thickness of UO 2 is 17 Å, and the multilayer mirror has a high reflectance of 26.10% at 304 Å and a low reflectance of 0.52% at 584 Å.

Passive remote sensing of the Earth's plasmasphere using Whistler mode waves

AbstractAs the uses of artificial satellites diversify, investigation of the propagation characteristics of electric waves surrounding the Earth has become an important task. These electric waves are strongly influenced by plasma, a propagation medium, but although on the one hand investigation of plasma in the ionosphere is proceeding with various different methods being used, current investigations into the density profile of plasma in the plasmasphere is not progressing since it is hampered by the fact that satellites produce only single point observations. In this paper we develop a method for estimating the density profile of the global electrical field of the plasmasphere from natural VLF band electromagnetic wave frequency spectra and propagation vector direction information observed by satellite by solving an ill‐posed inverse problem. We confirm the uniqueness of the solution by performing a brute force search using a dictionary and investigate the applicability of our method to actual data by using pseudo‐observation data. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 51–61, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20377

Температура холодных ионов в ночном секторе плазмосферы Земли

Температура холодных ионов в ночном секторе плазмосферы Земли

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.

Realistic magnetospheric density model for 29 August 2000

Using a two dimensional image of the Earth's plasmasphere taken by the Extreme Ultraviolet Imager (EUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, in-situ electron density measurements from the IMAGE Radio Plasma Imager (RPI) instrument, measurements of magnetospheric mass density inferred from field line resonant frequencies measured by magnetometers on the Earth's surface, and a model for the density field aligned variation, we construct a computer model for the magnetospheric density on 29 August 2000 at 1519 UT. The purposes of this study are to demonstrate how a density model can be constructed using multiple data sources, to document this particular model, which is being used in studies of ultra low frequency Pi-2 oscillations and plasmaspheric cavity modes, to describe some of the problems involved with EUV density inversion, and to demonstrate some features of the plasmaspheric density, particularly in the region of the dusk plasmatrough and plume.

INTERBALL-1 Observations of the Kilometric “Continuum” of the Earth's Magnetosphere

The electromagnetic radio-frequency emission of the inner region of the Earth's plasmasphere discovered recently by the GEOTAIL satellite [4] and referred to as the “kilometric continuum” was observed by the INTERBALL-1 satellite (1995–2000) in the 100–500 kHz band in the AKR-X experiment. During a period of low solar activity (1995–1997), this “continuum” was found leaving the inner plasmasphere at geocentric distances of 2–4RE as isolated pencil-like (1°–6°) beams located in the magnetic equator plane. During a time of high solar activity (1999–2000), the occurrence of the emission was extremely rare (it was observed only at a considerable fall of this activity). If detected, at the same geocentric distances (2–4RE) the “continuum” demonstrated a strongly variable and perturbed character, as well as a considerably larger extension of the beam over the geomagnetic latitude (10°–20° and more). In addition, quasi-periodic (QP) signals, similar to the observed QP emissions of Jupiter, were sometimes detected in this period. The probable nature of the observed features of the “kilometric continuum” is briefly discussed.

Unipolar induction as the origin of generation of electric fields and currents in plasmaspheres of planets

We study the generation of plasmaspheric electric fields and currents caused by differential rotation of inhomogeneously conducting plasma envelope together with a magnetized planet (a planetary generator model). The solution of the first considered model problem describing a plasmasphere flow with a discontinuity in the angular rotation velocity reveals that regions of strongly non-uniform rotation of a plasma envelope play an essential role in the generation of currents in the plasmasphere. Within the framework of the second problem we analyze the planetary generator operation under the conditions of the Earth's plasmasphere. The approximation of an abrupt decrease of the effective conductivity at ionospheric heights is used. The calculation results compared to experimental data show that the considered mechanism of current generation may be important when analyzing current systems in lower layers of the Earth's ionosphere.

Active and passive plasma wave investigations in the earth's environment: The cluster/whisper experiment

The Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation, WHISPER, performs high frequency electric field measurements on the four satellites of the CLUSTER mission. In active mode, the WHISPER behaves like a classical topside sounder. It provides, via the identification of resonances that are excited at characteristic frequencies of the encountered plasmas reliable and accurate determination of the total electron density and magnetic field strength. Whenever the transmitter is switched off, the WHISPER becomes a simple wave receiver (passive mode). The 2 to 80 kHz frequency range of the electric component of natural waves is then monitored. The main objective of the presentation is to highlight the plasma and natural waves diagnosis capabilities of the WHISPER instrument. The way the plasma resonances are extracted and identified is pointed out and results obtained from the solar wind down to the Earth's plasmasphere are shown.

International standard model of the Earth's inosphere and plasmasphere

International standard model of the Earth's inosphere and plasmasphere

Dynamics of Temperature and Density of Cold Protons of the Earth's Plasmasphere Measured by the Auroral Probe/Alpha-3 Experiment Data during Geomagnetic Disturbances

We present the results of temperature and density measurement of plasmaspheric protons under quiet and disturbed conditions in the night and dayside sectors of the plasmasphere obtained with the Auroral Probe/Alpha-3 instrument during September 1996 and January 1997. According to the experimental data, the proton temperature in the night sector of the plasmasphere depends on the level of geomagnetic disturbance: it is found that at night hours the values of temperatures inside the plasmasphere at 2.4 < L < 3.5 decreased considerably after the commencement of a geomagnetic storm. The temperature decrease, as a rule, was accompanied by the formation of a flat plateau on the density distribution n(L) at 2.4 < L < 3.5. The above experimental facts (decreasing proton temperature and formation of a flat part on the n(L) distribution) allow us to conclude that the decrease in the proton temperature in the night sector of the plasmasphere connected with magnetic disturbances is caused by the filling of field tubes (depleted after the commencement of the storm) with colder ionospheric plasma. The proton temperature in the dayside sector of the plasmasphere virtually does not depend on the level of the geomagnetic disturbance.

The Whisper Relaxation Sounder Onboard Cluster: A Powerful Tool for Space Plasma Diagnosis 1, 2 around the Earth

The WHISPER relaxation sounder that is onboard the four CLUSTER spacecraft has as its main scientific objectives to monitor the natural waves in the 2 kHz–80 kHz frequency range and, mostly, to determine the total plasma density from the solar wind down to the Earth's plasmasphere. To fulfill these objectives, the WHISPER uses the two long double sphere antennae of the Electric Field and Wave experiment as transmitting and receiving sensors. In its active working mode, the WHISPER works according to principles that have been worked out for topside sounding. A radio wave transmitter sends an almost monochromatic and short wave train. A few milliseconds after, a receiver listens to the surrounding plasma response. Strong and long lasting echoes are actually received whenever the transmitting frequencies coincide with characteristic plasma frequencies. Provided that these echoes, also called resonances, may be identified, the WHISPER relaxation sounder becomes a reliable and powerful tool for plasma diagnosis. When the transmitter is off, the WHISPER behaves like a passive receiver, allowing natural waves to be monitored. This paper aims mainly at the resonance identification process description and the WHISPER capabilities and performance highlighting.

Small‐scale field‐aligned plasmaspheric density structures inferred from the Radio Plasma Imager on IMAGE

Among the objectives of the Radio Plasma Imager (RPI) on IMAGE is the observation of the Earth's plasmasphere from the satellite's polar orbit, with apogee ≈8 RE geocentric distance and perigee near 1200 km altitude. This objective is here pursued by (1) remote sounding from high‐altitude regions outside the main plasmasphere, (2) sounding within the plasmasphere, and (3) in situ passive measurements of natural wave activity. During sounding of the plasmasphere from both outside and inside the plasmapause, RPI echoes that follow non‐field‐aligned ray paths are usually not the discrete traces on range‐versus‐frequency records (plasmagrams) that are predicted by ray‐tracing simulations in smooth magnetospheric density models. Instead, such RPI echoes exhibit various amounts of spreading, from ≈0.5 RE to ≈2 RE in virtual range (range assuming free‐space speed of light propagation). The range spreading is attributed to scattering from, partial reflection from, and propagation along geomagnetic field‐aligned electron density irregularities. There exists a substantial body of theoretical work on mechanisms that might explain the appearance of such irregularities both within and beyond the plasmasphere. That the spread‐producing irregularities are field‐aligned is suggested by the efficiency with which RPI excites discrete echoes that propagate along the geomagnetic field, sometimes into both hemispheres. The spatial distributions and scale sizes of the spread‐producing irregularities remain to be investigated. The RPI echo data, however, coupled with earlier evidence from topside sounders and whistler mode instruments, suggest that they can have cross‐field scale sizes within a range from ≈200 m to over 10 km and electron densities within ≈10% of background. RPI is found capable of detecting plasmapause locations from distances of ≈3 RE or more. When minimal signal integration is used, the location and range of density values of a steep plasmapause can be determined from distances of order 1 RE, and echoes can at times be returned from points extending inward from the plasmapause to locations where the electron density reaches ≈3000 cm−3, which is usually at L &lt; 3.

Modified electron whistler dispersion law

A modified electron whistler dispersion law is derived in the cold-plasma approximation for analytical treatment and simplified numerical calculations of wave propagation in a wide range of ratios ωc/ωp of electron gyro- to plasma frequencies if the wave frequency is much less than ωp. The net contribution of ions to the wave dispersion law is expressed through the value of the lower-hybrid resonance frequency ωlhr only. This approximate dispersion law is valid in a wide frequency domain, that is, from the range of ωlhr until the domain where the contribution of ions can be neglected. A comparison of geometrical-optics ray trajectories calculated by the use of modified and total cold-plasma electron whistler dispersion laws is presented for the case of the Earth's plasma environment. Computer simulations of dynamical spectra of whistler waves excited by lightning discharges and registered in remote regions of the Earth's plasmasphere reveal good numerical stability of the developed ray-tracing code.

Theory of low-scale mhd waves in the near equatorial region of the earth plasmasphere

Theory of low-scale mhd waves in the near equatorial region of the earth plasmasphere

Development of a compact EUV photometer for imaging the planetary magnetosphere

We have developed a lightweight, compact, and highly sensitive Extreme ultraviolet (EUV) photometer for a space‐borne instrument. The photometer is onboard Japan's Mars orbiter, Planet‐B, which was successfully launched on July 4, 1998, and stayed in the parking orbits around the Earth for 6 months. The new photometer is designed for studying the spatial distribution of helium ions and atoms by detecting He II (304 Å) and He I (584 Å), which are major emission lines detectable around a planet. The photometer is a type of normal‐incidence telescope that consists of a mirror, filters, and a detector. The mirror employs a new technology of a molybdenum/silicon multilayer coating and is designed to have peak reflectivity at 304 Å. The photometer is capable of taking two‐dimensional images by using the spin and orbital motions of the spacecraft. There are open questions concerning the Earth's plasmasphere and plasma sheet that cannot be resolved by in situ observations alone (e.g., global shape of the plasmasphere and cold ions in the plasma sheet). Our observations with the EUV photometer over a reasonable number of orbits will answer them. The photometer also shows an outstanding performance of measuring the Martian helium.