Light Ion Density Research Articles

Existence and propagation characteristics of ion-acoustic Kadomtsev–Petviashvili (KP) solitons in nonthermal multi-ion plasmas with kappa distributed electrons

The dynamics of two dimensional Kadomtsev–Petviashvili (KP) electrostatic solitary waves (ESWs) propagating in multi-ion unmagnetized plasma is investigated, in the presence of energetic (nonthermal) electrons. Two distinct ion components are considered as inertial fluids, while inertialess electrons are characterized by an excess superthermal population described by a kappa distribution. The primary (heavier and cold) ion population is assumed to be positively charged, while the charge and sign of the (lighter and warm) ions is left arbitrary in the model. A linear analysis reveals the existence of two harmonic modes propagating with different phase speeds, identified as slow and fast ion-acoustic waves i.e., SIAW, FIAW respectively. Nonlinear analysis, based on a multiscale (reductive perturbation) technique, leads to a two-dimensional Kadomtsev–Petviashvili (KP) equation for the electrostatic potential. Pulse-shaped electrostatic potential solitary wave solutions and associated bipolar electric field structures are obtained analytically as well numerically. A parametric investigation reveals that, if both ion species are positively charged, then either negative or positive polarity electrostatic potential solitary waves structures may occur for the slow (SIAW) mode case (only), depending on the light ion density and temperature. On the other hand, considering a negatively charged light (warm) ion fluid case, then solitary structures of SIAW are formed of positive polarity (only), while their fast counterpart FIAW is of opposite (negative) polarity. The (O, H) multi-ion plasma is considered and parametric dependence of nonlinear electrostatic solitary wave characteristics (amplitude, width) on the intrinsic plasma configurational parameters i.e., light-to-heavy ion density and light ion to electron temperature ratios and nonthermal electrons spectral index kappa is investigated.

Magnetoacoustic cnoidal waves and solitons in multi-ions plasmas with application to ionospheric plasmas

The magnetoacoustic nonlinear periodic (cnoidal) wave and solitons in multi-ion plasmas are studied, and its Korteweg–de Vries (KdV) equation is derived by applying the reductive perturbation (RP) method with appropriate boundary conditions. The dynamics of all species in a multi-ion plasma, which consists of warm (light) ions, cold (heavy) ions, and hot electrons, are taken in the electromagnetic field. Two types of multi-ion plasmas, i.e., H+-O+-e (positive ion plasma) and H+-O2−-e (negative ion plasma), are chosen, which can exist in different layers of the ionosphere. It is found that for the H+-O+-e plasma case, the nonlinear structure forms compressive magnetoacoustic wave pulses (which move with the super-Alfvénic speed of light ions in the lab frame) and depends on plasma parameters such as the external magnetic field intensity and light ion temperature and density. It is also found that the rarefactive magnetoacoustic wave structures (move with the sub-Alfvénic speed of light ions in the lab frame) are also formed in H+-O+-e plasma if heavy and light ions' density ratio is increased beyond a certain limit. In the case of negative ion (i.e., H+-O2−-e) plasma, again, compressive magnetoacoustic cnoidal waves and soliton structures are formed at a comparatively lower value of heavy to light ions' density ratio (χ) with the positive ion plasma case. Again, these compressive magnetoacoustic structures switch to the rarefactive ones in negative ion plasma when density ratio χ is increased beyond a certain limit. The parametric analysis and numerical plots are illustrated, and the obtained theoretical results are found to be consistent with the Freja experimental observations in the upper ionosphere.

Saturn's Dusty Ionosphere

AbstractMeasurements of electrons and ions in Saturn's ionosphere down to 1,500‐km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (Ne and Ni) near the closest approach. The small Ne/Ni ratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the Langmuir probe obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when Ne/Ni ≪ 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (Te) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2,500‐km altitude in a region where electron‐neutral collisions should be prominent. A well‐defined relationship between Te and Ne/Ni ratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere.

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.

On possible improvements of outer ionosphere ion composition model in IRI

The current version of the IRI model for the ion composition and the electron (total ion) density above 500 km is compared with the Bennett ion mass spectrometer data measured in the frame of the ACTIVE mission (maximum of the solar cycle 22). In both options (IRI standard and Danilov-Yaichnikov) the light ion density (H +, and He +) was found overestimated. Absolute O + density from IRI standard was found in general agreement with the measured data. The electron (total ion) density in altitudes above 1000 km was found also overestimated by the model employed in IRI. For period of high solar activity and altitude range of 500 to 2500 km a new global model of relative O + and H + density is presented as a first step to an improved model of the outer ionosphere ion composition.

Electrodynamic model of the lower atmosphere and the ionosphere coupling

Electrodynamic model of the ionosphere response to seismic related lower atmosphere disturbances is developed. The chain of processes forming the lithosphere–ionosphere coupling starts from the injection of radioactive substances and charged aerosols into the atmosphere. This leads to a change of the vertical electric current in the atmosphere and to modification of the electrical field in the ionosphere. Growth of the electric field and related development of acoustic-gravity wave instability is followed by formation of field-aligned currents and plasma density disturbances stretched along the geomagnetic field. Another effect of the electric field increase is an additional Joule heating of the lower ionosphere which results in an elevation of the F-layer maximum, a decrease of electron density in the maximum of this layer and a growth of light ion density in the upper ionosphere. Thus, the presented model connects disturbances of the key ionosphere parameters with increase of atmospheric radioactivity and injection of charged aerosols into the atmosphere.

Temporal Evolution of Laser Plasma Channeling in a High-Z Plasma Embedded with Light Ions

A high power laser of finite spot size, propagating through a high Z plasma embedded with light ions, exerts ponderomotive forces on the electrons. As the electrons move out of the axial region, a strong space charge field sets in that pulls the lighter and heavier ions together with the electrons. Thus a plasma channel evolves on a time scale τ = r0/cs where r0 is the spot size of the laser and cs is the characteristic sound speed. The ratio of fractional ion depletion to heavy ion depletion from the axial region is (Δnl/nl)/(Δnh/nh) = mhZln00l/mlZhn00h where mh and ml are the heavy and light ion masses, Zh and Zl, are the heavy and light ion charges, nh and nl are the heavy and light ion densities respectively. The channel is capable of self-ducting/self-focusing the laser when the power of the laser exceeds a threshold value.

Comparisons of modeled N+, O+, H+, and He+ in the midlatitude ionosphere with mean densities and temperatures from Atmosphere Explorer

In this study, Atmosphere Explorer data and model results for the ion and electron temperature and the density of N+, O+, H+, and He+ between 120 and 1400 km altitude are compared for two midlatitude ranges (L=2 and L=4), noon and midnight local time, winter and summer, at solar minimum. The data for the heavy atomic ions (O+ and N+) show that their densities are greater at noon than at midnight for a given season and greater in summer than winter for a given local time. There is only a weak latitudinal variation in the density of these ions. The data show that the light ion (H+ and He+) densities are greater at midnight than at noon and are generally greater in winter than summer. There is a strong latitudinal variation of the light ion densities, with the densities decreasing with increasing latitude. The model densities are in good agreement with the AE densities for N+, O+, and H+. Model He+ densities are lower, by a factor of 2 or more, than the measured densities. Model ion and electron temperatures agree well with the measured temperatures with only a modest increase in plasmaspheric heating.

Relative abundance of H + and He + in outer ionosphere

A mathematical model is used to study the relative abundance of H + and He + ions in the topside ionosphere. It is found that the daytime light-ion densities are strongly coupled with the neutral densities. This fact arises difficulties in modelling the ion composition for IRI without taking into account any particular reference atmosphere. As an example, the transition heights between O +H + and O +He + are shown, plotted against the neutral densities. The supposed linear dependance gives a clear evidence that all light-ion ionization below these heights will experience stronger influence by the neutral atmosphere.

Plasmaspheric refilling phenomena observed by the Intercosmos 24 satellite

The ion density, ion composition and electron temperature have been measured onboard the Intercosmos 24 satellite. Local increases of light ion density accompanied by electron temperature enhancements and simultaneously observed VLF wave phenomena are interpreted as a manifestation of the refilling ion fluxes within the plasmasphere.

Dual‐spacecraft measurements of plasmasphere‐ionosphere coupling

Nearly simultaneous and conjugate measurements of the thermal plasma density and temperature structure in the early evening ionosphere and plasmasphere are obtained with the DE 1 and 2 satellites. The results indicate a number of significant relationships in plasmasphere‐ionosphere thermal plasma interchange and coupling. The principal results are as follows: (1) A transition in the ionospheric electron temperature (Te) from a relatively smooth profile of low Te (<2000°K) at the base of the inner plasmasphere to enhanced and highly structured Te at higher invariant latitudes occurs near or along a plasmaspheric density gradient. (2) Plasmaspheric enhancements of the heavy ions O+ and O++ are often closely aligned with distinct ionospheric Te enhancements. (3) When the plasmaspheric light ion density profile contains a significant trough, there is a pronounced ionospheric Te peak aligned with the poleward plasmaspheric density enhancement or the poleward edge of the plasmaspheric trough. (4) The latitudinal structures of ionospheric Te and plasmaspheric TH+ are sometimes strikingly well‐correlated. (5) The plasmaspheric density ratio He+/H+ is generally of the order 0.2 and appears to be insensitive to such parameters as the invariant latitude or the plasmaspheric and ionospheric densities and temperatures. (6) Equatorward of the plasmapause region/outer plasmasphere there is no consistent relation between ionospheric and plasmaspheric density structure, with the ionospheric electron densities frequently displaying smooth profile regions across field lines where highly complex plasmaspheric density structure is seen. (7) The evolution of the plasmasphere and F region/topside ionosphere during the recovery phase of a magnetospheric storm illustrates how the time scales for replenishment of the ionosphere are significantly shorter than those of the plasmasphere. Certain of these observations are interpreted qualitatively in terms of extensions of current ideas on plasmasphere‐ionosphere coupling, in particular, ring current/plasmasphere/stable auroral red arc interactions and plasmasphere refilling. Other features are puzzles that await satisfactory theoretical explanation.

Dynamical interpretation of observed plasmasphere deformations

Based on all of the OGO-5 light ion density measurements (covering the period from March, 1968 to May, 1969), a definition of “isolated plasma regions” was employed to locate the most prominent patches of enhanced light ion densities in the midst of the depleted region, outside of the main plasmasphere. On the dayside, the distribution of these isolated plasma in L.T. vs. L coordinates was quite similar to that of the “detached plasma regions” by Chappell (1974a). On the nightside, however, the new distribution revealed more frequent occurrence of these regions. Elongated thick plasmatails produced during periods of sudden enhancement of convection electric fields and subsequentially thinning and corotating of the plasmatails during quieting periods, in general, could account for the statistical distribution as well as the individual events, such as those between March 27 and April 2, 1968 and Oct. 21 and Oct. 24, 1968. As demonstrated by Kivelson (1976), wave-particle interactions could produce tremendously complicated structures observed in the near vicinity of the plasmapause and far away from the plasmasphere. Examination of H + and He + density measurements for period of Aug. 12–Aug. 20, 1968 indicated that the density reduction of the plasmasphere during a magnetic storm was on the same order of magnitude as that obtained from whistler techniques during a magnetospheric substorm.

Diurnal variation of thermal plasma in the plasmasphere

All of the OGO-5 light ion density measurements (covering the period from March 1968 to May 1969) obtained from the Lockheed Light Ion Mass Spectrometer were used to determine the average global topology of the equatorial plasmasphere density distribution. The variation of the light ion equatorial density at L⩽3.2 with local time was deduced by determining the average density observed within one hour of a specific local time and within 0.1 of a given L coordinate. The average H + density showed a semidiurnal variation with peaks near noon and midnight. The He + observations also revealed multiple peaks throughout the day but with smaller amplitudes than those of H +. At L>3.2 plasma trough conditions increase the scatter of densities. The average variation of the H + density with L within the plasmasphere is found to be steepest near midnight and can be least squares fitted equally well to either an exponential variation exp (− bL) where b is between 0.85 and 1.5 or to a power law L − a where a varies from 3.2 to 5.

High-latitude proton precipitation and light ion density profiles during the magnetic storm initial phase

Measurements of precipitating protons and light ion densities by experiments on Ogo 4 indicate that widespread proton precipitation occurs in predawn hours during the magnetic storm initial phase from the latitude of the high-latitude ion trough, or plasmapause, up to Λ > 75°. A softening of the proton spectrum is apparent as the plasmapause is approached. The separation of the low-latitude precipitation boundaries for 7.3-kev and 23.8-kev protons is ≲1°, compared with a 3.6° separation that has been computed by using the formulas of Gendrin and Eather and Carovillano. Consideration of probable proton drift morphology leads to the conclusion that protons are injected in predawn hours, widespread precipitation occurring in the region outside the plasmapause. Protons less energetic than ∼7 kev drift eastward, whereas the more energetic protons drift westward, producing the observed dawn-dusk asymmetry for the lower-energy protons.