The reduction of ionograms from the bottomside and topside.
Method reducing ionograms to electron density height profiles on digital computer by representations as parabolic lamination
DIGITAL COMPUTER↗
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Behavior of topside and bottomside spread F at equatorial latitudes.
Diurnal behavior of topside and bottomside spread F at equatorial latitudes and association with geomagnetic activity
GEOMAGNETIC EFFECT↗
Observations of conjugate ducting by the fixed- frequency topside-sounder satellite.
Conjugate ducting observation via fixed frequency topside-sounder satellite, estimating electron concentration difference
MAGNETOSPHERIC INSTABILITY↗
The stable auroral red arc of October 31 - November 1, 1968 and its interaction with the neutral atmosphere
Satellite observations of electron temperature and the topside electron density structure are used to calculate the red arc according to the thermal conduction model. In this model, energy from the magnetosphere flows in the electron gas along geomagnetic field lines into the ionosphere. This energy heats the ambient F-region electrons sufficiently to excite the oxygen atoms to the O I(1D) level by collisional impact giving rise to the 6300 A emission characteristic of the arc. For the 31 October/1 November 1968 red arc, the calculated emission rate, geographical position, and horizontal extent of the red arc are in agreement with the photometric data obtained by airglow observatories. Almost all of the energy conducted into the red arc is ultimately transferred to the neutral gas through elastic and inelastic collisions. This energy drives a large thermal cell and the circulation extends the influence of the arc thousands of kilometers beyond the region of direct heat input. The calculated neutral gas temperature response to electron heating within the arc is small.
Roble, R. G.↗
A comparison of several methods of estimating the columnar electron content of the plasmasphere
Data from several different observation techniques are used to estimate the columnar electron content of the plasmasphere. The estimate is based upon the subtraction of the ionospheric electron content from the total content along the radio path from ground to the geostationary satellite ATS-6. The Radio Beacon Experiment on this satellite allows a very accurate determination of the total electron content up to the height of the satellite. For the ionospheric electron content (ground to appr. 2000 km) the following techniques are used: (1) Faraday effect on the ATS-6 signals, (2) differential Doppler effect on the signals of the low-orbiting NNSS satellites, (3) combination of bottomside and topside ionograms, and (4) extrapolation of bottomside ionograms. It is shown that the combination of group delay and Faraday effect data on the ATS-6 RBE signals provide the most reliable estimates of the columnar electron content of the plasmasphere. Data from low-orbiting satellites support this conclusion.
Davies, K.↗
Ionospheric plasma bubble encounters or F region bottomside traversals?
Data from in situ Atmospheric Explorer (AE) measurements and ground-based ionosonde measurements of the ion composition and concentration in the equatorial plasma bubbles are analyzed. The ionosonde produced data on the bottomside electron density (NE) profiles and aided in ascertaining the satellite measurements as being in the topside or bottomside of the F layer. The AE data were taken during low latitude evening conditions at various altitudes, and revealed ion compositions consistent with plasma bubbles originating at the altitude of the steep F region bottomside ionization gradient. The lifetimes of NO ions were observed to be short even if the ions were dominant in the regions where the bubbles form. Vertical distortions of tens of kilometers in the equatorial F region occurred in the unstable postsunset period to the extent that the bubble formation area and the bottomside plasma region became virtually indistinguishable.
Benson, R. F.↗
THE CALCULATION OF ELECTRON DENSITY PROFILES FROM TOPSIDE SOUNDER RECORDS
Converting observed topside curves into electron- density profiles by polynomial analysis developed from those used for analysis of ground-based ionograms
IONOSPHERIC ELECTRON DENSITY↗
Guest investigator program study: Physics of equatorial plasma bubbles
Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. Our research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz, 1976; Ott, 1978; Kelley and Ott, 1978). Our results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study and modeling of SM-D electric field instrument (EFI) measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge-shaped plasma bubbles. The second topic was pursued because the inability to predict the day-to-day occurrence of plasma bubbles indicated inadequate knowledge of the physics of plasma bubbles. An understanding of bubble formation requires an understanding of the roles of the various terms in the linearized growth rate of the collisional Rayleigh-Taylor instability. In our study, we examined electric-field perturbations found in SM-D EFI data and found that the seeding is more likely to be produced in the E region rather than the F region. The results of this investigation are presented in the Appendix of this report and will be submitted for publication in the Journal of Geophysical Research.
Tsunoda, Roland T.↗
The International Reference Ionosphere Today and in the Future
The international reference ionosphere (IRI) is the internationally recognized and recommended standard for the specification of plasma parameters in Earth's ionosphere. It describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 to 1,500 km. A joint working group of the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) is in charge of developing and improving the IRI model. As requested by COSPAR and URSI, IRI is an empirical model being based on most of the available and reliable data sources for the ionospheric plasma. The paper describes the latest version of the model and reviews efforts towards future improvements, including the development of new global models for the F2 peak density and height, and a new approach to describe the electron density in the topside and plasmasphere. Our emphasis will be on the electron density because it is the IRI parameter most relevant to geodetic techniques and studies. Annual IRI meetings are the main venue for the discussion of IRI activities, future improvements, and additions to the model. A new special IRI task force activity is focusing on the development of a real-time IRI (RT-IRI) by combining data assimilation techniques with the IRI model. A first RT-IRI task force meeting was held in 2009 in Colorado Springs. We will review the outcome of this meeting and the plans for the future. The IRI homepage is at http://www.IRI.gsfc.nasa.gov
Bilitza, Dieter↗
Hybrid simulations of the saturated Farley-Buneman instability in the ionosphere
Numerical simulations of the Farley-Buneman instability in 2-1/2 dimensions using particle ions and fluid electrons show the growth, saturation and nonlinear behavior of two-stream waves. This hybrid technique models the saturated state of the instability for a much longer period of time than the pure particle codes that preceded it. While focusing principally on modeling the topside E region equatorial electrojet, many of these results apply to the auroral two-stream instability as well. The following features are seen in all our hybrid simulations: (1) wave growth at an angle offset from the electron drift direction where the angle depends on the strength of the driving electric field, (2) nonlinear coupling to waves traveling perpendicular to the propagation direction of the principal two-stream waves, (3) a saturated wave phase velocity at or above the sound speed but well below the velocity predicted by linear theory and (4) phase velocities which remain almost constant as a simulated radar sweeps from a horizontal direction to nearly vertical. The nonlinear electron motion dominates the behavior of these waves. Further, these simulations indicate that ion kinetic effects are not essential for the saturation of the instability and that electron temperature effects have a minor impact on the final saturated state.
Oppenheim, Meers↗
Occurrence patterns of topside spread F on Alouette ionograms.
Occurrence frequency patterns of topside spread-F on Alouette satellite ionograms, discussing radio propagation, magnetic irregularities, electron density-induced refraction, etc
SPREAD-F↗
A comparative study of the time-dependent standard 8-, 13- and 16-moment transport formulations of the polar wind
The ionosphere, composed of O(+), H(+), and electrons is modeled with four different transport formulations. The equations corresponding to the standard set, the 8-, 13-, and 16-moment approximations are presented, and the collision terms are expressed. Using a time-dependent technique, the ionosphere is studied between altitudes of 200 and 8600 km. The production of electrons and O(+) ions is described by a neutral atmosphere simplified photoionization scheme, while the energy deposition is supported by a downward electron heat flow of -0.005 erg/sq cm per s imposed at the topside boundary. When the models reach a steady state equilibrium, the electron solutions show differences due to the introduction of temperature anisotropies and heat flows between the components parallel and perpendicular to the magnetic field. As a corollary, the ions show structures depending on the level of approximation. A depletion of a factor of 10 is then applied to the ion densities above a certain altitude, and the development of the perturbation is followed for 1000 s for all the models.
Blelly, P. L.↗
On the escape of oxygen and hydrogen from Mars
Escape rates of oxygen atoms from dissociative recombination of O2(+) above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process and our recently revised understanding of the Martian dayside ionosphere. Only about 60 percent of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured by Viking. If it is assumed that the ions are not lost from the gravitational field of the planet, as required by an analysis of nitrogen escape, the computed average O escape rate is 3 x 10 exp 6/sq cm/s, much less than half the H escape rates inferred from measurements of the Lyman-alpha dayglow, which are in the range (1-2) x 10 exp 8/sq cm/s. Suggestions for restoring the relative escape rates of H and O to the stoichiometric ratio of water are explored.
Fox, J. L.↗
Absolute electron density measurements in the equatorial ionosphere
Accurate measurement of the electron density profile and its variations is crucial to further progress in understanding the physics of the disturbed equatorial ionosphere. To accomplish this, a plasma frequency probe was included in the payload complement of two rockets flown during the Condor rocket campaign conducted from Peru in March 1983. This paper presents density profiles of the disturbed equatorial ionosphere from a night-time flight in which spread-F conditions were present and from a day-time flight during strong electrojet conditions. Results from both flights are in excellent agreement with simultaneous radar data in that the regions of highly disturbed plasma coincide with the radar signatures. The spread-F rocket penetrated a topside depletion during both the upleg and downleg. The electrojet measurements showed a profile peaking at 1.3 x 10 to the 5th per cu cm at 106 km, with large scale fluctuations having amplitudes of roughly 10 percent seen only in the upward gradient in electron density. This is in agreement with plasma instability theory. It is further shown that simultaneous measurements by fixed-bias Langmuir probes, when normalized at a single point to the altitude profile of electron density, are inadequate to correctly parameterize the observed enhancements and depletions.
Baker, K. D.↗
Correlation of ground-based and topside photometric observations with auroral electron spectra measurements at rocket altitudes
Data are collected by electron detectors aboard a sounding rocket measuring the primary electron spectrum and the energy flux on the field lines containing auroral light in the E region. These data are compared to calculations based on spectroscopic measurements of the auroral lines 4278, 5577, and 6300 A used in predicting the energy influx and the characteristic energy of an assumed Maxwellian primary electron spectrum for two auroral displays. Data were also collected by photometers sampling the auroral light from the E region magnetically conjugate to the rocket. These data are compared to those of current ionospheric models.
Arnoldy, R. L.↗
Magnetospheric space plasma investigations
A time dependent semi-kinetic model that includes self collisions and ion-neutral collisions and chemistry was developed. Light ion outflow in the polar cap transition region was modeled and compared with data results. A model study of wave heating of O+ ions in the topside transition region was carried out using a code which does local calculations that include ion-neutral and Coulomb self collisions as well as production and loss of O+. Another project is a statistical study of hydrogen spin curve characteristics in the polar cap. A statistical study of the latitudinal distribution of core plasmas along the L=4.6 field line using DE-1/RIMS data was completed. A short paper on dual spacecraft estimates of ion temperature profiles and heat flows in the plasmasphere ionosphere system was prepared. An automated processing code was used to process RIMS data from 1981 to 1984.
Comfort, Richard H.↗
On the Relative Importance of Convection and Temperature on the Behavior of the Ionosphere in North American during January 6-12, 1997
Measurements from a network of digisondes and an incoherent scatter radar In Eastern North American For January 6-12, 1997 have been compared with the Field Line Interhemispheric Plasma (FLIP) model which now includes the effects of electric field convective. With the exception of Bermuda, the model reproduces the daytime electron density very well most of the time. As is typical behavior for winter solar minimum on magnetically undisturbed nights, the measurements at Millstone Hill show high electron temperatures before midnight followed by a rapid decay, which is accompanied by a pronounced density enhancement in the early morning hours. The FLIP model reproduces the nighttime density enhancement well, provided the model is constrained to follow the topside electron temperature and the flux tube is full. Similar density enhancements are seen at Goose Bay, Wallops Island and Bermuda. However, the peak height variation and auroral images indicate the density enhancements at Goose Bay are most likely due to particle precipitation. Contrary to previously published work we find that the nighttime density variation at Millstone Hill is driven by the temperature behavior and not the other way around. Thus, in both the data and model, the overall nighttime density is lowered and the enhancement does not occur if the temperature remains high all night. Our calculations show that convections of plasma from higher magnetic latitudes does not cause the observed density maximum but it may enhance the density maximum if over-full flux tubes are convected over the station. On the other had, convection of flux tubes with high temperatures and depleted densities may prevent the density maximum from occurring. Despite the success in modeling the nighttime density enhancements, there remain two unresolved problems. First, the measured density decays much faster than the modeled density near sunset at Millstone Hill and Goose Bay though not at lower latitude stations. Second, we cannot fully explain the large temperatures before midnight nor the sudden decay near midnight.
Richards, P. G.↗
Temperatures of individual ion species and heating due to charge exchange in the ionosphere of Venus
The coupled electron and multispecies ion energy equations were solved for daytime conditions in the Venus ionosphere. The heating rates due to charge exchange between hot oxygen atoms and thermal oxygen ions were calculated and incorporated into the energy equations. The combination of the traditional EUV heating and this hot oxygen energy source leads to calculated electron and individual ion temperatures significantly lower than the measured values during solar cycle maximum conditions. Calculations were also carried out for solar cycle minimum conditions, which led to considerably lower temperatures; no data are available which would allow direct comparisons of these results with measurements. In order to obtain calculated temperature values consistent with the observed ones, for solar cycle maximum conditions, topside heat inflows into the ion and electron gases have to be introduced or the thermal conductivity must be reduced by considering the effect of steady and fluctuating magnetic fields, as was done in previous studies. The addition of hot oxygen heating leads to minor increases in the calculated ion temperatures except for the case of reduced thermal conductivities. Separate temperatures were calculated for each ion species for a number of different conditions and in general the differences were found to be relatively small.
Kim, Jhoon↗