Heat balance of the ionosphere: Implications for the international reference ionosphere

Theoretical considerations can be helpful tools in modelling ionospheric parameters in regions and for times where not enough experimental data are available. Our study asks whether results of heat balance calculations should be introduced to supplement the data base for the International Reference Ionosphere (IRI). We discuss the present status of our theoretical understanding and examine the influence of the following unresolved or neglected terms: (1) electron heating rate, (2) electron cooling by fine structure excitation of atomic oxygen, and (3) height-dependent Coulomb Logarithm. The ambiguity introduced by (1)–(3) leads up to 30% uncertainty in the electron temperature of the lower thermosphere. The electron temperature in the upper ionosphere is largely determined by heat conduction from above and depends critically on the conditions assumed at the boundary between ionosphere and plasmasphere.     

Comparison of ion composition from the goddard comprehensive ionosphere database with the international reference ionosphere model

We compared the IRI values of T_e, N_e, T_i, O⁺, H⁺, He⁺, O₂₊, and NO⁺ with AE-C values, obtained from the Goddard Comprehensive Ionosphere Database (GCID), composed of data from the satellites, AE-B, OGO-6, ISIS-2, AE-C, AE-D, and AE-E. O⁺ - H⁺ transition levels were derived from the IRI and AE-C altitude profiles. Some discrepancies were found between IRI and the AE-C data. The IRI electron density was found to be about a factor of 2 higher than the data. The H⁺ composition agreed best among the IRI ions, with an average AE-C/IRI ratio of 1.05. The temperatures of both electrons and ions agreed quite well: the average ratios of AE-C/IRI was found to be .99 for electrons and 1.17 for ions.     

Analysis of the ionosphere/plasmasphere electron content variability during strong geomagnetic storm

The ionosphere/plasmasphere electron content (PEC) variations during strong geomagnetic storms in November 2004 were estimated by combining of mid-latitude Kharkov incoherent scatter radar observations and GPS TEC data derived from global TEC maps. The comparison between two independent measurements was performed by analysis of the height-temporal distribution for specific location corresponding to the mid-latitudes of Europe. The percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 70%) during night-time. During day-time the lesser values (30–45%) were observed for quiet geomagnetic conditions and rather high values of the PEC contribution to GPS TEC (up to 90%) were observed during strong negative storm. These changes can be explained by the competing effects of electric fields and winds, which tend to raise the layer to the region with lower loss rate and movement of the ionospheric plasma to the plasmasphere.     

Interim report on empirical modelling of ionospheric motions in the light of the international reference ionosphere

Empirical modelling of wind and drifts at ionospheric levels in discussed. The most important features of a database describing ionospheric motions are outlined. The database includes the results of measurements carried out by groundbased remote sensing at a world-wide network of stations. Statistical models may be constructed from these data and used as reference models. Outlooks and future tasks are considered.     

Electron density reference profile in the lower ionosphere

The new IRI formula, as accepted at the 1983 Stara Zagora Workshop, prescribes the use of Epstein functions for reproducing logarithmic electron density profiles. In this paper we discuss solutions which might be applicable to the lower ionosphere. The experimental data base is briefly reviewed. It appears that the stratification near 80 km must be accepted as a regular feature of the daytime lower ionosphere. The C-layer problem is left open. In order to reproduce such profiles, one needs three LAY-functions. Examples show that the weighted sum of these does very well represent experimental profiles, the amplitudes being determined by a least square fit. For profile synthesis (as in IRI) a least square determination of the three amplitudes, admitting four linear conditions, is proposed.     

Plasma transport in the plasmasphere

The plasmasphere is filled with very low energy plasma upwelling from the topside ionosphere. The field-aligned distribution of this thermal ionospheric plasma is controlled by the gravitational and centrifugal potential distribution. There are two extreme types of hydrostatic plasma distribution in this field-aligned potential : the Diffusive Equilibrium distribution and the Exospheric Equilibrium distribution corresponding respectively to a saturated and to an almost empty magnetic flux tube. As a result of pitch angle scattering by Coulomb collisions an increasing number of ions escaping from the ionosphere are stored on trapped orbits with mirror points at high altitudes in the low density region. As a result of collisions the field-aligned density distribution gradually changes from exospheric equilibrium with a highly anisotropic pitch angle (cigar like) distribution to a diffusive equilibrium with a nearly isotropic pitch angle distribution. It is shown that the suprathermal ions become anisotropic much more slowly than ions of energies smaller than 1 eV. The Coulomb collision times have been estimated for flux tubes at different L values. A numerical simulation of the flux tube refilling process has been presented. The diurnal variation of the equatorial plasma density has been illustrated for plasma elements convected along drift paths which have a large dawn- dusk asymetry. The formation of a Light Ion Trough is discussed. Finally, evidence has also been given for the existence of a ‘plasmaspheric wind’ corresponding to a slow subsonic and continuous radial expansion of the plasma stored in the plasmasphere.     

Storm time behavior of topside scale height inferred from the ionosphere–plasmasphere model driven by the F2 layer peak and GPS-TEC observations

The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, presents global electron density profiles and total electron content, TECiri, up to the altitude of the GPS satellites (20,000 km). The model code is modified by input of GPS-derived total electron content, TECgps, so that the topside scale height, Hsc, is obtained minimizing in one step the difference between TECiri and TECgps observation. The topside basis scale height, Hsc, presents the distance in km above the peak height at which the peak plasma density, NmF2, decays by a factor of e (∼2.718). The ionosonde derived F2 layer peak density and height and GPS-derived TECgps data are used with IRI-Plas code during the main phase of more than 100 space weather storms for a period of 1999–2006. Data of seven stations are used for the analysis, and data from five other stations served as testing database. It is found that the topside basis scale height is growing (depressing) when the peak electron density (critical frequency foF2) and electron content are decreased (increased) compared to the median value, and vice versa. Relative variability of the scale height, rHsc, and the instantaneous Hsc are inferred analytically in a function of the instantaneous foF2, median fmF2 and median Hmsc avoiding a reference to geomagnetic indices. Results of validation suggest reliability of proposed algorithm for implementation in an operational mode.     

Further evidence for the ionospheric contribution to convection within the plasmasphere

VLF goniometers have been used to study the direction of plasma convection in the evening plasmasphere. The results suggest that sometimes even for L values greater than 4 the electric field associated with the ionospheric dynamo may be the source which drives convection.     

Whistler studies of the plasmasphere shape and dynamics

Whistler studies of the plasmapause/plasmasphere are traced from their beginnings during the IGY through the early 1960's, when extensive data from Antarctica became available. Highlights of this period include discovery of the ‘knee’ in the equatorial electron density profile, initial comparisons with results from the Lunik probes, identification of magnetic storm effects, and discovery of the duskside bulge, or region of larger plasmasphere radius, as well as smaller-scale (Δφ ≈ 20°) variations in radius with longitude. In the mid-1960's, whistlers provided the first evidence of cross-L plasma drift patterns in the outer plasmasphere. From a present day perspective, the plasmasphere is seen as a region penetrated, perhaps most efficiently in the dusk sector, by the unsteady component of high latitude electric fields. In the pre-dawn sector, post substorm outward drifts may be an aftereffect of the shielding of the plasmasphere against the steadier components of the substorm electric fields. The available indirect whistler evidence of plasmasphere erosion during large disturbances suggests that erosion occurs primarily in the dusk-premidnight sector.     

Electron density models for the lower ionosphere

Probably the only reliable method of checking an electron density model below 70 km is to calculate from it what would be obtained by VLF or LF propagation over certain paths, and to compare the results with actual observations. This has been done for the IRI at various frequencies from 16 to 70 kHz; the results agree in places but differ substantially elsewhere. Previous models described by the author give satisfactory results and it is suggested that certain features of them might be incorporated with advantage in the IRI. In particular, it is impossible to get agreement with VLF propagation in all seasons by means of a model varying only with solar zenith angle, such as the IRI from 50–90 km.     

Energy sources for the ionosphere—a survey

An outline is given of early aeronomical ideas about the formation of the ionosphere by solar wave radiation, and its development under the impetus of increasing basic knowledge. In particular, the development concerning solar radiation in the far ultraviolet and X-ray ranges is discussed (Sect. 1). General considerations on the relation with observable ionospheric parameters are given in Sect. 2 while the individual layers are discussed in Sect. 3. It is found that elder investigations, with wrong assumptions came to the right densities while their estimates of production rates were far too low. Since two years only satellite and laboratory data allow satisfying estimates.     

Determining electron density profiles for the middle ionosphere

Using daytime numerical ionospheric profiles from W. Becker's mid-latitude collection, the geometric parameters of 3 or 4 LAY-functions were determined by best fit while all amplitudes were redetermined step by step with a least squares criterion. It appeared that the transition height and scale of the main function are interrelated while all other geometric parameters are independent. Median values for a spring and a summer period are found, and relations with the peak altitude and half-density thickness of the input profile are established.     

Specification of the Earth’s plasmasphere with data assimilation

In this paper we report on initial work toward data assimilative modeling of the Earth’s plasmasphere. As the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, an accurate assimilative model of the plasmasphere is crucial for optimizing the accurate prediction of the radiation environments encountered by satellites. On longer time-scales the plasmasphere exhibits significant dynamics. Although these dynamics are modeled well by existing models, they require detailed global knowledge of magnetospheric configuration which is not always readily available. For that reason data assimilation can be expected to be an effective tool in improving the modeling accuracy of the plasmasphere. In this paper we demonstrate that a relatively modest number of measurements, combined with a simple data assimilation scheme, inspired by the ensemble Kalman filtering data assimilation technique does a good job of reproducing the overall structure of the plasmasphere including plume development. This raises hopes that data assimilation will be an effective method for accurately representing the configuration of the plasmasphere for space weather applications.     

Structure and properties of the Earth's plasmasphere

The widely used concept of the plasmapause as the last closed electric field equipotential in the equatorial plane of the magnetosphere is oversimplified. The field aligned plasma motions are of substantial importance in the plasmapause formation and should be taken into account. Distributions of the main plasma parameters measured from the Prognoz-5 satellite are presented. The diurnal variations of the plasmapause height and the plasmasphere thermal properties are discussed.