Photoelectron fluxes in the ionosphere
TL;DR: In this article, fluxes and energy spectra in ionosphere for predawn and sunlit atmospheres, taking into account elastic and inelastic collisions were analyzed. But the authors did not consider the effect of temperature variation.
Abstract: Photoelectron fluxes and energy spectra in ionosphere for predawn and sunlit atmospheres, taking into account elastic and inelastic collisions
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TL;DR: A low-latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2) as discussed by the authors, which treats the dynamic plasma and chemical evolution of seven ion species in the altitude range ∼ 100 km to several thousand kilometers.
Abstract: A new low-latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2). SAMI2 treats the dynamic plasma and chemical evolution of seven ion species (H + , He + , N + , O + , N + 2 , NO + , and O + 2 ) in the altitude range ∼ 100 km to several thousand kilometers. The ion continuity and momentum equations are solved for all seven species; the temperature equation is solved for H + , He + , O + , and the electrons. SAMI2 models the plasma along the Earth's dipole field from hemisphere to hemisphere, includes the E x B drift of a flux tube (both in altitude and in longitude), and includes ion inertia in the ion momentum equation for motion along the dipole field line. The final point is relevant for plasma dynamics at very high altitudes where ion inertia can be important. For example, we have found that ion sound waves, which are supported by ion inertia, may be generated in the topside ionosphere (> 1000 km) at sunrise and sunset [Huba et al., 2000b]. The neutral species are specified using tile Mass Spectrometer Incoherent Scatter model (MSIS86) and the Horizontal Wind Model (HWM93). In this paper we describe in detail the SAMI2 model and present representative results from the model.
503 citations
TL;DR: The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed in this paper, and a discussion of the various attempts to compare measured and calculated F region electron temperatures.
Abstract: The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed. The review is divided into three basic parts. In the first part the theory concerning electron heating, cooling, and energy transport processes is reviewed, and all the relevant expressions are updated. In the second part the behavior of F region electron temperatures, as measured by satellites, rockets, and incoherent scatter radars, is discussed. This portion covers electron temperature variations with altitude, latitude, local time, season, geomagnetic activity, and solar cycle. The third part is primarily devoted to a discussion of the various attempts to compare measured and calculated F region electron temperatures.
463 citations
TL;DR: In this article, the authors used the Sheffield University plasmasphere-ionosphere model for the ionosphere above Jicamarca under magnetically quiet equinoctial conditions at medium solar activity.
Abstract: The importance of diffusion, perpendicular electrodynamic drift, and neutral wind on the generation and modulation of the equatorial plasma fountain of the Earth's ionosphere is studied using the Sheffield University plasmasphere-ionosphere model for the ionosphere above Jicamarca under magnetically quiet equinoctial conditions at medium solar activity. The effects of the fountain, which include the equatorial anomaly, are also investigated. As expected, the F region electrodynamic (E×B) drift generates the plasma fountain and the anomaly, which are symmetric with respect to the magnetic equator. The neutral wind introduces asymmetries, with larger plasma flow (toward the hemisphere of stronger poleward wind) and stronger anomaly crest occurring in opposite hemispheres. During daytime, when the drift is upward, the fountain rises to about 800 km altitude at the equator and covers about ±30° magnetic latitude ; outside the reach of the fountain, plasma flows toward the equator from both hemispheres. This convergence of plasma leads to the formation of an additional layer (called the G layer) within ±10° of the magnetic equator during the prenoon hours when the drift is large. At the magnetic equator, the maximum plasma concentration of the G layer can be greater than that of the F layer for a short period of time just before noon and when the drift starts to decrease. In the evening, soon after the drift turns downward, the fountain becomes a reverse fountain with supply of ionization from both hemispheres from regions outside the fountain. The reverse fountain acts as the main source for the nighttime increase in ionization at equatorial anomaly latitudes, with some contribution from the prereversal strengthening of the forward fountain. The importance of the prereversal strengthening of the forward fountain, which rises to about 1000 km altitude at the equator, and the following reverse fountain on the generation and propagation of plasma bubbles and spread F irregularities is discussed. It is also shown that the equatorial anomaly in the vertical ionospheric electron content need not be as pronounced as the interpretation of the observations suggests.
319 citations
TL;DR: In this paper, a new computational model has been created to describe the interaction of auroral electrons with the atmosphere, which is used to compute energy spectrums, ionization rates, backscatter ratios, and optical emissions associated with different incident electron spectrums.
Abstract: A new computational model has been created to describe the interaction of auroral electrons with the atmosphere. For electrons of energy greater than 500 eV, continuous energy losses and small angle deflections are combined in a Fokker-Planck diffusion equation that computes energy spectrums over all pitch angles throughout the atmosphere. These fluxes are then used to determine the rates of secondary electron and degraded (E < 500 eV) primary electron production at all heights. This information is used to compute upward and downward hemispherical fluxes in the energy range 0–500 eV, taking into account discrete energy losses, large angle scattering, and particle transport along magnetic field lines. The model has been used to compute energy spectrums, ionization rates, backscatter ratios, and optical emissions associated with different incident electron spectrums. For monoenergetic electrons of energy 2 keV and above the results obtained agree well with the work of Rees (1969) and Rees and Maeda (1973). At lower energies the effects of transport and elastic collisions become progressively more important, and the present results differ significantly both from the Rees and Maeda results and from those obtained from the ideas of energy degradation. Finally, spectrums typical of the nighttime auroral oval and daytime polar cusp are used to obtain the altitude dependent fluxes, ionization rates, and optical emissions.
315 citations
TL;DR: In this article, a tomographic inversion is used to analyze measurements of the auroral atomic oxygen emission line at 6300 A made by the atmosphere explorer visible airglow experiment.
Abstract: A tomographic inversion is used to analyze measurements of the auroral atomic oxygen emission line at 6300 A made by the atmosphere explorer visible airglow experiment. A comparison is made between emission altitude profiles and the results from an electron transport and chemical reaction model. Measurements of the energetic electron flux, neutral composition, ion composition, and electron density are incorporated in the model.
295 citations
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04 Sep 2011TL;DR: Static diffusion models of upper atmosphere with empirical temperature profiles - atmospheric density and composition tables as mentioned in this paper were used for modeling the upper atmosphere of the United States in the 1970s and 1980s.
Abstract: Static diffusion models of upper atmosphere with empirical temperature profiles - atmospheric density and composition tables
361 citations
TL;DR: Modification of mathematical method of Jacchia for satellite drag density of upper atmosphere is discussed in this paper, where the satellite is assumed to be a fixed point in the upper atmosphere of the Earth.
Abstract: Modification of mathematical method of Jacchia for satellite drag density of upper atmosphere
191 citations
TL;DR: A theory of photoelectron transport that includes both elastic and inelastic collisional processes has been developed to describe the behavior of photo-electrons in the upper atmosphere as mentioned in this paper.
Abstract: A theory of photoelectron transport that includes both elastic and inelastic collisional processes has been developed to describe the behavior of photoelectrons in the upper atmosphere. Explicit solutions to the transport equations are obtained for a sunlit exponential atmosphere in which local production occurs, and for a predawn exponential atmosphere in which an influx of photoelectrons arrives from a magnetically conjugate region. The results indicate that elastic scattering significantly reduces the rate of photoelectron escape from a sunlit atmosphere while maintaining the up/down isotropy to higher altitudes than would be possible if elastic scattering did not occur. With regard to a predawn atmosphere, a substantial fraction (∼50%) of incoming photoelectrons are backscattered by means of elastic collisions. To illustrate a more realistic situation, the behavior of 28-ev photoelectrons in 750° and 1500°K model atmospheres is also discussed.
166 citations
01 Jan 1970
159 citations
TL;DR: In this article, it is shown that unless hydrogen atoms are being captured very rapidly from interplanetary space they must be very rare indeed at the base of the exosphere, and stress is laid on the importance of the steepness of the temperature gradient above the E layer in connexion with the thermal economy.
Abstract: Consideration is given to the significance of recent rocket and satellite studies relating to the structure of the thermosphere. It is shown that unless hydrogen atoms are being captured very rapidly from interplanetary space they must be very rare indeed at the base of the exosphere. Stress is laid on the importance of the steepness of the temperature gradient above the E layer in connexion with the thermal economy. Though no final conclusion is reached, it is thought that the view that the ionizing radiation from the sun is the main source of heat is more attractive than any alternative view yet put forward. An analytic model of the thermosphere is described in the appendix.
159 citations