A new empirical atmospheric density model, Jacchia-Bowman 2008, is developed as an improved revision to the Jacchia-Bowman 2006 model which is based on Jacchia's diffusion equations. Driving solar indices are computed from on-orbit sensor data are used for the solar irradiances in the extreme through far ultraviolet, including x-ray and Lyman-α wavelengths. New exospheric temperature equations are developed to represent the thermospheric EUV and FUV heating. New semiannual density equations based on multiple 81-day average solar indices are used to represent the variations in the semiannual density cycle that result from EUV heating. Geomagnetic storm effects are modeled using the Dst index as the driver of global density changes. The model is validated through comparisons with accurate daily density drag data previously computed for numerous satellites in the altitude range of 175 to 1000 km. Model comparisons are computed for the JB2008, JB2006, Jacchia 1970, and NRLMSIS 2000 models. Accelerometer measurements from the CHAMP and GRACE satellites are also used to validate the new geomagnetic storm equations.

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[1] Ultra Fast Kelvin (UFK) waves are eastward propagating planetary waves with periods between 3 and 5 days, which are capable of penetrating into the thermosphere and ionosphere where they may modulate phenomena occurring in this region. A sensitivity study has been conducted to examine the effect of an Ultra Fast Kelvin wave on the thermosphere and ionosphere using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) under June solstice solar minimum conditions. It is found that realistic ultra fast Kelvin waves with amplitudes in the MLT region of approximately 20-40 m s −1 in zonal wind fields and 10-20 K in temperature fields, can result in approximately 8-12% perturbations in hourly neutral density at 350 km, as well as hourly total electron content (TEC) perturbations of 25-50% in regions corresponding to the equatorial ionization anomalies (EIAs), with the largest relative changes resolved during the nighttime due to the lower electron densities. The electrodynamical calculations in the model were then disabled to identify the relative importance of ionospheric electrodynamics and direct wave propagation in generating the aforementioned changes. The subsequent results show that changes in thermospheric neutral density are relatively insensitive to the presence of the dynamo electric field, while UFK wave modulation of the dynamo accounts for most of the TEC perturbations due to changes of ionospheric vertical plasma drift.

[1] Orbit-averaged mass densities r and exospheric temperatures T 1 inferred from measurements by accelerometers on the Gravity Recovery and Climate Experiment (GRACE) satellites are used to investigate global energy E th and power P th inputs to the thermosphere during two complex magnetic storms. Measurements show r, T 1 , and E th rising from and returning to prevailing baselines as the magnetospheric electric field e VS and the Dst index wax and wane. Observed responses of E th and T 1 to e VS driving suggest that the storm time thermosphere evolves as a driven-but-dissipative thermodynamic system, described by a first-order differential equation that is identical in form to that governing the behavior of Dst. Coupling and relaxation coefficients of the E th , T 1 , and Dst equations are established empirically. Numerical solutions of the equations for T 1 and E th are shown to agree with GRACE data during large magnetic storms. Since T 1 and Dst have the same e VS driver, it is possible to combine their governing equations to obtain estimates of storm time thermospheric parameters, even when lacking information about interplanetary conditions. This approach has the potential for significantly improving the performance of operational models used to calculate trajectories of satellites and space debris and is also useful for developing forensic reconstructions of past magnetic storms. The essential correctness of the approach is supported by agreement between thermospheric power inputs calculated from both GRACE-based estimates of E th and the Weimer Poynting flux model originally derived from electric and magnetic field measurements acquired by the Dynamics Explorer 2 satellite.

Recent multiple satellite observations of compressional Pc 5 waves indicate for the first time that the field‐aligned mode structure of the compressional magnetic field was antisymmetric with respect to the earth's magnetic equator. To understand the mode structures of low frequency compressional waves, a comprehensive eigenmode analysis of compressional Alfven instabilities was performed for a two component anisotropic plasma in a dipole magnetic field. The eigenmode equations derived from the gyrokinetic equations are solved analytically and numerically for both the drift mirror and the drift compressional instabilities. The solutions indicate that the drift mirror mode has an antisymmetric compressional component with respect to the magnetic equator, whereas the drift compressional mode has a symmetric one. For typical storm time plasma parameters near geosynchronous orbit, it is suggested that the recently observed compressional Pc 5 wave was in a nonlinearly saturated state of the drift mirror instability.

ISEE spacecraft observations show that energetic, ≥ 16 keV electrons are injected into the region upstream from the Earth’s bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface. Lower energy electrons leave the shock over a much broader region. Although the energetic electron intensity varies, the sheet is nearly always present and may be a quasi‐steady state feature of the bow shock. The electron velocity distribution in the thin sheet is strongly peaked and is responsible for excitation of electron plasma waves.

Simultaneous plasma and wave data obtained by the DE-I satellite are used to study a correlation between electrostatic auroral hiss emissions at several kilohertz and upward electron beams at altitudes between 2 and 4 R e near the dayside polar cusp. Among five randomly selected DE-I passes, intense electrostatic hiss emissions at frequencies below the electron plasma frequency are found to be associated with strong upward electron beams for every pass. The frequency-time spectrum of auroral hiss near the polar cusp is sometimes characterized by a funnel shape, suggesting that the radiation is emitted from a wave source below the spacecraft. At the center of the enhanced wave region, the electron distribution function above 20 eV is characterized by two components: a hot Maxwellian component and an upward electron beam. The bqams generally have a peak energy around 50 eV, a temperature around 20 eV and a density of the order of I cm -3. The observed distribution functions are fitted by a drifting Maxwellian function for the electron beam and an isotropic Maxwellian function for the hot component. The empirically fitted plasma parameters are then used to solve the linear dispersion equation of electrostatic waves. The instability analyses indicate that whistler waves propagating with wave normal angles near a small resonance cone can be easily excited by low energy (<100 eV) upward electron beams. The frequencies of large growth rates are found below the electron plasma frequency, in agreement with the observations. On the basis of the model that cusp auroral hiss emissions are whistler waves propagating near the resonance cone, ray phth studies indicate that the low altitude boundary of the wave source of cusp hiss is located at about I R e. ß oo o ß ß ß 6 Oct 1981 o ß o ß o ß ß o ßo ß o o o 0o oß ß ß ß ß ßo ßo ß o o o ß ß ß o o ß :-ß ß .• o ß ß ß ß o o ß ß ß ß ß o ß 10:48 10:49

The low energy electron (LEE) experiment, consisting of an array of 19 electrostatic analyzers, was conducted on board the polar orbiting satellite Atmosphere Explorer D (AE‐D). Electron energy spectra and angular distributions obtained simultaneously with high temporal resolutions (∼62 ms) have been used to study structures of inverted‐V events. The principal results found are as follows: (1) Inverted‐V events occur in the auroral as well as the polar cap latitudes. The low‐latitude edge of the occurrence region varies from 62° near midnight to 80° invariant latitude at local noon. (2) The latitudinal width regularly observed is about 0.5° invariant latitude, and the longitudinal width can extend to at least 15° (3) The monoenergetic peak of the energy spectrum is found for pitch angles from 0° to 180° minus the local loss cone. (4) The temperature of precipitating electrons is linearly proportional to the peak energy. (5) The flux is field aligned at the peak energy and trapped above the peak energy. Immediately below the peak energy, the pitch angle distribution is V‐shaped, peaking toward both small and large pitch angles. At energies further below the peak energy the distribution function becomes isotropic. (6) Fast irregular flux fluctuations are frequently observed at energies below the monoenergetic peak. These fluxes produce a secondary monoenergetic peak in the spectrum. The occurrence map indicates that the inverted‐V occurrence region is not limited to the particle trapping boundary. The origin of the inverted‐V precipitating electrons appears to be in the plasma sheet and the neutral sheet. Most of the energy and pitch angle structures can be interpreted as electrons accelerated by an electrostatic field, while the V‐shaped pitch angle distributions suggest that particles were trapped between an electric potential and their mirror points. However, the existence of the monoenergetic peak at pitch angles larger than about 25° cannot be explained simply by an electrostatic field. The structural details are compared with predictions of three existing theories of creating the electrostatic field, and the results are qualitatively consistent with the theory of anomalous resistivity.