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.

Measurements of charged particles in the plasma sheet by the low energy proton and electron differential energy analyzer (LEPEDEA) and medium energy particle instrument (MEPI) on ISEE 1 are combined to obtain ion and electron differential energy spectra for use in studying eight plasma sheet temperature transitions, periods of low plasma bulk velocity typically ∼1 hour in length during which the plasma thermal energy either increases or decreases steadily. Over the entire kinetic energy range sampled (50 eV/e ≲ E ≲ 1 MeV), the plasma and energetic ion and electron populations respond collectively as a single unified particle population during these temperature transitions. In order to test the hypothesis that the energy spectra of plasma sheet ions and electrons can be represented by a single functional form, the observed particle energy spectra have been visually compared to three model distribution functions: the Maxwellian (, where ET is the thermal energy), the kappa (ƒ ∼ [1 + E/κET]−κ −1, where κ is a constant), and the velocity exponential (ƒ ∼ e−( E/ε)1/2, where ε is constant). The kappa and velocity exponential distributions both provide reasonable fits above ∼200 eV, with the kappa distribution being more successful at the highest energies but less successful at the lowest energies. The Maxwellian does not provide an adequate fit for the overall distributions observed in the temperature transitions. At high energies (E ≫ κET) the observed spectra are more often similar to the kappa than to the velocity exponential; that is, a roughly power law form (E−κ) is in evidence. Although the value of the index varies from event to event, the particle distributions maintain their overall shape throughout a transition, during which the spectral index at high energies stays roughly constant. This could indicate either that the relaxation time of the plasma is short with respect to the time scale of the temperature transitions or that the spatial regions being sampled were all maintaining a stationary state plasma population, or both. Both temporal and spatial effects are evident in the temperature transitions studied. An indication of temporal dependence during the transitions is that on the average, ET increases with geomagnetic activity as indicated by the AE index at low to moderate levels (∼30 to 600 nT). However, a spatial effect is evident as well, since temperature increases (decreases) occurred as ISEE 1 was traveling toward (away from) the geocentric solar magnetospheric equator.

We have determined the spectral characteristics of central plasma sheet ions and electrons observed during 71 hours when geomagnetic activity was at moderate to high levels (AE ≥ 100 nT). Particle data from the low‐energy proton and electron differential energy analyzer and the medium energy particle instrument on ISEE 1 are combined to obtain differential energy spectra (measured in units of particles/cm² s sr keV) in the kinetic energy range ∼30 eV/e to ∼1 MeV at geocentric radial distances >12 Re. Nearly isotropic central plasma sheet total ion and electron populations were chosen for analysis and were measured to be continuous particle distributions from our lowest to highest energies. During these high AE periods the >24 keV particle fluxes and the temperature of the entire particle distribution kT are significantly higher than during low AE periods (AE < 100 nT). The temperatures kTi and kTe are highly correlated during both quiet and disturbed periods. The active period spectral shape appears softer for ions and somewhat harder for electrons than during quiet periods. We find that the observed active period spectrum typically is complex and cannot be represented in general by a single functional form, as during quiet periods when it can be represented by the kappa distribution function. Although a power‐law shape is observed at higher energies, ion and electron spectral shapes deviate from a strictly kappalike form in different ways. In a limited energy range near the knee of the ion spectra (the knee is that portion of the spectrum at energies E ≳ Eo where the flux starts to decrease swiftly with increasing energy), the spectral shape can often be fit with a Maxwellian form, thus rolling over faster than the typical quiet time spectrum. At higher energies this shape merges into a harder nonthermal power‐law tail. Electron spectra also display this spectral characteristic, although at a lower occurrence frequency than for ions. The electron spectra are predominantly kappalike at energies near and above the knee. At energies below the knee, both ions and electrons often have an excess of flux with respect to the functional form that best fits the shape for energies at or above the knee, be it a kappa distribution or a Maxwellian distribution; the electron flux excess is significantly greater than the ion flux excess. We conclude that both ions and electrons participate in at least two separate acceleration mechanisms as geomagnetic activity evolves from low AE to high AE values. We suggest that both spectrum‐preserving and spectrum‐altering heating processes (possibly involving nonlocal betatron acceleration and crosstail current sheet acceleration, respectively) participate in overall particle energization during geomagnetic active periods. Observations are compared to model predictions.

[1] We have examined more than 75,000 latitudinal profiles of plasma densities measured by ion detectors on five Defense Meteorological Satellite Program (DMSP) satellites in the evening local time (LT) sector between 1989 and 2001. This survey established detection frequencies of equatorial bubbles (EPBs) at 840 km over the recent solar cycle. The annual rate of EPB detections decreased by more than an order of magnitude from >1000 during solar maximum to <100 during solar minimum years. EPB data were divided into 24 longitude sectors to determine seasonal and solar cycle variability in rates of encounter by DMSP. During the ascending and descending portions of the solar cycle, each longitude sector showed repeatable seasonal variations. The envelope of seasonally averaged rates of EPB encounters resembles the solar cycle variability for similar averages of the F 10.7 index. On both global and longitude sector scale sizes, annual rates of EPB encounters correlate with the yearly averages of F 10.7 . We also find that throughout the solar cycle the EPB detections were overrepresented during times of high geomagnetic activity signified by Kp ! 5. During solar minimum years, about one third of the EPBs occurred when traces of the Dst index had significant negative slopes (dDst/dt À5 nT/hr). This suggests that electric field penetration of the inner magnetosphere is responsible for driving many EPBs. Comparisons of plasma and neutral density profiles in the evening sector, calculated using the Parameterized Ionospheric Model (PIM) and MSIS-86 Model, indicate that the height of the bottomside of the F layer is >100 km lower during solar minimum than solar maximum. However, the overall effect is to increase the growth rate of the Rayleigh-Taylor instability at solar maximum in the bottomside F layer only by about a factor of 2. We suggest that the variability of electric fields in the postsunset equatorial ionosphere is the source of the observed discrepancy between EPB detections under solar maximum/minimum conditions.

We analyze 127 one‐hour average samples of central plasma sheet ions and electrons in order to determine spectral characteristics of these magnetotail particle populations during periods of low geomagnetic activity (AE<100 nT). Particle data from the low energy proton and electron differential energy analyzer (LEPEDEA) and medium energy particle instrument (MEPI) on ISEE 1 were combined to obtain differential energy spectra in the plasma sheet at geocentric radial distances R>12 RE. We find that, for even the longest periods sampled, the nearly isotropic central plasma sheet total ion and electron populations were measured to be continuous particle distributions from our lowest energy of tens of eV/e to a few hundred keV. The kappa distribution function (f ∼ [1 + E/κEo]−κ−1, where Eo, the energy of the peak differential number flux (measured in particles/cm² s sr keV), is related to the temperature through κ, a constant) most often reproduces the observed differential energy spectra. Spectra dominated by a single kappa functional form are observed during 83 (99) hours for ions (electrons). Spectra which are not dominated by a single kappa functional form can usually be closely approximated by superposed kappa functional forms. For both ions and electrons κ is typically in the range 4–8, with a most probable value between 5 and 6, so that the spectral shape is distinctly non‐Maxwellian. Eoi and Eoe are highly correlated, whereas κi and κe are not correlated; κi is roughly proportional to Eoi½, whereas κe is not correlated with Eoe. We statistically investigate the importance of flux and energy contributions from extramagnetospheric sources by separately analyzing intervals when simultaneously measured interplanetary particle fluxes are either enhanced or at low levels. A linear superposition of plasma sheet fluxes and interplanetary fluxes that have entered the magnetosphere is observed. The presence of interplanetary particles does not affect the average values of plasma sheet Eo or κ. We conclude that for AE<100 nT the nonthermal shape of plasma sheet particle distributions results from ongoing magnetospheric processes which are probably independent of geomagnetic activity as measured by AE.

Throughout most of the growth phase of a substorm, the cross‐tail current at x ∼ −10 Re can be supplied by the curvature drift of a bi‐directional field aligned distribution of ∼1 keV electrons. Just prior to its local disruption after substorm onset, the cross‐tail current in the now thin (∼400 km) current sheet is carried by the cross‐tail serpentine motion of non‐adiabatic ions (Speiser, 1965). The instability of this latter current leads to the local disruption of the near‐earth current sheet.

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A comprehensive survey of ISEE and IMP LEPEDEA plasma measurements in the earth's magnetotail reveals that the magnetospheric boundary layer and the plasma sheet boundary layer are the primary transport regions there. These plasma measurements also distinguish various components of the plama sheet, including the central plasma sheet and plasma sheet boundary layer. A significant new result reported here is the existence of cold‐and hot‐plasma components that are spatially copresent within the central plasma sheet. Such plasma components cannot be explained merely by temporal variations in spectra involving the entire plasma sheet. Contributions to a low‐temperature component of the plasma sheet enter directly from the boundary layer located along the magnetotail flanks. Field‐aligned flows predominate within the plasma sheet boundary layer, which is almost always present and is located near the northern and southern border of the plasma sheet. The plasma sheet boundary layer comprises highly anisotropic ion distributions, including counterstreaming ion beams, that evolve into the hot, isotropic component of the plasma sheet. Tailward acceleration regions generate these ion beams with plasma input from the magnetospheric boundary layer. Antisunward flowing ion beams, at E/q < 1 kV and of ionospheric composition, are frequently observed in the plasma sheet boundary layer and in the tail lobes. These ion beams are likely accelerated at low altitude over the polar cap and especially along auroral field lines. An ionospheric component of the plasma sheet is supplied from this source via the plasma sheet boundary layer. On the basis of a survey of ∼2000 three‐dimensional velocity distribution functions sampled by the ISEE LEPEDEA in the magnetotail we find that interpretations based solely on moments parameters are inevitably inadequate for inferring plasma sources and acceleration processes. We find that earthward flowing ions or counterstreaming beams are often observed near expansive phase onset under conditions for which antisunward ion flow is predicted by the near‐earth neutral line model of magnetospheric substorms. Magnetotail plasma flows sampled out to 38 RE and reported as typical of onset and recovery of magnetospheric substorms can only be adequately understood by considering spatial and temporal variations of the boundary layers described above.