SM42A-01
Ionospheric O+ Outflows in the Multi-Fluid LFM
The presence of O+ ions of ionospheric origin is known to significantly modify the shape of and flows within the magnetosphere, yet until recently most global magnetospheric MHD models could not include this plasma source. We present initial results of the newly-developed multi-fluid version of the Lyon-Fedder-Mobarry (LFM) global MHD code. The ionospheric O+ source is implemented by an outflow module using the Strangeway formula [Strangeway et al., 2005]. The module takes as input the Poynting flux from the LFM and outputs O+ density and velocity at the ionospheric boundary of the LFM. Using idealized solar wind conditions to drive the sunward boundary of the code, we examine the resulting outflow at the LFM inner boundary and investigate how the ionospheric O+ outflow affects the configuration and dynamics of the magnetosphere. In this initial study we focus on global characteristics of the magnetosphere such as its global geometry (the location of the night-side reconnection line, in particular), the cross-polar cap potential, and ionospheric and magnetospheric convection patterns.
SM42A-02
The Response of Dayside Ionospheric Upflows to Solar Wind Forcings
The ionosphere is clearly a significant source of magnetospheric plasma [Chappell et al., 1987] since terrestrial ions have been discovered in the ring current [Johnson et al., 1977], the plasma sheet [Peterson et al., 1981], and the tail lobes [Eastman et al., 1984]. The escape of plasma from the ionosphere to the magnetosphere is a multi-step process that begins with upwelling of ionospheric plasma in the topside. Some distance above the topside, the heavier ions (O+, N+, N2+, O2+, NO+) gain escape energy by one or more of a multitude of wave-particle energization processes. Ionospheric upwelling does not always lead to plasma escape since it can be part of the normal "breathing" of the atmosphere as it responds to changes in the inputs of solar or magnetospheric energy. When upwelling does participate in ion outflow, it can control the flux of escaping ions by the rate at which it feeds thermal plasma to the higher altitude energization regions. In that regard, it is important to understand ionospheric upwelling that occurs in places where escaping ions are generated routinely such as the so-called cleft ion fountain [Lockwood et al., 1985; Valek et al., 2002] and the dayside auroral zone. Using ion driftmeter and RPA data from several DMSP satellites we demonstrate how topside plasma upflow on the dayside responds to variations in the solar wind. We have observed that the intensity of the upflow flux, the location of the upflow region, and the size of the upflow region are highly correlated with solar wind parameters such as the merging electric field and dynamic pressure.
SM42A-03
The Spatial Variation of Polar Rain Electrons and its Cause
It is generally accepted that field aligned electrons in the solar wind can follow field lines connected to Earth and precipitate in the polar ionosphere where they are known as polar rain. Few-hundred eV, field-aligned electrons of the solar wind "strahl" carry the interplanetary heat flux moving out from the sun and these electrons precipitate in either the northern or southern hemisphere depending on the magnetic field direction. These electrons produce enhanced polar rain in one hemisphere or the other although weaker polar rain is usually produced in the opposite hemisphere by whatever electrons are moving in the opposite direction. Although much evidence exists for this simple free entry mechanism, it has also long been known that there are spatial variations in the energies and intensities of the precipitating electrons. The present work compares electron distribution functions measured by the ACE spacecraft in the solar wind with those measured by the DMSP spacecraft at 800 km altitude over the polar cap. It is found that shifting the DMSP distribution functions in energy by amounts ranging from 10's to a few hundred eV produces quite good agreement with simultaneous ACE measurements. Over most of the polar cap this DMSP energy shift must be positive to achieve this agreement, suggesting the electrons have been decelerated by a field aligned potential as they move from the solar wind to low altitudes. The largest shifts occur on the nightside and on the dawn or dusk side, with the latter depending on the plasma convection pattern which is controlled by the orientation of the IMF. Nearer the cusp the shift is smaller or even negative. Since more massive tailward flowing magnetosheath ions are unable to follow the field lines into the magnetotail like the electrons, a field aligned potential is expected to develop to exclude low energy electrons and prevent an excessive charge imbalance. Such a potential would also produce the deceleration of those electrons that reach low altitudes. This improved understanding of polar rain should increase the utility of polar rain measurements as a diagnostic of the magnetosphere magnetic field configuration.
SM42A-04
Artificial Ionospheric Heating Experiments Conducted by a Magnetosphere-Ionosphere Coupling Model
This presentation discusses computational dynamics and results of artificial heating in the ionosphere. The results are then compared to experiments including a geophysical experiment conducted at the Polar Aeronomy and Radio Science Summer School (PARS) in conjunction with the High Frequency Active Auroral Research Program (HAARP) The computational model includes the following terms: ion inertia, Ohm's law (Hall term, electron pressure term, electron neutral and electron ion collisions), ionization, recombination, electron energy (heat advection, conduction, heating through ionization, ohmic heating, gravity, energy loss to neutrals and ions), as well as parameterized collisions frequencies, and a height resolved neutral atmosphere. Atmospheric conditions for the time of the experiment (plasma density, temperature, etc) are used as initial conditions. The power and frequency of the heater facility are then used to compute the heating of the ionosphere. Data processing for the experiment and model are ongoing.
SM42A-05
Improved Model for Analysis of Thermal Charged-Particle Spectrograph Data for Ionospheric Research
As a source of mass for the magnetosphere, and a sink of electromagnetic energy via Joule heating, the cold, dense plasma of the ionosphere plays key roles in magnetosphere-ionosphere-thermosphere coupling. It also hosts a variety of interesting wave-particle processes that give rise to structure and acceleration. Obtaining accurate measurements of the thermal electron and ion velocity distribution functions at ionospheric altitudes has proven to be challenging, largely because the particle trajectories are disrupted by stray electric fields within and surrounding the particle analyzers. The Whalen analyzer is a compact two-dimensional energy-angle analyzer tailored towards the low-energy (<1 eV) core of ionospheric plasmas. It has flight heritage with the Freja satellite and several sounding rockets, and it will be used on several upcoming satellite missions. In this paper we present an improved model of the Whalen analyzer that takes into account abberations arising from fringing electric fields and Debye sheaths within the analyzer. We use this model to refine ion velocity and temperature estimates from the Cusp-2002 and Joule I and II rockets. We discuss implications for interpreting low-energy particle measurements from the forthcoming Canadian ePOP satellite and the ESA Swarm mission.
SM42A-06
Wave Probe – New Instrument For Space Research
The dispersion relations are very important for the wave activity study in space plasmas. One of the most efficient methods for their analysis is the simultaneous measurements of spatial current density and magnetic field fluctuations during such a wave process. Whereas the measurement of the magnetic field is a routine task realized onboard practically every spacecraft (SC), the direct measurement of spatial current density (SCD) still remains a complicated scientific and technological problem. First attempt to solve it was executed in late 60-ties by a group headed by F. Mozer. They proposed and launched in a rocket experiment the device named "Split Langmuir Probe" (SLP) – two conducting plates separated by a thin insulated split. Unfortunately this experiment failed what diverted the attention of experimenters in space branch from this instrument for many years, practically till now. But the importance to know the SCD stimulated the development of new principles and devices to measure it. A short review of known versions is discussed. The newly evoked interest to this problem caused next attempt to improve the SLP construction and methodology of its application for SCD measurements, which resulted in first successful attempt in 1985: the measured SCD onboard Prognos-10 SC in the bow shock region was in rather good agreement with the calculated value. This attempt was continued onboard Interball-Tail SC (1995-2000) where again a qualitatively good coincidence of measured and calculated values was observed. The obtained experience and further theoretical research allowed developing a new instrument – Wave Probe – which is a combination of induction magnetometer and SLP in one body. Both on-ground tests in plasma chamber and the spatial experiment executed onboard Ukrainian "Sich-1M" SC (2004) showed that the combined in-situ simultaneous measurements of SCD and magnetic field fluctuations allowed obtaining the wave number of the whistler wave. The same wave number was calculated theoretically from dispersion relations of whistler wave using known ionosphere model and the comparison of measured and calculated values of both wave number and SCD gave a good quantitative agreement. The details of theoretical and experimental study are discussed in the report. There is a pleasant duty of the authors to thank Prof. F. Mozer and Prof. S. Klimov for continuous attention and practical support of this work. It was also supported by NSAU contract No 1-02/03.
SM42A-07
Stand-alone WIreless Magnetometer System: Concept Design and Development Status
The Stand-alone WIreless Magnetometer System (SWIMS) is intended to serve as a technology suitable for large scale deployment for magnetometer networks in sub-auroral latitudes with minimal logistical support and maintenance. SWIMS is based on a new magnetometer developed and licensed by JHU/APL. A SWIMS installation will consist of up to three solar/battery powered Sensor Modules (SM) each equipped with a new Mirror Image Differential Induction Amplitude Magnetometer (MIDIAM). The SMs are linked via wireless, radio frequency (RF) connection to a Central Node (CN). The RF link allows wireless installation over distances up to 300 meters between SMs. The CN may communicate either via land lines or wireless links to a central data facility. Because each SM is wireless, SWIMS can use more than one SM at a single site to discriminate against local noise sources. The present project objective is to develop a prototype SWIMS system of three SMs communicating via local RF link to a CN. The MIDIAM has yielded sub-nT performance with less than 1W power consumption in continuous operation. A conceptual system design using commercial solar/batter power system and RF communication components has been developed that is expected to achieve continuous operation at 1- second or higher rate sampling using a moderately sized solar cell array, 12" x 18", and a 6"x6"x4" AGM battery (144 W-hour). By monitoring the battery depth of discharge and duty cycling MIDIAM as required if incident effective power is low due to inclement conditions, the SM is expected to support continuous unattended operation with no coarser than one sample per minute on as little as four hours of sunlight every ten days.
SM42A-08
The distribution of plasma velocity fluctuations observed in the high-latitude ionosphere.
This paper presents a statistical study of the ionospheric plasma velocities observed by the Super Dual Auroral Radar Network (SuperDARN) HF radar network. The study was undertaken with the goal of determining the level of velocity fluctuations due to internal magnetospheric processes. A secondary goal was to examine the probability of observing significant velocity fluctuations within any given time interval. The study included six years of observations from periods when the interplanetary magnetic field (IMF) was moderately southward and steady. The choice of such conditions was motivated by the goal of examining internal sources of variability and sought periods when the fluctuations of the main external driver, the IMF, were minimized. Inherent in this study is the assumption that the IMF that encounters the magnetosphere is the same as that observed at a spacecraft located upstream from the Earth, and that all variability of the plasma convection is due either to variability of the IMF driver or to internal magnetospheric processes. For the purposes of this study, structure of the solar wind and IMF away from the satellite cannot be accounted for, and variability generated at the bow shock is considered to be an internal magnetospheric process. IMF variability away from the satellite was examined by comparing observations for the ACE and Wind satellites. The distribution of velocity fluctuations and their waiting time distribution were examined over a grid of latitude and local time. It was found that the waiting time is scale free over the range of times that could be examined. From the waiting time distributions, the probability of observing fluctuations within various time intervals was determined over the grid.