Magnetic Signatures of low- to mid-Latitude Ionospheric Irregularities as Oobserved by CHAMP from 2000 to 2008
We investigate the magnetic signatures of low- to mid-latitude ionospheric irregularities as observed by the CHAMP satellite. Equatorial plasma bubbles (EPBs) and low-latitude plasma blobs are accompanied by variations of magnetic field strength (magnetic pressure), which balances the change in plasma pressure. These features also show magnetic fluctuations perpendicular to the mean field, implying that field-aligned currents (FACs) are flowing around the irregularities. EPB Poynting flux in events occurring before 21LT, when they evolve actively, is directed downward along the magnetic field lines. This implies that FACs are driven by a high-altitude equatorial source. Perpendicular magnetic deflections of EPBs are tilted westward from the magnetic meridional direction, implying that the depleted volume of EPBs and the FAC structures are tilted westward above the magnetic equator. The peak-to-peak amplitude of the FAC density is found to range between 0.1-0.5 μA/m2. Blobs have a field-aligned structure spanning several hundred kilometers. And their magnetic properties corroborate the close relationship between EPBs and blobs. Medium-scale traveling ionospheric disturbances (MSTIDs) also have clear magnetic signatures perpendicular to the mean field with a good linear polarization. However, they are generally not accompanied by variations of the magnetic field strength at CHAMP altitudes (~400 km). MSTID magnetic signatures are practically absent above the southern Atlantic ocean and weak during the solar minimum. It means that other factors than MSTIDs, e.g. ionospheric conductivity, sporadic E-layer or plasma instabilities may play a non-negligible role in generating the FACs. The peak-to-peak amplitude of the FAC density also ranges between 0.1-0.5 μA/m2.
DC Electric Fields and Associated Plasma Drifts Observed with the C/NOFS Satellite
Initial DC electric field observations and associated plasma drifts are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite. We present statistical averages of the vector fields for the first year of operations that include both the zonal and radial components of the resulting E x B plasma flows at low latitudes. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. The DC electric field detector reveals zonal and radial electric fields that undergo strong diurnal variations, typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night. There is considerable variation in the large scale DC electric field data, in both the daytime and nighttime cases, with enhanced structures typically observed at night. In general, the measured zonal DC electric field amplitudes include excursions that extend within the 0.4 - 2 mV/m range, corresponding to E x B drifts of the order of 30- 150 m/s. The average vertical or radial electric fields may exceed the zonal fields in amplitude by a factor of 1.5 to 2. Although the data compare well, in a general sense, with previous satellite observations and statistical patterns of vertical ion drifts, the E x B drifts we report from C/NOFS rarely show a pronounced pre-reversal enhancement after sunset. We attribute this to a combination of extreme solar minimum conditions and the fact that the C/NOFS orbit of 401 by 867 km carries the probes essentially above the lower altitude regions where the wind-driven dynamo might be expected to create enhanced upwards drifts in the early evening. Evidence for wavenumber 4 tidal effects and other longitudinal signatures have been detected and will be presented. We also discuss off-equatorial electric fields and their relation to the ambient plasma density.
Observations of Unusual Travelling Ionospheric Disturbances (TIDs) and Enhancements in Mid-Latitude E Region Irregularity Backscatter
The SuperDARN HF radar at NASA Wallops Flight Facility observed unusual enhancements in the backscattered power from the E region ionosphere around the time of a heavily instrumented sounding rocket launch in October 2007. This activity appeared to coincide with the passage of remarkable TIDs that were due to equatorward propagating atmospheric gravity waves. We discuss the observations and their interpretation in terms of irregularity formation in sporadic E Layers and seeding by TIDs. We make comparisons with the diagnostics of TIDs, sporadic E, and spread F that were carried out in support of the rocket launch. We show how the unusual activity can be traced continuously with the long-range radar observations to the onset of disturbance at high latitudes.
The Canadian High Arctic Ionospheric Network (CHAIN)
Polar cap ionospheric measurements are important for the complete understanding of the various processes
in the solar wind - magnetosphere - ionosphere (SW-M-I) system as well as for space weather applications.
Currently the polar cap region is lacking high temporal and spatial resolution ionospheric measurements
because of the orbit limitations of space-based measurements and the sparse network providing ground-
based measurements. Canada has a unique advantage in remedying this shortcoming because it has the
most accessible landmass in the high Arctic regions and the Canadian High Arctic Ionospheric Network
(CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of
the Sun-Earth system.
CHAIN is a distributed array of ground-based radio instruments in the Canadian high Arctic. The instruments
components of CHAIN are ten high data-rate Global Positioning System ionospheric scintillation and total
electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have
been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper
briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN.
Swarm Measurements of Ionospheric Electric Field and Plasma
Swarm is a three-spacecraft European Space Agency Earth Explorer mission that will include precision in-situ measurements of magnetic field, electric field, and plasma parameters at altitudes up to 530 km, twice per second for four years beginning in late 2010. Electric fields in the direction perpendicular to the local magnetic field will be measured by the Swarm Electric Field Instruments (EFI) using a technique based on measurements of ion drift. The Swarm EFI's represent a new generation of ion drift measurement in that they use an intensified CCD-based technique to generate 2-D images of low-energy ion distribution functions from which both ion drift velocity and temperature are derived. These measurements will be complemented by Langmuir-probe measurements of electron density, electron temperature and spacecraft potential. We present an overview of the mission and of the predicted performance characteristics of the EFI, and examine the benefits of the Swarm configuration for ionospheric research relative to previous precision magnetic field research missions such as Ørsted and CHAMP.
New Capabilities for Ionospheric Observations in the Upcoming Enhanced Polar Outflow Probe (e-POP) Mission
The CASSIOPE Enhanced Polar Outflow Probe (e-POP) is a Canadian small-satellite mission dedicated to the study of polar ion outflows and related magnetosphere-ionosphere coupling processes in the topside ionosphere. The mission will carry a total of 8 instruments, including imaging plasma and neutral particle sensors, magnetometers, dual-frequency GPS receivers, CCD cameras, a radio wave receiver and a beacon transmitter. We present the measurement capabilities of these instruments, with special emphasis on the new capabilities for observations of ionospheric responses to various drivers. These will include the capability to resolve sub-decameter plasma and field-aligned current structures using 2D imaging measurements of detailed low-energy ion and electron velocity distributions up to 100 distributions per second and magnetic field vector measurements exceeding 100 samples per second; the capability of measuring neutral mass composition and velocity in-situ; the capability of two-dimensional (altitude-latitude) tomography of ion outflow using the GPS receivers in conjunction with occulting GPS satellites above the horizon; the capability of continuous imaging of sub-km auroral structures using the CCD imagers in nadir or slew pointing mode; and the capability of trans-ionospheric radio propagation measurement using the radio receiver in conjunction with coordinated ground transmitters.
Plasma Heating by Charge Exchange Friction
Observations show that transverse heating and resultant outflow of ionospheric plasmas is highly correlated with DC electromagnetic energy flux into the ionosphere. This suggests a mechanism powered by the motion of plasmas through the neutral upper atmosphere, rather than by magnetic field-aligned current flow. The frictional interaction between plasma and gas is closely related to the familiar ion pick up process at heights where the ions are nearly magnetized and dominated by charge exchange interactions with gas. At such heights, a phenomenon called "charge exchange friction" powers velocity space instabilities when the convective drift motion exceeds the neutral thermal speed. The result is a "ring-beam" or toroidal velocity distribution. These have been detected in the ionosphere by direct plasma measurements, inferred from observations of the associated waves, and inferred from the echo spectra of incoherent radar observations of rapidly convecting ionospheric regions. They are unstable to plasma wave growth, and the driven waves must be such as to thermalize the distributions, mainly via perpendicular energy diffusion when ion speeds are much less than the local Alfvén speed. Simple diffusive simulations yield exponential (in v) distributions with power law tails, as observed. The e-folding speed is double the local ion-neutral relative flow speed, as expected for ion pickup. When this process acts along auroral magnetic field lines, the escape flux of ionospheric oxygen increases rapidly with Poynting flux in agreement with observations. Charge exchange friction is a universal plasma process that will produce ion acceleration and heating wherever fast plasma flows are driven through neutral gas.