Johnathan Kerr Burchill

Statistical survey of nighttime midlatitude magnetic fluctuations: Their source location and Poynting flux as derived from the Swarm constellation

This is the first statistical survey of field fluctuations related with medium-scale traveling ionospheric disturbances (MSTIDs), which considers magnetic field, electric field, and plasma density variations at the same time. Midlatitude electric fluctuations (MEFs) and midlatitude magnetic fluctuations (MMFs) observed in the nighttime topside ionosphere have generally been attributed to MSTIDs. Although the topic has been studied for several decades, statistical studies of the Poynting flux related with MEF/MMF/MSTID have not yet been conducted. In this study we make use of electric/magnetic field and plasma density observations by the European Space Agencys Swarm constellation to address the statistical behavior of the Poynting flux. We have found that (1) the Poynting flux is directed mainly from the summer to winter hemisphere, (2) its magnitude is larger before midnight than thereafter, and (3) the magnitude is not well correlated with fluctuation level of in situ plasma density. These results are discussed in the context of previous studies.

Earth Magnetic Field Effects on Particle Sensors on LEO Satellites

Kinetic simulation results are presented for the interaction of spacecraft with space environment in low Earth orbit. Case studies are considered for DEMETER, for which small but distinctive potential variations have been measured on Instrument Champ Electrique (ICE) sensors, as the satellite goes through regions where the magnetic field B→ is nearly parallel to the satellite velocity v→. Our results point to a small variation in the potential of ICE probes under these conditions, but owing to the smallness of the signal and inherent statistical noise in our simulations, it is not possible to unambiguously explain observations. An earlier study of magnetic field effects on the Swarm electric field instrument is extended by computing Langmuir probe characteristics with and without a magnetic field. The possibility of probe crosstalk is also examined by comparing collected currents when the two probes have same and opposite bias voltages. Accounting for a representative ionospheric magnetic field is found to lead to appreciable quantitative differences in the probe characteristics. No significant crosstalk or mutual coupling is predicted between the probes under normal operation.

Spatial resolution and relative brightness of a microchannel plate detector system with P20 and P43 phosphor screens

A detector consisting of two biased microchannel plates and a P20 or P43 phosphor screen was illuminated with 500-eV electrons in order to characterize the size and amplitude of individual microchannel plate (MCP) firings as a function of phosphor-to-MCP distance d and voltage Vacc. The P43 phosphor was significantly brighter (71%) than P20 at Vacc = 4250 V, and brighter but less so (4%) at Vacc = 8000 V. Events were Gaussian-shaped with full widths at half maximum of order 0.27 mm for Vacc = 4250 V and d = 2 mm. Widths decreased by 23% to 28% when Vacc was increased to 8000 V, and increased between 9 to 34% when doubling d, depending on Vacc and phosphor type. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

Heavy (O+) ion energization and field-aligned motion in and near the ionosphere are still not well understood. Based on observations from the CASSIOPE Enhanced Polar Outflow Probe (e-POP) at altitudes between 325 km and 730 km over one year, we present a statistical study (24 events) of ion heating and its relation to field-aligned ion bulk flow velocity, low-frequency waves and field-aligned currents (FACs). The ion temperature and field-aligned bulk flow velocity are derived from 2-D ion velocity distribution functions measured by the suprathermal electron imager (SEI) instrument. Consistent ion heating and flow velocity characteristics are observed from both the SEI and the rapid-scanning ion mass spectrometer (IRM) instruments. We find that transverse O+ ion heating in the ionosphere can be intense (up to 4.5 eV), confined to very narrow regions (∼ 2 km across B), is more likely to occur in the downward current region, and is associated with broadband extremely low frequency (BBELF) waves. These waves are interpreted as linearly polarized perpendicular to the magnetic field. The amount of ion heating cannot be explained by frictional heating, and the correlation of ion heating with BBELF waves suggest that significant wave-ion heating is occurring and even dominating at altitudes as low as 350 km, a boundary that is lower than previously reported. Surprisingly, the majority of these heating events (17 out 24) are associated with core ion downflows rather than upflows. This may be explained by a downward-pointing electric field in the low-altitude return current region.

Strong ambipolar‐driven ion upflow within the cleft ion fountain during low geomagnetic activity

We investigate low-energy ( 1.6 km/s) ion upflow velocities near 1000 km altitude during quiet geomagnetic activity (Kp<3). Such large ion upflow velocities have been reported previously at or below 1000 km, but only during active periods. Analysis of the core ion distribution images allows us to demonstrate that the ion temperature within the CIF does not rise by more than 0.3 eV relative to background values, which is consistent with RISR-N observations in the F-region. The presence of soft electron precipitation seen by DMSP and lack of significant ion heating indicate that the ion upflows we observe near 1000 km altitude are primarily driven by ambipolar electric fields. DC field-aligned currents (FACs) and convection velocity gradients accompany these events. The strongest ion upflows are associated with downward current regions, which is consistent with some (although not all) previously published results. The moderate correlation coefficient (0.51) between upflow velocities and currents implies that FACs serve as indirect energy inputs to the ion upflow process.

Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground-Based Radars and Satellite Radio Occultation Measurements: Calibration and Validation of Swarm data

In this study we calibrate and validate in situ ionospheric electron density (N-e) and temperature (T-e) measured with Langmuir probes (LPs) on the three Swarm satellites orbiting the Earth in circ ...

Low-energy particle imaging on swarm and ePOP: A new view of the ionosphere

Summary form only given. In-situ diagnostics of ionospheric plasma are made most commonly by instruments that provide only bulk properties such as electron density and temperature (by Langmuir probes), and ion temperature, flow velocity and composition (by retarding potential analyzers and ion drift meters). Instruments that measure full particle distribution functions (e.g. top-hat analyzers) typically do not function well in the ionosphere because of the low particle energies involved. Thermal Ion Imaging is a new technique that allows high-resolution, 2-D (angle-energy) imaging of plasma populations having characteristic energies in the range 0.1-100 eV. By using a charged-coupled device-based imaging detector, particle distributions are recorded with 64×64 pixel resolution, and at rates of up to 100 distribution images per second. Four TII-based instruments have been launched into orbit in the past year, three in November 2013 on the European Space Agencys Swarm satellites, and another, the Suprathermal Electron Imager, on Canadas Enhanced Polar Outflow Probe (ePOP) satellite launched in September 2013. This talk will describe the TII/SEI sensors and present results from their first year in orbit.

First results from the Langmuir Probes on the Swarm satellites

Langmuir Probes (LP) are well-proven simple instruments allowing to estimate the electron density (Ne) and temperature (Te) of a plasma. They are also used to estimate the electric potential of satellites to the benefit of other instruments and technical systems. On the Swarm satellites the LPs are part of the Electric Field Instruments (EFI) featuring thermal ion imagers (TII) measuring 3-d ion distributions. The main task of the Langmuir probes is to provide measurements of spacecraft potentials influencing the ions before they enter the TIIs. In addition also electron density (Ne) and temperature (Te) are estimated from EFI LP data. The design of the Swarm LP includes a standard current sampling under sweeps of the bias voltage, and also, for most of the time, a novel ripple technique yielding derivatives of the current-voltage characteristics at three points in a rapid cycle. In normal mode the time resolution of the Ne and Te measurements so becomes only 0.5 s. We show first Ne and Te estimates from the EFI LPs obtained. The data feature very low instrumental noise thanks to the ripple technique. The LP data are compared with observations by incoherent scatter radars, namely EISCAT UHF, VHF, the ESR, and also Arecibo.

Lower hybrid ion heating cavities in the auroral ionosphere

Summary form only given. Lower hybrid cavities (LHCs) are localized, density-depleted regions of enhanced VLF wave amplitude found within regions of VLF hiss. They can cause ion heating to the level of a few eV in the direction transverse to the geomagnetic field B0. Statistical studies indicate that the cavities are cylindrical or ellipsoidal in shape, are aligned with B/sub 0/, and have diameters of order 20-50 m. There are many outstanding questions surrounding the formation of LHCs, including the origin of their density depletion, their B/sub 0/ aligned length, and the detailed relation between wave fields, plasma density and ion acceleration. The GEODESIC sounding rocket, launched in early 2000, brings some new information to bear on these problems. Over 100 LHCs were encountered near the leading edge of an auroral substorm expansion. A Suprathermal Ion Imager (SII) newly developed for the flight provides 2D ion distribution function images from 0-20 eV with a time resolution of 11 ms, sufficient to resolve core and tail ion distributions at the edges and interiors of individual LHCs cavities. The measurements show tail heating to 1-2 eV superimposed on an unaffected core distribution. Magnetic field observations on GEODESIC indicate a significant enhancement of 0-10 kHz magnetic field fluctuations inside LHCs, in contrast to all previous attempts to detect such fields.