The effects and correction of the geometric factor for the POES/MEPED electron flux instrument using a multisatellite comparison

Measurements from the Polar-Orbiting Environmental Satellite (POES) Medium Energy Proton and Electron Detector (MEPED) instrument are widely used in studies into radiation belt dynamics and atmospheric coupling. However, this instrument has been shown to have a complex energy-dependent response to incident particle fluxes, with the additional possibility of low-energy protons contaminating the electron fluxes. We test the recent Monte Carlo theoretical simulation of the instrument by comparing the responses against observations from an independent experimental data set. Our study examines the reported geometric factors for the MEPED electron flux instrument against the high-energy resolution Instrument for Detecting Particles (IDPs) on the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions satellite when they are located at similar locations and times, thereby viewing the same quasi-trapped population of electrons. We find that the new Monte Carlo-produced geometric factors accurately describe the response of the POES MEPED instrument. We go on to develop a set of equations such that integral electron fluxes of a higher accuracy are obtained from the existing MEPED observations. These new MEPED integral fluxes correlated very well with those from the IDP instrument (>99.9% confidence level). As part of this study we have also tested a commonly used algorithm for removing proton contamination from MEPED instrument observations. We show that the algorithm is effective, providing confirmation that previous work using this correction method is valid

Ground-based estimates of outer radiation belt energetic electron precipitation fluxes into the atmosphere

AARDDVARK data from a radio wave receiver in Sodankyla, Finland have been used to monitor transmissions across the auroral oval and just into the polar cap from the very low frequency communications transmitter, call sign NAA (24.0 kHz, 44 degrees N, 67 degrees W, L = 2.9), in Maine, USA, since 2004. The transmissions are influenced by outer radiation belt (L = 3-7) energetic electron precipitation. In this study, we have been able to show that the observed transmission amplitude variations can be used to determine routinely the flux of energetic electrons entering the upper atmosphere along the total path and between 30 and 90 km. Our analysis of the NAA observations shows that electron precipitation fluxes can vary by 3 orders of magnitude during geomagnetic storms. Typically when averaging over L = 3-7 we find that the >100 keV POES "trapped" fluxes peak at about 10(6) el. cm(-2) s(-1) sr(-1) during geomagnetic storms, with the DEMETER >100 keV drift loss cone showing peak fluxes of 105 el. cm(-2) s(-1) sr(-1), and both the POES >100 keV "loss" fluxes and the NAA ground-based >100 keV precipitation fluxes showing peaks of similar to 10(4) el. cm(-2) s(-1) sr(-1). During a geomagnetic storm in July 2005, there were systematic MLT variations in the fluxes observed: electron precipitation flux in the midnight sector (22-06 MLT) exceeded the fluxes from the morning side (0330-1130 MLT) and also from the afternoon sector (1130-1930 MLT). The analysis of NAA amplitude variability has the potential of providing a detailed, near real-time, picture of energetic electron precipitation fluxes from the outer radiation belts

Statistics of counter-streaming solar wind suprathermal electrons at solar minimum : STEREO observations

Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March–December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15–20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs

Une étude du processus de pénétration d'accélération et de chauffage des ions dans la magnétosphère terrestre

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Conception et réalisation d'un spectromètre de masse à temps de vol spatialisable de type "réflectron" électronique et tête de mesure

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Etude de la source solaire et des pertes de plasma de la magnétosphère terrestre à l'aide de satellites interball

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

CMOS Analog Front End Design for Particle Energy Measurement in Space Environment

International audienceIn situ studies of the geospace environment, including space weather monitoring, is mainly based on the measurements of particles and fields. The particle content of the Earth’s magnetosphere is studied with electron and ion detectors in various energy ranges, from the cold and dense eV solar wind to the MeV radiation belts. Here, the in situ high-energy (50 keV to 725keV) electron measurement is targeted. The design and development of space embedded electronic equipment require a specific approach . An Analog-Front-End (AFE) design methodology is proposed to optimizenoise, bandwidth, consumption, crosstalk and radiation hardness performances of such AFEs for Si semiconductor detectors. The conception ofan Analog-Front-End optimized in noise, band width, consumption, crosstalk and radiation hardness, dedicated to a silicon (SiA) detector. Each channel includes an 8 bits successive approximation register (SAR) ADC in order to digitize the incident electron energy. The chip was designed in a0.35 μm HV CMOS process. The ASIC measurements have shown that for a charge range of 0.6 fC to 32 fC , the charge - to - voltage conversion gainis approximately 60 mV/fC. The equivalent noise charge (ENC) is 3119 e- for 40pF input parasitic capacitance while consuming 2.5 mW. The circuitcan perform measurements up to a 650 kHz rate. The next step is to characterize the ASIC associated with the SC detector in a vacuum chamber. Furthermore, the total ionisation dose (TID) and the single event effect ( SEE ) tolerances must also be evaluate

Low Noise CMOS Analog Front-End Circuit With an 8-bit 1-MS/s ADC for Silicon Sensors for Space Applications

International audienceA low-power analog front-end circuit for silicon (Si) detectors has been fabricated in 0.35- μm CMOS technology. It has been designed to readout signals from large-capacitance Si detectors for incident electron energy ranging from 50 to 725 keV. In order to quantify electron energy, the front-end integrates a charge preamplifier, a pulse shaper, a peak detector, and an event-driven analog-to-digital converter (ADC). The complete front end, including the ADC dissipates 2.5 mW for a maximum electron detecting rate of 650 kHz. The charge-to-voltage gain is 60 mV/fC for a charge range of 0.6 to 32 fF. The measured equivalent noise charge is 3119 e- for a 40-pF detector parasitic capacitance

Contrasting the efficiency of radiation belt losses caused by ducted and nonducted whistler-mode waves from ground-based transmitters

It has long been recognized that whistler-mode waves can be trapped in plasmaspheric whistler ducts which guide the waves. For nonguided cases these waves are said to be "nonducted", which is dominant for L < 1.6. Wave-particle interactions are affected by the wave being ducted or nonducted. In the field-aligned ducted case, first-order cyclotron resonance is dominant, whereas nonducted interactions open up a much wider range of energies through equatorial and off-equatorial resonance. There is conflicting information as to whether the most significant particle loss processes are driven by ducted or nonducted waves. In this study we use loss cone observations from the DEMETER and POES low-altitude satellites to focus on electron losses driven by powerful VLF communications transmitters. Both satellites confirm that there are well-defined enhancements in the flux of electrons in the drift loss cone due to ducted transmissions from the powerful transmitter with call sign NWC. Typically, similar to 80% of DEMETER nighttime orbits to the east of NWC show electron flux enhancements in the drift loss cone, spanning a L range consistent with first-order cyclotron theory, and inconsistent with nonducted resonances. In contrast, similar to 1% or less of nonducted transmissions originate from NPM-generated electron flux enhancements. While the waves originating from these two transmitters have been predicted to lead to similar levels of pitch angle scattering, we find that the enhancements from NPM are at least 50 times smaller than those from NWC. This suggests that lower-latitude, nonducted VLF waves are much less effective in driving radiation belt pitch angle scattering