In the companion paper, we identified a repeatable sequence of events leading to substorm onset in THEMIS all‐sky imager observations: enhanced flows bring new plasma into the plasma sheet. The new ...plasma then moves earthward as a flow channel, bringing it to the near‐Earth plasma sheet and where it produces onset instability. New plasma entering the dusk (dawn) convection cell drifts equatorward and eastward and then around the Harang reversal, leading to pre‐midnight (near‐ and post‐midnight) onset. Here we present evidence supporting this sequence using incoherent scatter radar (ISR) ionospheric observations. Using the Sondrestrom ISR, we find that enhanced flows of new plasma commonly enter the plasma sheet from the polar cap ∼8 min prior to onset. These flows are related to poleward boundary intensification signatures, consistent with the inferences from the imagers. Using the Poker Flat ISR (PFISR), we find that shortly before onset, enhanced westward flows reach the subauroral polarization streams (SAPS) region equatorward of the Harang reversal (dusk‐cell onsets) or enhanced eastward flows enter the onset region from the poleward direction (dawn‐cell onset). PFISR proton precipitation signatures are consistent with the possibility that the enhanced flows consist of reduced‐entropy plasma sheet plasma, and that onset occurs poleward of much of the enhanced SAPS flow (dusk‐cell onsets) or equatorward of the enhanced eastward flows (dawn‐cell onsets). Consistency with reduced entropy plasma is seen only within the enhanced flows, leading us to suggest that intrusion of low‐entropy plasma may alter the radial gradient of entropy toward onset instability.
We present coordinated ground satellite observations of solar wind compression‐related dayside electromagnetic ion cyclotron (EMIC) waves from 25 September 2005. On the ground, dayside structured ...EMIC wave activity was observed by the CARISMA and STEP magnetometer arrays for several hours during the period of maximum compression. The EMIC waves were also registered by the Cluster satellites for half an hour, as they consecutively crossed the conjugate equatorial plasmasphere on their perigee passes at L ∼ 5. Simultaneously, conjugate to Cluster, NOAA 17 passed through field lines supporting EMIC wave activity and registered a localized enhancement of precipitating protons with energies >30 keV. Our observations suggest that generation of the EMIC waves and consequent loss of energetic protons may last for several hours while the magnetosphere remains compressed. The EMIC waves were confined to the outer plasmasphere region, just inside the plasmapause. Analysis of lower‐frequency Pc5 waves observed both by the Cluster electron drift instrument (EDI) and fluxgate magnetometer (FGM) instruments and by the ground magnetometers show that the repetitive structure of EMIC wave packets observed on the ground cannot be explained by the ultra low frequency (ULF) wave modulation theory. However, the EMIC wave repetition period on the ground was close to the estimated field‐aligned Alfvénic travel time. For a short interval of time, there was some evidence that EMIC wave packet repetition period in the source region was half of that on the ground, which further suggests bidirectional propagation of wave packets.
The South Korean meteorological and environmental satellite GEO-KOMPSAT-2A (GK-2A) was launched into geostationary orbit at
128.2
∘
East on 4 December 2018. The space weather observation aboard GK-2A ...is performed by the Korea Space Environment Monitor. It consists of three particle detectors, a charging monitor and a four-sensor Service Oriented Spacecraft Magnetometer (SOSMAG).
The magnetometer design aims for avoiding strict magnetic cleanliness requirements for the hosting spacecraft and an automated on-board correction of the dynamic stray fields which are generated by the spacecraft. This is achieved through the use of two science grade fluxgate sensors on an approximately one meter long boom and two additional magnetoresistance sensors mounted within the spacecraft body.
This paper describes the instrument design, discusses the ground calibration methods and results, presents the post-launch correction and calibration achievements based on the data which were acquired during the first year in orbit and demonstrates the in-flight performance of SOSMAG with two science cases.
The dynamic stray fields from the GK-2A spacecraft, which was built without specific magnetic cleanliness considerations, are reduced up to a maximum factor of 35. The magnitude of the largest remnant field from an active spacecraft disturber is 2.0 nT. Due to a daily shadowing of the SOSMAG boom, sensor intrinsic offset oscillations with a periodicity up to 60 minutes and peak-to-peak values up to 5 nT remain in the corrected data product.
The comparison of the cleaned SOSMAG data with the Tsyganenko 2004 magnetic field model and the magnetic field data from the Magnetospheric Multiscale mission demonstrates that the offset error is less than the required 5 nT for all three components and that the drift of the offsets over 10 months is less than 7 nT.
Future work will include a further reduction of the remaining artefacts in the final data product with the focus on lessening the temperature driven sensor oscillations with an epoch based identification and correction.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
After the Rosetta mission reached its target comet 67P/Churyumov–Gerasimenko, the lander Philae touched down on the surface on 2014 November 12. During the First-Science-Sequence after ...touchdown the lander magnetometer ROMAP and the orbiter magnetometer RPC-MAG were both operating simultaneously which allowed for in situ magnetic two-point observations of the comet. This analysis aims at determining the characteristics of the low-frequency plasma waves present in the nucleus surface region, including frequency, propagation direction and velocity. These waves propagate predominantly from the nucleus towards the Sun with a mean phase velocity of ∼5.3 km s−1, a wavelength of ∼660 km and an average frequency of ∼8 mHz.
Venus has no significant internal magnetic field, which allows the solar wind to interact directly with its atmosphere2,3. A field is induced in this interaction, which partially shields the ...atmosphere, but we have no knowledge of how effective that shield is at solar minimum. (Our current knowledge of the solar wind interaction with Venus is derived from measurements at solar maximum.) The bow shock is close to the planet, meaning that it is possible that some solar wind could be absorbed by the atmosphere and contribute to the evolution of the atmosphere. Here we report magnetic field measurements from the Venus Express spacecraft in the plasma environment surrounding Venus. The bow shock under low solar activity conditions seems to be in the position that would be expected from a complete deflection by a magnetized ionosphere. Therefore little solar wind enters the Venus ionosphere even at solar minimum.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The accurate measurement of the magnetic field along the orbits of the four Cluster spacecraft is a primary objective of the mission. The magnetic field is a key constituent of the plasma in and ...around the magnetosphere, and it plays an active role in all physical processes that define the structure and dynamics of magnetospheric phenomena on all scales. With the four-point measurements on Cluster, it has become possible to study the three-dimensional aspects of space plasma phenomena on scales commeasurable with the size of the spacecraft constellation, and to distinguish temporal and spatial dependences of small-scale processes. We present an overview of the instrumentation used to measure the magnetic field on the four Cluster spacecraft and an overview the performance of the operational modes used in flight. We also report on the results of the preliminary in-orbit calibration of the magnetometers; these results show that all components of the magnetic field are measured with an accuracy approaching 0.1 nT. Further data analysis is expected to bring an even more accurate determination of the calibration parameters. Several examples of the capabilities of the investigation are presented from the commissioning phase of the mission, and from the different regions visited by the spacecraft to date: the tail current sheet, the dusk side magnetopause and magnetosheath, the bow shock and the cusp. We also describe the data processing flow and the implementation of data distribution to other Cluster investigations and to the scientific community in general.Key words. Interplanetary physics (instruments and techniques) – magnetospheric physics (magnetospheric configuration and dynamics) – space plasma physics (shock waves)
Knowledge of the magnetization of planetary bodies constrains their origin and evolution, as well as the conditions in the solar nebular at that time. On the basis of magnetic field measurements ...during the descent and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko (67P), we show that no global magnetic field was detected within the limitations of analysis. The Rosetta Magnetometer and Plasma Monitor (ROMAP) suite of sensors measured an upper magnetic field magnitude of less than 2 nanotesla at the cometary surface at multiple locations, with the upper specific magnetic moment being <3.1 × 10
−5
ampere–square meters per kilogram for meter-size homogeneous magnetized boulders. The maximum dipole moment of 67P is 1.6 × 10
8
ampere–square meters. We conclude that on the meter scale, magnetic alignment in the preplanetary nebula is of minor importance.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The Venus Express mission is scheduled for launch in 2005. Among many other instruments, it carries a magnetometer to investigate the Venus plasma environment. Although Venus has no intrinsic ...magnetic moment, magnetic field measurements are essential in studying the solar wind interaction with Venus. Our current understanding of the solar wind interaction with Venus is mainly from the long lasting Pioneer Venus Orbiter (PVO) observations. In this paper, we briefly describe the magnetic field experiment of the Venus Express mission. We compare Venus Express mission with PVO mission with respect to the solar wind interaction with Venus. Then we discuss what we will achieve with the upcoming Venus Express mission.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude ...side of the auroral oval. The pulsating aurora was observed by a 30‐Hz sampled all‐sky imager (ASI) at Gillam (56.4°N, 265.4°E), Canada, at ∼0840‐0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at ∼0.1–0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian‐scanning photometer. After auroral pulsation began at ∼0842 UT, both THD and THEMIS E which was near THD in the mid‐tail at 11.6–11.8 RE, observed enhanced field‐aligned electron fluxes at energies of 1–10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5–9 RE. We suggest that the observed field‐aligned electrons, which are probably caused by Fermi‐type acceleration associated with earthward plasma flow in the mid‐tail plasma sheet, are modulated by some wave processes to cause pulsating auroras.
Key Points
A ground‐satellite conjugate observation of pulsating aurora at 12 Re
Whistler‐mode and ECH wave amplitudes were weak
Modulation of field‐aligned electrons by some processes
The THEMIS Fluxgate Magnetometer Auster, H. U.; Glassmeier, K. H.; Magnes, W. ...
Space science reviews,
12/2008, Volume:
141, Issue:
1-4
Journal Article
Peer reviewed
The THEMIS Fluxgate Magnetometer (FGM) measures the background magnetic field and its low frequency fluctuations (up to 64 Hz) in the near-Earth space. The FGM is capable of detecting variations of ...the magnetic field with amplitudes of 0.01 nT, and it is particularly designed to study abrupt reconfigurations of the Earth’s magnetosphere during the substorm onset phase. The FGM uses an updated technology developed in Germany that digitizes the sensor signals directly and replaces the analog hardware by software. Use of the digital fluxgate technology results in lower mass of the instrument and improved robustness. The present paper gives a description of the FGM experimental design and the data products, the extended calibration tests made before spacecraft launch, and first results of its magnetic field measurements during the first half year in space. It is also shown that the FGM on board the five THEMIS spacecraft well meets and even exceeds the required conditions of the stability and the resolution for the magnetometer.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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