445 research outputs found
Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined
Combining STEREO, ACE and Hinode observations has presented an opportunity to
follow a filament eruption and coronal mass ejection (CME) on the 17th of
October 2007 from an active region (AR) inside a coronal hole (CH) into the
heliosphere. This particular combination of `open' and closed magnetic
topologies provides an ideal scenario for interchange reconnection to take
place. With Hinode and STEREO data we were able to identify the emergence time
and type of structure seen in the in-situ data four days later. On the 21st,
ACE observed in-situ the passage of an ICME with `open' magnetic topology. The
magnetic field configuration of the source, a mature AR located inside an
equatorial CH, has important implications for the solar and interplanetary
signatures of the eruption. We interpret the formation of an `anemone'
structure of the erupting AR and the passage in-situ of the ICME being
disconnected at one leg, as manifested by uni-directional suprathermal electron
flux in the ICME, to be a direct result of interchange reconnection between
closed loops of the CME originating from the AR and `open' field lines of the
surrounding CH.Comment: 13 pages, 13 figures, accepted Annales Geophysica
On the problem of Plasma Sheet Boundary Layer identification from plasma moments in Earth's magnetotail
The problem of identification of the interface region between the lobe and
the Plasma Sheet (PS) – the Plasma Sheet Boundary Layer (PSBL) – using ion
moments and magnetic field data often arises in works devoted to statistical
studies of various PSBL phenomena. Our experience in the identification of this
region based on the analysis of ion velocity distribution functions
demonstrated that plasma parameters, such as the ion density and bulk
velocity, the plasma beta or the dynamic pressure vary widely depending on
the state of magnetotail activity. For example, while field-aligned beams of
accelerated ions are often observed propagating along the lobeward edge of
the PSBL there are times when no signatures of these beams could be
observed. In the last case, a spacecraft moving from the lobe region to the
PS registers almost isotropic PS-like ion velocity distribution. Such events
may be classified as observations of the outer PS region. In this paper, we
attempt to identify ion parameter ranges or their combinations that result
in a clear distinction between the lobe, the PSBL and the adjacent PS or the
outer PS regions. For this we used 100 crossings of the lobe-PSBL-PS
regions by Cluster spacecraft (s/c) made in different periods of magnetotail
activity. By eye inspection of the ion distribution functions we first
identify and separate the lobe, the PSBL and the adjacent PS or outer PS
regions and then perform a statistical study of plasma and magnetic field
parameters in these regions. We found that the best results in the
identification of the lobe-PSBL boundary are reached when one uses plasma
moments, namely the ion bulk velocity and density calculated not for the
entire energy range, but for the energies higher than 2 keV. In addition, we
demonstrate that in many cases the plasma beta fails to correctly identify
and separate the PSBL and the adjacent PS or the outer PS regions
A Comprehensive View of the 2006 December 13 CME: From the Sun to Interplanetary Space
The biggest halo coronal mass ejection (CME) since the Halloween storm in
2003, which occurred on 2006 December 13, is studied in terms of its solar
source and heliospheric consequences. The CME is accompanied by an X3.4 flare,
EUV dimmings and coronal waves. It generated significant space weather effects
such as an interplanetary shock, radio bursts, major solar energetic particle
(SEP) events, and a magnetic cloud (MC) detected by a fleet of spacecraft
including STEREO, ACE, Wind and Ulysses. Reconstruction of the MC with the
Grad-Shafranov (GS) method yields an axis orientation oblique to the flare
ribbons. Observations of the SEP intensities and anisotropies show that the
particles can be trapped, deflected and reaccelerated by the large-scale
transient structures. The CME-driven shock is observed at both the Earth and
Ulysses when they are separated by 74 in latitude and 117
in longitude, the largest shock extent ever detected. The ejecta seems missed
at Ulysses. The shock arrival time at Ulysses is well predicted by an MHD model
which can propagate the 1 AU data outward. The CME/shock is tracked remarkably
well from the Sun all the way to Ulysses by coronagraph images, type II
frequency drift, in situ measurements and the MHD model. These results reveal a
technique which combines MHD propagation of the solar wind and type II
emissions to predict the shock arrival time at the Earth, a significant advance
for space weather forecasting especially when in situ data are available from
the Solar Orbiter and Sentinels.Comment: 26 pages, 10 figures. 2008, ApJ, in pres
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
The composition of heavy molecular ions inside the ionopause of Comet Halley
The RPA2-PICCA instrument aboard the Giotto spacecraft obtained 10-210 amu mass spectral of cold thermal molecular ions in the coma of Comet Halley. The dissociation products of the long chain formaldehyde polymer polyoxymethylene (POM) have recently been proposed as the dominant complex molecules in the coma of Comet Halley; however, POM alone cannot account for all of the features of the high resolution spectrum. An important component of the dust at Comet Halley is particles highly enriched in carbon, hydrogen, oxygen, and nitrogen relative to the composition of carbonaceous chondrites. Since this dust could be a source for the heavy molecules observed by PICCA, a search was conducted for other chemical species by determining all the molecules with mass between 20 and 120 amu which can be made from the relatively abundant C, H, O, and N, without regard to chemical structure
Pulsed flows at the high-altitude cusp poleward boundary, and associated ionospheric convection and particle signatures, during a cluster - FAST - SuperDARN - sondrestrom conjunction under a southwest
Particle and magnetic field observations during a magnetic conjunction Cluster 1-FAST-Søndrestrøm within the field of view of SuperDARN radars on 21 January 2001 allow us to draw a detailed, comprehensive and self-consistent picture at three heights of signatures associated with transient reconnection under a steady south-westerly IMF (clock angle ≈130◦). Cluster 1 was outbound through the high altitude (∼12RE ) exterior northern cusp tailward of the bifurcation line (geomagnetic Bx>0) when a solar wind dynamic pressure release shifted the spacecraft into a boundary layer downstream of the cusp. The centerpiece of the investigation is a series of flow bursts observed there by the spacecraft, which were accompanied by strong field pertur- bations and tailward flow deflections. Analysis shows these to be Alfven waves. We interpret these flow events as being due to a sequence of reconnected flux tubes, with field-aligned currents in the associated Alfven waves carrying stresses to the underlying ionosphere, a view strengthened by the other observations. At the magnetic footprint of the region of Cluster flow bursts, FAST observed an ion energy- latitude disperison of the stepped cusp type, with individual cusp ion steps corresponding to individual flow bursts. Simultaneously, the SuperDARN Stokkseyri radar observed very strong poleward-moving radar auroral forms (PMRAFs) which were conjugate to the flow bursts at Cluster. FAST was traversing these PMRAFs when it observed the cusp ion steps. The Søndrestrøm radar observed pulsed ionospheric flows (PIFs) just poleward of the convection reversal boundary. As at Cluster, the flow was eastward (tailward), implying a coherent eastward (tailward) motion of the hypothesized open flux tubes. The joint Søndrestrøm and FAST observations indicate that the open/closed field line boundary was equatorward of the convection reversal boundary by ∼2 deg. The unprecedented accuracy of the conjunction argues strongly for the validity of the interpretation of the various signatures as resulting from transient reconnection. In particular, the cusp ion steps arise on this pass from this origin, in consonance with the original pulsating cusp model. The observations point to the need of extending current ideas on the response of the ionosphere to transient reconnection. Specifically, it argues in favor of re-establishing the high-latitude boundary layer downstream of the cusp as an active site of momentum transfer
Comparative study of the Martian suprathermal electron depletions based on Mars Global Surveyor, Mars Express and Mars Atmosphere and Volatile EvolutioN missions observations
Nightside suprathermal electron depletions have been observed at Mars by three spacecraft to date: Mars Global Surveyor, Mars Express, and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. This spatial and temporal diversity of measurements allows us to propose here a comprehensive view of the Martian electron depletions through the first multispacecraft study of the phenomenon. We have analyzed data recorded by the three spacecraft from 1999 to 2015 in order to better understand the distribution of the electron depletions and their creation mechanisms. Three simple criteria adapted to each mission have been implemented to identify more than 134,500 electron depletions observed between 125 and 900 km altitude. The geographical distribution maps of the electron depletions detected by the three spacecraft confirm the strong link existing between electron depletions and crustal magnetic field at altitudes greater than ~170 km. At these altitudes, the distribution of electron depletions is strongly different in the two hemispheres, with a far greater chance to observe an electron depletion in the Southern Hemisphere, where the strongest crustal magnetic sources are located. However, the unique MAVEN observations reveal that below a transition region near 160–170 km altitude the distribution of electron depletions is the same in both hemispheres, with no particular dependence on crustal magnetic fields. This result supports the suggestion made by previous studies that these low-altitudes events are produced through electron absorption by atmospheric CO2
- …