| 1. |
|
|
| 2. |
- Giang, Tony, et al.
(författare)
-
Outflowing protons and heavy ions as a source for the sub-keV ringcurrent
- 2009
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:2, s. 839-849
-
Tidskriftsartikel (refereegranskat)abstract
- Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+ ) char- acteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+ ) were identified out of two years (2001 and 2002) of Cluster data. Allevents took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics. In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrialsub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the out-flow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particleinteraction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Allen, R. C., et al.
(författare)
-
A statistical study of EMIC waves observed by Cluster : 1. Wave properties
- 2014
-
Ingår i: 2014 XXXITH URSI General Assembly And Scientific Symposium (URSI GRASS). - 9781467352253
-
Konferensbidrag (refereegranskat)abstract
- Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the L-MLT frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001-2010) of data from Cluster, totaling 17,987 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The current paper focuses on the wave occurrence distribution as well as the distribution of wave properties.
|
|
| 6. |
- Allen, R. C., et al.
(författare)
-
A statistical study of EMIC waves observed by Cluster : 2. Associated plasma conditions
- 2016
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:7, s. 6458-6479
-
Tidskriftsartikel (refereegranskat)abstract
- This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10years (2001-2010) of Cluster observations. In the first paper, an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)-distance as well as magnetic local time (MLT)-L frames. This paper focuses on the distribution of EMIC wave-associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H+ anisotropy, electron and hot H+ density measurements, hot H+ parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well-known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off-equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere.
|
|
| 7. |
- Allen, R. C., et al.
(författare)
-
A statistical study of EMIC waves observed by Cluster : 1. Wave properties
- 2015
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:7, s. 5574-5592
-
Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10years (2001-2010) of data from Cluster, totaling 25,431min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
|
|
| 8. |
- Bavassano Cattaneo, M. Bice, et al.
(författare)
-
Kinetic signatures during a quasi-continuous lobe reconnection event : Cluster Ion Spectrometer (CIS) observations
- 2006
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:A9, s. A09212-
-
Tidskriftsartikel (refereegranskat)abstract
- On 3 December 2001 the Cluster spacecraft observed a long-lasting lobe reconnection event in the southern high-latitude dusk magnetopause (MP) tailward of the cusp, during a 4 hour interval of mainly northward interplanetary magnetic field ( IMF) and of sub-Alfvenic magnetosheath flow. Almost all the MP encounters have accelerated flows ( for which the Walen test has been successfully verified by Retino et al. ( 2005)) as well as a large number of secondary populations related to reconnection, that is, ions of magnetosheath or magnetospheric origin which cross the MP either way. The detailed analysis of the distribution functions shows that the reconnection site frequently moves relative to the spacecraft, but simultaneous measurements by two spacecraft on opposite sides of the reconnection site indicate that the spacecraft's distance from the X line is small, i.e., below 3200 km. The vicinity to the X line throughout the event is probably the reason why the distribution functions characteristics agree with theoretical expectations on both sides of the reconnection site throughout this long event. Moreover, the detailed analysis of the distribution functions shows evidence, during a few time intervals, of dual reconnection, i.e., of reconnection simultaneously going on also in the northern hemisphere.
|
|
| 9. |
- Hamrin, Maria, et al.
(författare)
-
Energy conversion regions as observed by Cluster in the plasma sheet
- 2011
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A00K08-
-
Tidskriftsartikel (refereegranskat)abstract
- In this article we present a review of recent studies of observations of localized energy conversion regions (ECRs) observed by Cluster in the plasma sheet at altitudes of 15-20R(E). By examining variations in the power density, E . J, where E is the electric field and J is the current density, we show that the plasma sheet exhibits a high level of fine structure. Approximately three times as many concentrated load regions (CLRs) (E . J > 0) as concentrated generator regions (CGRs) (E . J < 0) are identified, confirming the average load character of the plasma sheet. Some ECRs are found to relate to auroral activity. While ECRs are relevant for the energy conversion between the electromagnetic field and the particles, bursty bulk flows (BBFs) play a central role for the energy transfer in the plasma sheet. We show that ECRs and BBFs are likely to be related, although details of this relationship are yet to be explored. The plasma sheet energy conversion increases rather simultaneously with increasing geomagnetic activity in both CLRs and CGRs. Consistent with large-scale magnetotail simulations, most of the observed ECRs appear to be rather stationary in space but varying in time. We estimate that the ECR lifetime and scale size are a few minutes and a few R(E), respectively. It is conceivable that ECRs rise and vanish locally in significant regions of the plasma sheet, possibly oscillating between load and generator character, while some energy is transmitted as Poynting flux to the ionosphere.
|
|
| 10. |
- Hamrin, Maria, et al.
(författare)
-
Evidence for the braking of flow bursts as they propagate toward the Earth
- 2014
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 119:11, s. 9004-9018
-
Tidskriftsartikel (refereegranskat)abstract
- In this article we use energy conversion arguments to investigate the possible braking of flow bursts as they propagate toward the Earth. By using EJ data (E and J are the electric field and the current density) observed by Cluster in the magnetotail plasma sheet, we find indications of a plasma deceleration in the region -20 R-E < X < - 15 R-E. Our results suggest a braking mechanism where compressed magnetic flux tubes in so-called dipolarization fronts (DFs) can decelerate incoming flow bursts. Our results also show that energy conversion arguments can be used for studying flow braking and that the position of the flow velocity peak with respect to the DF can be used as a single-spacecraft proxy when determining energy conversion properties. Such a single-spacecraft proxy is invaluable whenever multispacecraft data are not available. In a superposed epoch study, we find that a flow burst with the velocity peak behind the DF is likely to decelerate and transfer energy from the particles to the fields. For flow bursts with the peak flow at or ahead of the DF we see no indications of braking, but instead we find an energy transfer from the fields to the particles. From our results we obtain an estimate of the magnitude of the deceleration of the flow bursts, and we find that it is consistent with previous investigations.
|
|
