| 11. |
- Alm, Love, et al.
(författare)
-
Magnetotail Hall Physics in the Presence of Cold Ions
- 2018
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing Ltd. - 0094-8276 .- 1944-8007. ; 45:20, s. 10,941-10,950
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first in situ observation of cold ionospheric ions modifying the Hall physics of magnetotail reconnection. While in the tail lobe, Magnetospheric Multiscale mission observed cold (tens of eV) E × B drifting ions. As Magnetospheric Multiscale mission crossed the separatrix of a reconnection exhaust, both cold lobe ions and hot (keV) ions were observed. During the closest approach of the neutral sheet, the cold ions accounted for ∼30% of the total ion density. Approximately 65% of the initial cold ions remained cold enough to stay magnetized. The Hall electric field was mainly supported by the j × B term of the generalized Ohm's law, with significant contributions from the ∇·P e and v c ×B terms. The results show that cold ions can play an important role in modifying the Hall physics of magnetic reconnection even well inside the plasma sheet. This indicates that modeling magnetic reconnection may benefit from including multiscale Hall physics.
|
|
| 12. |
- Alm, Love, et al.
(författare)
-
MMS Observations of Multiscale Hall Physics in the Magnetotail
- 2019
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007.
-
Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T similar to 1.5 keV) and hot ions (T similar to 20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma.
|
|
| 13. |
- An, Lu, et al.
(författare)
-
Bathymetry of Southeast Greenland From Oceans Melting Greenland (OMG) Data
- 2019
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 46:11, s. 197-205
-
Tidskriftsartikel (refereegranskat)abstract
- Southeast Greenland has been a major participant in the ice sheet mass loss over the last several decades. Interpreting the evolution of glacier fronts requires information about their depth below sea level and ocean thermal forcing, which are incompletely known in the region. Here, we combine airborne gravity and multibeam echo sounding data from the National Aeronautics and Space Administration's Oceans Melting Greenland (OMG) mission with ocean probe and fishing boat depth data to reconstruct the bathymetry extending from the glacier margins to the edges of the continental shelf. We perform a three-dimensional inversion of the gravity data over water and merge the solution with a mass conservation reconstruction of bed topography over land. In contrast with other parts of Greenland, we find few deep troughs connecting the glaciers to the sources of warm Atlantic Water, amidst a relatively uniform, shallow (350 m) continental shelf. The deep channels include the Kangerlugssuaq, Sermilik, Gyldenlove, and Tingmiarmiut Troughs.
|
|
| 14. |
- Andersson, Andreas, et al.
(författare)
-
Air-sea gas transfer in high Arctic fjords
- 2017
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:5, s. 2519-2526
-
Tidskriftsartikel (refereegranskat)abstract
- In Arctic fjords and high-latitude seas, strong surface cooling dominates during a large part of the year, generating water-side convection (w*w) and enhanced turbulence in the water. These regions are key areas for the global carbon cycle; thus, a correct description of their air-sea gas exchange is crucial. CO2-data were measured via the eddy covariance technique in marine Arctic conditions and reveal that water-side convection has a major impact on the gas transfer velocity. This is observed even at wind speeds as high as 9 m s-1, where convective motions are generally thought to be suppressed by wind-driven turbulence. The enhanced air-sea transfer of CO2 caused by water-side convection nearly doubled the CO2uptake, after scaled to open sea conditions the contribution from to the CO2 flux remained as high as 34%; this phenomenon is expected to be highly important for the total carbon uptake in marine Arctic areas.
|
|
| 15. |
- André, Mats, et al.
(författare)
-
Low-energy ions : A previously hidden solar system particle population
- 2012
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L03101-
-
Tidskriftsartikel (refereegranskat)abstract
- Ions with energies less than tens of eV originate from the Terrestrial ionosphere and from several planets and moons in the solar system. The low energy indicates the origin of the plasma but also severely complicates detection of the positive ions onboard sunlit spacecraft at higher altitudes, which often become positively charged to several tens of Volts. We discuss some methods to observe low-energy ions, including a recently developed technique based on the detection of the wake behind a charged spacecraft in a supersonic flow. Recent results from this technique show that low-energy ions typically dominate the density in large regions of the Terrestrial magnetosphere on the nightside and in the polar regions. These ions also often dominate in the dayside magnetosphere, and can change the dynamics of processes like magnetic reconnection. The loss of this low-energy plasma to the solar wind is one of the primary pathways for atmospheric escape from planets in our solar system. We combine several observations to estimate how common low-energy ions are in the Terrestrial magnetosphere and briefly compare with Mars, Venus and Titan.
|
|
| 16. |
- André, Mats, et al.
(författare)
-
Magnetic reconnection and cold plasma at the magnetopause
- 2010
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37:22, s. L22108-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on detailed observations by the four Cluster spacecraft of magnetic reconnection and a Flux Transfer Event (FTE) at the magnetopause. We detect cold (eV) plasma at the magnetopause with two independent methods. We show that the cold ions can be essential for the electric field normal to the current sheet in the separatrix region at the edge of the FTE and for the associated acceleration of ions from the magnetosphere into the reconnection jet. The cold ions have small enough gyroradii to drift inside the limited separatrix region and the normal electric field can be balanced by this drift, E approximate to -v x B. The separatrix region also includes cold accelerated electrons, as part of the reconnection current circuit.
|
|
| 17. |
- André, Mats, et al.
(författare)
-
Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
- 2016
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
-
Tidskriftsartikel (refereegranskat)abstract
- Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
|
|
| 18. |
- André, Mats, et al.
(författare)
-
Thin electron-scale layers at the magnetopause
- 2004
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 31, s. L03803-
-
Tidskriftsartikel (refereegranskat)
|
|
| 19. |
- Andrews, David J., et al.
(författare)
-
Ionospheric plasma density variations observed at Mars by MAVEN/LPW
- 2015
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:21, s. 8862-8869
-
Tidskriftsartikel (refereegranskat)abstract
- We report on initial observations made by the Langmuir Probe and Waves relaxation sounding experiment on board the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. These measurements yield the ionospheric thermal plasma density, and we use these data here for an initial survey of its variability. Studying orbit-to-orbit variations, we show that the relative variability of the ionospheric plasma density is lowest at low altitudes near the photochemical peak, steadily increases toward higher altitudes and sharply increases as the spacecraft crosses the terminator and moves into the nightside. Finally, despite the small volume of data currently available, we show that a clear signature of the influence of crustal magnetic fields on the thermal plasma density fluctuations is visible. Such results are consistent with previously reported remote measurements made at higher altitudes, but crucially, here we sample a new span of altitudes between similar to 130 and similar to 300 km using in situ techniques.
|
|
| 20. |
- Andriopoulou, M., et al.
(författare)
-
Study of the spacecraft potential under active control and plasma density estimates during the MMS commissioning phase
- 2016
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:10, s. 4858-4864
-
Tidskriftsartikel (refereegranskat)abstract
- Each spacecraft of the recently launched magnetospheric multiscale MMS mission is equipped with Active Spacecraft Potential Control (ASPOC) instruments, which control the spacecraft potential in order to reduce spacecraft charging effects. ASPOC typically reduces the spacecraft potential to a few volts. On several occasions during the commissioning phase of the mission, the ASPOC instruments were operating only on one spacecraft at a time. Taking advantage of such intervals, we derive photoelectron curves and also perform reconstructions of the uncontrolled spacecraft potential for the spacecraft with active control and estimate the electron plasma density during those periods. We also establish the criteria under which our methods can be applied.
|
|
