| 1. |
- Collinson, Glyn A., et al.
(författare)
-
Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus
- 2023
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:18
-
Tidskriftsartikel (refereegranskat)abstract
- Shocklets and short large-amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady-state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach-number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.
|
|
| 2. |
- Jones, Geraint H., et al.
(författare)
-
The Comet Interceptor Mission
- 2024
-
Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
-
Tidskriftsartikel (refereegranskat)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
|
|
| 3. |
- Karlsson, Tomas, et al.
(författare)
-
Investigating the anatomy of magnetosheath jets - MMS observations
- 2018
-
Ingår i: Annales Geophysicae. - : COPERNICUS GESELLSCHAFT MBH. - 0992-7689 .- 1432-0576. ; 36:2, s. 655-677
-
Tidskriftsartikel (refereegranskat)abstract
- We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10 s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40 mu Wm(-2) and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies.
|
|
| 4. |
- Karlsson, Tomas, 1964-, et al.
(författare)
-
Short large-amplitude magnetic structures (SLAMS) at Mercury observed by MESSENGER
- 2024
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 42:1, s. 117-130
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first observations of short large-amplitude magnetic structures (denoted SLAMS) at Mercury. We have investigated approximately 4 years of MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) data to identify SLAMS in the Mercury foreshock. Defining SLAMS as magnetic field compressional structures, with an increase in magnetic field strength of at least twice the background magnetic field strength, when MESSENGER is located in the solar wind, we find 435 SLAMS. The SLAMS are found either in regions of a general ultra-low frequency (ULF) wave field, at the boundary of such a ULF wave field, or in a few cases isolated from the wave field. We present statistics on several properties of the SLAMS, such as temporal scale size, amplitude, and the presence of whistler-like wave emissions. We find that SLAMS are mostly found during periods of low interplanetary magnetic field strength, indicating that they are more common for higher solar wind Alfv & eacute;nic Mach number ( M A ). We use the Tao solar wind model to estimate solar wind parameters to verify that M A is indeed larger during SLAMS observations than otherwise. Finally, we also investigate how SLAMS observations are related to foreshock geometry.
|
|
| 5. |
- Liljeblad, Elisabet, 1986-
(författare)
-
Structures and Processes at the Mercury Magnetopause
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mechanism involved in the transfer of energy, momentum and plasma from the solar wind to any planetary magnetosphere is considered one of the more important topics in space plasma physics. With the use of the Mercury spacecraft MESSENGER’s (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) data, it has been possible to study these processes in an environment different, yet similar, to Earth’s. These data have resulted in unprecedented investigations advancing not only the extraterrestrial space plasma research, but also the general space physics field.This work aims to investigate the Kelvin-Helmholtz (KH) instability at Mercury’s magnetopause, which is believed to be one of the main drivers for the transfer of matter and energy into Earth’s magnetosphere, and the low- latitude boundary layer (LLBL) which is in direct connection to the magnetopause. The studies use data from MESSENGER’s magnetometer (MAG) and fast imaging plasma spectrometer (FIPS) instruments during the first three years in orbit. Results show that KH waves are observed almost exclusively on the duskside magnetopause, something that has not been observed at Earth. In contrast, the LLBL shows an opposite asymmetry as it occurs more often on the dawnside. Both the KH instability and the LLBL are observed mainly during northward interplanetary magnetic field. This, together with the distinct opposite asymmetry, suggests that the KH instability and LLBL are somehow connected. Previous theoretical studies, simulations and observations have shown or indicated that the sodium ions have a large impact on the Hermean magnetospheric environment, including the boundary layer where the KH instability arises. One possibility is that the sodium ions also induce the observed dawn-dusk asymmetry in the LLBL. Another explanation could be that the LLBL on its own influences the KH wave occurrence by reducing the KH wave growth rates on the dawnside where most of the LLBLs are observed. Furthermore, observations agree with some formation mechanisms that should give rise to the observed dawn-dusk LLBL asymmetry.The processes responsible for the dawn-dusk occurrence asymmetry in both the KH instability and the LLBL are yet to be confirmed. Future work may also include determination of the contribution of KH waves to the energy and plasma transfer from the solar wind to the Hermean magnetosphere.
|
|
| 6. |
- Nakamura, Rumi, et al.
(författare)
-
Multiscale Currents Observed by MMS in the Flow Braking Region
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:2, s. 1260-1278
-
Tidskriftsartikel (refereegranskat)abstract
- We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold ExB drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.
|
|
| 7. |
- Nakamura, Rumi, et al.
(författare)
-
Near-Earth plasma sheet boundary dynamics during substorm dipolarization
- 2017
-
Ingår i: Earth Planets and Space. - : Springer Berlin/Heidelberg. - 1343-8832 .- 1880-5981. ; 69
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL similar to -1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 RE were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) Bz disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another fieldaligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.
|
|
| 8. |
- Plaschke, Ferdinand, et al.
(författare)
-
Jets Downstream of Collisionless Shocks
- 2018
-
Ingår i: Space Science Reviews. - : Springer. - 0038-6308 .- 1572-9672. ; 214:5
-
Forskningsöversikt (refereegranskat)abstract
- The magnetosheath flow may take the form of large amplitude, yet spatially localized, transient increases in dynamic pressure, known as "magnetosheath jets" or "plasmoids" among other denominations. Here, we describe the present state of knowledge with respect to such jets, which are a very common phenomenon downstream of the quasi-parallel bow shock. We discuss their properties as determined by satellite observations (based on both case and statistical studies), their occurrence, their relation to solar wind and foreshock conditions, and their interaction with and impact on the magnetosphere. As carriers of plasma and corresponding momentum, energy, and magnetic flux, jets bear some similarities to bursty bulk flows, which they are compared to. Based on our knowledge of jets in the near Earth environment, we discuss the expectations for jets occurring in other planetary and astrophysical environments. We conclude with an outlook, in which a number of open questions are posed and future challenges in jet research are discussed.
|
|
| 9. |
- Pöppelwerth, Adrian, et al.
(författare)
-
Scale size estimation and flow pattern recognition around a magnetosheath jet
- 2024
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 42:1, s. 271-284
-
Tidskriftsartikel (refereegranskat)abstract
- Transient enhancements in the dynamic pressure, so-called magnetosheath jets or simply jets, are abundantly found in the magnetosheath. They travel from the bow shock through the magnetosheath towards the magnetopause. On their way through the magnetosheath, jets disturb the ambient plasma. Multiple studies already investigated their scale size perpendicular to their propagation direction, and almost exclusively in a statistical manner. In this paper, we use multi-point measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission to study the passage of a single jet. The method described here allows us to estimate the spatial distribution of the dynamic pressure within the jet. Furthermore, the size perpendicular to the propagation direction can be estimated for different cross sections. In the jet event investigated here, both the dynamic pressure and the perpendicular size increase along the propagation axis from the front part towards the center of the jet and decrease again towards the rear part, but neither monotonically nor symmetrically. We obtain a maximum diameter in the perpendicular direction of about 1 RE and a dynamic pressure of about 6 nPa at the jet center.
|
|
| 10. |
- Raptis, Savvas, et al.
(författare)
-
Classifying Magnetosheath Jets Using MMS : Statistical Properties
- 2020
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:11
-
Tidskriftsartikel (refereegranskat)abstract
- Using Magnetospheric Multiscale (MMS) data, we find, classify, and analyze transient dynamic pressure enhancements in the magnetosheath (jets) from May 2015 to May 2019. A classification algorithm is presented, using in situ MMS data to classify jets ( N=8,499) into different categories according to their associated angle between interplanetary magnetic field (IMF) and the bow shock normal vector (theta(Bn)). Jets appearing for theta(Bn) < 45 are referred to as quasi-parallel, while jets appearing for theta(Bn) > 45 as quasi-perpendicular jets. Furthermore, we define those jets that occur at the boundaries between quasi-parallel and quasi-perpendicular magnetosheath as boundary jets. Finally, encapsulated jets are jet-like structures with similar characteristics to quasi-parallel jets while the surrounding plasma is of quasi-perpendicular nature. We present the first statistical results of such a classification and provide comparative statistics for each class. Furthermore, we investigate correlations between jet quantities. Quasi-parallel jets have the highest dynamic pressure while occurring more often than quasi-perpendicular jets. The infrequent quasi-perpendicular jets have a much smaller duration, velocity, and density and are therefore relatively weaker. We conclude that quasi-parallel and boundary jets have similar properties and are unlikely to originate from different generation mechanisms. Regarding the encapsulated jets, we suggest that they are a special subset of quasi-parallel jets originating from the flanks of the bow shock, for large IMF cone angles although a relation to flux transfer events (FTEs) and magnetospheric plasma is also possible. Our results support existing generation theories, such as the bow shock ripple and SLAMS-associated mechanisms while indicating that other factors may contribute as well.
|
|
