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Direct evidence for kinetic effects associated with solar wind reconnection.

Xu X, Wang Y, Wei F, Feng X, Deng X, Ma Y, Zhou M, Pang Y, Wong HC - Sci Rep (2015)

Bottom Line: Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas.Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown.The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Space Science and Technology, Nanchang University, Nanchang 330031, China [2] State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, China [3] Space Science Institute, Macau University of Science and Technology, Macao, China.

ABSTRACT
Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.

No MeSH data available.


Related in: MedlinePlus

Diagram of the spatial scale of the encounter of ACE and Wind with the exhaust and pitch angle distributions of 272 eV electrons.The M direction is almost along +y in GSE, so the reconnection plane is nearly in the X-Z plane. The spacecraft trajectories are along the +x. The top small panel shows the pitch angle distributions of 272 eV electrons continuously crossing the exhaust.
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f3: Diagram of the spatial scale of the encounter of ACE and Wind with the exhaust and pitch angle distributions of 272 eV electrons.The M direction is almost along +y in GSE, so the reconnection plane is nearly in the X-Z plane. The spacecraft trajectories are along the +x. The top small panel shows the pitch angle distributions of 272 eV electrons continuously crossing the exhaust.

Mentions: Figures 2a–d show selected measurements around the exhaust in the LMN coordinates. The profiles of velocity and magnetic field coincide well with the features of reconnection outflow region: the field reversal almost occurs in BL and the plasma jet is nearly along VL. Apparent bipolar BM is presented by both ACE and Wind through the whole current sheet. However, the Hall magnetic fields here are much turbulent rather than laminar as it performs close to the X-line. The magnetic shear across the exhaust is about 168° corresponding to a weak guide field of ~0.35 nT. The bipolar structure is consistent with the prediction of reconnection Hall effect as illustrated in Figure 3. The velocity of the ion jet is 35 km/s in the rest frame of the solar wind. The inflow Alfven speed for asymmetric magnetic strengths24, , is about 56 km/s based on a density of 1.8 cm3 and BL of 4 nT and 3 nT in opposite sides, respectively. The normal speed of the current sheet, VN, is about 180 km/s. In this event, the shift in VN across the current sheet is very small (Figure 2d). It is beyond the accuracy of the plasma measurements and boundary normal determination from the minimum variance analysis so that we cannot use the half of this shift to estimate the inflow speed, Vin. Therefore the dimensionless reconnection rate can hardly be derived by using Vin/VA.


Direct evidence for kinetic effects associated with solar wind reconnection.

Xu X, Wang Y, Wei F, Feng X, Deng X, Ma Y, Zhou M, Pang Y, Wong HC - Sci Rep (2015)

Diagram of the spatial scale of the encounter of ACE and Wind with the exhaust and pitch angle distributions of 272 eV electrons.The M direction is almost along +y in GSE, so the reconnection plane is nearly in the X-Z plane. The spacecraft trajectories are along the +x. The top small panel shows the pitch angle distributions of 272 eV electrons continuously crossing the exhaust.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308709&req=5

f3: Diagram of the spatial scale of the encounter of ACE and Wind with the exhaust and pitch angle distributions of 272 eV electrons.The M direction is almost along +y in GSE, so the reconnection plane is nearly in the X-Z plane. The spacecraft trajectories are along the +x. The top small panel shows the pitch angle distributions of 272 eV electrons continuously crossing the exhaust.
Mentions: Figures 2a–d show selected measurements around the exhaust in the LMN coordinates. The profiles of velocity and magnetic field coincide well with the features of reconnection outflow region: the field reversal almost occurs in BL and the plasma jet is nearly along VL. Apparent bipolar BM is presented by both ACE and Wind through the whole current sheet. However, the Hall magnetic fields here are much turbulent rather than laminar as it performs close to the X-line. The magnetic shear across the exhaust is about 168° corresponding to a weak guide field of ~0.35 nT. The bipolar structure is consistent with the prediction of reconnection Hall effect as illustrated in Figure 3. The velocity of the ion jet is 35 km/s in the rest frame of the solar wind. The inflow Alfven speed for asymmetric magnetic strengths24, , is about 56 km/s based on a density of 1.8 cm3 and BL of 4 nT and 3 nT in opposite sides, respectively. The normal speed of the current sheet, VN, is about 180 km/s. In this event, the shift in VN across the current sheet is very small (Figure 2d). It is beyond the accuracy of the plasma measurements and boundary normal determination from the minimum variance analysis so that we cannot use the half of this shift to estimate the inflow speed, Vin. Therefore the dimensionless reconnection rate can hardly be derived by using Vin/VA.

Bottom Line: Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas.Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown.The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Space Science and Technology, Nanchang University, Nanchang 330031, China [2] State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, China [3] Space Science Institute, Macau University of Science and Technology, Macao, China.

ABSTRACT
Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.

No MeSH data available.


Related in: MedlinePlus