Velocity shear instabilities in the multicomponent plasma sheet region

2000 ◽  
Vol 7 (3) ◽  
pp. 1014-1019 ◽  
Author(s):  
Lu Li ◽  
Liu Zhen-Xing ◽  
Li Zhong-Yua
Keyword(s):  
Plasma Sheet ◽  
Velocity Shear ◽  
Multicomponent Plasma ◽  
Shear Instabilities

scholarly journals EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere

2011 ◽  
Vol 29 (2) ◽  
pp. 299-319 ◽  
Author(s):  
T. Pitkänen ◽  
A. T. Aikio ◽  
O. Amm ◽  
K. Kauristie ◽  
H. Nilsson ◽  
...  
Keyword(s):  
High Resolution ◽  
Plasma Flow ◽  
Plasma Sheet ◽  
Velocity Shear ◽  
Optical Measurements ◽  
Return Flow ◽  
Quiet Time ◽  
Reconnection Rate ◽  
Plasma Bubble ◽  
Return Flows

Abstract. We report observations of a sequence of quiet-time Earthward bursty bulk flows (BBFs) measured by the Cluster spacecraft in the near-tail plasma sheet (XGSM ~ −12 to −14 RE) in the evening sector, and by simultaneous high-resolution measurements in the northern conjugate ionosphere by the EISCAT radars, a MIRACLE all-sky camera and magnetometers, as well as a meridian-scanning photometer (MSP) in the Scandinavian sector on 17 October 2005. The BBFs at Cluster show signatures that are consistent with the plasma "bubble" model (Chen and Wolf, 1993, 1999), e.g. deflection and compression of the ambient plasma in front of the Earthward moving bubble, magnetic signatures of a flow shear region, and the proper flows inside the bubble. In addition, clear signatures of tailward return flows around the edges of the bubble can be identified. The duskside return flows are associated with significant decrease in plasma density, giving support to the recent suggestion by Walsh et al. (2009) of formation of a depleted wake. However, the same feature is not seen for the dawnside return flows, but rather an increase in density. In the ionosphere, EISCAT and optical measurements show that each of the studied BBFs is associated with an auroral streamer that starts from the vicinity of the polar cap boundary, intrudes equatorward, brakes at 68–70° aacgm MLAT and drifts westward along the proton oval. Within the streamer itself and poleward of it, the ionospheric plasma flow has an equatorward component, which is the ionospheric manifestation of the Earthward BBF channel. A sharp velocity shear appears at the equatorward edge of a streamer. We suggest that each BBF creates a local velocity shear in the ionosphere, in which the plasma flow poleward of and inside the streamer is in the direction of the streamer and southeastward. A northwestward return flow is located on the equatorward side. The return flow is associated with decreased plasma densities both in the ionosphere and in the magnetosphere as measured by EISCAT and Cluster, respectively. In summary, we present the first simultaneous high-resolution observations of BBF return flows both in the plasma sheet and in the ionosphere, and those are in accordance with the bubble model. The results apply for the duskside return flows, but the manifestation of dawnside return flows in the ionosphere requires further studies. Finally, EISCAT measurements indicate increased nightside reconnection rate during the ~35-min period of BBFs. We suggest that the observed temporal event of IMF rotation to a more southward direction produces enhanced open flux transport to the nightside magnetotail, and consequently, the nightside reconnection rate is increased.

Parallel velocity shear instabilities in an inhomogeneous plasma

1979 ◽  
Vol 62 (2) ◽  
pp. 353-366 ◽  
Author(s):  
K. M. Srivastava ◽  
D. N. Vyas
Keyword(s):  
Inhomogeneous Plasma ◽  
Velocity Shear ◽  
Shear Instabilities

Shear flow instabilities in the earth's plasma sheet region

1994 ◽  
Vol 12 (1) ◽  
pp. 25-32 ◽  
Author(s):  
Sunayna Kalra ◽  
G. S. Lakhina
Keyword(s):  
Shear Flow ◽  
Plasma Sheet ◽  
Flow Instability ◽  
Velocity Shear ◽  
Mhd Equations ◽  
Data Sets ◽  
Neutral Sheet ◽  
Data Set ◽  
Central Plasma ◽  
Central Plasma Sheet

Abstract. Shear flow instability arising from the velocity shear between the inner and the outer central plasma sheet regions is studied by treating the plasma as compressible. Based on the linearized MHD equations, dispersion relations for the surface wave modes occurring at the boundary of the inner central plasma sheet (ICPS) and the outer central plasma sheet (OCPS) are derived. The growth rates and the eigenmode frequencies are obtained numerically. Three data sets consisting of parameters relevant to the earth's magnetotail are considered. The plasma sheet region is found to be stable for constant plasma flows unless MA>9.6, where MA is the Alfvén Mach number in the ICPS. However, for a continuously varying flow velocity profile in the ICPS, the instability is excited for MA\\geq1.4. The excited modes have oscillation periods of 2-10 min and 1.5-6 s, and typical transverse wavelengths of 30-100 RE and 0.5-6 RE for data sets 1 and 2 (i.e., case of no neutral sheet) respectively. For the data set 3, which corresponds to a neutral sheet at the center of the plasma sheet, the excited oscillations have periods of 2 s-1 min with transverse wavelengths of 0.02-1 RE.

Vortical flow in the plasma sheet: Non-linear growth of flow burst surface wave?

2020 ◽  
Author(s):  
Ghai Siung Chong ◽  
Alexandre De Spiegeleer ◽  
Maria Hamrin ◽  
Timo Pitkanen ◽  
Sae Aizawa ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
High Speed ◽  
Velocity Shear ◽  
Vortical Flow ◽  
Boundary Crossing ◽  
Moving Plasma ◽  
Flow Evolution ◽  
Slow Moving ◽  
Flow Burst

<p>In contrast to the simple conventional plasma flow convection governed by the Dungey Cycle, past studies have revealed that the plasma flows in the magnetotail region are more complicated, hosting high-speed bursty and meandering vortical flows. We have utilized magnetic field and plasma data from the Cluster mission to investigate a high speed earthward propagating flow burst with a peak velocity of ~530 km/s in the magnetotail plasma sheet (X<sub>GSM</sub> ~ -17R<sub>E</sub>) on 20 September 2002. In the vicinity of this flow burst, a vortical flow, whose plasma vectors are first directed tailward then earthward, is also observed. The plasma data shows that the plasma population in the vortical flow is likely to originate from the associated flow burst. In addition, the boundaries of both structures are also found to be tangential discontinuities, clearly surrounded by the ambient slow moving plasma sheet. Inside the vortical flow, there exists a region where plasma originating from the flow burst and ambient plasma sheet are mixed. The local segment of inbound boundary crossing of the vortical flow is shown to have a thickness that is non-uniform. Coupled with the flow evolution in the vortical flow, these characteristics are consistent to a boundary crossing of a vortical flow. The magnetic field on the flow burst is quasi-perpendicular to the large velocity shear (~460 km/s) across the flow burst boundary. These results suggest that the formation of vortical flow can arise from the development and subsequent growth of flow burst boundary wave as a result of Kelvin-Helmholtz instability. In summary, this article presents a detailed observational study of a vortical flow and the formation of which would serve as the first direct observational consequence of an excited and growing flow burst boundary wave. Continuous scattering of the detached vortices may play an important role in the braking mechanism of earthward propagating flow bursts. </p>

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