56 research outputs found
The Earth: Plasma Sources, Losses, and Transport Processes
This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed
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Cluster observations of continuous reconnection at the magnetopause under steady interplanetary magnetic field conditions
On 26 January 2001, the Cluster spacecraft detected high-speed plasma jets
at multiple crossings of the high-latitude duskside magnetopause (MP) and
boundary layer (BL) over a period of more than 2h. The 4 spacecraft
combined spent more than half of this time in the MP/BL and jets were
observed whenever a spacecraft was in the MP. These observations were made
under steady southward and dawnward interplanetary magnetic field (IMF)
conditions. The magnetic shear across the local MP was ~100° and
β~1 in the adjacent magnetosheath. The jet velocity is in
remarkable agreement with reconnection prediction throughout the entire
interval, except for one crossing that had no ion measurements inside the
current layer. The flow speed measured in the deHoffmann Teller frame is
90% of the Alfvén speed on average for the 10 complete MP current
layer crossings that are resolved by the ion measurements. These findings
strongly suggest that reconnection was continuously active for more than two
hours. The jets were directed persistently in the same northward and
anti-sunward direction, implying that the X-line was always below the
spacecraft. This feature is inconsistent with patchy and random reconnection
or convecting multiple X-lines. The majority of MP/BL crossings in this
two-hour interval were partial crossings, implying that they are caused by
bulges sliding along the MP, not by inward-outward motion of a uniformly
thin MP/BL. The presence of the bulges suggests that, although reconnection
is continuously active under steady IMF conditions, its rate may be
modulated. The present investigation also reveals that (1) the predicted ion
D-shaped distributions are absent in all reconnection jets on this day, (2)
the electric field fluctuations are larger in the reconnecting MP than in
the magnetosheath proper, but their amplitudes never exceed 20mV/m, (3) the
ion-electron differential motion is ~20km/s for the observed MP
current density of ~50nA/m2 (∇× B), thus inconsequential for the deHoffmann-Teller and
Walén analyses, (4) flows in an isolated flux transfer event (FTE) are
directed in the same direction as the MP jets and satisfy the Walén
relation, suggesting that this FTE is also generated by reconnection.
Finally, the present event cannot be used to evaluate the validity of
component or anti-parallel merging models because, although the magnetic
shear at the local MP was ~100°(≪180°), the X-line
may be located more than 9RE away (in the opposite hemisphere), where
the shear could be substantially different
Cluster observations of continuous reconnection at the magnetopause under steady interplanetary magnetic field conditions
On 26 January 2001, the Cluster spacecraft detected high-speed plasma jets at multiple crossings of the high-latitude duskside magnetopause (MP) and boundary layer (BL) over a period of more than 2h. The 4 spacecraft combined spent more than half of this time in the MP/BL and jets were observed whenever a spacecraft was in the MP. These observations were made under steady southward and dawnward interplanetary magnetic field (IMF) conditions. The magnetic shear across the local MP was ~100&deg; and &beta;~1 in the adjacent magnetosheath. The jet velocity is in remarkable agreement with reconnection prediction throughout the entire interval, except for one crossing that had no ion measurements inside the current layer. The flow speed measured in the deHoffmann Teller frame is 90% of the Alfv&#233;n speed on average for the 10 complete MP current layer crossings that are resolved by the ion measurements. These findings strongly suggest that reconnection was continuously active for more than two hours. The jets were directed persistently in the same northward and anti-sunward direction, implying that the X-line was always below the spacecraft. This feature is inconsistent with patchy and random reconnection or convecting multiple X-lines. The majority of MP/BL crossings in this two-hour interval were partial crossings, implying that they are caused by bulges sliding along the MP, not by inward-outward motion of a uniformly thin MP/BL. The presence of the bulges suggests that, although reconnection is continuously active under steady IMF conditions, its rate may be modulated. The present investigation also reveals that (1) the predicted ion D-shaped distributions are absent in all reconnection jets on this day, (2) the electric field fluctuations are larger in the reconnecting MP than in the magnetosheath proper, but their amplitudes never exceed 20mV/m, (3) the ion-electron differential motion is ~20km/s for the observed MP current density of ~50nA/m<sup>2</sup> (<b>&#x2207;</b>&#x00D7; <b>B</b>), thus inconsequential for the deHoffmann-Teller and Wal&#233;n analyses, (4) flows in an isolated flux transfer event (FTE) are directed in the same direction as the MP jets and satisfy the Wal&#233;n relation, suggesting that this FTE is also generated by reconnection. Finally, the present event cannot be used to evaluate the validity of component or anti-parallel merging models because, although the magnetic shear at the local MP was ~100&deg;(&#x226A;180&deg;), the X-line may be located more than 9<i>R<sub>E</sub></i> away (in the opposite hemisphere), where the shear could be substantially different
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