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The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by × drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H + , He + , and O + ) appear in the energy spectrum, consistent with ion acceleration to a common velocity.

The Cenozoic Xuelong Shan antiformal dome is located along the northern segment of the Ailao Shan-Red River shear zone in Yunnan, China. Subhorizontal foliation in the gneiss core is recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike-slip shear zone. Microfabrics of crystallographicpreferred orientations (CPOs) in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust (300-5008C) in the mantling schist to the midcrust (15 km or more, 6508C) in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which range from garnet 1 amphibole 1 biotite 1 sillimanite 1 rutile 1 feldspar in the core to garnet 1 staurolite 1 biotite 1 epidote 1 muscovite within the limb units. The dome experienced the following deformation history: (1) a broad top-to-NE shear in the subhorizontal foliation of the gneiss core during the first stage of deformation (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2-D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The structural-thermal patterns suggest the antiformal dome formation was roughly coeval with top-to-NE ductile shearing in the midcrust of Tibet at 32 Ma or earlier. A major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike-slip deformation.

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An important source of the terrestrial magnetospheric plasma is the Earth's ionospheric outflows from the high-latitude regions of both hemispheres. The ionospheric ion outflows have rarely been observed at the dayside magnetopause. We report Cluster observations of the ionospheric ion outflows observed at the dayside magnetopause. The low-energy (up to 1.5 keV) electrons are detected with bidirectional pitch angle distributions indicating that the magnetic field lines are closed. The unidirectional cold ions (< 200 eV) are observed in the magnetosphere by both C1 and C3. The pitch angle distributions (0 ∘ -75 ∘ ) of the cold ions (< 1 keV) at the dayside magnetopause indicate that these cold ions are the ionospheric outflows coming only from the Southern Hemisphere. The cold ions (< 200 eV) fluxes are modulated by the ULF wave electric field. Two different species (possibly H + and He + ) are observed in the magnetosphere. Our results suggest that the ionospheric outflows can directly reach the dayside magnetopause region and may participate in the reconnection process.