Bogdanova, Y. V. and Owen, C. J. and Dunlop, M. W. and Wild, J. A. and Davies, J. A. and Lahiff, A. D. and Taylor, M. G. G. T. and Fazakerley, A. N. and Dandouras, I. and Carr, C. M. and Lucek, E. A. and Rème, H. (2008) Formation of the low-latitude boundary layer and cusp under the northward IMF:simultaneous observations by cluster and double star. Journal of Geophysical Research, 113 (A7). ISSN 0148-0227
Abstract
On 28 February 2004 the configuration of the Cluster and Double Star TC1 satellites facilitated a simultaneous study of plasma properties inside the low-latitude boundary layer (LLBL) near the subsolar magnetopause and inside the midaltitude cusp during an interval with strong northward IMF. TC1, crossing the dayside magnetopause, observed a complex structure of boundary layers. We suggest that one part of the LLBL, characterized by high fluxes of magnetosheath-like electrons, is formed due to reconnection processes. We can identify three different plasma populations inside this region: on open field lines outside the magnetopause which are reconnected in the northern hemisphere lobe sector; on open field lines inside the magnetosphere which are reconnected in the northern hemisphere lobe sector and sink inside the magnetosphere; and on reclosed field lines, which undergo a second reconnection in the southern hemisphere lobe sector. Another part of the LLBL, characterized by equal fluxes of magnetosheath-like and plasma sheet populations, is formed by diffusion processes as strong pitch angle diffusion and formation of a loss cone are observed inside this region. Cluster, moving from the polar cap toward the dayside magnetosphere via the cusp region, crossed many different sublayers with different plasma properties. Comparison of plasma populations inside the different subregions of the LLBL and cusp shows that the complex LLBL observed at the dayside magnetopause maps into the midaltitude cleft/cusp region and that observed sublayers inside the cusp can be explained by reconnection in the lobe sector of one or both hemispheres and by diffusion processes.