Formation of dayside low-latitude boundary layer under northward interplanetary magnetic field

A three-dimensional (3-D) global hybrid simulation is carried out to study the formation of the dayside low-latitude boundary layer (LLBL) under a purely northward interplanetary magnetic field (IMF). Magnetic reconnection in both northern and southern hemispheres leads to a continued formation of newly closed field lines on the dayside, and a subsequent formation of the LLBL by capture of the magnetosheath ions on the original magnetosheath field lines, as the newly closed field lines shorten. The formation of the LLBL is associated with the tailward spreading of the transmitted ions along the magnetopause as the newly closed flux tubes convect tailward. Meanwhile, compressional waves and transverse waves in magnetic field are generated in the magnetosphere. The ion distributions in the cusp and the boundary layer show the presence of multiple ion beams of the transmitted magnetosheath ions, as well as ion heating.