We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind
reconnection exhaust in the presence of a guide field BM which is almost four times as strong as the reversing field
BL. The novel tripolar field consists of two narrow regions of depressed BM, with an observed 7%–14% ΔBM
magnitude relative to the external field, which are found adjacent to a wide region of enhanced BM within the
exhaust. A stronger reversing field is associated with each BM depression. A kinetic reconnection simulation for
realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially
form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge
into fewer and larger islands. The simulated ΔBM/ΔXN over the normal width ΔXN between a BM minimum and
the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar
guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting
magnetic islands at individual solar wind current sheets with a strong guide field.