Investigation of the large scale topology of the dayside merging region using global simulations J. Berchem (1), V. Peroomian (1), J. M. Bosqued (2), H. U. Frey (3), S. A. Fuselier (4) and C. P. Escoubet (5) (1) IGPP, University of California, Los Angeles, California (2) CESR, Toulouse, France (3) SSL, University of California, Berkeley, California (4) Lockheed Martin Advanced Technology Center, Palo Alto, California (5) ESA/ESTEC, Noordwijk, Netherlands Recent observations from the IMAGE and CLUSTER spacecraft offer a unique opportunity to evaluate models of the large-scale topology of the dayside merging region. We report results from a study that employs three-dimensional magnetohydrodynamic (MHD) and large-scale kinetic (LSK) simulations. The study focuses on determining the large-scale topology of the dayside merging region using the results from the simulation of actual events and proton precipitation observations. Solar wind magnetic field and plasma parameters measured by spacecraft located upstream of the bow shock are used to determine the upstream boundary conditions of the global MHD simulations. Results from the global MHD simulations are validated by comparing them to CLUSTER CIS observations and images from the FUV SI-12 imager on board the IMAGE spacecraft. Once validated, time-dependent electromagnetic fields from the global MHD simulations are used to follow the trajectories of solar wind ions as they penetrate the dayside magnetosphere. The topology of the merging region determined from both the MHD and LSK simulations is then compared with merging patterns predicted by the antiparallel and component merging models. _______________ Presented at the 35th COSPAR Scientific Assembly, Paris, France, July 18-25, 2004.