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Abstract Reconnection at Earth's magnetopause drives magnetospheric convection and provides mass and energy input into the magnetosphere/ionosphere system thereby driving the coupling between solar wind and terrestrial magnetosphere. Despite its importance, the factors governing the location of dayside magnetopause reconnection are not well understood. Though a few models can predict X‐line locations reasonably well, the underlying physics is still unresolved. In this study we present results from a comparative analysis of 274 magnetic reconnection events as observed by the Magnetospheric Multiscale (MMS) mission to determine what quantities affect the accuracy of such models and are most strongly associated with the occurrence of dayside magnetopause reconnection. We also attempt to determine under what upstream solar wind conditions each global X‐line model becomes least reliable. 

Abstract Magnetic reconnection at the magnetopause has long been studied with multi‐spacecraft observations. In this work, data from the five satellite THEMIS mission during the years of 2008–2010 are used to generate statistics regarding the spatial extent of magnetopause reconnection. The presence of a reconnecting magnetopause is determined with the Walén relation as two satellites cross the magnetopause simultaneously. In some cases both satellites measure reconnection whereas in others one satellite measures reconnection and the other does not. This study finds that two spacecraft are more likely to observe a contiguous reconnection region the closer they are spatially, and that reconnection is not always extended around the entire magnetopause. Plasmaβgradient drifts are investigated as a cause of local reconnection suppression. Spacecraft position along the magnetopause flanks is also investigated as a possible spatial limitation to reconnection due to changes in shear flow or boundary thickness.