Distribution of magnetic fluctuations in the terminator plane for a quasi-parallel (top) and quasi-perpendicular (bottom) IMF. (a, a′) Solar wind upstream of the bow shock (d_BS > 0.2 R_M), (b, b′) magnetosheath downstream of the bow shock (0.8 < F < 1), (c, c′) magnetosheath upstream of the magnetopause (0 < F < 0.2), and (d, d′) cross-sectional cut of the tail (−2.5 R_M < X < −1.5 R_M). The three black circles from the inside out are the Mercury surface, the magnetopause, and the bow shock in the terminator. No data were recorded northward of the magnetosphere in this X range because of the high inclination of the highly eccentric MESSENGER spacecraft orbit. The solar wind and magnetosheath data are displayed in the SWI coordinate system, and the magnetosphere data are displayed in the aberrated MSM coordinate system.