and the strength and orientation of the field in the LISM should be correct. Therefore should not measure a large rotation of across the HP. B The initial profiles for the magnetic field density and temperature for the 2-D PIC simulations of the HP (dotted lines in Fig. S1) were constructed with input from the profiles from the MHD model. The simulations are evolved in time with no initially imposed magnetic perturbations. Because of the lower density in the HS, which leads to a locally higher Alfvén speed, magnetic reconnection first starts in the sectored HS (movie S1). Small magnetic islands grow on individual current layers in the HS and merge to become larger islands until they are comparable in size to the sector spacing (Figs. S2A, S3A, 2A) (1). A chain of small islands gr at the HP (movie S1, Fig. S2A). These islands merged to form larger islands and then compressed by islands in the HS pushing against the HP (movie S1, Figs. S3A, 2A). By late time the HS magnetic field has reconnected with that of the LISM, forming a complex, nested chain of islands (Fig. 2A) at the HP with sizes scales comparable to the original sector spacing. In our PIC model we are able to independently track all particles and therefore can explore the mixing of the LISM and HS particles as reconnection at the HP takes place. Overall, reconnection at the HP produces a highly structured distribution in the density of LISM (nLISM) and HS (nHS) plasma with the density of each species undergoing sharp jumps across the separatrices that bound the outflows of plasma ejected from reconnection sites (Figs. S2, S3, The particles initially in the LISM continue to dominate the number density of the field in the LIM, have mixed with HS particles in the nested islands formed as a result of reconnection between the HS and LISM fields, and are largely excluded from islands
and the strength and orientation of the field in the LISM should be correct. Therefore should not measure a large rotation of B across the HP. The initial profiles for the magnetic field density and temperature for the 2-D PIC simulations of the HP (dotted lines in Fig. S1) were constructed with input from the profiles from the MHD model. The simulations are evolved in time with no initially imposed magnetic perturbations. Because of the lower density in the HS, which leads to a locally higher Alfvén speed, magnetic reconnection first starts in the sectored HS (movie S1). Small magnetic islands grow on individual current layers in the HS and merge to become larger islands until they are comparable in size to the sector spacing (Figs. S2A, S3A, 2A) (1). A chain of small islands gr at the HP (movie S1, Fig. S2A). These islands merged to form larger islands and then compressed by islands in the HS pushing against the HP (movie S1, Figs. S3A, 2A). By late time the HS magnetic field has reconnected with that of the LISM, forming a complex, nested chain of islands (Fig. 2A) at the HP with sizes scales comparable to the original sector spacing. In our PIC model we are able to independently track all particles and therefore can explore the mixing of the LISM and HS particles as reconnection at the HP takes place. Overall, reconnection at the HP produces a highly structured distribution in the density of LISM (nLISM) and HS (nHS) plasma with the density of each species undergoing sharp jumps across the separatrices that bound the outflows of plasma ejected from reconnection sites (Figs. S2, S3, The particles initially in the LISM continue to dominate the number density of the field in the LIM, have mixed with HS particles in the nested islands formed as a result of reconnection between the HS and LISM fields, and are largely excluded from islands
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