Top panel: column density N_sw derived from COPS density measurements (using Eq. (4)), adjusted to the direction of solar wind flow. Bottom panel: calculated flux ratio for solar wind particles that reach the cometary surface and sputtered atoms back to the ROSINA observation point (black lines), using Eq. (5). The sputtered Si signal is shown as red lines. Interruptions in the lines were caused at times when the sensors were turned off.