Themis: Locations of Dayside Bow Shock and Magnetopause

The paper presents a statistical study of bow shock and magnetopause positions in the subsolar region during the years 2007 and 2008 based on observation of five Themis spacecraft. The main attention is paid to a bias caused by a low apogee of the spacecraft which limits distances where bow shock crossings could be recorded. To overcome these problems, we developed a method eliminating this bias and an automatic technique to recognise bow shock and magnetopause positions. A comparison of results obtained by these methods shows a good agreement for low values of the upstream dynamic pressure. Our results suggest that the generally used scaling of the magnetopause and bow shock with the sixth root of the upstream dynamic pressure is a good approximation for a low pressure but that there is a systematic deviation for pressures above 3-4 nPa.