The Influence of IMF Byon the Bow Shock: Observation Result

In this study we use the bow shock crossings contained in the Space Physics Data Facility database, collected by four spacecraft (IMP 8, Geotail, Magion‐4, and Cluster1) to analyze the effect of the interplanetary magnetic field (IMF) Bycomponent on the bow shock position and shape. Although the IMF Bzcomponent is usually considered much more geoeffective than By, we find that the dayside bow shock is more responsive to the eastward component of the IMF than the north‐south one. We believe that the explanation lies in the changes that the Bzcomponent induces on the magnetopause location and shape, which largely compensate the corresponding changes in the dayside bow shock location. In the tail, we find that the bow shock cross section is elongated roughly in the direction perpendicular to the IMF direction, which agrees with earlier modeling studies. The dayside bow shock is more responsive to the eastward component of the IMF than to the north‐south oneAs the eastward Byincreases, the bow shock standoff distance increases, while the flaring angle decreasesThe BS tail's cross section is elongated roughly in the direction perpendicular to the IMF, which agrees with earlier modeling studies