GEOTAIL observation of 2f _p emission around the terrestrial electron foreshock

GEOTAIL has observed 2f _p emission in the upstream of the terrestrial bow shock at a distance of 10-30 RE from the Earth. We determined geometry of the 2f _p radio source by three statistical methods; analyses of propagation angles of 2f _p emissions, bifurcation of 2f _p emission lines associated with passage of density jump, and spatial distributions of 2f _p emissions and Langmuir waves. We found that the source can be generally superposed on the electron foreshock, while not concentrated around the contact point of the IMF line tangent to the bow shock surface. Typical distance of the source centroid from the contact point is about 10-40 RE.