Latitudinal Distribution of Dayside Magnetospheric Currents Based on Cluster Observations

Based on the curlometer method, we calculate the azimuthal component of the current density from nearly 19 years of Fluxgate Magnetometer (FGM) data of Cluster and investigate its latitudinal distribution in the dayside noon sector (09:00–15:00 magnetic local time, MLT). A crossing event in the noon meridian plane shows an unexpected eastward current at a geocentric distance of 8 R_E, away from the equator with latitudes of 30–40°. Further statistical results of the current distribution show that, the topology of the current can be radially divided into the inner and outer branches over the whole r_xy − z plane (r_xy = $\sqrt{x^2+y^2}$ and z are in solar magnetic (SM) coordinates), with the separation point of these two branches at a geocentric distance of about 8 R_E. The current variations of the inner and outer branches are different under different Kp, solar wind flow speed V_sw, and solar wind dynamic pressure P_dyn. It is shown that the current densities in both the inner and outer branches increase significantly with the Kp. High solar wind dynamic pressure enhances the current density of the outer branch, while high solar wind speed, on the contrary, enhances that of the inner branch. The formation of the outer branch may be related to the anisotropy of plasma pressure.