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The electric fields, ion currents, and charge densities at ground level under a HVdc transmission line are described and compared with ambient levels. Measurements of field and current density under the Â±400 kV Celilo-Sylmar dc Intertie made during fair weather low wind conditions are described and the results are compared with values calculated from an idealized model. Deviations of the measurements from the theoretical values are attributed to the effects of wind on ion movement and the different characteristics of positive and negative corona. A predominance of the space charge generated at the negative conductor is observed.