First results of a ULF wave injected on open field lines by Space Plasma Exploration by Active Radar (SPEAR)

We present strong evidence that on 23 February 2007 between 2230 and 2330 UT the Space Plasma Exploration by Active Radar (SPEAR) system successfully modified the ionospheric electron density inside the northern polar cap. The modulated modification led to the generation of a small-scale ultralow frequency (ULF) wave on open field lines which was detected by ground-based magnetometers in the vicinity of the radar. It was not registered by magnetometer stations elsewhere inside the northern polar cap or at lower latitudes. The solar wind conditions are investigated, and although wave activity at the modulation frequency is present, it is shown that the local ULF wave is unlikely to originate from that activity.