When the plasma source is operated, supersonic outflows of ionospheric plasma have now been observed throughout the polar cap for the first time. These outflows are seen in the figure as a series of bright green strips that descend in energy range as indicated at the right end of the plot frames. Each strip of bright green in the series corresponds to the spin modulation of the flux recorded as the spacecraft spun about its axis. Significant plasma flux is seen only when TIDE views downward along the local magnetic field. Higher energy, narrowly collimated flows of Oxygen and Helium are also seen. The Hydrogen flows have a flow velocity of ~ 40 kilometers/second, and a thermal speed of ~10 kilometers/second.
Thus, the polar caps, though low in plasma density, are anything but empty and are carrying substantial fluxes of ionospheric plasma upward and then down the tail into the region of storm plasma energization.
As the POLAR spacecraft loops upward to its apogee high over the north pole, it traverses the cusp region, where solar wind plasma enters directly and penetrates along field lines to the dayside auroral oval. The cusp appears in data from the Thermal Ion Dynamics Experiment as a bright white region (high fluxes over a wide range of angles, for both hydrogen ions and m/q=2 ions, i.e. doubly ionized Helium ions) at the left side of the figure. The figure includes over 10 hours of data as POLAR passes from the dayside to the nightside of the polar cap through apogee at nearly 9 Earth radii. On a day without plasma source operation, the polar cap would be devoid of any observable plasma flux.