Coupling of Earth's Ionosphere, Magnetosphere and Solar Wind

The average composition of the solar wind (SW) is about 95% H+, 5% He++ and minute amounts of heavier ions such as O+6. Here we report highly unexpected new Cluster observations of O+ (oxygen) and He+ (helium) ions in the SW upstream of the bow shock. Although He+ ions can be produced in the SW by collisional detachment of pick up ions with the SW He++, such He+ ions are not generally measured in the vicinity of 1 AU. Moreover, the SW at 1 AU is not a suitable environment to collisionally neutralize O+6 ions and produce O+ ions. Another way to produce O+ and He+ ions is to transport the ionospheric neutral O and He atoms across the geomagnetic field into the upstream SW region where they are ionized. However, our observations have ruled out this mechanism because the average velocity ratios of O+ and He+ field-aligned beams is ~1/2, which is strong evidence that the ions have been accelerated in the ionosphere by a field-aligned potential drop. Existing theories and models do no predict the flux tubes containing the ionospheric O+ and He+ ions are transported to the upstream SW. To provide a comprehensive picture of the escaping ions, we will show examples of O+ and He+ velocity distributions measured in the neighborhood of the plasmasphere followed by observations in the magnetosheath and then SW. Our observations indicate the ionosphere, magnetosphere and SW must be treated as a closely coupled system and not as independent entities. The challenge for theorists is to develop a self-consistent model to explain how the fundamental SW-magnetosphere-ionosphere coupling mechanisms work in our solar system and elsewhere in the plasma Universe.