In 2007, a research paper said that Plasma fountain (or Polar wind) is "an ambipolar outflow of thermal plasma from the [the ionosphere near the North pole and South pole, or] high-latitude ionosphere"; That plasma moves from the ionosphere to the magnetosphere.[6]
Decades of research has led to a body of scientific work; A thing that it says, is that there is at least one electric field on the outer limits (of the ionosphere).
The electric field gets called different things, such as
polarization field (and polarization electric field)
ambipolar field (and ambipolar electric field)
Causes of the plasma fountain (or polar wind)
About 30 years of research [as of the 2020s], says that the cause of the plasma fountain (or polar wind) is ambipolar outflow of thermal plasma: ion acceleration by a polarization electric field at high altitudes.[7]: 451
The polarization electric field or ambipolar electric field was originally proposed in the 1920s for ionized stellar atmospheres.[8]: 1927
The field is very small but, unlike other forces, it points away from gravity.[8]: 1927 In low-density plasma at high altitude (above Earth), it overwhelms gravity for light ions.