Observed characteristics of polar cleft Hα and OI emissions

Observations at Godhavn, Greenland show that the intersection of the polar cleft with the ionosphere can be recognized by simultaneous occurrence of hydrogen emissions (H_α, H_β>) and enhanced OI 6300 Å emission. The H_α-line reveals a characteristic narrow and symmetric Doppler profile which is interpreted as indicating that the solar wind protons retain their typical flux and energy spectrum all the way down to the ionosphere. The cleft intersection seems to cover the sector 04:00–22:00 geomagnetic time.