Global observations of nitric oxide in the thermosphere

Nitric oxide density in the lower thermosphere (97–150 km) has been measured from the polar‐orbiting Student Nitric Oxide Explorer (SNOE) satellite as a function of latitude, longitude, and altitude for the 2 1/2 year period from 11 March 1998 until 30 September 2000. The observations show that the maximum density occurs near 106–110 km and that the density is highly variable. The nitric oxide density at low latitudes correlates well with the solar soft X‐ray irradiance (2–7 nm), indicating that it is the solar X‐rays that produce thermospheric nitric oxide at low and midlatitudes. Nitric oxide is produced at auroral latitudes (60°–70° geomagnetic) by the precipitation of electrons (1–10 keV) into the thermosphere. During high geomagnetic activity, increased nitric oxide may be present at midlatitudes as the result of meridional winds that carry the nitric oxide equatorward.