Production of odd nitrogen in the stratosphere and mesosphere: An intercomparison of source strengths

This study intercompares several sources of odd nitrogen (ON) in the stratosphere and mesosphere (middle atmosphere) so as to place galactic cosmic rays (GCRs), nuclear explosions, lightning, solar proton events (SPEs), relativistic electron precipitation, meteors, and the downward diffusion of NO from the thermosphere in their proper context relative to the oxidation of nitrous oxide. Use of published measurements of O 3 and N 2 O show that the source of ON owing to the reaction of O( 1 D ) + N 2 O peaks between 25 and 35 km and is by far the largest source in an annually, globally averaged sense with a magnitude of 4.5×10 34 molecules yr −1 . At solar minimum the GCRs add about the same amount of ON as N 2 O oxidation (1.7×10 33 molecules yr −1 ) for geographic latitudes greater than 50°. Nuclear explosions in 1961 and 1962 added 1.1 and 2.2×10 34 NO molecules, respectively, to the total global ON content. SPEs produced more ON at latitudes above 50° than did N 2 O oxidation for the years 1958, 1959, 1960, and 1972. Analysis of available measurements shows the downward flux of NO from the thermosphere to be between 8 and 33% of the integrated N 2 O source. Large variations in measurements of ON should be expected at geographic latitudes above 50° where the highly variable SPE source of ON is substantial. Because of the long lifetime of ON in the middle atmosphere, significant variations in its content may also be expected to occur at mid‐latitudes.