Behaviour of nitric oxide trails deposited in the mesosphere and stratosphere

Abstract

The transient behavior of a nitric oxide trail deposited in the atmosphere has been studied by numerical solution of the multidimensional diffusion equation including the effects of chemical reactions between nitric oxide and constituents of the ambient atmosphere. Starting with an initial nitric oxide concentration of 2 × 10¹² molecules/cm³ and a trail radius of 90 m, computations have been carried out for 20 km as well as 60 km. As the trail expands, atmospheric ozone interacts with nitric oxide to form nitrogen dioxide and molecular oxygen. During the day nitrogen dioxide is photodissociated to form nitric oxide, leading to a further decrease in ozone. Destruction of ozone by nitric oxide results in a depletion of ozone in the vicinity of the trail. For a quiescent atmosphere this ozone “hol” typically reaches a maximum extent in 4 to 6 hours and collapses again in 12 hours. At its maximum the 50% or greater depletion region is one kilometer wide and 300 m thick. Trail behavior is relatively independent of altitude and background ozone but depends strongly on the magnitude of eddy diffusivity and the initial nitric oxide concentration. Wind shear stretches the trail into a thin oval, enhancing the rate of trail dissipation.