Role of NOy as a diagnostic of small‐scale mixing in a denitrified polar vortex

Abstract

Observations of three stratospheric species (N2O, CH4, and NOy) are examined for their suitability as mixing tracers in the inner Arctic vortex region between late February and mid‐March 2000. NOy is highly inhomogeneous on isentropic surfaces and has little systematic vertical gradient between the 420 and 470 K potential temperature surfaces due to severe and extensive denitrification. Probability distribution functions of NOy calculated from in situ measurements do not show systematic and significant change as a function of time, indicating that mixing was too slow to substantially homogenize NOy distribution and therefore to strongly affect photochemical O3 destruction rates during the period. We propose that the NOy inhomogeneity is useful for diagnosing small‐scale, irreversible mixing rates during the measurement period. A simple kinematic model is used to show that the NOy standard deviation on an isentropic level in the vortex has desirable properties for quantifying these rates. A practical method for deriving mixing rates for chemistry and transport models has been proposed for future studies.