Comparison of Aura MLS stratospheric chemical gradients with north polar vortex edges calculated by two methods

Abstract

The edge of the winter polar vortex is thought to isolate chemistry between inside and outside. A way to test how accurately it is estimated is to examine chemical mixing ratios along a path that crosses its edge. Two edge methods are tested, one is the “Q-edge” (Harvey et al., 2002), which chooses a specific streamline; the other is scaled potential vorticity, “sPV”, which identifies an inner and outer edge depending on the local value of potential vorticity scaled according to the static stability (Manney et al., 1994). Aura MLS mixing ratios show that, statistically overall, sPV edge area agrees better with the N2O mixing ratio gradient below ∼700K, albeit with more scatter.Finally direct comparison statistics on a few 10day winter intervals show that the Q-edge is usually outside the sPV outer edge below potential temperature levels ∼400–500K, agrees up to ∼700K, and inside to ∼1200K. Above that, both methods tend to agree again.