Post‐Pinatubo optical depth spectra vs. latitude and vortex structure: Airborne tracking sunphotometer measurements in AASE II

In January and March 1992, DC‐8‐measured stratospheric particle optical depth spectra, τ p (λ), peaked broadly at midvisible or longer wavelengths. At mid‐to‐high northern latitudes outside the vortex, τ p (526 nm) above about 11 km was as large as 0.22 in both January and March, reflecting continued Pinatubo volcanic influence. In both months, in‐vortex τ p (λ) above 11 km was smaller than outside‐vortex values by a factor of two or more, and in January a strong anticorrelation was observed between τ p (λ) and HF column content (an indicator of vortex penetration). In late January at 18–20S, near the edge of the southern subtropical jet, τ p (526 nm) above 12 km was only about 0.07–0.09, with a flatter spectral shape than northern mid‐ to high‐latitude measurements in both January and March. Occasional high‐latitude vertical profiles indicate 6–11‐km slab optical depths, Δτ p (526 nm), of 0.05 to 0.1, which should be added to the above‐11‐km values to yield values above 6 km.