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, τp(λ), peaked broadly at midvisible or longer wavelengths. At mid‐to‐high northern latitudes outside the vortex, τp(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 τp(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 τp(λ) and HF column content (an indicator of vortex penetration). In late January at 18–20S, near the edge of the southern subtropical jet, τp(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, Δτp(526 nm), of 0.05 to 0.1, which should be added to the above‐11‐km values to yield values above 6 km.