Abstract
Abstract. Herein, the Halogen Occultation Experiment (HALOE) aerosol extinction coefficient data is evaluated in the low aerosol loading period after 1996 as the first necessary step in a process that will eventually allow the production of a combined HALOE/SAGE II (Stratospheric Aerosol and Gas Experiment) aerosol climatology of derived aerosol products including surface area density. Based on these analyses, it is demonstrated that HALOE's 3.46 μm is of good quality above 19 km and suitable for scientific applications above that altitude. However, it is increasingly suspect at lower altitudes and should not be used below 17 km under any circumstances after 1996. The 3.40 μm is biased by about 10% throughout the lower stratosphere due to the failure to clear NO2 but otherwise appears to be a high quality product down to 15 km. The 2.45 and 5.26 μm aerosol extinction coefficient measurements are clearly biased and should not be used for scientific applications after the most intense parts of the Pinatubo period. Many of the issues in the aerosol data appear to be related to either the failure to clear some interfering gas species or doing so poorly. For instance, it is clear that the 3.40 μm aerosol extinction coefficient measurements can be improved through the inclusion of an NO2 correction and could, in fact, end up as the highest quality overall HALOE aerosol extinction coefficient measurement. It also appears that the 2.45 and 5.26 μm channels may be improved by updating the Upper Atmosphere Pilot Database which is used as a resource for the removal of gas species otherwise not available from direct HALOE measurements. Finally, a simple model to demonstrate the promise of mixed visible/infrared aerosol extinction coefficient ensembles for the retrieval of bulk aerosol properties demonstrates that a combined HALOE/SAGE II aerosol climatology is feasible and may represent a substantial improvement over independently derived data sets.
Highlights
In the stratosphere, where aerosol composition is predominately mixtures of H2SO4 and H2O, aerosol extinction at Halogen Occultation Experiment (HALOE) wavelengths is dominated by absorption
1an9d9106oNaanndd192960a0n5d 20(0l5e(frtig)hta).nd the median relative standard based on a 3-month running in the four HALOE aerosol extinction channels and the SAGE II 1020nm aerosol extinction channel between 10◦ S and 10◦ N and 1996 and 2005
The goal of this paper is to evaluate the HALOE aerosol extinction coefficient data as the first necessary step in a process that will eventually allow the production of a combined HALOE/SAGE II aerosol climatology of derived aerosol products including surface area density (SAD) and a mechanism to produce complete aerosol extinction/absorption spectra suitable for use in climate modeling
Summary
In the stratosphere, where aerosol composition is predominately mixtures of H2SO4 and H2O, aerosol extinction at Halogen Occultation Experiment (HALOE) wavelengths is dominated by absorption. This stands in contrast to similar measurements in the visible and near infrared where absorption by sulfate aerosol is effectively zero and extinction is dominated by the positive wing of the aerosol size distribution with limited dependence on the smallest aerosol present In addition to the gas species, aerosol extinction coefficient profiles for the upper troposphere through the stratosphere are reported at four wavelengths (2.45, 3.40, 3.46, and 5.26 μm) These data show the immediate aftermath of the June 1991 Pinatubo eruption and the long recovery of stratospheric aerosol levels throughout the 1990s. The HALOE size distribution fits reported in the official data files are based on multiple HALOE aerosol extinction coefficient values and may mask or exacerbate issues at individual wavelengths
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