Retrieval of stratospheric aerosol size distribution parameters using SAGE-III/ISS extinction measurements at three wavelengths

Abstract

Abstract. In this work a novel approach to determine the particle size distribution (PSD) parameters of stratospheric sulfate aerosols is presented. For this, ratios of extinction coefficients obtained from SAGE III/ISS solar occultation measurements at 449 nm, 756 nm and 1544 nm were used to retrieve the mode width and median radius of a size distribution assumed to be monomodal lognormal. The estimated errors at the peak of the stratospheric aerosol layer on average lie between 20 % and 25 % for the median radius and 5 % and 7 % for the mode width. The results are consistent in magnitude with other retrieval results from the literature, but a robust comparison is difficult, mainly because of differences in temporal and spatial coverage. Other quantities like number density and effective radius were also calculated. A major advantage of the described method over other retrieval techniques is that both the median radius and the mode width can be retrieved simultaneously, without having to assume one of them, due to the broad wavelength spectrum covered by the SAGE III/ISS measurements. Also the extinction coefficients from SAGE III/ISS solar occultation measurements, on which the retrieval is based, are calculated without a priori assumptions about the PSD. For those reasons, the data produced with the presented retrieval technique may be a valuable contribution to better understand the variability of stratospheric aerosol size distributions, e.g. after volcanic eruptions. While this study focuses on describing the retrieval method and a future study will discuss the PSD parameter data set produced in depth, some exemplary results for background conditions in June 2017 are shown.

Observation of the aerosol plume from the 2022 Hunga Tonga - Hunga Ha’apai eruption with SAGE III/ISS

“…We use a method implemented by Wrana et al (2021) to retrieve the SA size distribution which is based on the two color ratios 449 nm / 755 nm and 1543 nm / 755 nm for the aerosol extinction coefficients. These ratios are modeled for spherical liquid SA through Mie calculations using miepython, a python code where the Mie theory is implemented following the procedure described by Wiscombe (1979).…”

Growth and global persistence of stratospheric sulfate aerosols from the 2022 Hunga Tonga-Hunga Haápai volcanic eruption

“…Contrary to spaceborne occultation/limb-scattering measurements (Wrana et al, 2021;, AERONET inversions present the advantage of not requiring any apriori assumption on particle size distribution or chemical composition for the retrieval of volume size distribution. Together with satellite observations, exhaustive analysis of photometric observations from the AERONET network allows us to track the size of HT-HH sulfate aerosols with time.…”

“…Balloonborne experiments are useful to provide direct constraints on the size distribution of stratospheric aerosols with altitude but, due to operational difficulty, cannot capture the detailed spatio-temporal evolution of aerosol microphysics . Satellite occultation or limb-scattering measurements require prerequisite assumptions on particle size distribution or chemical composition (Wrana et al, 2021;. Here, we analyze open-access data from the AERONET ground network of photometers that provide, at >600 stations worldwide, information on the optical, microphysical and absorption properties of aerosols in the atmospheric column (B. Holben et al, 2001;.…”

Inversion method of particle size distribution of milk fat based on improved MPGA

“…Excel 2016 was used to process the experiment’s preliminary statistical data. Data and graphics were analyzed and processed with Matlab 2016a, including the calculation of apparent extinction coefficient ( Fu and Sun, 2001 ; Yang et al, 2002 ; Fu and Sun, 2006 ; Ding et al, 2020 ; Wrana et al, 2020 ), regularization parameter and Mie scattering coefficient. Matlab 2016a was used to inverse different algorithms for calculating particle size distribution.…”

“…Based on the extinction spectra calculated by known specific parameters, an inversion algorithm is built to generate a more precise particle size distribution. Apparent optical parameters ( Fu and Sun, 2001 ; Yang et al, 2002 ; Fu and Sun, 2006 ; Ding et al, 2020 ; Wrana et al, 2020 ) are introduced based on total light scattering to solve the extinction coefficient and create an objective function. This effectively overcomes the influence of the light-absorbing medium.…”