Evaluation of the OMPS/LP stratospheric aerosol extinction product using SAGE III/ISS observations

Zhong Chen,Pawan K Bhartia,Ghassan Taha,Robert Damadeo,Glen Jaross,Omar Torres,Robert Loughman,Peter Colarco,Matthew Deland

doi:10.5194/amt-13-3471-2020

Abstract

Abstract. The Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) has been taking limb-scattered measurements since April 2012. It is designed to produce ozone and aerosol vertical profiles at a 1.6 km vertical resolution over the entire sunlit globe. The Version 1.5 (V1.5) aerosol extinction retrieval algorithm provides aerosol extinction profiles using observed radiances at 675 nm. The algorithm assumes Mie theory and a gamma function aerosol size distribution for the stratospheric aerosol that is derived from results calculated by the Community Aerosol and Radiation Model for Atmospheres (CARMA). In this paper, we compare V1.5 LP aerosol profiles with SAGE III/ISS solar occultation observations for the period from June 2017 to May 2019, when both measurements were available to evaluate our ability to characterize background aerosol conditions. Overall, LP extinction profiles agree with SAGE III/ISS data to within ±25 % for altitudes between 19 and 27 km, even during periods perturbed by volcanic eruptions or intense forest fires. In this altitude range, the slope parameter of linear fitting of LP extinction values with respect to SAGE III/ISS measurements is close to 1.0, with Pearson correlation coefficients of r≥0.95, indicating that the LP aerosol data are reliable in that altitude range. Comparisons of extinction time series show that both instruments capture the variability of the stratospheric aerosol layer quite well, and the differences between the two instruments vary from 0 % to ±25 % depending on altitude, latitude, and time. In contrast, we find erroneous seasonal variations in the OMPS/LP Version 1.5 dataset, which usually exist below 20 km in the Southern Hemisphere due to the lack of sensitivity to particles when the scattering angle (SA) is greater than 145∘. We also find that LP-retrieved extinction is systematically higher than SAGE III/ISS observations at altitudes above 28 km and systematically lower below 19 km in the tropics with significant biases up to ±13 %. This is likely due in part to the fact that the actual aerosol size distribution is altitude dependent. There are also other reasons related to cloud contamination, wavelength limitations, aerosol loading, and the influence of the viewing configuration.

Highlights

The stratospheric aerosol layer is an important component of Earth’s atmosphere through its impacts on climate and stratospheric ozone physico-chemistry (Vernier et al, 2011; Ridley et al, 2014; Bingen et al, 2017)
For the background aerosol condition based on the June 2017 to June 2018 period, Limb Profiler (LP) and SAGE III/ISS are within 20 % of each other at 20.5 and 25.5 km, indicating that the assumed aerosol size distribution (ASD) in the LP V1.5 algorithm is adequate in this altitude range
While the SAGE III/ISS algorithm does not require any assumptions about aerosol microphysics, aerosol extinction profiles from Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) suffer from uncertainties due to assumed ASD and refractive index

Summary

Introduction

The stratospheric aerosol layer is an important component of Earth’s atmosphere through its impacts on climate and stratospheric ozone physico-chemistry (Vernier et al, 2011; Ridley et al, 2014; Bingen et al, 2017). The stratospheric aerosol layer was first observed by Junge in 1960 (Junge et al, 1961). The importance of possible changes in the background stratospheric aerosol layer led to the analysis of each volcanically quiescent period (Deshler et al, 2006). For the considered period from January 1979 through to the end of 2004, the variability of stratospheric aerosol layer is explored using measurements from space-based instruments such as SAGE II (Thomason et al, 2008), CALIPSO (Winker et al, 2010), GOMOS/Envisat (Vanhellemont et al, 2010), SCIAMACHY (von Savigny et al, 2015), OSIRIS/Odin (Bourassa et al, 2007), SAGE III/ISS (Chu and Veiga, 1998), and OMPS/LP (Loughman et al, 2018)

Methods

Results

Conclusion