Aerosol particle size distribution in the stratosphere retrieved from SCIAMACHY limb measurements

Abstract

Abstract. Information about aerosols in the Earth's atmosphere is of a great importance in the scientific community. While tropospheric aerosol influences the radiative balance of the troposphere and affects human health, stratospheric aerosol plays an important role in atmospheric chemistry and climate change. In particular, information about the amount and distribution of stratospheric aerosols is required to initialize climate models, as well as validate aerosol microphysics models and investigate geoengineering. In addition, good knowledge of stratospheric aerosol loading is needed to increase the retrieval accuracy of key trace gases (e.g. ozone or water vapour) when interpreting remote sensing measurements of the scattered solar light. The most commonly used characteristics to describe stratospheric aerosols are the aerosol extinction coefficient and Ångström coefficient. However, the use of particle size distribution parameters along with the aerosol number density is a more optimal approach. In this paper we present a new retrieval algorithm to obtain the particle size distribution of stratospheric aerosol from space-borne observations of the scattered solar light in the limb-viewing geometry. While the mode radius and width of the aerosol particle size distribution are retrieved, the aerosol particle number density profile remains unchanged. The latter is justified by a lower sensitivity of the limb-scattering measurements to changes in this parameter. To our knowledge this is the first data set providing two parameters of the particle size distribution of stratospheric aerosol from space-borne measurements of scattered solar light. Typically, the mode radius and w can be retrieved with an uncertainty of less than 20 %. The algorithm was successfully applied to the tropical region (20 • N-20 • S) for 10 years (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) of SCIAMACHY observations in limb-viewing geometry, establishing a unique data set. Analysis of this new climatology for the particle size distribution parameters showed clear increases in the mode radius after the tropical volcanic eruptions, whereas no distinct behaviour of the absolute distribution width could be identified. A tape recorder, which describes the time lag as the perturbation propagates to higher altitudes, was identified for both parameters after the volcanic eruptions. A quasi-biannual oscillation (QBO) pattern at upper altitudes (28-32 km) is prominent in the anomalies of the analysed parameters. A comparison of the aerosol effective radii derived from SCIAMACHY and SAGE II data was performed. The average difference is found to be around 30 % at the lower altitudes, decreasing with increasing height to almost zero around 30 km. The data sample available for the comparison is, however, relatively small.

Improvement of stratospheric aerosol extinction retrieval from OMPS/LP using a new aerosol model

“…The SAGE series of occultation measurements have been extensively evaluated and compared with other spacebased instruments and have been found to have relatively high precision and accuracy (Bourassa et al, 2012). A general description of the solar occultation measurement technique is provided by McCormick et al (1979). The ISS travels in a low Earth orbit at an altitude of 330-435 km at an inclination of 51.6 • .…”

Issues related to the retrieval of stratospheric-aerosol particle size information based on optical measurements

“…The effects studied here should, however, also be investigated for aerosol size retrievals from limb-scatter measurements in future studies. We would like to point out that different aspects of the sensitivity of satellite limb-scatter measurements on the stratospheric-aerosol particle size distribution have been already investigated in the studies by Rieger et al (2014) and Malinina et al (2019).…”

A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from OPC measurements

“…A discussion of fitting LN distributions to the aerosol measurements obtained from OPC is given by Horvath et al (1990). LN aerosol size information for stratospheric aerosols has also been been retrieved from LS measurements (Rault and Loughman, 2013;Rieger et al, 2014;Malinina et al, 2018). The UMLN distribution consists of three parameters: The total aerosol concentration and two parameters that indicate the median radius and width of the ASD.…”