On the accuracy of stratospheric aerosol extinction derived from in situ size distribution measurements and surface area density derived from remote SAGE II and HALOE extinction measurements

Abstract

In situ stratospheric aerosol measurements, from University of Wyoming optical particle counters (OPCs), are compared with Stratospheric Aerosol Gas Experiment (SAGE) II (versions 6.2 and 7.0) and Halogen Occultation Experiment (HALOE) satellite measurements to investigate differences between SAGE II/HALOE-measured extinction and derived surface area and OPC-derived extinction and surface area. Coincident OPC and SAGE II measurements are compared for a volcanic (1991)(1992)(1993)(1994)(1995)(1996) and nonvolcanic (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) period. OPC calculated extinctions agree with SAGE II measurements, within instrumental uncertainty, during the volcanic period, but have been a factor of 2 low during the nonvolcanic period. Three systematic errors associated with the OPC measurements, anisokineticity, inlet particle evaporation, and counting efficiency, were investigated. An overestimation of the OPC counting efficiency is found to be the major source of systematic error. With this correction OPC calculated extinction increases by 15-30% (30-50%) for the volcanic (nonvolcanic) measurements. These changes significantly improve the comparison with SAGE II and HALOE extinctions in the nonvolcanic cases but slightly degrade the agreement in the volcanic period. These corrections have impacts on OPC-derived surface area density, exacerbating the poor agreement between OPC and SAGE II (version 6.2) surface areas. This disparity is reconciled with SAGE II version 7.0 surface areas. For both the volcanic and nonvolcanic cases these changes in OPC counting efficiency and in the operational SAGE II surface area algorithm leave the derived surface areas from both platforms in significantly better agreement and within the ± 40% precision of the OPC moment calculations.

The Sectional Stratospheric Sulfate Aerosol module (S3A-v1) within the LMDZ general circulation model: description and evaluation against stratospheric aerosol observations

“…Recently Mills et al (2016) used the WACCM model to simulate the time evolution of the stratospheric aerosol over the period 1990-2014. They find a good agreement in stratospheric aerosol optical depth (SAOD) with SAOD derived from several available lidar measurements by Ridley et al (2014) and in surface area density (SAD) with balloon-borne optical particle counter (OPC) measurements at the University of Wyoming (Kovilakam and Deshler, 2015).…”

The Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP): motivation and experimental design

“…Furthermore aerosol extinction vertical profiles are available from limb-profiling instruments, such as the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY;2002-2012Bovensmann et al, 1999;von Savigny et al, 2015), the Optical Spectrograph and InfraRed Imager System (OSIRIS;2001-present;Bourassa et al, 2007), and the Ozone Mapping and Profiler SuiteLimb Profiler (OMPS-LP;2011-present;Rault and Loughman, 2013), and from the active sensor lidar measurements such as the Cloud-Aerosol Transport System (CATS; 2015-present; Yorks et al, 2015) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP;2006-present;Vernier et al, 2009). Existing measurements have become more robust, for example by homogenizing the observations of aerosol properties derived from optical particle counter (OPC) and satellite measurements during stratospheric aerosol background periods (Kovilakam and Deshler, 2015), which previously showed large differences (Thomason et al, 2008). Other efforts include combining and comparing different satellite data sets (e.g.…”

The Aerosol Limb Imager: acousto-optic imaging of limb-scattered sunlight for stratospheric aerosol profiling

“…These have provided a reliable, accurate, and essentially continuous long-term record of vertically resolved aerosol extinction coefficient measurements, mostly from the series of Stratospheric Aerosol and Gas Experiment (SAGE) instruments (Russell and McCormick, 1989;Thomason and Taha, 2003). These SAGE measurements, which have a vertical resolution of approximately 1 km, have generally compared well with ground-based and in situ measurements, although there are challenges associated with determining microphysical parameters and comparison between instruments can be challenging (Russell and McCormick, 1989;Kovilakam and Deshler, 2015). However, solar occultation is generally a robust and stable technique as it directly measures atmospheric optical depth, along with the exoatmospheric solar spectrum with each scan, allowing for straightforward retrieval of aerosol extinction coefficient (Damadeo et al, 2013).…”

“…In situ balloon observations continue to be used and have provided highly valuable data sets, including most notably the long time series of optical particle counter measurements from Laramie, WY (Deshler et al, 2003(Deshler et al, , 2006Kovilakam and Deshler, 2015). Aircraft-borne nephelometers (Beuttell and Brewer, 1949;Charlson et al, 1969) acquire detailed in situ measurements, providing, for example, plume composition (Murphy et al, 2014), but are spatially limited to the aircraft track.…”