Validation of aerosol measurements from the improved stratospheric and mesospheric sounder

Abstract

The retrieval and validation of the infrared measurements of the stratospheric aerosol layer derived from the improved stratospheric and mesospheric sounder (ISAMS) on board the Upper Atmsophere Research Satellite (UARS) are discussed in detail. The retrieval method is presented and an error analysis and sensitivity study are used to provide an error budget. The validation involves internal consistency checks, comparisons with coincident aerosol observations from other satellite-based instruments (cryogenic limb array etalon spectrometer (CLAES) and Stratospheric Aerosol and Gas Experiment II (SAGE II)) and in situ particle counters. The internal comparisons show that the precision of the 6.20-/•m retrievals are better than 30% for the data on the 32-hPa and 22-hPa pressure surfaces and that the 12.11-/•m retrievals are better than 20% and 25% for the data on pressure surfaces at 46 hPa and 32 hPa, respectively. Comparison of the ISAMS aerosol extinctions with the simultaneous CLAES measurements show systematic biases for both the 6-tim and the 12-tim retrievals with ISAMS generally measuring lower extinction values than CLAES. The comparison with calculated extinctions from balloon dustsonde data at 41 øN shows that the aerosol extinctions are systematically too high for pressures less than 40 hPa. Ballard et al. [1996]. The middle atmosphere contains a ubiquitous layer of particulate matter in the lower stratosphere which consists mainly of sulphuric acid-water drops [Turco et al., 1982]. This layer originates from the transport of background sulphurous gases, mainly OCS, from the troposphere and from the direct injection of SO2 by volcanic eruptions. Major volcanic explosions such as E1 Chich6n (1982) and Mount Pinatubo (1991) inject tens of megatonnes of SO2 into the stratosphere. The SO2 gas is converted over a period of months into sulphuric acid-water droplets [Bluth et al., 1992; Read et al., 1993], but the removal of the resulting submicron-size aerosol particles from the stratosphere by the process of sedimentation takes several years [Holmann, 1990]. The aerosol layer affects the radiative, chemical, and dynamical properties of the stratosphere. Evidence is increasing for the view that heterogeneous reactions on the background and volcanic sulphate aerosols can cause global changes in reactive nitrogen species, activation of chlorine reservoirs, and lead to ozone depletion [Holmann and Solomon, 1989; Granier and Brasseur, 1992; Grant et al., 1994; Hanson et al. , 1994; Holmann et al. , 1994; Rinsland et al., 1994a]. The interaction of aerosols with the solar and the Earth's radiation field can produce substantial dynamical changes in the lower stratosphere which affect transport of trace species [Kinne et al., 1992; Lacis et al., 1992]. The particle size distribution and chemical composition of aerosols are important factors in determining their radiative properties [Bohren and Huffman, 1983]. A wide variety of techniques are used to measure aerosol microphysical properties and abundances with height [...

A global, space-based stratospheric aerosol climatology: 1979 to 2016

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“…GloSSAC is most closely related to the Assessment of Stratospheric Aerosol Properties (ASAP) (SPARC, 2006) and CMIP Phase 5 data sets and follows the same basic paradigm that produce those versions. We build it primarily using space-based measurements by a number of instruments including the SAGE series, the (Optical Spectrograph and InfraRed Imager System OSIRIS) (Rieger et al, 2015), the Cloud-Aerosol Lidar 20 and Infrared Pathfinder Satellite Observation (CALIPSO) (Vernier et al, 2011), Cryogenic Limb Array Etalon Spectrometer (CLAES) (Massie et al, 1996), and the Halogen Occultation Experiment (HALOE) (Thomason, 2012). We compile the data set in monthly depictions for 80°S to 80°N and from the tropopause to 40 km.…”

Known and unknown unknowns: uncertainty estimation in satellite remote sensing

“…The concept is also known as "fair-weather bias" as the exclusively clear-sky conditions considered are not necessarily representative of the long-term average conditions that the measurand purports to describe (an example can found in Levy et al, 2009). Ensemble techniques can be used to characterise this error either by demonstrating the changes in coverage as a function of the cloud filter used or by explicitly considering cloudy conditions as an alternative realisation of the system (for which the state vector will likely be different).…”

“…More common is the sampling of the same point in successive orbits (often near the poles), assembling pairs of measurements of similar (if not identical) atmospheric states (e.g. Lambert et al, 1996). If the first observation is x 1 with uncertainty σ 1 and the second x 2 with σ 2 , then a histogram of…”

“…Levy et al, 2013). Ideally, the fit to the measurements would indicate a best choice of system, shown schematically in Fig.…”