Abstract
Aerosol composition and optical scattering from particles in the lowermost stratosphere (LMS) have been studied by comparing in-situ aerosol samples from the IAGOS-CARIBIC passenger aircraft with vertical profiles of aerosol backscattering obtained from the CALIOP lidar aboard the CALIPSO satellite. Concentrations of the dominating fractions of the stratospheric aerosol, being sulphur and carbon, have been obtained from post-flight analysis of IAGOS-CARIBIC aerosol samples. This information together with literature data on black carbon concentrations were used to calculate the aerosol backscattering which subsequently is compared with measurements by CALIOP. Vertical optical profiles were taken in an altitude range of several kilometres from and above the northern hemispheric extratropical tropopause for the years 2006-2014. We find that the two vastly different measurement platforms yield different aerosol backscattering, especially close to the tropopause where the influence from tropospheric aerosol is strong. The best agreement is found when the LMS is affected by volcanism, i.e., at elevated aerosol loadings. At background conditions, best agreement is obtained some distance (>2 km) above the tropopause in winter and spring, i.e., at likewise elevated aerosol loadings from subsiding aerosol-rich stratospheric air. This is to our knowledge the first time the CALIPSO lidar measurements have been compared to in-situ long-term aerosol measurements.
Highlights
Aerosol composition and optical scattering from particles in the lowermost stratosphere (LMS) have been studied by comparing in-situ aerosol samples from the IAGOS-CARIBIC passenger aircraft with vertical profiles of aerosol backscattering obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite
Hygroscopic growth, particle size distribution, and particle composition are important parameters determining the aerosol backscattering measured by CALIOP
The primary goal of this study is to evaluate the compatibility of two long-term stratospheric aerosol data sets: the lidar measurements of the CALIOP sensor aboard the CALIPSO satellite and elemental concentrations from aerosol samples together with ozone, H2O and particle size measurements collected during intercontinental flights from the IAGOS-CARIBIC observatory
Summary
Aerosol composition and optical scattering from particles in the lowermost stratosphere (LMS) have been studied by comparing in-situ aerosol samples from the IAGOS-CARIBIC passenger aircraft with vertical profiles of aerosol backscattering obtained from the CALIOP lidar aboard the CALIPSO satellite. Best agreement is obtained some distance (>2 km) above the tropopause in winter and spring, i.e., at likewise elevated aerosol loadings from subsiding aerosol-rich stratospheric air This is to our knowledge the first time the CALIPSO lidar measurements have been compared to in-situ long-term aerosol measurements. It has only recently been shown that a significant fraction of the stratospheric aerosol optical depth (AOD) is located in the LMS10–12 In both major and medium-sized eruptions, the most important aerosol related emissions from volcanoes are ash and sulphur dioxide (SO2). Stratospheric air is rich in sulphuric aerosol particle mass compared to the upper tropospheric air This leads to a concentration gradient of sulphuric aerosol in the LMS which is modulated by seasonal variation of the BD circulation and the exchange of air across the tropopause[28]. Sulphurous aerosol in the tropopause region shows this seasonal variation because during the first six months of a year the down-transported stratospheric air dominates and during the remaining six months the tropospheric air dominates[31]
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