Abstract
Abstract. The article presents new high-quality continuous stratospheric aerosol observations spanning 1994–2015 at the French Observatoire de Haute-Provence (OHP, 44° N, 6° E) obtained by two independent, regularly maintained lidar systems operating within the Network for Detection of Atmospheric Composition Change (NDACC). Lidar series are compared with global-coverage observations by Stratospheric Aerosol and Gas Experiment (SAGE II), Global Ozone Monitoring by Occultation of Stars (GOMOS), Optical Spectrograph and InfraRed Imaging System (OSIRIS), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and Ozone Mapping Profiling Suite (OMPS) satellite instruments, altogether covering the time span of OHP lidar measurements. Local OHP and zonal-mean satellite series of stratospheric aerosol optical depth are in excellent agreement, allowing for accurate characterization of stratospheric aerosol evolution and variability at northern midlatitudes during the last 2 decades. The combination of local and global observations is used for a careful separation between volcanically perturbed and quiescent periods. While the volcanic signatures dominate the stratospheric aerosol record, the background aerosol abundance is found to be modulated remotely by the poleward transport of convectively cleansed air from the deep tropics and aerosol-laden air from the Asian monsoon region. The annual cycle of background aerosol at midlatitudes, featuring a minimum during late spring and a maximum during late summer, correlates with that of water vapor from the Aura Microwave Limb Sounder (MLS). Observations covering two volcanically quiescent periods over the last 2 decades provide an indication of a growth in the nonvolcanic component of stratospheric aerosol. A statistically significant factor of 2 increase in nonvolcanic aerosol since 1998, seasonally restricted to late summer and fall, is associated with the influence of the Asian monsoon and growing pollution therein.
Highlights
The role of the stratospheric aerosol burden in climate variability and ozone chemistry is well recognized
This may be due to zonal averaging for Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which incorporates the mid-Asian part of Asian monsoon, where Asian Tropopause Aerosol Layer (ATAL) is better developed in August (Fig. 2 in Vernier et al, 2015)
Over the last 2 decades the Northern Hemisphere (NH) stratosphere was perturbed by a series of minor volcanic eruptions, leaving strong but transient signals in the stratospheric aerosol load
Summary
The role of the stratospheric aerosol burden in climate variability and ozone chemistry is well recognized. Several further studies (Hoffmann et al, 2009; Vernier et al, 2011a; Trickl et al, 2013) reported an increase in stratospheric aerosol levels since 2002, but the source of this increase has been debated This increase was attributed by Hoffmann et al (2009) to a rapid rise in Asian sulfur emissions, uplifted by deep convection within the Asian monsoon. It is widely accepted that volcanic eruptions largely determine the observed variability in the stratospheric aerosol load (Kremser et al, 2016). In an effort to better characterize the evolution of the stratospheric aerosol load and its variability at northern midlatitudes during the post-Pinatubo era we utilize a continuous 22-year observation record from the Observatoire de Haute-Provence and a variety of satellite data sets.
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