Volcanic impact on the climate - The stratospheric aerosol load in the period 2006-2015
2018
Abstract. We present a study on the stratospheric aerosol load during 2006–2015,
discuss the influence from volcanism and other sources, and reconstruct an
aerosol optical depth (AOD) data set in a resolution of 1 ∘
latitudinally and 8 days timewise. The purpose is to include the “entire”
stratosphere, from the tropopause to the almost particle-free altitudes of
the midstratosphere. A dynamic tropopause of 1.5 PVU was used, since it enclosed almost all
of the volcanic signals in the CALIOP data set. The data were successfully
cleaned from polar stratospheric clouds using a temperature threshold of
195 K. Furthermore, a method was developed to correct data when the CALIOP
laser beam was strongly attenuated by volcanic aerosol, preventing a negative
bias in the AOD data set. Tropospheric influence, likely from upwelling dust,
was found in the extratropical transition layer in spring. Eruptions of both
extratropical and tropical volcanoes that injected aerosol into the
stratosphere impacted the stratospheric aerosol load for up to a year if
their clouds reached lower than 20 km altitude. Deeper-reaching tropical
injections rose in the tropical pipe and impacted it for several years. Our
AODs mostly compare well to other long-term studies of the stratospheric AOD.
Over the years 2006–2015, volcanic eruptions increased the stratospheric AOD
on average by ∼40 %. In absolute numbers the stratospheric AOD and
radiative forcing amounted to 0.008 and −0.2 W m −2 , respectively.
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