Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport

Indirect Injection Aerosols in the stratosphere, especially submicron-hydrated sulfuric acid droplets, are an important factor influencing climate variability. Stratospheric sulfate aerosols can form from sulfur dioxide that has been transported from the underlying troposphere. Large volcanic eruptions can inject sulfur dioxide and other material into the stratosphere, but smaller volcanoes have been thought not to be energetic enough to do so. Bourassa et al. (p. 78) used satellite data to show that sulfur dioxide from the 2011 eruption of the Nabro stratovolcano in Eritrea was lofted into the stratosphere by deep convection associated with the Asian summer monsoon. Even moderate volcanic eruptions can inject sulfur dioxide into the stratosphere with the help of the Asian monsoon. The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO2) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO2 was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.

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