Record-breaking aerosol levels explained by smoke injection into the stratosphere

The early months of 2020 showed record-breaking levels of aerosol optical depth (AOD) over the Southern Hemisphere (SH). Apart from the tropics, monthly AOD values over most of the SH exceeded the average by more than three standard deviations. This anomalous AOD is attributed to a combination of the intensity and location of the Australian bushfires. The fires took place south enough, where the tropopause altitude is relatively low, within the mid-latitude cyclone belt. This location allowed for deep convection over and downwind of the fires, which transported the smoke to the stratosphere, where its lifetime is an order of magnitude longer than it would have been in the lower atmosphere. The lower bound of the stratospheric smoke mass in January 2020 was similar to 2.1 +/- 1 teragrams, which lead to cooling by more than 1.0 +/- 0.6 watts per square meter over cloud-free oceanic areas.

Automated summary

The early months of 2020 saw record-breaking levels of aerosol optical depth (AOD) over the Southern Hemisphere, mainly due to the intensity and location of the Australian bushfires. The fires taking place in a region with relatively low tropopause altitude contributed to deep convection and transported smoke to the stratosphere, resulting in cooling over cloud-free oceanic areas.