EarthCARE’s view of volcanic plume boosts air safety

Anak Krakatau erupted a few weeks before this report, and ESA's EarthCARE satellite captured vertical profiles of different constituents in the volcanic plume. Although EarthCARE was designed primarily to advance understanding of how clouds and aerosols influence Earth's climate, it also provided valuable information to support safe air travel, and the observations offer new insights into volcanic eruptions' impact on the climate system. Anak Krakatau, meaning "Child of Krakatoa," has been active sporadically since it emerged from the sea at the beginning of the last century in the caldera formed after the 1883 eruption of Mount Krakatoa.

While Anak Krakatau did not explode with the terrifying power of Krakatoa, which caused a devastating tsunami, even relatively minor volcanic eruptions today can have a major impact on air travel. Located in the Sunda Strait between Sumatra and Java in Indonesia, Anak Krakatau started erupting on 4 September, leading to thousands of flights being grounded and hundreds of thousands of passengers stranded. Volcanic ash can damage or cause aircraft engines to stall and reduce pilots' visibility by scratching cockpit windows, while toxic gases such as sulphur dioxide can contaminate the cabin air supply.

To mitigate these risks, a global network of nine Volcanic Ash Advisory Centres (VAACs) provides aviation advice, each responsible for a specific part of the globe. The Anak Krakatau eruption came under the Darwin VAAC, operated by the Australian Bureau of Meteorology (BOM), which was quick to add EarthCARE's unique atmospheric lidar (ATLID) data to its suite of satellite monitoring tools. ATLID is one of EarthCARE's four instruments, along with the cloud profiling radar (CPR), multispectral imager (MSI), and broadband radiometer (BBR), all used in synergy to measure clouds and aerosols and deepen understanding of how they regulate Earth's energy balance.

ATLID sends pulses of ultraviolet light toward Earth and measures the light that scatters back to the satellite, providing a unique view of cloud tops and vertical profiles of atmospheric aerosols. It not only yields information about aerosol altitude and concentration but can also be used with advanced algorithms to estimate aerosol types such as ash, smoke, sulphate, sea salt, and desert dust. An accompanying image uses a Copernicus Sentinel-3 capture from 5 September overlaid with data from EarthCARE's MSI, ATLID, and CPR instruments, and notes aircraft flight levels: most aircraft cruise around FL350, or 35,000 ft (about 10,700 m). EarthCARE distinguishes volcanic aerosols, with the MSI swath showing the volcanic plume in false colour and purple areas highlighting ash.