This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Anak Krakatau, which means 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, today even relatively minor volcanic eruptions can have a major impact on air travel.
Located in the Sunda Strait between Sumatra and Java in Indonesia, Anak Krakatau started erupting on Sept. 4, leading to thousands of flights being grounded and hundreds of thousands of passengers stranded. Volcanic ash can damage aircraft engines or even cause them to stall, while also reducing pilots' visibility by scratching cockpit windows. Toxic gases, such as sulfur dioxide, can further contaminate the cabin air supply.
To mitigate these risks, a global network of nine Volcanic Ash Advisory Centers (VAAC) provides aviation advice, each responsible for a specific part of the globe. The Anak Krakatau eruption fell under the responsibility of 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. Along with the cloud profiling radar (CPR), the multispectral imager (MSI) and the broadband radiometer (BBR), ATLID is one of EarthCARE's four instruments—all of which work together to measure clouds and aerosols to deepen our understanding of how they regulate Earth's energy balance.
ATLID is a highly specialized laser instrument. It sends pulses of ultraviolet light toward Earth and measures the light that scatters back to the satellite, providing a unique view of the tops of clouds and vertical profiles of atmospheric aerosols. Not only does ATLID yield important information about the altitude and concentration of aerosols, but it can also be used with advanced algorithms to estimate aerosol types—such as ash, smoke, sulfate, sea salt and desert dust.
Robin Hogan, from the European Center for Medium-Range Weather Forecasts (ECMWF), explained, "The CPR has a very different sensitivity to atmospheric particles than ATLID: its much longer wavelength means that it is much more sensitive to large particles and much less sensitive to small particles. Normally we would expect the particles in a volcanic plume 200 km (124 miles) from the source to be too small to be detected by a radar. "However, thanks to the unprecedentedly high sensitivity of the CPR, it detects a feature extending from the surface up to around 6 km (3.7 miles) (dark brown), which is believed to correspond to larger ash aggregates that are settling out of the plume." Helen Dacre, from the University of Reading in the U.K., added, "If confirmed, this would provide useful evidence that large ash particles can remain aloft for longer, and travel farther, than is often assumed.
The observation, therefore, offers a valuable opportunity to constrain both ash sedimentation rates and long-range transport processes in volcanic ash dispersion models." While there remains speculation as to what's actually in the gray area, and this requires further study, the message to aviation authorities is simple: Do not fly aircraft here. Andy Prata of BOM said, "Together with the VAAC forecasters, we were able to verify the forecast guidance of the westward-moving plume at FL500, which is at an altitude of around 15 km (9.3 miles). ATLID was crucial to help forecasters verify the altitude of the upper-level component of the plume." Shannon Mason, also from ECMWF, said, "The separate, layered and interacting plumes of ash, clouds, gases and aerosols from volcanic eruptions are complex and evolve rapidly.
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