Anthropogenic greenhouse gas emissions are warming the planet, but this warming varies from one region to another and also in different seasons.
Scientists have observed a continuous austral summer cooling on the eastern side of Antarctica in the last four decades. This enigmatic feature has received global attention, as it is not far away from a familiar global warming hotspot — the Antarctica Peninsula.
A new study, published in the Science Advances journal, has revealed a new mechanism that can shed light on the regional warming and cooling patchwork across Antarctica.
The study was performed by researchers from the IBS Center for Climate Physics at Pusan National University based in South Korea, Nanjing University of Information Science and Technology, NOAA Geophysical Fluid Dynamics Laboratory, University Corporation for Atmospheric Research, Ewha Woman's University, and National Taiwan University.
At the core of the mechanism are clusters of rainfall events that occurred in the western tropical Pacific. These events emit large amounts of heat into the air by condensation of water vapor, causing warm air to rise over the organized clusters of rainfall and sink further away. The resulting pressure difference generates winds that are additionally influenced by the impact of Earth’s rotation. The interplay of these factors creates a large-scale atmospheric pressure wave that travels from the west to east direction along the equator at a velocity of hundreds of kilometers per day, dragging along with it the initial clusters of rainfall.
This atmospheric wave propagation is called the Madden-Julian Oscillation (MJO), dubbed after Roland Madden and Paul Julian, who identified this phenomenon in 1971. The typical atmospheric pressure, wind and convection anomalies, which change on timescales of 20 to 70 days, can extend into the extratropics and even reach Antarctica.
The global research team reached their conclusions after assessing observational datasets and uniquely developed supercomputer climate model simulations.
Our analysis provides clear evidence that tropical weather systems associated with the Madden-Julian Oscillation can directly impact surface temperatures over East Antarctica.
Pang-Chi Hsu, Study Co-Lead and Professor, Nanjing University of Information Science and Technology
In particular, as the clusters of MJO rainfall travel into the western Pacific toward the site of the Solomon Islands, the accompanying global atmospheric wave tends to cool East Antarctica 3 to 11 days later, as shown in the right panel of the above image. On the other hand, when the MJO-related rainfall takes place in the Indian Ocean, pronounced warming is seen in East Antarctic, as illustrated in the left panel of the above image.
During recent decades, MJO rainfall and pressure changes preferably occurred over the western tropical Pacific but decreased over the Indian Ocean. This situation has favored cooling of East Antarctica during austral summer.
June-Yi Lee, Study Co-Leader and Professor, IBS Center for Climate Physics, Pusan National University
The researchers estimated that around 20% to 40% of the observed summer cooling trend in East Antarctica between 1979 and 2014 can be linked to the long-term changes in the longitudinal core location and character of the MJO. Other factors, such as the ozone hole and the Interdecadal Pacific Oscillation — a gradually changing weaker companion of the El Nino-Southern Oscillation — also contributed to these changing trends.
The study further emphasized that climate change in remote areas, including Antarctica, can be associated with the processes occurring almost 10,000 km away.
Hsu, P-.C., et al. (2021) East Antarctic cooling induced by decadal changes in Madden-Julian oscillation during austral summer, Science Advances. doi.10.1126/sciadv.abf9903.