Rainfall Patterns in the Tropics and Climatic Developments in Antarctica are Linked in Several Ways

Our globe is warming as a result of manmade greenhouse gas emissions, although the rate of warming varies by place and season. Scientists have seen a continuous austral summer cooling on the eastern side of Antarctica for the past four decades. Because it is not far from one of the well-known global warming hotspots, the Antarctic Peninsula, this perplexing feature has attracted worldwide interest.

The worldwide average annual precipitation over land is 715 mm (28.1 in), but it is significantly higher, at 990 mm, throughout the whole Earth (39 in). Average annual rainfall is used in climate classification systems like the Köppen classification system to assist distinguish between various climatic regimes. Rain gauges are used to measure rainfall. Weather radar can estimate rainfall quantities.

A team of scientists from the IBS Center for Climate Physics at Pusan National University in South Korea, Nanjing University of Information Science and Technology, NOAA Geophysical Fluid Dynamics Laboratory, University Corporation for Atmospheric Research, Ewha Womans University, and National Taiwan University published a new study in the journal Science Advances that uncovered a new mechanism that can explain the regional warming/cooling patchwork over Antarctica.

Our analysis provides clear evidence that tropical weather systems associated with the Madden-Julian Oscillation can directly impact surface temperatures over East Antarctica.

Prof. Pang-Chi Hsu

The Transantarctic Mountains separate East Antarctica from West Antarctica, which covers an area of around 10,200,000 square kilometers. This massive mountain range stretches from the Ross Ice Shelf’s eastern edge to the Ronne-Filchner Ice Shelf’s western edge.

View of East Antarctic

Clusters of rainfall events in the western tropical Pacific are at the center of the process, releasing vast quantities of heat into the atmosphere by condensation of water vapor. Warm air rises and falls further away from the ordered rainfall clusters. Winds are created by this pressure differential, which are further impacted by the earth’s rotation.

Raindrops collide at their terminal velocity, which is higher for bigger drops since their mass to drag ratio is higher. 0.5 mm (0.020 in) drizzle falls at 2 m/s (6.6 ft/s) or 7.2 km/h (4.5 mph) at sea level in the absence of wind, whereas massive 5 mm (0.20 in) drops fall at roughly 9 m/s (30 ft/s) or 32 km/h (20 mph).

The interaction of these elements produces a large-scale air pressure wave that moves from west to east down the equator at a speed of several hundred kilometers per day, dragging the initial rainfall clusters behind it. The Madden-Julian Oscillation (MJO) is a propagating atmospheric wave named after Roland Madden and Paul Julian, who discovered the phenomena in 1971.

The typical atmospheric pressure, convection, and wind anomalies, which change on 20-70-day timeframes, can stretch into the extratropics, even reaching Antarctica. By evaluating observational records and carefully constructed supercomputer climate model simulations, the worldwide study team came to their results.

“Our analysis provides clear evidence that tropical weather systems associated with the Madden-Julian Oscillation can directly impact surface temperatures over East Antarctica.” says Prof. Pang-Chi Hsu from Nanjing University of Information Science and Technology, who co-led the study.

More particular, as MJO rainfall clusters migrate westward towards the Solomon Islands, the associated global atmospheric wave tends to chill East Antarctica three to eleven days later (Image, right panel). When MJO-related rainfall occurs in the Indian Ocean, however, East Antarctica warms significantly (Image, left panel).

“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,” says Prof. June-Yi Lee from the IBS Center for Climate Physics and Pusan National University, and co-leader of the study.

According to the researchers, long-term changes in the nature and longitudinal core position of the MJO can account for up to 20% to 40% of the observed summer cooling trend in East Antarctica from 1979 to 2014. Other reasons include the ozone hole and the Interdecadal Pacific Oscillation, a weaker version of the El Nio-Southern Oscillation that varies slowly.

Climate change can be connected to activities that take place approximately 10,000 kilometers distant, according to a recent study published in Science Advances.