PNNL

The polar regions are central to many climate-related processes, showing signs of climate change first. Researchers need to understand the underlying natural behavior and cycles that affect the Arctic and Antarctic to model the global climate more accurately. A recent study found a previously unrecognized periodicity to atmospheric pressure around the Antarctic.

The 150-day pattern is in the Southern Annular Mode (SAM), a north-south movement in the midlatitudes also known as the Antarctic Oscillation. The SAM is important to the climate of the Southern Hemisphere, including Australia, New Zealand, and Antarctica. Researchers across the globe have studied the SAM for decades. Previous research suggested that the changes and dynamics within the SAM had no pattern, happening chaotically on short timescales.

New research done by Earth scientists combines observational data, model data, and theory to identify a 150-day periodicity in the movement of air associated with the SAM. The team derived new equations to represent the turbulent flow of the SAM. Upon careful examination, they saw that the equations predicted a possible natural periodicity.

“We really weren’t sure what we would find,” said Sandro Lubis, an Earth scientist at Pacific Northwest National Laboratory. “Given how much research had been done showing a lack of periodicity, we were skeptical. But when we went into the observational data, there it was.”

Previously, studies focused on changes in the SAM at shorter time scales. These north-south shifts generally last for a couple of weeks, but the timing and duration for these oscillations are random. The newly identified, longer-scale periodicity arises from the internal dynamics of the atmosphere.

The 150-day oscillation affects precipitation and the near-surface ocean winds across the Southern Hemisphere, likely playing a role in the broader climate. However, many state-of-the-art climate models cannot reproduce this oscillation accurately; this potentially explains the reported problems in modeling the SAM. Next steps include finding ways to incorporate this periodicity into state-of-the-science climate models.

This work was done by Lubis and Pedram Hassanzadeh of Rice University and is the subject of an Eos Editor's Highlight. The research was performed at Rice University and supported by the Office of Naval Research, the National Science Foundation, and the Department of Energy. Computational resources were provided by the Extreme Science and Engineering Discovery Environment, the National Center for Atmospheric Research, and the Rice University Center for Research Computing.