Stormier Southern Hemisphere induced by topography and ocean circulation

Area of Science:

• Climatology
• Atmospheric Science
• Oceanography

Background:

• Earth's climate exhibits a notable storminess asymmetry, with the Southern Hemisphere being significantly stormier than the Northern Hemisphere.
• This asymmetry is characterized by a stronger jet stream and more frequent extreme weather events in the Southern Hemisphere.
• Understanding the drivers of this hemispheric difference is crucial for interpreting climate change projections.

Purpose of the Study:

• To investigate the relative contributions of topography, radiative processes, and ocean circulation to the Southern Hemisphere's increased storminess.
• To quantify the impact of land-ocean contrast on hemispheric storminess asymmetry.
• To interpret recent storminess trends using an energetic perspective and assess their consistency with climate model projections.

Main Methods:

• Diagnostic energetic analyses were performed on observational data and climate model simulations.
• Climate model simulations were conducted with modified surface boundary conditions, including flattened topography and hemispherically symmetric surface energy fluxes.
• An energetic perspective was used to analyze storminess trends since the satellite era.

Main Results:

• Topography and ocean circulation contribute nearly equally to the stormier Southern Hemisphere.
• Flattening topography in a climate model reduced storminess asymmetry by 23% to 12%.
• Prescribing symmetric surface energy fluxes reduced storminess asymmetry by 11%, highlighting the role of ocean energy transport.

Conclusions:

• The stormier Southern Hemisphere is primarily driven by topography and ocean circulation's energy transport.
• The Southern Hemisphere has become stormier, consistent with changes in Southern Ocean energy transport.
• Northern Hemisphere storminess has remained stable due to opposing oceanic and radiative influences, aligning with climate model projections.