Connecting Antarctica to the Tropics: Understanding and Predicting Subseasonal Bridges to the Southern Hemisphere Atmosphere and Cryosphere

Tropical convection has many implications for the mid- and high-latitude atmosphere, exciting Rossby and Kelvin waves that propagate poleward thus modulating both frequency and extremity of a number of important weather processes. One of the leading modes of variability of the tropical atmosphere, and indeed the leading mode on the subseasonal (30-60 day) time scale, is the Madden-Julian Oscillation (MJO). Rossby wave trains excited by MJO convection have been identified as a key “bridge” in the atmospheric system, linking the extratropics with the tropics spatially, and weather and climate temporally. However, our understanding of connections between intraseasonal tropical variability and the Southern Hemisphere atmosphere lags that of the Northern Hemisphere, despite several studies that highlight the important role of the MJO in the Southern Hemisphere. This study seeks to fill this gap by investigating the physical mechanisms that support modulation of the Antarctic cryosphere via forcing from the tropics, focusing on the intraseasonal timescale.

To establish and analyze those links, two publicly available datasets were examined: first, hourly anomalies of the atmospheric state of circulation, temperature, and pressure (in the lower and upper troposphere, and at the surface) from the just-released ERA5 reanalysis were composted by phase of the active MJO. The MJO state was determined using the daily revised Real-time Multivariate MJO (RMM-r) index. Second, anomalies of daily change in sea ice concentration were also composited by MJO phase. Preliminary results suggest that the mid- and high-latitude atmospheric circulation is different when MJO convection is centered in the Indian Ocean versus when it is centered in the western Pacific Ocean. Furthermore, preliminary results suggest regional differences in sea ice variability surrounding Antarctica, depending on the geographic location of the MJO convection. Physical mechanisms responsible for those differences will be explored in more depth in the presentation.