Abstract
Some studies have discussed potential influences of Antarctic sea ice anomalies, Atlantic Multi-decadal Variability (AMV), and Interdecadal Pacific Oscillation (IPO) on the Southern Hemisphere (SH) climate, individually. However, it is not clear how different combinations of them influence the extratropical SH climate. Here we select three different combinations of strong anomalies in Antarctic sea ice (SI), AMV and/or IPO identified from observations, and investigate their influence on the winter extratropical SH climate using the Community Atmosphere Model. The model results show that atmospheric responses vary with different combinations. When both SI and AMV are in strong positive polarity (SI + AMV), the polar jet shifts equatorward while the subtropical jet shifts poleward, the amplitude of zonal wave number 1 is reduced in high-latitudes with minimal changes in wave number 2, and a north-south circulation dipole occurs in both the Atlantic and Pacific. Different from SI + AMV, when SI is in strong positive polarity and IPO is in strong negative polarity (SI-IPO), the reduction of wave number 1 is dramatically increased, accompanied by remarkably increased wave number 2. The north-south circulation dipole only occurs in the Pacific and is confined to the central and eastern Pacific, whereas the Atlantic is dominated by anomalously anticyclonic circulation. Together, SI + AMV-IPO leads to the largest reduction of wave number 1 in high-latitudes and subtropics, the strongest north-south circulation dipole in the Pacific as well as the Amundsen Sea Low. As a result, the three combinations produce different patterns of surface temperature and precipitation anomalies over Antarctica, Australia and South America.
Highlights
Most of surface area in the extra-tropics of the Southern Hemisphere (SH) is covered by the ocean
We present three different phase combinations of Antarctic sea ice, AMO, and/or Interdecadal Pacific Oscillation (IPO) on the winter extratropical Southern Hemisphere climate based on the targeted atmospheric model experiments
The key findings are as follows: 1) When both Antarctic sea ice cover and Atlantic Multi-decadal Variability (AMV) are in anomalously strong positive phases (SI + AMV), the eddydriven polar jet shifts equatorward, the subtropical jet shifts poleward, and the north-south circulation dipole pattern occurs in both the Atlantic and Pacific
Summary
Most of surface area in the extra-tropics of the Southern Hemisphere (SH) is covered by the ocean. This leads to atmospheric circulation that is more zonally symmetric compared to its counterpart in the Northern Hemisphere (Thompson and Wallace 2000; Hall and Visbeck 2002; Sen Gupta and England 2006). As the interface between the atmosphere and the ocean, variability of Antarctic sea ice can result in large changes in surface heat and moisture fluxes (Simmonds and Budd 1991), which might have profound influence on weather and climate in the SH extra-tropics (Mesquita et al, 2011). Some studies examined the impacts of decreased Antarctic sea ice on SH atmosphere and showed different results. Menéndez et al (1999) and Bader et al (2013) found an equatorward shift of the tropospheric jet stream in winter, while Kidston et al (2011) suggested that there is no significant change of the jet. England et al (2018) showed an equatorward shift of the SH atmospheric jet in winter based on the CESM whole atmosphere model simulation. Ayres and Screen (2019) suggested a weakening of the eddy-driven jet, and to a lesser extent, an equatorward shift of the jet based on the simulation of 11 models involved in the Coupled Model Intercomparison Project phase 5
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