Aractic and Antarctic Climate Variability in the Last Glacial Maximum

Abstract

In the Arctic and Antarctic, the main climate drivers are the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO), respectively. When the AO is in positive phase, the subarctic regions especially Eurasia and western North America are warmer than normal and vice versa, while the AAO is in positive phase, the southern hemisphere (SH) polar vortex and circumpolar westerly tend to be stronger, sea ice production increases, and Antarctica becomes colder but the Antarctic Peninsula warmer. In recent decades, both the AO and AAO have been in an increasing trend. The increasing AO mode is believed to impact the recent Arctic warming, while the positive AAO mode is associated with the slight East Antarctic cooling and the warming in the Antarctic Peninsula. In order to examine the change in the AO and AAO under the cold climate background, we analyzed the change in these two modes for the Last Glacial Maximum (LGM) compared to the pre-industrial (PI) simulation using coupled ocean-atmosphere models (i.e. CCSM, FGOALS, IPSL, MIROC3.2, and UBRIS-HadCM3M2) from the second phase of Paleoclimate Modeling Intercomparison Project (PMIP 2). In the LGM, the amplitude of the simulated AO decreases in all models, weakening the polar vortex and westerly winds with its center displaced into mid-latitudes . For the case of the AAO, its amplitude appears to be smaller than the PI with a small decrease in the standard deviation of the AAO in HadCM3M2, IPSL, FGOALS, but in CCSM and MIROC the AAO amplitude is slightly larger in the LGM. The overall weaker AAO in the LGM is consistent with the weaker SH polar vortex and westerly winds found in some proxy records. This result implies that under global warming the polar vortex and westerly winds will be stronger in both hemispheres.