The Arctic Oscillation in the mid-Holocene and Last Glacial Maximum:A comparison between PMIP2 models

The Arctic Oscillation in the mid-Holocene and Last Glacial Maximum:

A comparison between PMIP2 models

Jun Mei Lü1,2, Seong-Joong Kim2

1 Chinese Academy of Meteorological Sciences, Beijing 100081, China

2 Korea Polar Research Institute, KORDI, Incheon, 406-840, Korea

Abstract

The changes in the Arctic Oscillation (AO) for the mid-Holocene (MH) and the Last Glacial Maximum (LGM) compared to the pre-industrial (PI) simulation are studied using 5 coupled ocean-atmosphere models (i.e. CCSM, ECHAM5-MPIOM1, IPSL, MIROC3.2, and UBRIS-HadCM3M2) from the second phase of Paleoclimate Modeling Intercomparison Project (PMIP2). In the MH, the amplitude of the simulated AO is a little smaller than the PI for all models. The vertical structures of the zonal-mean zonal wind, geopotential height, and temperature in association with the AO are similar to that in the PI, while the polar westerlies are slightly weakened and displaced downward to the lower stratosphere accompanied with the weakening of the polar vortex and the warming of cold polar cap region. In the LGM, the amplitude of the AO decreases more than the MH with an evident smaller standard deviation of the AO index. Accordingly, the strength of the polar vortex and westerlies weakens further with the center of westerlies displaced into mid-latitudes upper troposphere. Meantime, the polar cap region becomes slightly warm in the stratosphere, while it remains cold in the troposphere. The colder climate regimes in the MH and LGM winter appear to be unfavorable for the intensification of the AO.