1129 / 2019-07-29 17:03:54

Projected Uncertainties in the Northern Winter Climate: Role of Interhemispheric Sea Surface Temperature Gradient and Arctic Sea Ice Cover

9、大气科学与全球变化 > 专题2：数值模式与模拟

This study attempts to better understand the inter-model differences in the projected northern winter future climate based on the forced response in the CMIP5 RCP8.5 scenario. Inter-model empirical orthogonal function (EOF) analysis reveals that the dominant uncertainties in the projections of sea level pressure (SLP) are in the eastern-to-southeastern flank of both the Aleutian low and the Icelandic low; these are captured by the EOFΔSLP mode. These uncertainties in SLP are linearly related to a sea surface temperature (SST) pattern that represents the interhemispheric SST gradient while the related sea ice cover (SIC) pattern represents the total Arctic sea ice extent. Corresponding monthly-varying SST and SIC patterns are perturbed in two atmospheric-only general circulation models (AGCMs) in order to assess the contributions of these perturbation patterns in driving the projected uncertainties in SLP.

The atmospheric response to the SST and SIC perturbations has a zonal wavenumber-2 pattern with a dipole-like SLP response over the North Atlantic resembling the North Atlantic Oscillation (NAO). A Rossby wavetrain driven by the SST perturbation, through accompanying convection anomalies over the tropical central-eastern Pacific, explains well the atmospheric response in the North Pacific. Downstream of the Pacific, the SST-driven Rossby wavetrain is modulated by the SIC perturbation, suggesting that the SST and SIC perturbations jointly explain the SLP response in North America and the NAO-like pressure response. These results highlight the primary role of the interhemispheric SST gradient and the secondary role of the Arctic SIC in the projected uncertainties in the Northern Hemisphere SLP.