Decadal Variation of the Aleutian Low-Icelandic Low Seesaw Simulated by a Climate System Model(CAS-ESM-C)

Based on a simulation using a newly developed climate system model(Chinese Academy of Sciences-Earth System Model-Climate system component, CAS-ESM-C), the author investigated the Aleutian Low- Icelandic Low Seesaw(AIS) and its decadal variation. Results showed that the CAS-ESM-C can reasonably reproduce not only the spatial distribution of the climatology of sea level pressure(SLP) in winter, but also the AIS and its decadal variation. The period 496–535 of the integration by this model was divided into two sub-periods: 496–515(P1) and 516–535(P2) to further investigate the decadal weakening of the AIS. It was shown that this decadal variation of the AIS is mainly due to the phase transition of the Pacific Decadal Oscillation(PDO), from its positive phase to its negative phase. This transition of the PDO causes the sea surface temperature(SST) in the equatorial eastern(northern) Pacific to cool(warm), resulting in the decadal weakening of mid-latitude westerlies over the North Pacific and North Atlantic. This may be responsible for the weakening of the inverse relation between the Aleutian Low(AL) and the Icelandic Low(IL).

Modulation of the Aleutian–Icelandic Low Seesaw and Its Surface Impacts by the Atlantic Multidecadal Oscillation

Early studies suggested that the Aleutian–Icelandic low seesaw(AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation(AMO) during late winter(February–March) is explored with observational data. It is shown that, in the cold phase of the AMO(AMO|-),a clear AIS is established, while this is not the case in the warm phase of the AMO(AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low(AL). For example, the weak AL in AMO|-displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe,but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+.The mechanism underlying the influence of AMO|-on the AIS can be described as follows: AMO|-weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.

Relationship between Arctic Oscillation and Pacific Decadal Oscillation on decadal timescale

The relationship between the Pacific Decadal Oscillation (PDO) and the Arctic Oscillation (AO) on decadal timescale in the extended winter (November-March) is investigated in this study. The results indicate that AO plays an important role in the low frequency variability of PDO. When AO leads PDO by 7-8 years, the lagging correlation between them becomes the strongest with correlation coeffi- cient 0.77. The leading decadal variability of AO pro- vides a valuably precursory signal for predicting the variability of PDO. The results of regression and lag- ging correlation reveal the possible mechanism for the AO-PDO coupling: A strong AO would lead to an enhanced Aleutian Low that is linked to PDO by ocean-atmosphere interaction in the North Pacific, and vice versa.

北半球冬季阿留申低压-冰岛低压相关关系的年代际变化及其模拟

使用多种长期观测和再分析资料，分析了北半球冬季阿留申低压和冰岛低压相关关系的年代际变化。结果表明，两低压存在显著的负相关关系，使北太平洋和北大西洋海平面气压形成跷跷板式的变化（Aleutian Low-Icelandic Low Seesaw, AIS）。此外，AIS还存在显著的年代际变化，在1935～1949年和1980年后较为显著，其余时期并不显著。对1980年代的年代际转变分析表明，太平洋年代际振荡（Pacific Decadal Oscillation，PDO）在1970年代末的位相转变是AIS这次年代际转变的主要原因。PDO由负位相转变为正位相，使全球大部分大洋海表温度升高，而北太平洋海表温度降低，两低压显著变深，低压南部西风增强，从而通过 Rossby 波的频散效应使两低压强度形成显著负相关。1930年代中期的年代际转变与此类似，但强度较弱。同时，年代际背景的变化也影响到两低压的年际变化。在给定海表温度和海冰分布的驱动下，大气环流模式IAP AGCM4能基本模拟出AIS年代际转变的过程和机理，但仍存在一些偏差。

冬季白令海海冰范围变化及其对大气响应机制研究

白令海是冬季北极海冰变化最明显的区域之一,该区域海冰的季节和长期变化与局地的气候、水文环境和生态系统密切相关,并会影响我国的天气气候过程。为了识别该区冬季海冰的长期变化,基于Hadley中心数据,采用滑动t检验和线性回归分析方法对白令海1960–2020年海冰范围的变化趋势及其空间差异进行分析,并分析了海冰变化对大气环流等大气强迫的影响。结果表明:白令海冬季海冰范围在1960–2020年显著减小,20世纪70年代和2000年前后白令海海冰范围存在显著的均值突变。其过程中伴随着阿留申低压中心低压加强、核心位置向白令海西部偏移以及对应风场分布的变化,这个过程存在一个近20 a周期的振荡。同时,太平洋年代际震荡的相位变化可以通过改变海平面气压来调节经向风,改变进入白令海的热平流,进而影响白令海冬季海冰范围。因此,阿留申低压系统和北太平洋年代际振荡对冬季白令海海冰的变化起到重要的调节作用。