Major Modes of Short-Term Climate Variability in the Newly Developed NUIST Earth System Model(NESM)

A coupled earth system model（ESM） has been developed at the Nanjing University of Information Science and Technology（NUIST） by using version 5.3 of the European Centre Hamburg Model（ECHAM）, version 3.4 of the Nucleus for European Modelling of the Ocean（NEMO）, and version 4.1 of the Los Alamos sea ice model（CICE）. The model is referred to as NUIST ESM1（NESM1）. Comprehensive and quantitative metrics are used to assess the model＇s major modes of climate variability most relevant to subseasonal-to-interannual climate prediction. The model＇s assessment is placed in a multi-model framework. The model yields a realistic annual mean and annual cycle of equatorial SST, and a reasonably realistic precipitation climatology, but has difficulty in capturing the spring–fall asymmetry and monsoon precipitation domains. The ENSO mode is reproduced well with respect to its spatial structure, power spectrum, phase locking to the annual cycle, and spatial structures of the central Pacific（CP）-ENSO and eastern Pacific（EP）-ENSO; however, the equatorial SST variability,biennial component of ENSO, and the amplitude of CP-ENSO are overestimated. The model captures realistic intraseasonal variability patterns, the vertical-zonal structures of the first two leading predictable modes of Madden–Julian Oscillation（MJO）, and its eastward propagation; but the simulated MJO speed is significantly slower than observed. Compared with the T42 version, the high resolution version（T159） demonstrates improved simulation with respect to the climatology, interannual variance, monsoon–ENSO lead–lag correlation, spatial structures of the leading mode of the Asian–Australian monsoon rainfall variability, and the eastward propagation of the MJO.

南大洋增暖及其气候影响

过去几十年南大洋在南极平流层臭氧消耗和大气二氧化碳浓度增加的共同作用下大幅增暖,显著影响着南极冰架和冰盖的融化、海平面上升、南北半球的降水分配以及热带海洋和大气环流等,引发了深远的气候效应.全球变暖背景下南大洋西风表现为极向加强,同时进入南大洋的热辐射和淡水通量持续增加,由此上翻的海水可吸收更多的热量和碳,经由更强的平均流向北输送,更多地在45°S附近海域下沉并存储.当前对南大洋增暖背后诸多复杂的物理过程仍缺乏足够的理解,比如来自冰架、冰盖及海洋涡旋的作用、热带-极地相互作用、南大洋本身对全球变暖的响应等,尤其是有限的观测数据和较低分辨率的模式无法准确呈现快速变化的物理现象和机理.因此,南大洋的未来增暖存在很大的不确定性且可能长期持续,但近期的进展为深入认知南大洋增暖及其气候影响奠定了坚实的基础.

Zonal mean and shift modes of historical climate response to evolving aerosol distribution

Anthropogenic aerosols are effective radiative forcing agents that perturb the Earth’s climate. Major emission sources shifted from the western to eastern hemisphere around the 1980 s. An ensemble of single-forcing simulations with an Earth System Model reveals two stages of aerosol-induced climate change in response to the global aerosol increase for 1940–1980 and the zonal shift of aerosol forcing for 1980–2020, respectively. Here, using idealized experiments with hierarchical models, we show that the aerosol increase and shift modes of aerosol-forced climate change are dynamically distinct, governed by the inter-hemispheric energy transport and basin-wide ocean–atmosphere interactions, respectively.The aerosol increase mode dominates in the motionless slab ocean model but is damped by ocean dynamics. Free of zonal-mean energy perturbation, characterized by an anomalous North Atlantic warming and North Pacific cooling, the zonal shift mode is amplified by interactive ocean dynamics through Bjerknes feedback. Both modes contribute to a La Ni?a-like pattern over the equatorial Pacific. We suggest that a global perspective that accommodates the evolving geographical distribution of aerosol emissions is vital for understanding the aerosol-forced historical climate change.