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Climate Change


It is crucial to monitor and understand regional sea-level changes that can differ from Global Mean Sea Level (GMSL) both in terms of magnitude as well as governing forcing and mechanisms (Stammer et al., 2013). For instance, while changes in salinity can have significant distinct impact on regional sea level change, such as in the Arctic Ocean, it has minor effect on GMSL. Quantifying the natural variability in the regional sea level change is also urgent in order to distinguish it from a potentially forced (anthropogenic) signal. Furthermore, the role of remote impact of climate variability in one region on the other needs to be well-understood. Climate change in the Pacific can, for instance, impact Arctic warming and the sea ice (Li et al., 2015; Svendsen et al., 2018; Yang et al., 2020). How this translates to sea level change remains unclear. The aim of this study is to examine and relate the sea level variability of the Beaufort Gyre (BG) in the Arctic Ocean to natural climate variability of the Pacific Ocean. The sea level variability of the Beaufort Gyre (BG) is influenced by the changes in steric height and ocean mass. Hence the freshwater and heat stored in the BG can have significant impact on the sea surface height. The anticyclonic circulation of BG is driven by a semi-permanent atmospheric circulation pattern, the Beaufort High (BH). The resulting Ekman convergence associated with BH advects and stores freshwater and sea-ice in the Beaufort Sea and can contribute to halosteric changes in sea-level. Since the altimetry era the sea-level in the Beaufort Sea basin has increased much faster than the average rate of increase in the Arctic Ocean sea-level (Zhang et al., 2016). Although many studies (e.g., Armitage et al., 2016, 2017; Zhang et al., 2016) have investigated this there are still many unanswered questions. The project objectives are to: (i) assess the role of variability of atmospheric modes in the Pacific Ocean and the Arctic Ocean on the BH and on the sea level variability of the region; (ii) advance the current understanding of the different mechanisms influencing the sea-level variability in the BG; (iii) validate climate models using observations and assess the sea level change with respect to natural versus anthropogenic origin; A suite of satellite data, ocean (TOPAZ, GREP) and atmospheric reanalysis data (ERA-I, ERA-5) together with climate model outputs (CMIP5, CMIP6) will be used to address these objectives. Methodologies include: Spatio-temporal analysis of observed sea level in conjunction with atmospheric forcing; EOF and composite analysis of regional atmospheric data to capture seasonal to decadal changes in the dominant atmospheric forcing; statistical analysis (e.g., correlation analysis) of monthly ocean model data and satellite data to understand the changes in the sea ice and halo steric and thermosteric variability; use of monthly climate model output (CMIP5 models and CMIP6) from control as well as historical simulations to assess whether the observed changes can be attributed to natural variability (in a first step by using a moving window analysis to detect the observed pattern in the simulations). Outcomes include: Advanced understanding of the mechanisms governing observed sea-level variability in the BG; The role of teleconnection between Pacific and the Arctic sea level; An assessment of the observed variability reproduced by CMIP5 (and eventually CMIP6) models, setting the stage for computing model weights by developing a performance metric and eventually decrease uncertainty in projections of sea level in the considered regions. Deliverables: Technical report; 3 publications in high impact journals; training of young scientists. Funding Sources: Bjerknes Center for Climate Research, Norway and internal funding from NERSC. Support from Chinese resources. Possible future funding from RCN, ESA, and Horizon Europe projects.


PI Europe
Prof.. Johnny Andre Johannessen, Nansen Environmental and Remote Sensing Center, NORWAY
PI China
Prof.. Jianqi Sun, Institute of Atmospheric Physics, CHINA