Arctic cyclones, the Atlantic Meridional Overturning Circulation (AMOC), and the Atlantic Multidecadal Oscillation (AMO) represent major circulation systems and variability mode in the atmosphere and ocean, respectively. Intense cyclones often drive occurrence of extreme events in winds, temperature, precipitation, and sea ice/ice sheet melt, which can significantly influence ocean stratification, mixing, and currents. In particular, one of the major cyclone tracks extends from the northern North Atlantic Ocean to the Nordic Seas, where ocean deep convection acts to drive the AMOC. The AMOC plays an essential role in global energy and water cycle, providing heat source for the northern high latitudes and the Arctic. AMOC-driven heat transport is found coincident with AMO variability. Both the AMOC and the AMO modulate North Atlantic-Nordic Seas temperature distribution to shape large-scale thermodynamic environment, influencing the overlying atmosphere. However, the coupling between Arctic cyclones, the AMOC, and the AMO are not understood, in particular in the Nordic Seas which is suggested by new observations to play dominant roles in the AMOC. Coupled Model Intercomparison Project (CMIP) models have also shown large biases and uncertainties in simulating Arctic cyclones, the AMOC, and the AMO. The objective of this project is therefore to use DOE’s modeling infrastructure to improve understanding of theses coupling processes and feedbacks. 

To achieve the objectives, we hypothesize that enhanced poleward heat transport by the AMOC and warm phase of the AMO intensify cyclones and shift cyclone tracks northward, which increase ocean heat loss and, in turn, strengthen the AMOC and support the warm phase of the AMO, leading to a positive feedback. At the same time, intensified cyclones thermodynamically increase or decrease ocean surface energy budgets and sea ice/Greenland ice sheet melt depending on season, which then impacts the rate of ocean heat loss and AMOC strength, resulting in positive or negative feedback. To test the hypotheses, we will utilize the newly developed hierarchical modeling framework with variable and high-resolution grids in E3SM. A set of atmosphere-only and fully coupled modeling experiments will be conducted using E3SM with the Arctic Regionally Refined Mesh (Arctic-RRM). We will first evaluate the model simulations against observational data and reanalysis products. We will then examine response of Arctic cyclones to prescribed AMO forcing. Transient forcing-effect processes will be analyzed in the fully coupled modeling experiments. Forcing mechanisms of cyclone activity for ocean mixing, deep convection, and AMOC variability under different scenarios of freshwater input from Greenland ice sheet melt will be evaluated in specifically designed sensitivity experiments. 

The proposed research is innovative and responsive to the scientific topics required for RGMA-topic applications. The research results will improve understanding of sensitivities of Arctic cyclone, the AMOC and the AMO to the warming climate, and will guide improvement of Earth system models and their climate prediction/projection capabilities.