Climate Variability of Coupled and Partially Coupled Numerical Experiments: a study based on AWI-ESM

The variability of the climate system is majorly impacted by the air-sea interaction. Climate model simulations for the past, present, and future provide an estimate of climate variability and climate change. This study investigates the response of the Ocean to the wind stress engendered changes in the North Atlantic region. Feedback in the complex climate system is however not fully explored yet. Partially coupled experiments with fixed wind stress provide an excellent test of wind-stress feedback in the climate system. The focus is on the behavior of the variability using a partial coupling method to constrain the Ocean with prescribed wind forcing in an otherwise fully coupled Earth system model. This enables the assessment of the direct oceanic and the indirect atmospheric response to idealized forced scenarios of prescribed winds over the North Atlantic region. A partially coupled model as used in this study is a model in which the Ocean and Sea-Ice component has been forced by prescribed wind stress which drives the said component with inherent climatological wind field as the fully coupled model. While I discuss major climate variability mechanisms, we focus on four principal modes of climate variability related to the dynamics of Earth’s Oceans as they react to wind stress forcing: the El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO) and Atlantic Meridional Overturning Circulation (AMOC). These Principal oscillation modes are of broad interest and considerable importance in understanding the climate trend and dynamics. These variability mechanisms are examined using the partially coupled climate model with the fully coupled model as the reference source. The results show that there is negative feedback from the Ocean as the interactive wind stress dampens the examined variability indices. Also, the Sea Surface temperature increases Southward and decreases Northward in the partially coupled simulations (the reverse is the case for the fully coupled simulations) as a link between wind stress and heat transport is established