Impact of the Antarctic bottom water formation on the Weddell Gyre and its northward propagation characteristics in GFDL CM2.1 model

Abstract

The impact of Antarctic bottom water (AABW) formation on the Weddell Gyre and its northward propagation characteristics are studied using a 4000 year long control run of the GFDL CM2.1 model as well as sensitivity experiments. In the control run, the AABW cell and Weddell Gyre are highly correlated when the AABW cell leads the Weddell Gyre by several years, with an enhanced AABW cell corresponding to a strengthened Weddell Gyre and vice versa. An additional sensitivity experiment shows that the response of the Weddell Gyre to AABW cell changes is primarily attributed to interactions between the AABW outflow and ocean topography, instead of the surface wind stress curl and freshwater anomalies. As the AABW flows northward, it encounters topography with steep slopes that induce strong downwelling and negative bottom vortex stretching. The anomalous negative bottom vortex stretching induces a cyclonic barotropic stream function over the Weddell Sea, thus leading to an enhanced Weddell Gyre. The AABW cell variations in the control run have significant meridional coherence in density space. Using passive dye tracers, it is found that the slow propagation of AABW cell anomalies south of 35°S corresponds to the slow tracer advection time scale. The dye tracers escape the Weddell Sea through the western limb of the Weddell Gyre and then go northwestward to the Argentine Basin through South Sandwich Trench and Georgia Basin. This slow advection by deep ocean currents determines the AABW cell propagation speed south of 35°S. North of 35°S the propagation speed is determined both by advection in the deep western boundary current and through Kelvin waves.

Impact of Antarctic Meltwater Forcing on East Asian Climate Under Greenhouse Warming

“…Interestingly, the sea ice response gradually weakens even though the meltwater forcing is constant. In a linear framework, this is possibly due to ocean adjustments caused by subsurface warming related to the limitation of the deep heat reservoir; a similar mechanism has been suggested in previous studies (Martin et al, 2013; Zhang et al, 2017; Zhang & Delworth, 2016). SAT around the Antarctica significantly decreases due to the negative downward sensible heat flux and the ice‐albedo feedback as a consequence of both cold sea surface temperature (SST) and additional sea ice formation.…”

SPEAR: The Next Generation GFDL Modeling System for Seasonal to Multidecadal Prediction and Projection

“…We also examined the impact of the PDO on North American precipitation. Consistent with observations and the FLOR model (Zhang & Delworth, 2016a, 2016b, the PDO warm phase corresponds to wet conditions in the southwestern United States in both warm and cold seasons and vice versa. This is because the anomalous southerly winds associated with the Pacific-North-American teleconnection during the PDO warm phase enhance moisture transport from south to north and therefore leads to an excess of precipitation and vice versa.…”

Impact of Antarctic meltwater forcing on East Asian climate under greenhouse warming

“…Interestingly, the sea ice response gradually weakens even though the meltwater forcing is constant. In a linear framework, this is possibly due to ocean adjustments caused by subsurface warming related to the limitation of the deep heat reservoir; a similar mechanism has been suggested in previous studies (Martin et al, 2013;Zhang et al, 2017;Zhang & Delworth, 2016). SAT around the Antarctica significantly decreases due to the negative downward sensible heat flux and the ice-albedo feedback as a consequence of both cold sea surface temperature (SST) and additional sea ice formation.…”