Fast and slow responses of Southern Ocean sea surface temperature to SAM in coupled climate models

Abstract

differences in the models' climatological thermal ocean stratification in the region of seasonal sea ice around Antarctica. Exploiting this relationship, we use observational data for the time-mean meridional and vertical temperature gradients to constrain the real Southern Ocean response to SAM on fast and slow timescales.

Arctic Ocean Freshwater Content and Its Decadal Memory of Sea‐Level Pressure

“…We follow the approach of Kostov et al (2017) to determine the response of Arctic FWC in the HiGEM control integration to a step change in atmospheric forcing. We first define an index of integrated FWC, relative to a reference salinity S ref = 34.8 (Aagaard & Carmack, 1989) and integrated down to the 34.8 isohaline over the entire Arctic domain shown in Figure 1c:…”

Southern Ocean Warming

“…The stability of subpolar surface ocean temperature might therefore be key to global ocean heat uptake. The stability of sub polar ocean temperature has been explained by at least two mechanisms that might be at play in parallel in different parts of the ocean, or that might be associated with different timescales (Ferreira et al, 2015;Kostov et al, 2017): (1) increased near-surface stratification, and (2) mean meridional overturning circulation continuously feeding the surface waters with old mid-depth waters (CDW; see Figure 1) that have been isolated from atmospheric warming (Frölicher et al, 2015;Armour et al, 2016;Morrison et al, 2016).…”

Eddy Compensation Dampens Southern Ocean Sea Surface Temperature Response to Westerly Wind Trends

“…It should be noted that the historical simulations from the CMIP5 archive models underestimate the trend in westerly winds when compared with observations (Purich et al, ). While this should not bias the results of Kostov et al (, ), since those analyses present temperature changes per unit change in the SAM, the underestimation of the westerly wind trend likely contributed to the inability of CMIP5 models to capture observed Antarctic sea ice trends (Purich et al, ).…”

“…While the magnitude of this negative SST anomaly decreases during the 10‐year simulation, we do not see sustained long‐term warming. The initial cooling is consistent with that found in the CMIP5 models by Kostov et al (). Our model does not exhibit long‐term warming at the temperature inversion.…”

“…(a) Climate response functions of the SST to a one standard deviation step change in the SAM index inferred from various Coupled Model Intercomparison Project Phase 5 models, modified from Kostov et al (). The response of the coupled model used here, developed at GISS and described in the supporting information, is shown by the thick black line.…”