5:15 PM - 7:15 PM
[ACG36-P05] SST anomaly forcing in the Kuroshio Extension and its effect on subtropical-midlatitude interaction in AGCM experiments
Keywords:Air-Sea interaction, Teleconnection, General Circulation Model (GCM), Extratropics / Kuroshio
Tropics-to-extratropics atmospheric teleconnections are well established as stationary Rossby wave train responses driven by perturbed convective heating over the anomalous tropical ocean surface. In contrast, the mechanisms governing extratropics-to-tropics teleconnections remain unclear, because the strong internal variability of the extratropical atmosphere often dominates, potentially masking the influence of extratropical Sea Surface Temperature (SST) anomalies on the overlying atmosphere and their remote effects on tropical atmospheric circulation. However, a recent study suggested the possibility of a bidirectional mechanism between the tropical eastern Pacific and the Southern Ocean near the southeastern Pacific.
In this study, we investigate the potential equatorward remote influence of North Pacific SST anomalies using Atmospheric General Circulation Model (AGCM) experiments forced by perpetual SST anomalies in the Kuroshio Extension region. We used the Model for Interdisciplinary Research on Climate version 6 (MIROC6) AGCM, configured with a horizontal resolution of T85 (approximately 150 km) and 81 vertical levels.
We first conducted a control experiment by integrating the model for a total of 100 years, forced with monthly climatological values of SST and sea ice concentration. Subsequently, we performed a forced experiment in which +2 [K] SST anomalies were imposed over the Kuroshio Extension region during each winter of the control experiment.
The response of the large-scale atmospheric circulation to the positive wintertime SST anomalies in the Kuroshio Extension region is primarily seen in Sea Level Pressure (SLP) anomalies associated with the Aleutian Low. The warm SST anomalies in the Kuroshio Extension region induce a slight shift in the frequency distribution of Aleutian Low intensities, while the intensity itself varies across ensemble members due to internal atmospheric variability. However, composite analyses based on strong, moderate, and weak Aleutian Low events consistently show that surface wind anomalies over the tropical and subtropical Pacific regions exhibit westerly anomalies, regardless of the variability among ensemble members, possibly weakening the trade winds.
These results were consistent with additional experiments using the atmospheric component of the Community Earth System Model (CESM2.1.3).
In this study, we investigate the potential equatorward remote influence of North Pacific SST anomalies using Atmospheric General Circulation Model (AGCM) experiments forced by perpetual SST anomalies in the Kuroshio Extension region. We used the Model for Interdisciplinary Research on Climate version 6 (MIROC6) AGCM, configured with a horizontal resolution of T85 (approximately 150 km) and 81 vertical levels.
We first conducted a control experiment by integrating the model for a total of 100 years, forced with monthly climatological values of SST and sea ice concentration. Subsequently, we performed a forced experiment in which +2 [K] SST anomalies were imposed over the Kuroshio Extension region during each winter of the control experiment.
The response of the large-scale atmospheric circulation to the positive wintertime SST anomalies in the Kuroshio Extension region is primarily seen in Sea Level Pressure (SLP) anomalies associated with the Aleutian Low. The warm SST anomalies in the Kuroshio Extension region induce a slight shift in the frequency distribution of Aleutian Low intensities, while the intensity itself varies across ensemble members due to internal atmospheric variability. However, composite analyses based on strong, moderate, and weak Aleutian Low events consistently show that surface wind anomalies over the tropical and subtropical Pacific regions exhibit westerly anomalies, regardless of the variability among ensemble members, possibly weakening the trade winds.
These results were consistent with additional experiments using the atmospheric component of the Community Earth System Model (CESM2.1.3).