5:15 PM - 6:45 PM
[ACG32-P06] A far deepening of the Aleutian Low in the AGCM experiment forced by SST anomaly in the Kuroshio and its extension
Keywords:Air-Sea interaction, Teleconnection, Atmospheric General Circulation Model, Western Boundary Current, Kuroshio Extension, Extratropics
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. On the other hand, an extratropics-to-tropics teleconnection is still unclear because internal variability of the extratropical atmosphere will overwhelm effects of the extratropical ocean onto the overlying atmosphere, and thereby mask possible remote influences to the 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 attempt to investigate a possible equatorward remote influence of the North Pacific by conducting atmospheric general circulation model (AGCM) experiments forced by perpetual sea surface temperature (SST) anomalies in the Kuroshio/Kuroshio Extension region.
We used the Community Atmosphere Model (CAM 6; 0.9° × 1.25° horizontal resolution, 32 vertical levels), an atmospheric model of the Community Earth System Model (CESM2.1.3). The model is integrated for 15 years under the boundary condition of monthly climatological SST and sea ice concentration. We employ the model output for the last 10 years as the control experiment. We also conducted the following three types of forcing experiments. Exp1. An experiment with +2 K SST anomaly forcing in the Kuroshio/Kuroshio Extension region, Exp2. An experiment with the +2 K SST anomaly forcing in the central tropical Pacific region, and Exp3. An experiment with the same SST anomalies in both of those regions. In the individual experiments, the model is integrated for 10 years with the same SST anomaly forcing.
In the 10-year average, the dominant atmospheric responses in the North Pacific are deepening of the Aleutian Low in all of these three experiments. Specifically, in the Exp1, several negative outliers are distinct in the histogram of sea level pressure anomalies near the Aleutian Island. These outliers represent a southward extension of the extremely strengthened Aleutian low, which result in surface westerly anomalies over the subtropical North Pacific and possibly weakening the trade winds. These results indicate that extratropical SST anomalies can induce frequent formation of the extremes of the Aleutian low, which could bring about an equatorward remote influence from the extratropics.
We used the Community Atmosphere Model (CAM 6; 0.9° × 1.25° horizontal resolution, 32 vertical levels), an atmospheric model of the Community Earth System Model (CESM2.1.3). The model is integrated for 15 years under the boundary condition of monthly climatological SST and sea ice concentration. We employ the model output for the last 10 years as the control experiment. We also conducted the following three types of forcing experiments. Exp1. An experiment with +2 K SST anomaly forcing in the Kuroshio/Kuroshio Extension region, Exp2. An experiment with the +2 K SST anomaly forcing in the central tropical Pacific region, and Exp3. An experiment with the same SST anomalies in both of those regions. In the individual experiments, the model is integrated for 10 years with the same SST anomaly forcing.
In the 10-year average, the dominant atmospheric responses in the North Pacific are deepening of the Aleutian Low in all of these three experiments. Specifically, in the Exp1, several negative outliers are distinct in the histogram of sea level pressure anomalies near the Aleutian Island. These outliers represent a southward extension of the extremely strengthened Aleutian low, which result in surface westerly anomalies over the subtropical North Pacific and possibly weakening the trade winds. These results indicate that extratropical SST anomalies can induce frequent formation of the extremes of the Aleutian low, which could bring about an equatorward remote influence from the extratropics.