2:50 PM - 3:10 PM
[ACG44-05] Impact of Kuroshio Large Meander on Wintertime Large-Scale Atmospheric Field
★Invited Papers
Keywords:Kuroshio Large Meander, Aleutian Low, Decadal Variability, Air-Sea Interaction
The Aleutian Low strengthened in 2014/15 and it was pointed out that the regime shift may have occurred for the first time in about 20 years (Sugimoto and Suga 2022). Due to wind forcing associated with the strengthening of Aleutian Low, the Kuroshio Extension (KE) path transitioned from a stable state to an unstable state in mid-2016, but returned to a stable state with the onset of the Kuroshio large-meander (LM) path in August 2017. Then, the Aleutian Low began to weaken in winter of 2017, and the influence of the Kuroshio LM path is expected as its cause.
The Kuroshio LM path, which began in August 2017, has lasted more than four years and the longest record in the observation history is about to be broken. In this study, we investigate the impact of the oceanic conditions associated with the Kuroshio LM path on the large-scale atmospheric field through data analysis and numerical experiments.
First, we performed a composite analysis for five LM events that have occurred since 1980 using atmospheric reanalysis data. Results showed an anticyclonic anomaly over the central/eastern North Pacific, characterized by an equivalent barotropic structure throughout the troposphere, during the LM periods. This represents a weakening of the Aleutian Low and is consistent with the termination of the regime in winter of 2017. The KE path has been reported to be in a stable state during the Kuroshio LM path (Qiu and Chen 2005, Sugimoto and Hanawa 2012). Therefore, we focused on the sea surface temperature (SST) front on the northern boundary of KE. The composite results qualitatively indicated that the SST front, reflecting the KE stable path state, during the LM periods strengthens and its-associated enhancement of baroclinic instability in the lower atmosphere leads to change in transition eddy activity, resulting in the formation of anticyclonic anomalies over the central/eastern North Pacific. Next, we conducted numerical experiments using Japan Meteorological Agency non-hydrostatic model to evaluated the effects of Kuroshio LM path on large-scale atmospheric fields. The conclusions supported that the interpretation derived from the reanalysis data. This study suggests that the Kuroshio LM path, i.e., KE stable path state, would act as a negative feedback mechanism to the atmospheric fields.
The Kuroshio LM path, which began in August 2017, has lasted more than four years and the longest record in the observation history is about to be broken. In this study, we investigate the impact of the oceanic conditions associated with the Kuroshio LM path on the large-scale atmospheric field through data analysis and numerical experiments.
First, we performed a composite analysis for five LM events that have occurred since 1980 using atmospheric reanalysis data. Results showed an anticyclonic anomaly over the central/eastern North Pacific, characterized by an equivalent barotropic structure throughout the troposphere, during the LM periods. This represents a weakening of the Aleutian Low and is consistent with the termination of the regime in winter of 2017. The KE path has been reported to be in a stable state during the Kuroshio LM path (Qiu and Chen 2005, Sugimoto and Hanawa 2012). Therefore, we focused on the sea surface temperature (SST) front on the northern boundary of KE. The composite results qualitatively indicated that the SST front, reflecting the KE stable path state, during the LM periods strengthens and its-associated enhancement of baroclinic instability in the lower atmosphere leads to change in transition eddy activity, resulting in the formation of anticyclonic anomalies over the central/eastern North Pacific. Next, we conducted numerical experiments using Japan Meteorological Agency non-hydrostatic model to evaluated the effects of Kuroshio LM path on large-scale atmospheric fields. The conclusions supported that the interpretation derived from the reanalysis data. This study suggests that the Kuroshio LM path, i.e., KE stable path state, would act as a negative feedback mechanism to the atmospheric fields.