1:45 PM - 3:15 PM
[ACG30-P18] Statistical analysis of meso- to synoptic-scale cyclone activity over the Kuroshio and Kuroshio Extension regions
Keywords:Kuroshio Extension, storm track
The Kuroshio and its downstream, the Kuroshio Extension, are western boundary currents, and supplies substantial amount of heat and moisture to the mid-latitude atmosphere. Some recent studies showed that the diabatic heating related to this heat and moisture supply can contribute to the rapid development of extratropical cyclone (Hirata et al. 2015) and persistent surface wind convergence (Masunaga et al. 2020). In the Kuroshio region, the track and development rate of extratropical cyclones are shown to be affected by the Kuroshio path (Nakamura et al. 2012). However, there are few studies that statistically analyzed the path, genesis, and development of extratropical cyclones over the Kuroshio Extension region. In this study, we make a statistical analysis on the meso- to synoptic-scale cyclone activity over the Kuroshio and Kuroshio Extension region, especially focusing on the differences in the behavior of cyclones depending on their spatial scales.
We use the ERA5 global reanalysis (0.25°, hourly) to identify the cyclones. We also use sea level anomalies from CMEMS (0.25°, daily) to identify the axis of the Kuroshio and the Kuroshio Extension. The analysis period is from 2000 to 2019. To track the cyclones, the Neighbor Enclosed Area Tracking (NEAT) algorithm (Inatsu and Amada 2013) was applied to 10-day high-pass filtered relative vorticity and geopotential height at 850hPa.
The tracking analysis showed that the frequency of meso-scale cyclones is high around 35°N, nearly over the Kuroshio Extension region, regardless of the season with higher frequency in winter. On the other hand, the frequency of synoptic-scale cyclones exhibits a seasonal migration associated with the seasonal change of the subtropical jet.
The higher frequency of meso-scale cyclones over the Kuroshio Extension region may be a combined result of hydrostatic adjustment and vertical mixing effects (e.g., Tanimoto et al. 2011). Large-scale surface winds form a characteristic convergence-divergence field over the Kuroshio and Kuroshio Extension regions, and the convergence area may contribute to the genesis and development of meso-scale cyclones over the region. Diabatic heating associated with the supply of heat and moisture from the Kuroshio Extension may also strengthen the convergence of surface winds and promote the genesis and development of cyclones. We will analyze the development process of meso-scale cyclones over the Kuroshio and Kuroshio Extension region, especially focusing on the role of diabatic heating, as well as surface wind convergence, surface heat flux, upper level forcing, and low level baroclinicity.
We use the ERA5 global reanalysis (0.25°, hourly) to identify the cyclones. We also use sea level anomalies from CMEMS (0.25°, daily) to identify the axis of the Kuroshio and the Kuroshio Extension. The analysis period is from 2000 to 2019. To track the cyclones, the Neighbor Enclosed Area Tracking (NEAT) algorithm (Inatsu and Amada 2013) was applied to 10-day high-pass filtered relative vorticity and geopotential height at 850hPa.
The tracking analysis showed that the frequency of meso-scale cyclones is high around 35°N, nearly over the Kuroshio Extension region, regardless of the season with higher frequency in winter. On the other hand, the frequency of synoptic-scale cyclones exhibits a seasonal migration associated with the seasonal change of the subtropical jet.
The higher frequency of meso-scale cyclones over the Kuroshio Extension region may be a combined result of hydrostatic adjustment and vertical mixing effects (e.g., Tanimoto et al. 2011). Large-scale surface winds form a characteristic convergence-divergence field over the Kuroshio and Kuroshio Extension regions, and the convergence area may contribute to the genesis and development of meso-scale cyclones over the region. Diabatic heating associated with the supply of heat and moisture from the Kuroshio Extension may also strengthen the convergence of surface winds and promote the genesis and development of cyclones. We will analyze the development process of meso-scale cyclones over the Kuroshio and Kuroshio Extension region, especially focusing on the role of diabatic heating, as well as surface wind convergence, surface heat flux, upper level forcing, and low level baroclinicity.