Impact of Explosive Cyclones on the Deep Ocean in the North Pacific: Simulations and Observations

The Northwestern Pacific Ocean is the deepest ocean above which explosive cyclones frequently develop in winter. Recently, high-resolution atmospheric models show that Kuroshio affects explosive cyclones and precipitation over the northwestern Pacific. However, it remains an open question whether explosive cyclones affect ocean. To understand oceanic response to explosive cyclones, we analyze results of eddy-resolving ocean simulations and observe internal ocean under explosive cyclones by Argo floats in the Northwestern Pacific. Composite analyses of long-term ocean simulation at 165°E and 42.5°N where explosive cyclones are most active show that explosive cyclones induce large horizontal divergence within the surface-mixed layer and upward flow that reaches 2000 m depth. In addition, interannual variability of explosive cyclone activity affects the amplitude of vertical motion and the daily-scale temperature variations in the deep ocean. To observe oceanic responses to explosive cyclones, we deployed six Argo floats in two winters in 2015/2016 and 2016/2017 in the Northwestern Pacific. The Argo floats used for the special observations allow real-time change of observation mission including time interval and depth of profile observation through satellite communication. The mission change was operated based on medium-range ensemble forecast data by Japan Meteorological Agency. When an explosive cyclone was predicted with high probability by the forecast, 6-hourly observations with 650 m depth were conducted. Otherwise daily observations with 2000 m depth were conducted between November and March in each winter. Argo floats observed 1148 profiles totally. While several floats observed under explosive cyclones, only 73 profiles observed under explosive cyclones.