Instability in boundary layer between the North Equatorial Current and underlying zonal jets based on mooring observatio
- PDF / 5,143,870 Bytes
- 14 Pages / 595.276 x 841.89 pts (A4) Page_size
- 5 Downloads / 145 Views
Instability in boundary layer between the North Equatorial Current and underlying zonal jets based on mooring observations* WANG Fujun1, 2, 3, **, FENG Junqiao1, 2, 3, WANG Qingye1, 2, 3, ZHANG Linlin1, 2, 3, HU Shijian1, 2, 3, HU Dunxin1, 2, 3 1 2
Key Laboratory of Ocean Circulation and Wave, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Function Laboratory for Ocean Dynamics and Climate, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266000, China
3
Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
Received Jan. 16, 2020; accepted in principle Mar. 19, 2020; accepted for publication Apr. 9, 2020 © Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Instability/stability in the North Equatorial Current (NEC) basin is studied based on data obtained from nine moorings deployed at 8.5°N, 10.5°N, 11.0°N, 12.5°N, 13.0°N, 15.0°N, 15.5°N, 17.5°N, and 18.0°N along 130.0°E during cruises in 2015–2017. In low latitudes, the Coriolis parameter and stratification ratio play important roles in NEC stability, whereas velocity shear and the layer depth ratio are important for NEC stability in high latitudes. Beneath the westward NEC, eastward zonal jets occur intermittently centered around 8.5°N, 12.5°N, and 17.5°N along 130.0°E. Similar to the NEC, the main body of these zonal jets also deepens with latitude. In the boundary layer comprising the bottom NEC and upper zonal jets, the growth rate of the NEC is attributed not only to velocity shear but also to zonal jet velocity based on the longwave assumption. Based on the shortwave assumption, the growth rate is proportional to zonal jet velocity but has no relationship with velocity shear. Climatologically, the growth rate in the boundary layer is not zero at 8.5°N, 12.5°N, and 13.0°N, where the velocity shear and zonal jets are larger than at other stations. The instability also occurs at the time node when the zonal jets are strong enough, although the mean zonal jets may disappear at this station. Keyword: instability; North Equatorial Current (NEC); zonal jets
1 INTRODUCTION A westward flow called the North Equatorial Current (NEC), which is confined between 8°N–17°N in the surface layer of the North Pacific Ocean, is an important region for water mass exchange and mixing (e.g., Fine et al., 1994; Qu et al., 1998). The main body of the NEC is concentrated within a layer shallower than the 26.5–26.8 potential density (σθ) surfaces (Qiu et al., 2015). To the east of Mindanao Island, the NEC bifurcates into the southward-flowing Mindanao Current (MC) (e.g., Nitani, 1972; Hu and Cui, 1991; Wang et al., 2016) and the northwardflowing Kuroshio Current (KC) (e.g., Lien et al., 2014; Qiu et al., 2014; Chen et al., 2015). On interannual timescales, NEC transport increases (decreases) during El Niño (La Niña) periods (Qiu and
Lukas, 1996; Kim et al., 2004). Seasonally, the NEC is strong in spring and weak in autumn. Dyn
Data Loading...
