Instability in boundary layer between the North Equatorial Current and underlying zonal jets based on mooring observations -- Journal of Oceanology and Limnology,2020,38(5):1368-1381

	Cite this paper:
	WANG Fujun, FENG Junqiao, WANG Qingye, ZHANG Linlin, HU Shijian, HU Dunxin. Instability in boundary layer between the North Equatorial Current and underlying zonal jets based on mooring observations[J]. Journal of Oceanology and Limnology, 2020, 38(5): 1368-1381

Instability in boundary layer between the North Equatorial Current and underlying zonal jets based on mooring observations

WANG Fujun^1,2,3, FENG Junqiao^1,2,3, WANG Qingye^1,2,3, ZHANG Linlin^1,2,3, HU Shijian^1,2,3, HU Dunxin^1,2,3

1 Key Laboratory of Ocean Circulation and Wave, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;
2 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

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.

Key words: instability|North Equatorial Current (NEC)|zonal jets

Received: 2020-01-16 Revised: 2020-03-19

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