Annual versus semi-annual eddy kinetic energy variability in the Celebes Sea
- PDF / 21,385,457 Bytes
- 18 Pages / 595.276 x 790.866 pts Page_size
- 41 Downloads / 191 Views
ORIGINAL ARTICLE
Annual versus semi‑annual eddy kinetic energy variability in the Celebes Sea Chengcheng Yang1 · Xiao Chen1,2 · Xuhua Cheng1 · Bo Qiu3 Received: 17 November 2019 / Revised: 19 May 2020 / Accepted: 22 May 2020 © The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. 2020
Abstract Eddy kinetic energy (EKE) in the Celebes Sea (CS) is investigated using a global, eddy-resolving, ocean general circulation model (OGCM) output. The OGCM simulation shows that a strong EKE is confined in the upper 300-m layer. The period of EKE variability varies with depth. In the 0–100-m layer, EKE has a distinct annual cycle that is strong in winter (December–February) and weak in summer (June–August). However, in the 100–300-m layer, semi-annual variation is dominant, which shows stronger EKE in spring and fall and weaker EKE in summer and winter. An eddy energy budget analysis reveals that the barotropic eddy energy conversion rate has a vertical structure similar to that of EKE. Compared to the barotropic eddy energy conversion rate, the baroclinic eddy energy conversion rate is much smaller and does not match the EKE vertical pattern. The budget analysis indicates that the variation in EKE in the CS is governed by barotropic instability of the background circulation. Further analysis reveals that the variation in the regional background circulation with depth is due to a combination of the forcing of the local monsoon and the Mindanao Current (MC) in the western tropical Pacific. Keywords Celebes Sea · Eddy kinetic energy · Annual cycle · Semi-annual cycle · Barotropic instability
1 Introduction The Celebes Sea (CS) is located in the archipelagos between Asia and Australia. The CS is known as a choke point of the pathway of global thermohaline circulation. The CS, the Makassar Strait and the Lombok Strait constitute the western route of the Indonesian throughflow (ITF), which transfers warmer and fresher Pacific water into the Indian Ocean and influences the large-scale climate and ecosystem (e.g., Broecker 1991; Fine et al. 1994; Ffield and Gordon 1996; Gordon 1986, 2005; Kashino et al. 2001). In addition, previous studies indicated that the transport via the western route accounts for 77% of the total ITF transport capacity (e.g., Li et al. 2018).
* Xiao Chen [email protected] 1
College of Oceanography, Hohai University, 1 Xikang Road, Nanjing 210098, China
2
Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
3
Department of Oceanography, University of Hawaii at Manoa, Honolulu, HI, USA
The CS is upstream of the ITF western route, and previous studies have revealed that intense mesoscale signals exist in the CS. Kashino et al. (1999) analysed the current metre moorings data, and observed 50-day oscillation signals in the horizontal velocity field at the entrance of the CS. Using a reduced gravity model, Qiu et al. (1999) pointed out that the intense 50-day oscillation in the CS basin is the result of the resonance of the gravest mode, a
