Dynamics of intraseasonal oscillations in the Bay of Bengal during summer monsoons captured by mooring observations

Enhanced Intraseasonal Variability of the Upper Layers in the Southern Bay of Bengal During the Summer 2016

“…The zonal flow is stronger in summer (June–August) from 2015 to 2017, while the strong meridional flow usually occurs in summer and autumn. Previous results also show that the SBOB's upper currents are stronger in summer than in winter (Pirro, Wijesekera, et al., 2020; Wijesekera, Wang, et al., 2016). In general, strong currents occur in the upper layers (200 m).…”

“…The multiscale variability of ocean circulation in the BOB with the complex air‐sea interactions and the intraseasonal variability (ISV) of currents are also significant components of upper ocean dynamics, affecting the region's marine ecosystem and the south Asian monsoon system (Schott et al., 2009; Webster et al., 1999). Recent studies have shown that the variability of BOB current is closely linked to the equatorial Indian Ocean (e.g., Chen et al., 2017, 2018; Huang et al., 2019; Nagura, 2018; Pirro, Wijesekera, et al., 2020; Vinayachandran et al., 2018; Wijesekera, Teague, et al., 2016).…”

“…Comparing to the local wind forcing, the remote forcing driven by the equatorial wind stress contributes more to the ISV of upper circulations in the BOB (e.g., Han et al., 2011; Iskandar & McPhaden, 2011; Lee et al., 2019; Suresh et al., 2013; Vialard et al., 2009). The atmospheric intraseasonal oscillation in the equatorial Indian Ocean forces the intraseasonal equatorial Kelvin wave to propagate eastward, with a portion propagating poleward along Sumatra and Java coasts after hitting the eastern boundary (e.g., Chen et al., 2015; Han et al., 2001; Iskandar et al., 2006; Rao et al., 2010), and another part reflected as the Rossby wave propagating westward to influence the ISV of sea level (Cheng et al., 2013, 2017), thermocline layer (Girishkumar et al., 2013; Pirro, Wijesekera, et al., 2020), and upper circulation (Chen et al., 2017) in BOB. Chen et al.…”

Progress in understanding of Indian Ocean circulation, variability, air–sea exchange, and impacts on biogeochemistry

“…Girishkumar et al, 2013), and past research has identified roughly three distinct ISO bands in the context of the thermocline: 30-60, 60-90, and 120 d Girishkumar et al, 2013). Pirro et al (2020b) discussed interaction between 30-60 d ISOs and the SMC in the southern BoB using long-term moored observations. They estimated that the background mean flow acceleration resulting from the meridional divergence of wave momentum flux in the thermocline was about 10 −8 m s −2 .…”

“…A mechanism for the anticyclonic eddy formation has been proposed by Vinayachandran and Yamagata (1998), where the interaction of the SMC with Rossby waves arriving from the eastern boundary leads to the anticyclonic eddy. Pirro et al (2020a) proposed a new hypothesis wherein the anticyclonic eddy is generated by a topographically trapped Rossby wave response of the SMC to perturbations by the Sri Lankan coast. They reported that observations of the size, location, and origin of the SLD were broadly consistent with their hypothesis, based on a laboratory experiment designed to mimic natural flow in the BoB by creating an eastward jet (SMC) on a simulated β plane.…”