Role of interannual equatorial forcing on the subsurface temperature dipole in the Bay of Bengal during IOD and ENSO events

Pramanik, Saikat; Sil, Sourav; Mandal, Samiran; Dey, Dipanjan; Shee, Abhijit

doi:10.1007/s10236-019-01303-0

Cited by 15 publications

(7 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Due to the presence of SLD and AE, in mid‐summer, the SMC usually diverges into two branches at 87°E, the northward one associated with the SLD, and the other eastward one related to the AE (Figure 1). SMC has complex variability in the strength and location of its flow axis (Pramanik et al., 2019; Somayajulu et al., 2003). By analyzing the strength of the currents along 5°N, it is found to the SMC also shows significant interannual variability (Figure 8).…”

Section: Modulation Of the Smcmentioning

confidence: 99%

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

et al. 2021

View full text Add to dashboard Cite

Intraseasonal variability (ISV) of the upper 500 m circulation in the southern Bay of Bengal (SBOB) is investigated by using mooring observations and analyzing model outputs. An enhanced ISV is found in the upper 500 m currents during summer 2016. In summer 2016, a boreal summer intraseasonal oscillation (BSISO) propagated northward in tropical Indian Ocean. The intraseasonal easterly anomaly associated with the BSISO forces the equatorial wave to propagate into SBOB, driving the ISV of the upper currents. However, the analysis shows that the enhancement of ISV may be more related to the oceanic instability. During summer 2016, the intensity of the southwest monsoon current (SMC) significantly increased with the position of the flow axis closer to the SBOB's eastern boundary. Energy analysis reveals that the SMC could strengthen the westward propagating Rossby wave through baroclinic and barotropic instability, which can lead to the enhanced ISV of the upper currents in SBOB.

show abstract

Section: Modulation Of the Smcmentioning

confidence: 99%

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

et al. 2021

View full text Add to dashboard Cite

show abstract

“…However, how the subsurface parameters response to the IOD affects its local upper ocean still needs more study. Previous studies have demonstrated the importance of forcing from the Equator to the BoB, such as sea surface height, thermocline, and circulation structure (Girishkumar et al, 2013;Chatterjee et al, 2017;Pramanik et al, 2019), especially for the mechanisms forcing the East India Coastal Current (Yu et al, 1991;McCreary et al, 1996;Shankar et al, 1996). The response of the subsurface salinity field we discussed may also affect the local flow field and mesoscale eddies.…”

Section: Discussionmentioning

confidence: 73%

“…Especially during the nIOD phase, the increase of the zonal subsurface salinity gradients makes it easier to excite high-mode westward Rossby waves, suggesting the effect of IOD on the subsurface thermohaline circulation in the BoB. The biological processes are significantly affected by the salinity stratification and vertical mixing in the BoB (Prasanna Kumar et al, 2002). As our results show, the IOD significantly modulates the BoB subsurface salinity and further potentially affects the ocean barrier layer and mixed layer depth through the Kelvin and Rossby waves.…”

Section: Discussionmentioning

confidence: 99%

“…The Andaman and Nicobar Islands, as well as the eastern border of the Andaman Sea, significantly alter the circulation in the BoB (Chatterjee et al, 2017). A recent numerical study suggests that the equatorial forcing plays a dominant role in interannual variations of sea surface height and thermocline in the BoB during Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) events, especially relating to their spatial pattern (Pramanik et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Correlation between subsurface salinity anomalies in the Bay of Bengal and the Indian Ocean Dipole and governing mechanisms

Zhang¹,

Pohlmann²,

Chen

2021

Ocean Sci.

View full text Add to dashboard Cite

Abstract. Lead–lag correlations between the subsurface temperature and salinity anomalies in the Bay of Bengal (BoB) and the Indian Ocean Dipole (IOD) are revealed in model results, ocean synthesis, and observations. Mechanisms for such correlations are further investigated using the Hamburg Shelf Ocean Model (HAMSOM), mainly relating to the salinity variability. It is found that the subsurface salinity anomaly of the BoB positively correlates to the IOD, with a lag of 3 months on average, while the subsurface temperature anomaly correlates negatively. The model results suggest the remote forcing from the equatorial Indian Ocean dominates the interannual subsurface salinity variability in the BoB. The coastal Kelvin waves carry signals of positive (negative) salinity anomalies from the eastern equatorial Indian Ocean and propagate counterclockwise along the coasts of the BoB during positive (negative) IOD events. Subsequently, westward Rossby waves propagate these signals to the basin at a relatively slow speed, which causes a considerable delay of the subsurface salinity anomalies in the correlation. By analyzing the salinity budget of the BoB, it is found that diffusion dominates the salinity changes near the surface, while advection dominates the subsurface; the vertical advection of salinity contributes positively to this correlation, while the horizontal advection contributes negatively. These results suggest that the IOD plays a crucial role in the interannual subsurface salinity variability in the BoB.

show abstract

“…In the northern Indian Ocean (NIO), winds significantly impact the seasonal to interannual variability of upper surface processes (Girishkumar et al., 2013, 2011; Pramanik et al., 2019; Sengupta & Ravichandran, 2001). The Madian‐Julian Oscillation (MJO, Madden & Julian, 1994; Zhang, 2005) and northward propagating monsoon intraseasonal oscillation (MISO, Girishkumar et al., 2017, Goswami & Ajaya Mohan, 2001; Krishnamurti & Subrahmanyam, 1982; Li et al., 2017; Yasunari, 1980) are the dominant modes of intraseasonal oscillation (ISO) in the tropical ocean.…”

Section: Introductionmentioning

confidence: 99%

Assessment of SCATSat‐1 Scatterometer Winds on the Upper Ocean Simulations in the North Indian Ocean

Pramanik

Sil

2021

JGR Oceans

Self Cite

View full text Add to dashboard Cite

are the dominant modes of intraseasonal oscillation (ISO) in the tropical ocean. These processes are described by the 30-90 days fluctuations of low-level winds and convection over the Indian Ocean (IO) and propagating from the equator to the southeast Asian region. Strong intraseasonal variability of sea surface temperature (SST) during MISO events in the tropical IO is well established and modulated by air-sea interactions, which is confirmed by both observational studies (Duvel & Vialard, 2007;Sengupta & Ravichandran, 2001) as well as modeling studies (Achuthavarier & Krishnamurthy, 2011;Fu et al., 2002). Additionally, mixed layer depth (MLD), barrier layer thickness (BLT), and salinity stratification influence the amplitude of SST in intraseasonal variability (Li et al., 2017). Strong intraseasonal SST variability is associated with shallower MLD (Sengupta Abstract The performance of a new scatterometer SCATSat-1 winds with TropFlux on simulating the upper oceanic processes is analyzed over the northern Indian Ocean (IO) using Regional Ocean Modeling System (ROMS). The nutrient, phytoplankton, zooplankton, and detritus (NPZD) ecosystem model are included for studying the postcyclonic responses on biophysical parameters during three cyclones of different intensities (Maarutha, Mora, and Ockhi) in 2017. The SCATSat-1 (TropFlux) winds showed that skill scores are higher than 0.85 (0.66), and RMSEs are less than 0.48 (1.96) m s −1 with RAMA and OMNI buoy observations. Two SCATSat-1 wind experiments, one with 1/4° (SS-E) and other regridded wind to 1° (SSR-E), are compared with the simulation by TropFlux air-sea fluxes available at 1° (TF-E). Seasonal variability of simulated oceanic parameters in SS-E and SSR-E showed marginal improvement than TF-E as compared with observations. However, SSHA variability associated with downwelling Kelvin waves along the Bay of Bengal coast and southward east India coastal current (EICC) during postmonsoon is better simulated in SCATSat-1 experiments. All experiments showed observed intraseasonal oscillations (30-90 days) with higher variability in thermocline than upper layers at RAMA locations over the equator. On western (eastern) equatorial IO, the signals are stronger during boreal winter (premonsoon) and summer (monsoon). Drop in temperature up to 2.5°C during cyclonic events is reasonably better captured in SS-E and SSR-E than TF-E due to better accuracy in SCATSat-1 winds. During cyclones, surface chlorophyll attained a peak after 5-10 days of cyclone passage in SCATSat-1 winds experiments and satellite observations. Plain Language Summary Wind plays an important role in driving the surface circulation of the ocean. Therefore, winds with reasonable accuracy are required to simulate the ocean processes at different timescales through numerical modeling. The ocean simulations are useful for studying oceanic processes and air-sea interaction. The study evaluated the performance of a scatterometer wind and a reanalysis wind. The validations with satellite and in situ observat...

show abstract

Role of interannual equatorial forcing on the subsurface temperature dipole in the Bay of Bengal during IOD and ENSO events

Cited by 15 publications

References 92 publications

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

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

Correlation between subsurface salinity anomalies in the Bay of Bengal and the Indian Ocean Dipole and governing mechanisms

Assessment of SCATSat‐1 Scatterometer Winds on the Upper Ocean Simulations in the North Indian Ocean

Contact Info

Product

Resources

About