Equatorial Oceanic Waves and the Evolution of 2007 Positive Indian Ocean Dipole

Abstract

The role of equatorial oceanic waves on the evolution of the 2007 positive Indian Ocean Dipole (pIOD) event was evaluated using available observations and output from a quasi-analytical linear wave model. It was found that the 2007 pIOD event was a weak and short-lived event: developed in the mid-summer (July), matured in the early-fall (September), and terminated in the mid-fall (October). The evolution of the 2007 pIOD event was linked to the equatorial wave dynamics. The event development was associated with the generation of upwelling equatorial Kelvin waves (westward current anomalies) generated by easterly wind anomalies. The event termination was associated with the occurrence of eastward zonal current anomalies resulting from a complex interplay between the wind-forced down welling Kelvin waves and the eastern-boundary-reflected Rossby waves. Results from a quasi-analytical linear wave model show that during the event development and maturation, the wind-forced Kelvin waves played a dominant role in generating zonal current anomalies along the equatorial Indian Ocean, while the easternboundary-reflected Rossby waves tended to weaken the wind-forced Kelvin wave signals. During the event termination our model shows that the initiation of anomalous eastward current resulted from the reflected Rossby waves at the eastern boundary. The wind-forced Kelvin waves associated with the seasonal reversal of the monsoon further strengthened the eastward zonal currents generated by the boundary-generated Rossby waves in late-October/early-November. This highlights the importance of the eastern-boundary-reflected Rossby waves on the IOD event termination.

Spatial and temporal variability of surface chlorophyll-a in the Gulf of Tomini, Sulawesi, Indonesia

“…However, the chl-a concentration was higher and distributed across the GoT during the pure IOD event in 2003 (Rao and Yamagata 2004) than that during the positive IOD event co-occurred with weak El Niño event in 2006 (Horii et al 2008). Interestingly, when the positive IOD event co-occurred with the Niña event in 2007 and 2011 (Iskandar et al 2014a), chl-a concentration in the GoT also increased, in particular during July-August 2007 (Figure 4.F2-F3) and August-September 2011 ( Figure 4.I3-I4). Opposite situation was observed during La Niña and/or negative IOD events.…”

Spatio-temporal variability of temperature and chlorophyll-a concentration of sea surface in Bali Strait, Indonesia

“…However, chlorophyll-a concentrations were higher and distributed throughout the Bali Strait waters during pre-IOD in 2003 (Rao et al 2009) compared to positive IOD events along with an El Niño event in 2006 (Ningsih et al 2013). When positive IOD events coincided with La Niña events in 2007 and 2011 (Iskandar et al 2014), Chlorophyll-a concentrations in the Bali Strait increased, particularly during July-August 2007 and August-September 2011. Opposite situations occurred during La Niña and/or negative IOD events.…”

Spatio-temporal variations of sea surface temperature in the Banda Sea during the period of 2002-2008

“…It is not surprising that the most apparent feature of the first EOF time series is a seasonal cycle, which is associated with the seasonal change in the monsoon winds. The Ekman pumping generated by the local wind is suggested to be the main driving force for this seasonal cycle [2,3] [10]. This result may suggest that the strengthening of the third EOF mode is associated with the IOD event.…”