The dynamics of wind-driven intraseasonal variability in the equatorial Indian Ocean

This commentary provides a discussion of the concept of `bounded rationality' as it applies to the theses advanced by Lopes (1991) and Evans (1991). Lopes's (1991) assessment of the irrationalist consequences of Tversky and Kahneman's (1974) work on heuristics and biases is premature because bounded rationality implies that people could not employ optimal strategies. Considerations of bounded rationality also provide additional criteria by which to judge the theories of deductive reasoning discussed by Evans (1991). Judged by this criterion, theories whose goal is to explain logically competent performance are inadequate (Oaksford & Chater, 1991). Thus Evans's assessment of the state of current theories of reasoning requires revision

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

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 eastern-boundary-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

The Role of Temperature Inversions in the Generation of Seasonal and Interannual SST Variability in the Far Northern Bay of Bengal

The northern Bay of Bengal is characterized by freshwater supply from the Ganges and Brahmaputra Rivers. The resulting shallow haline stratification and thick barrier layer lead to temperature inversions in fall and winter, that is, cool surface water overlaying warm subsurface water. This study examines sea surface temperature (SST) variability off Bangladesh and shows that temperature inversions play an essential role in generating seasonal and interannual SST variability there. Two satellite SST datasets reveal that the magnitude of SST variability has a local peak near the coast of Bangladesh on seasonal and interannual time scales. Output from a high-resolution ocean general circulation model, which is validated by satellite SST and Argo float observations, is used to calculate the mixed layer heat budget. Results show that inverted temperature profiles lead to SST warming on the seasonal time scale via heat exchange at the bottom of the mixed layer, which balances climatological atmospheric cooling in fall and winter. On interannual time scales, surface heat flux tends to damp SST variability, whereas heat exchange at the base of the mixed layer contributes to the growth of SST anomalies. SST off Bangladesh tends to be anomalously high in the year after an El Nino event and in the year of negative Indian Ocean dipole and La Nina events. The atmospheric circulations related to these climate modes force anomalous Ekman pumping, which advects more subsurface warm water to the surface in fall and winter, resulting in anomalous mixed layer warming. The deepening of the mixed layer entrains more subsurface warm water, which also contributes to anomalous warming