BY J. VIALARD,+ J. P. DUVEL, M. J. MCPHADEN,

A field experiment in the southwestern Indian Ocean provides new insights into ocean–atmosphere interactions in a key climatic region. W hile easterly trade winds blow year-round over the southern Indian Ocean, surface winds experience a striking reversal north of 10°S. During boreal summer, the low-level easterly flow penetrates northward, is deflected when crossing the equator, and forms the strong Indian monsoon jet. During boreal winter, north-easterly winds also bend while crossing the equa-tor southward and form a weak low-level westerly jet between the equator and 10°S (Fig. 1a). The cyclonic circulation at the meeting point of these two wind regimes is responsible for the formation of a peculiar oceanic structure: the “Seychelles Chagos thermocline ridge ” (SCTR; Hermes and Reason 2008; see the “Seychelles–Chagos thermocline ridge ” sidebar for a more complete explanation of the formation of this feature). This region has attracted attention because it is home to distinct oceanic and atmospheric vari-ability at multiple time scales, each time with sig-nificant climatic consequences. Anomalously warm sea surface temperature (SST) in the SCTR region is associated with increased X Underwater photograph of ASIP. See “The Air–Sea Interaction profiler ” sideba