An ocean reanalysis that covers the period from 1871 to 2008 is used to analyze the interannual variability of sea surface salinity (SSS) in the tropical Indian Ocean. The reanalysis SSS and the SSS anomaly patterns during Indian Ocean Dipole (IOD) and El Niño–Southern Oscillation (ENSO) events are compared with patterns from Argo SSS data. The mean seasonal SSS variation is large in the northern Bay of Bengal compared with variations in the Arabian Sea and equatorial Indian Ocean. During a positive IOD event, positive SSS anomalies are found along the Sumatra coast that are due to the combination of wind‐driven upwelling of subsurface high‐salinity waters, enhanced evaporation, and anomalous surface circulation. The opposite is true, to a lesser extent, during negative IOD events. A dipole mode index for salinity (DMIS) based on SSS data and a new index based on the average of salinity in a region off the coast of Sumatra are introduced to monitor SSS variability during IOD and ENSO events. The impact of concomitant El Niño events on a positive IOD event is large with freshening (a negative SSS anomaly) in the equatorial Indian Ocean and salting (positive SSS anomaly) off the southern Sumatra coast. The (impact of) intense freshening reaches into the southwestern tropical Indian Ocean. The impact of concomitant La Niña with negative IOD is also large with an intense freshening in the southeastern Arabian Sea and salting off the northern Sumatra coast.

[1] The effect of a tropical cyclone on the variation of phytoplankton biomass in terms of surface chlorophyll-a is brought out based on satellite observations and mixed layer model simulations in the Arabian Sea during 21 May -3 June 2001. Along the cyclone's passage, chlorophyll-a was high with extreme values (5 -8 mg m À3 ) in the blooms of phytoplankton. The model simulations indicate deepening of mixed layer on the southeastern edge of the cyclone. This forced mixed layer deepening, due to intense wind stirring and cyclone-induced divergent geostrophic currents, has lead to the injection of nutrients into the surface layer, resulting in higher chlorophyll-a. This study suggests that the short-lived tropical cyclones would alter the generally prevailing oligotrophic (nutrient depleted) conditions into a productive surface layer in the Arabian Sea during spring intermonsoon. INDEX TERMS: 4532

The biophysical responses of the upper ocean to three major Gulf of Mexico (GoM) hurricanes in 2005 were analyzed using satellite observations. The degree and orientation of the responses exhibited by Hurricanes Katrina, Rita, and Wilma were greatly affected by the oceanic processes that occur within the GoM, as well as the translation speed of each hurricane. Maximum sea surface temperature change was 6–7°C, 4–5°C, and 5–6°C; whereas, chlorophyll‐a (chl‐a) enhancement was 3 mg m−3, 2 mg m−3, and 4 mg m−3, respectively. Areas of chl‐a enhancement (i.e., increases in phytoplankton biomass accumulation at the ocean's surface) were observed days after passage of each hurricane. Comparison of thermocline displacement estimates and depth approximations of the nitracline and deep chl‐a maximum suggests that the increases in surface phytoplankton biomass associated with Hurricanes Katrina and Rita were the result of new production from nutrient influx, as well as entrainment of phytoplankton from the deep chlorophyll maximum, while chl‐a enhancement linked with Hurricane Wilma appears to be attributable to the latter.

[1] The Madden-Julian Oscillation (MJO) impacts a wide range of weather and climate phenomena. Current global coupled ocean-atmospheric general circulation models exhibit considerable shortcomings in representing and predicting the MJO, specifically its initiation, due to a lack of in situ observations. Here we show, for the first time, that the MJO propagation can be detected from the newly launched NASA Aquarius Salinity mission. The magnitude and extent of sea surface salinity (SSS) variations during the MJO is established, providing a useful tool for data assimilation into models to correctly represent both oceanic and atmospheric processes during intraseasonal variations. Salinity observation allows for atmospheric conditions to be inferred from freshwater flux, on which surface salinity is highly dependent. Increased observations of global SSS from the Aquarius mission will be particularly valuable in remote regions of the tropics and will increase our dynamical understanding and advance prediction of the MJO through model improvement.

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The role of the El Niño–Southern Oscillation (ENSO) on the modulation of tropical cyclone activity over the Bay of Bengal (BoB) for the 1979–2011 period is examined. It is shown that Niño-3.4 sea surface temperature (SST) anomalies are negatively correlated with the BoB tropical cyclone activity to a statistically significant percentage by a lead time of 5 months. Composites of 10-m zonal winds exhibit greater variance during La Niña events, favoring the development of low-level cyclonic vorticity. Low vertical wind shear over the central and northern BoB also aids in the development of tropical cyclones during La Niña events. Increased relative humidity is the result of enhanced moisture transport and higher precipitable water under La Niña conditions. Furthermore, storm-relative composites of relative humidity show stronger moisture pulses over the BoB during La Niña. The enhanced moisture associated with tropical cyclogenesis likely aids in the development and strengthening of the systems. ENSO forces modulations in oceanic conditions as well. The observed negative (positive) SST anomalies during La Niña (El Niño) could be seen as the result of increased (decreased) net heat flux across the sea surface. Tropical cyclone activity varies between El Niño and La Niña as a result of anomalous wind and moisture patterns during each ENSO phase.

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The Tasman Sea contains the largest noncoastal surface chlorophyll‐a concentrations within the South Pacific Ocean. Observations of ocean color from SeaWiFS demonstrate that the chlorophyll‐a seasonal cycle is characterized by a large austral spring bloom and a much smaller fall bloom separated by periods of lower concentrations, typical of communities within the North Atlantic Ocean. However, the seasonal cycle of the mixed layer depth of the Tasman Sea is much more similar to the North Pacific Ocean, whose persistent winter stratification results in relatively constant chloropohyll‐a concentrations. Examination of eddy kinetic energy from satellite altimetry (TOPEX/Poseidon and ERS‐2 blended product) reveals that the western Tasman Sea contains a large number of eddies originating within the East Australian Current that coincide spatially with the blooms. Upwelling and downwelling associated with these eddies greatly increase vertical mixing within the upper ocean, offsetting the normally shallow winter mixed layer, which leads to a chlorophyll‐a seasonal cycle much like that of the North Atlantic Ocean.