Abstract. A major accomplishment of the recently completed Tropical Ocean-Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal-to-interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database. A primary phenomenological focus of TOGA was interannual variability of the coupled oceanatmosphere system associated with E1 Nifio and the Southern Oscillation (ENSO). Prior to the start of TOGA, our understanding of the physical processes responsible for the ENSO cycle was limited, our ability to monitor variability in the troi•ical oceans was primitive, and the capability to predict ENSO was nonexistent. TOGA therefore initiated and/or supported efforts to provide real-time measurements of the following key oceanographic variables: surface winds, sea surface temperature, subsurface temperature, sea level and ocean velocity. Specific in situ observational programs developed to provide these data sets included the Tropical AtmosphereOcean (TAO) array of moored buoys in the Pacific, a surface drifting buoy program, an island and coastal tide gauge network, and a volunteer observing ship network of expendable bathythermograph measurements. Complementing these in situ efforts were satellite missions which provided near-global coverage of surface winds, sea surface temperature, and sea level. These new TOGA data sets led to fundamental progress in our understanding of the physical processes responsible for ENSO and to the development of coupled ocean-atmosphere models for ENSO prediction.And thorough this distemperature we see the seasons alter

Abstract. An anomalous climatic event occurred in the Indian Ocean (IO) region during [1997][1998], which coincided with a severe drought in Indonesia and floods in parts of eastern Africa. Cool sea surface temperature anomalies (SSTAs) were present in the eastern IO along and south of the equator. Beginning in July 1997, warm SSTAs appeared in the western IO, and they peaked in February 1998. An ocean general circulation model is employed to investigate the dynamic and thermodynamic processes that caused the SSTAs associated with this and other similar IO events. The eastern cooling resulted from unusually strong upwelling along the equator and Sumatra. The Sumatran upwelling was forced both locally by the stronger alongshore winds and remotely by equatorial and coastal Kelvin waves. By the end of 1997, weakening of the winds and the associated reduction in latent heat loss led to the elimination of the cold SST anomalies in the east.The western warming was initiated by weaker Southwest Monsoon winds and maintained by enhanced precipitation forcing, which resulted in a barrier layer structure. Analysis of the mixed layer temperature equation indicates that a downwelling Rossby wave contribution was crucial for sustaining the warming into February 1998. It is tempting to suppose that the 1997 event was related to the E1 Nifio-Southern Oscillation (ENSO) event that took place in the Pacific at the same time. Indeed, weaker IO events occur quite regularly in the control run that evolve similarly to the 1997 event, and they are often but not always related to ENSO. We speculate that these events represent a natural mode of oscillation in the IO, which is externally forced by ENSO but also excited by ocean-atmosphere interactions internal to the IO. IntroductionAn extreme climatic event took place in the Indian Ocean (IO) during 1997 and early 1998. It was associated with the second-largest sea surface temperature anomalies (SSTAs) occurring in the region during the past half century. Plate la illustrates the time development of observed SSTAs along the equator during the event. In the late spring of 1997 a surface warming ensued over the western region. (Throughout this paper, seasons always refer to those in the Northern Hemisphere.) It peaked in February 1998, by which time it had spread across most of the tropical IO.Strong cooling was evident in the eastern ocean by September 1997, and it continued into January 1998. As a consequence of these changes, there was an equatorial SST gradient from east to west, a reversal of the climatological situation. The wind stress field was also highly unusual during the fall, with easterlies along the equator replacing the climatological west½rli½s (Plate 2a) and strengthened alongshore winds off It is reasonable to suppose that this remarkable IO event was related to the E1Nifio-Southern Oscillation (ENSO) event that took place at the same time in the Pacific. In fact, a number of similar but weaker IO events occurred during the past 40 years that are also related to ENSO (s...

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A coupled ocean-atmosphere data assimilation procedure yields improved forecasts of El Niño for the 1980s compared with previous forecasting procedures. As in earlier forecasts with the same model, no oceanic data were used, and only wind information was assimilated. The improvement is attributed to the explicit consideration of air-sea interaction in the initialization. These results suggest that EI Niño is more predictable than previously estimated, but that predictability may vary on decadal or longer time scales. This procedure also eliminates the well-known spring barrier to EI Niño prediction, which implies that it may not be intrinsic to the real climate system.

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The Caribbean region shows maxima in easterly winds greater than 12 m s Ϫ1 at 925 hPa in July and February, herein referred to as the summer and winter Caribbean low-level jet (LLJ), respectively. It is important to understand the controls and influences of the Caribbean LLJ because other LLJs have been observed to be related to precipitation variability. The purpose of this study is to identify the mechanisms of the Caribbean LLJ formation and variability and their association to the regional hydroclimate. Climatological fields are calculated from the North American Regional Reanalysis and the 40-yr ECMWF Re-Analysis from 1979 to 2001. It is observed that the low-level (925 hPa) zonal wind over the Caribbean basin has a semiannual cycle and an interannual variability, with greater standard deviation during boreal summer. The semiannual cycle has peaks in February and July, which are regional amplifications of the large-scale circulation. High mountains to the south of the Caribbean Sea influence the air temperature meridional gradient, providing a baroclinic structure that favors a stronger easterly wind. The boreal summer strengthening of the Caribbean LLJ is associated with subsidence over the subtropical North Atlantic from the May-to-July shift of the ITCZ and the evolution of the Central American monsoon. Additionally, the midsummer minimum of Caribbean precipitation is related to the Caribbean LLJ through greater moisture flux divergence. From May to September the moisture carried by the Caribbean LLJ into the Gulf of Mexico is strongest. The summer interannual variability of the Caribbean LLJ is due to the variability of the meridional pressure gradient across the Caribbean basin, influenced by tropical Pacific variability during summer.

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