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The Gulf Stream (GS) is a strong, fast moving ocean current off the East Coast of the United States that transports warm tropical/subtropical waters northward in the Atlantic Ocean. The GS is easily identified from satellite observations. In the past, it has been idealized as a smooth stream, but the GS actually moves like an unrestrained garden hose on full blast, meandering as it propagates along the US East Coast. After the Gulf Stream separates from the coast near Cape Hatteras, North Carolina, it becomes more unstable with meanders growing larger downstream. Meanders often pinch off from the current creating circular vortices, otherwise known as eddies or rings.
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Because of the intimate relationship between salinity and processes associated with the water cycle (evaporation, precipitation, ice freezing and melting, river discharge, and ocean circulation), ocean salinity is a key indicator of the Earth’s water cycle and thus has crucial societal relevance.
Salinity is an important factor (temperature being another) that determines the density of water parcels. Spatial variations of ocean density can create pressure forces that drive ocean circulation. Ocean circulation can redistribute salinity and spatial variations of salinity can in turn affect density and thus ocean circulation.
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The northern polar region, including the Arctic Ocean’s sea ice cover, is rapidly evolving in association with climate change. In this remote and harsh environment, satellites provide excellent observational tools to identify and monitor these changes. The longest continuous satellite record of the Arctic commenced in 1979 with the identification of areal sea ice extent using passive microwave data.
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Over twenty years ago NASA and French partners, CNES, collaborated on what became the first of a series of important oceanographic missions that have been measuring ocean surface topography from space ever since. This first mission, TOPEX/Poseidon (T/P), is no longer operational, having exceeded its expected lifetime of 5 years to provide over 13 years of data. Two follow-on missions, Jason-1, and the Ocean Surface Topography Mission/Jason-2 (OSTM/Jason-2) launched in 2001 and 2008, respectively, and have extended the time series of data to over 20 years.
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There's an old adage (with several variations) that California has four seasons: earthquake, fire, flood and drought. While Californians happily cede the title of Hurricane Capital of America to U.S. East and Gulf coasters, every once in a while, Mother Nature sends a reminder to Southern Californians that they are not completely immune to the whims of tropical cyclones. Typically, this takes the form of rainfall from the remnants of a tropical cyclone in the eastern Pacific, as happened recently when the remnants of Hurricane John brought rain and thunderstorms to parts of Southern California. But could a hurricane ever make landfall in Southern California?
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![Global mean sea level from altimetry from 1992 to 2012 with annual and semi-annual variations removed and smoothed with a 60-day running mean filter [Nerem et al., 2010].](/sites/default/files/content/OceanStory-GRACE-2012-10-fig1.PNG) |
Satellite altimetry shows that global mean sea level (GMSL) dropped by 5 mm over the course of a few months during 2010-11. Currently, GMSL rises by about 3.3 mm/yr due to thermal expansion and increased water mass from melting ice sheets. Observations from the Gravity Recovery And Climate Experiment (GRACE) reveal that the sudden drop in sea level was related to a temporary loss of ocean water that was redistributed by evaporation, rain, and winds to the continents. High precipitation events occurred during the 2010-11 La Niña and brought a massive amount of water to Australia and northern South America. Comparing GRACE measurements of continental water storage in these regions to the loss in global ocean mass suggests that this vast amount of rain was equivalent to the water that was "lost" from the ocean in 2010-11.
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Final preparations of the research vessel (R/V) Knorr are underway at the Woods Hole Oceanographic Institute for one of a series of 5 cruises during 2012 and 2013 that are part of an innovative research program called SPURS. Funded by NASA in collaboration with NSF, NOAA and also involving European participation (e.g. France, Spain), the Salinity Processes in the Upper Ocean Regional Study (SPURS) project aims to improve our understanding of salinity processes in the upper ocean and their importance to the global oceanic water cycle.
The R/V Knorr cruise starts on September 6, 2012 and runs for 33 days. During this time, 3 SPURS moorings with diverse instrumentation will be deployed, a 6 day period of control volume sampling within a 200x200km2 region for both bulk and micro salinity structure characterization will occur, and a similar period of dynamical feature site sampling is scheduled for the tail end of the cruise before it terminates in the Azores on October 9 (Figure 1).
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Aquarius' salinity observations show a clear signature of TIWs near the equator in the Pacific Ocean where large contrasts in salinity occur between the saltier waters of the South Pacific and fresher waters of the North Pacific. Salinity variability associated with TIWs is larger near the equator, while sea surface temperature and sea level variability associated with the waves is larger a few degrees north of the equator. The Aquarius data reveal that TIWs travel faster at the equator than they do a few degrees to the north, a feature that had not been previously captured by TIW studies using SST and SSHA.
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Sea surface temperature anomalies (SSTA) in the Eastern Pacific, specifically off the Peruvian coast, have shown a recent warming. SSTA is defined as the difference between the actual temperature and normal conditions for that time of year. Negative anomalies indicate cooler than normal temperatures, while positive anomalies indicate warmer than normal temperatures. Warm anomalies greater than 2°C have been persistent off the northern to central coast of Peru for over one month. Such warming events off Peru have been historically known to precede El Niño conditions in the Equatorial Pacific. Although it is too early to determine whether such warm anomalies will lead to a shift to El Niño conditions in the Equatorial Pacific, some local effects have already been seen.
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In late September 2011, local reports indicated the presence of intense algal blooms along the Southern California coastline.
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This was followed in early October by an unusual congregation of blue whales feeding near Los Angeles, including shipping lanes where the whales could be at severe risk. The continued presence of these whales indicated a readily available and concentrated food source of krill, small shrimp-like crustaceans.
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An examination of satellite data available through PO.DAAC provides information on the oceanographic conditions that existed then and how the conditions may have been conducive to intense algal blooms.
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