Jerry L. Miller

Interannual variability of the sea surface temperature in the South Brazil Bight

In the austral winter of 1993, during a COROAS hydrographic cruise in the South Brazil Bight (SBB), an unexpected mass of cold and fresh water was observed on the continental shelf near 23°S. Subsequent analyses of different data sets suggested that the origin of that water was probably the Argentine continental shelf, near the Rio de la Plata mouth. In this article, a 13-year time series of AVHRR Sea Surface Temperature anomalies is analyzed to investigate the occurrence of this phenomenon in other periods. The results of these analyses and a good correlation with the Southern Oscillation Index suggest that the penetration of these waters into the SBB occurs in a frequency that may be associated with ENSO events.

Airborne Salinity Mapper Makes Debut in Coastal Zone

New technology has been developed through a joint public-private partnership that could greatly improve the ocean sciences communitys ability to study coastal oceanography in the same way that satellitebased infrared imaging revolutionized basinscale oceanography. Recent advances in passive microwave technologies and novel means of integrating those advances haveled to the development of the Scanning Low-Frequency Microwave Radiometer (SLFMR) for remote sensing of sea-surface salinity. Designed and built for the National Oceanic and Atmospheric Administration (NOAA), the SLFMR—also known as the salinity mapper—was recently used by a team of scientists from government and industry to generate the first remotely sensed image of sea-surface salinity (Figure 1). This image of salinity was obtained near the mouth of Chesapeake Bay, Virginia, during the Naval Research Laboratorys (NRL) Chesapeake Outflow Plume Experiment (COPE), elements of which were conducted in collaboration with NOAA.

A Modelling Study of Coastal Upwelling Driven by Wind and Meanders of the Brazil Current

Abstract A numerical model is used to investigate coastal upwelling in the South Brazil Bight. The wind in the area is predominantly from the northeast, especially in summer, which is upwelling favorable. Reversals of the wind direction are frequent and intense during the winter, due to the passage of frontal systems. The offshore circulation is dominated by the Brazil Current, which flows southward meandering around the 200 m isobath. Significant shelf-break upwelling has being associated with Brazil Current cyclonic meanders. To assess the relative importance of the two processes in the pumping of South Atlantic Central Water (SACW) onto the continental shelf, three cases are analyzed: (1) wind-driven upwelling; (2) upwelling induced by Brazil Current meanders and (3) both effects acting together. The results show that in the coastal area upwelling/downwelling is mainly caused by the wind, whereas the cyclonic meanders of the Brazil Current are the dominant mechanism in the generation of vertical velocities over the shelf break and slope. This meander-induced upward motion brings the SACW to shallower depths, where it is influenced by the wind. In this situation, when both effects act together, the SACW penetrates all the way to the coast.

Updated bathymetry of the Anegada- Jungfern Passage complex and implications for Atlantic inflow to the abyssal Caribbean Sea

Recent bathymetric, hydrographic and direct velocity measurements indicate that a previously unexplored deep passage in the northeastern Caribbean Sea may play a significant role in the abyssal ventilation of this basin. The Anegada-Jungfern Passage complex has long been recognized as the sole pathway for deep Atlantic inflow to the eastern Caribbean. The Anegada Passage (sill depth 1915 m) connects the Atlantic Ocean with the small Virgin Islands Basin, while Jungfern Passage (sill depth 1815 m) connects the latter with the large and deep Venezuela Basin comprising the eastern third of the Caribbean Sea. In the region of Jungfem Passage recent bathymetric measurements reveal additional, shallower routes for Atlantic inflow at depths between 1710 and 1630 m. Despite the relatively shallow controlling depths of these passages, direct measurements of velocity and watermass properties reveal an active inflow of water of Atlantic origin. Bathymetric and other oceanographic observations indicate that the previously unexplored Grappler Channel (sill depth 17 10 m; located just west of Jungfern Passage) is responsible for up to 20% of the total inflow to the abyssal Caribbean from the mid-depth Atlantic (about 0.2 Sv).

A numerical study of the Plata River plume along the southeastern South American continental shelf

The Rio de la Plata, one of the largest rivers on Earth, discharges into the ocean waters from basin that covers a large area of South America. Its plume extends along northern Argentina, Uruguay, and southern Brazil shelves strongly influencing the ecosystems. In spite of this, little is known about the mechanisms that control it. Here we report results of simulations with POM carried out to investigate the roles of wind and river discharge in Plata plume dynamics. Different outflows were explored, including an average climatological value and magnitudes representative of La Nina and El Nino. Forcing the model with river discharge the average plume speed was directly related to the outflow intensity. The Plata northward extension varied from 850 to 1550 km and for average discharge a band of low salinity waters formed from the estuary up to 30oN of South Brazilian Shelf. Upwelling and downwelling winds were applied after 130 days. The distribution of low salinity waters over the shelf was more sensitive to the wind direction than to the river outflow variability. Downwelling winds were very capable of advecting the low salinity signal downshelf. Upwelling winds were efficient in eroding the plume, which was basically detached from the coast by Ekman drift. Abnormal plume intrusions toward low latitudes may be a result of the original plume position coupled with events of persistent strong downwelling favorable winds.

Deriving Sea Surface Salinity and Density Variations From Satellite and Aircraft Microwave Radiometer Measurements: Application to Coastal Plumes Using STARRS

Using brightness temperature Tb measurements from L-band airborne microwave radiometers, with independent sea surface temperature (SST) observations, sea surface salinity (SSS) can be remotely determined with errors of about 1 psu in temperate regions. Nonlinearities in the relationship between Tb, SSS, and SST produce variations in the sensitivity of salinity S to variations in Tb and SST. Despite significant efforts devoted to SSS remote sensing retrieval algorithms, little consideration has been given to deriving density D from remotely sensed SSS and SST. Density is related to S and T through the equation of state. It affects the oceans static stability and its dynamical response to forcings. By chaining together two empirical relationships (flat-sea emissivity and equation of state) to form an inversion algorithm for sea surface density (SSD) in terms of Tb and SST, we develop a simple L-band SSD retrieval algorithm. We use this to investigate the sensitivity of SSD retrievals to observed Tb and SST and infer errors in D for typical sampling configurations of the airborne Salinity, Temperature, And Roughness Remote Scanner (STARRS) and satellite-borne Soil Moisture and Ocean Salinity (SMOS) and Aquarius radiometers. We then derive D from observations of river plumes obtained using STARRS and demonstrate several oceanographic applications: the observations are used to study variations in T and S effects on D in the Mississippi plume, and the across-shelf density gradient is used to infer surface geostrophic shear and subsurface geostrophic current in the Plata plume. Future basin-scale applications of SSD retrievals from satellite-borne microwave radiometers such as SMOS and Aquarius are anticipated.

Development and applications of STARRS: a next generation airborne salinity imager

A new generation of airborne salinity imager, the Salinity Temperature and Roughness Remote Scanner (STARRS), has been designed and is currently under construction with delivery expected shortly. With both significantly lower noise levels and enhanced capability to measure secondary parameters, including sea surface temperature and roughness, STARRS will serve as both an operational survey tool and as a test-bed for refinement of retrieval algorithms.

Enhanced stratification in the lower Chesapeake Bay following northeasterly winds

Abstract Density data from a lower Chesapeake Bay transect obtained after two northeasterly wind events were used to describe the effects of these events on the density field in the lower estuary. The first northeaster occurred in early August 1995 and the second northeaster was related to the passage of hurricane Felix off the lower bay in mid-August 1995. The latter northeaster prolonged a period of persistent winds from the N and NE that began in early August and caused storm surges of similar magnitude to the former northeaster. The salinity fields observed after the early August event suggested encroachment of coastal waters into the lower bay as reflected by high salinities throughout the transect. Two days after weakening of the winds related to Felix, the density distribution across the lower bay showed strongly stratified conditions. This behavior suggested that the inflow of coastal water into the lower bay and the wind mixing related to Felix combined to produce a vertically uniform density gradient perpendicular to the bay entrance that relaxed after the winds weakened. This weakening of the winds coincided with neap tidal currents, which were not energetic enough to maintain vertical homogeneity and must have allowed the self-adjustment of the density gradient and the seaward advection of relatively buoyant waters near the surface. These mechanisms were illustrated with simplified numerical experiments. The findings of this study are used to propose the hypothesis that, in general, enhanced stratification and flushing in the lower bay will ensue the relaxation of a northeasterly wind event, provided that this relaxation coincides with a weak friction regime, i.e., neap tides.

Chapter 19 Sea surface salinity: Toward an operational remote-sensing system

Abstract Salinity is an important component of biological and physical processes in the ocean, but its distribution throughout the ocean is poorly known. Passive microwave sensors are capable of measuring sea surface salinity, and recent advances in technology suggest that such measurements may soon be feasible on a global basis from Earth orbit. Aircraft-mounted instruments have been developed to validate the technology and address the problem of developing robust algorithms for remote sensing of sea surface salinity. Two aircraft instruments, the Scanning Low Frequency Microwave Radiometer (SLFMR) and the Electronically Scanned Thinned Array Radiometer (ESTAR), have successfully demonstrated remote sensing of salinity in the coastal ocean. Sensors for monitoring salinity from space that utilize the thinned array technology demonstrated by ESTAR have recently been proposed to the National Aeronautics and Space Administration and the European Space Agency.

Optimizing Performance of a Microwave Salinity Mapper: STARRS L-Band Radiometer Enhancements*

Abstract Airborne microwave radiometers for salinity remote sensing have advanced to a point where operational surveys can be conducted over the inner continental shelf to observe the evolution of freshwater plumes emanating from rivers and estuaries. To determine seawater microwave emissivity, and hence conductivity and salinity, precisely and accurately demands high instrument sensitivity, stability, and sampling rates; such requirements involve significant design trade-offs. The Salinity, Temperature, and Roughness Remote Scanner (STARRS) was developed to enhance these features relative to existing instruments. The authors describe here key elements of the STARRS design and the results of early performance assessments and deployments. During early deployments, the instrument performed well in areas of moderate to high salinity signal-to-noise ratio, but more homogenous areas revealed band-limited random signal fluctuations on the order of a 6-min period and ∼1-K amplitude that were of internal origin. ...