Showing papers by "Robert Evans published in 1985"

Calibration of advanced very high resolution radiometer infrared observations

Abstract: A detailed analysis of the calibration procedures for the NOAA advanced very high resolution radiometer (AVHRR) based on thermal vacuum test data was performed as part of the Warm Core Rings Experiment. We find systematic differences in the derived calibration results and those reported in the various addenda to work by Lauritson et al. (1979). A weak, but important, dependence in calibration upon internal operating temperature is also observed. Calibration results for various AVHRR radiometers show instrument specific changes in the relative emittance between internal and external calibration targets. A consistent calibration methodology is developed based on this analysis of the thermal vacuum test data. Use of these new results provides an improvement of radiometer calibration at the ±0.2°C level. Such an improvement is quite important to the absolute accuracy of surface thermal fields which are derived from these data utilizing various multichannel atmospheric water vapor correction schemes. Demonstration of such accuracies with presently operational sensors is of importance to climate related studies being planned for the next decade since it shows that appropriate processing can lead to higher-quality SST fields.

Chronology of warm-core ring 82B

Abstract: The chronology presently derived from satellite thermal imagery to describe the formation and life history of the warm core ring 82B furnishes insight into a classification of features and discrete events associated with Gulf Stream warm core rings; these events are thereby put in a broader spatial and temporal context. The interactions of the ring with surrounding waters are noteworthy, and the existence of vortex-vortex interactions is shown to be a significant cause of local water advection through streamer activity. Acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and its environs.

Phytoplankton blooming off the u.s. East coast: a satellite description.

Abstract: A "bloom" of near-surface phytoplankton occurs in the Atlantic Slope region of the western Atlantic Ocean off the U.S. East Coast in the spring. Satellite time series of sea-surface temperature and phytoplankton pigment concentration, derived from measurements of the National Oceanic and Atmospheric Administration NOAA-7 Advanced Very-High-Resolution Radiometer and the National Aeronautics and Space Administration Nimbus-7 Coastal Zone Color Scanner, respectively, give information on the spatial extent and temporal development of such a bloom for a 28-day period in April through May 1982. The phytoplankton concentration of the slope area is comparable to that of the Atlantic Shelf. Total primary productivity of the slope during this period is equivalent to that of the shelf. The primary productivity within a warm-core ring and in the Gulf Stream system is less by a factor of 2.

The form of the density profile at a liquid-gas interface

Abstract: The form of the density profile at the liquid-gas interface of some model fluids is investigated using a simple free-energy functional For fluids with attractive Yukawa potentials we find that the profile decays exponentially into the bulk regions with a decay length greater than the appropriate bulk correlation length; the two lengths become closer and diverge in the same fashion at the critical temperature We contrast this decay with that found for fluids with attractive van der Waals potentials where the profile decays asymptotically as z -3 The results of numerical calculations suggest that the effects of van der Waals' potentials would be difficult to observe in experiments or in computer simulations of liquid-gas interfaces We compare the results of our calculations for fluids with truncated Lennard-Jones potentials with those of recent simulations The theory provides a rather good account of the interfacial width and surface tension as a function of temperature Our results show that truncatio

Small-scale cyclones on the periphery of a Gulf Stream warm-core ring

Abstract: Small-scale cyclones found around Gulf Stream warm-core ring 82B are investigated by using infrared satellite images and current information obtained with an acoustic-Doppler velocimeter. Currents in these cyclones reveal speeds ranging from 20 to 80 cm/s. One small cyclone or 'ringlet' found in June 1982 was studied extensively by removing the basic rotational velocities of 82B. The azimuthal velocity field for this ringlet was used with the gradient current equation to calculate the absolute dynamic topography at 100 dbar. It was found that the ringlet was 13 dyn-cm lower than its surroundings. In addition, neglect of the centrifugal term would have changed the dynamic topography of the ringlet by 30 percent. From a comparison with CTD data the absolute reference level was determined, and a vertical profile of horizontal currents was calculated for the ringlet. Other cyclones were found throughout the slope water region around warm-core ring 82B with observable lifetimes of 1 to 2 weeks. The northeast quadrant of 82B was a favored generation site for ringlets. Two cyclones were observed to form in this region and were advected anticyclonically around 82B. Typically, at any one time, six cyclones with diameters of approximately 40 to 50 km can be detected north of the Gulf Stream by using satellite images.

Pairwise correlations at a fluid-fluid interface The influence of a wetting film

Abstract: Density-density correlations in a planar interface of a neutral, multi-component fluid mixture are analysed. For a ‘normal’ liquid-gas or liquid-liquid interface the transverse (parallel to the interface) correlations exhibit Ornstein-Zernike behaviour with a common correlation length ξT = (σ/b)1/2, where σ is the surface tension and b is determined by the external fields. If, however, the interface corresponds to a near complete wetting situation so that a thick film of a third fluid phase (β) intrudes between the two bulk phases α and γ, the transverse correlations do not, in general, exhibit Ornstein-Zernike behaviour. Rather they exhibit more complex structure for small transverse wave numbers which depends on the ‘stiffness’ of the wetting film. In the limit of a very thick film Ornstein-Zernike behaviour occurs in both edges, the correlation length depending on the value of σ and b appropriate to the individual interface so that ξαβ T = (σαβ/b αβ)1/2 and ξβγ T = (σβγ/b βγ)1/2. The theoretical analys...