bluuebunny/crossref_metadata_2025 huggingface dataset:
Radar tests of the precipitation hypothesis for thunderstorm electrification
Authors: Williams Earle R. , Lhermitte Roger M.
Published: February 2008

The contribution of falling precipitation to thunderstorm electrification is examined from an energy standpoint by means of radar measurements of precipitation. The gravitational power associated with falling precipitation is compared with estimates of the thunderstorm electrical output as a test of a causal relationship between these two quantities. The relative importance of the gravitational and electrical forces acting on precipitation particles is investigated by monitoring the stability of particle vertical motions to lightning‐associated changes in electric field. The general absence of abrupt particle velocity changes is difficult to reconcile with the gravitational power determinations in electrically active storms unless the electrical energy contribution from convective motions is substantial.
Sheetlike plumes near a heated bottom plate at large Rayleigh number
Authors: Tamai Nobuyuki , Asaeda Takashi
Published: February 2008

Fundamental mechanisms of sheetlike plumes generated on a heated bottom plate have been studied experimentally by flow visualization and confirmed by temperature measurements. The range of the flux Rayleigh number was between 106 and 1012. The Prandtl number was between 6.0 and 8.7. The values of aspect ratio were 3 to 50. A plan of sheetlike plumes adjacent to the bottom plate takes a polygonal pattern, and these sheetlike plumes are named bursting lines in this paper. The average length of the side of these bursting lines is expressed as a sole function of flux Rayleigh number Raƒ when the length is nondimensionalized by fluid depth. It is confirmed that sheetlike plumes consist of a set of thermals that are repeatedly discharged along bursting lines and that essentially show a stochastic nature from a microscopic point of view. It is also shown that the nondimensional frequency of the production of thermals is proportional to Raƒ, and the dimensionless duration is inversely proportional to the square root of Raƒ. The accordance of intervals of thermals in the initial stage with those in the quasi‐steady convective motion infers that the generation mechanism of thermals remains unchanged under the existence of global circulation.
Seasonal variation in wind speed and sea state from global satellite measurements
Authors: Sandwell David T. , Agreen Russell W.
Published: February 2008

The GEOS 3 altimeter, which collected data intermittently for nearly 4 years, has measured significant wave heights and surface wind speeds over most of the world's oceans. Using these data, we have constructed contour maps of spatial variations in sea state and wind speed for winter and summer. To obtain reliable averages in the southern oceans, we low‐pass filtered the data using a two‐dimensional Gaussian filter with a half width of 600 km. The wind speed maps show that the zonal surface wind patterns, such as the westerlies, the horse latitudes, the trade winds, and the doldrums, shift south by about 10° between winter and summer. As expected, the highest wind speeds and sea states occur during the winter months in the mid‐latitudes, 30°–60°. The most striking feature of the maps, however, is the large asymmetry in the summer to winter variation between the two hemispheres. The largest seasonal variations in sea state and wind speed occur in the northern hemisphere oceans and especially in the North Atlantic, where there is almost a factor of 2 variation. In contrast, the summer to winter variation in wind speed and sea state in the southern hemisphere oceans is relatively small. For example, the summer to winter increase in wind speed at 50°S is less than 10%, while at 50°N it is more than 50%. This differing variability can be attributed to the asymmetric distribution of continental area between the two hemispheres and the low effective heat capacity of the continents relative to the oceans.
The variation of fine structure within a Gulf Stream ring
Authors: Mied Richard P. , Lindemann Gloria J.
Published: February 2008

We examine the isotherm displacement fine structure spectra obtained from expendable bathythermograph casts at different places within a Gulf Stream ring. If N is the Brunt‐Väisälä frequency and N0 = 1 cph, we find that spectra from different depths group together fairly well with (N/N0) scaling and roll off as ∼k−2. If ζ is the isotherm displacement, scaled displacement variances (N/N0)n 〈ζ2〉 (n = 0, 1, 2; N0 = 1 cph) formed from the wave number decade 0.04≤k ≤0.4 cpm are regressed upon the vertical mesoscale shear. It is found that when n = 0 or 1, the scaled variance and the shear are negatively correlated, but the potential energy variance (n = 2) and the shear are uncorrelated. An explanation for the correlation when n = 0 is offered by examining the effect which a vertically sheared flow has upon internal waves and upon a patch of mixed fluid.
Seasonal variability of alongshore geostrophic velocity off central California
Authors: Chelton Dudley B.
Published: February 2008

Seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central California (one off Point Sur and the other off Point Conception). The seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods. Attention is focused on variability over the outer continental slope. Geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from February to September and poleward flow from October to January. The flow deeper than 100 m is distinctly different along the two sections. The nearshore deep flow is predominantly semiannual off Point Conception (notably different from surface flow) and poleward all year with maxima in December and June. This semiannual variability at depth is a prevalent feature of the California Current system. The nearshore deep flow off Point Sur is unusual in that it is predominantly annual with maximum poleward flow in December and weak equatorward flow from March to May. The seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects: (1) The surface flow leads the predominantly annual wind forcing in this region by about one month; and (2) the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations, with a phase lag of approximately 2 months. However, contrary to the results of existing dynamical models, the semiannual poleward pressure gradient and undercurrent off Point Conception appear to be unrelated to the wind forcing, which is predominantly annual in this region. These semiannual variations are highly coupled to the semiannual flow throughout the water column inside the Southern California Bight, suggesting that they may be topographically generated.
A numerical model of interactions between a polar ice stream and the ocean: Application to ice stream E, West Antarctica
Authors: Lingle Craig S.
Published: February 2008

A time‐dependent numerical model has been developed to study the dynamics of a polar ice stream grounded below sea level. The model was applied to ice stream E, one of the two most active ice streams draining the Ross Sea sector of the West Antarctic ice sheet. The retarding force, or back stress, from the floating Ross Ice Shelf needed to hold the model grounding line in dynamic equilibrium was found to compare closely with retarding force mapped from field data by earlier investigators. This implies that the grounding line of ice stream E is in fact close to dynamic equilibrium, neither advancing nor retreating rapidly, if the ice stream and its catchment area are approximately in mass balance. Sensitivity tests showed that the model ice stream is more sensitive to changes in back stress from the ice shelf than to changes in the accumulation rate. Changes in back stress can be caused by changes in the average thickness of the ice shelf. The model was used to simulate retreat of the ice stream from the edge of the continental shelf in the Ross Sea during the Holocene period of rising sea level. The sea‐floor was assumed to be isostatically depressed but to remain rigid during retreat. The effect of the assumed retreat history of the Ross Ice Shelf on the computed timing of grounding‐line retreat was investigated by considering several alternative ice shelf histories. The results support the conclusion of earlier investigators that the Ross Ice Shelf caused the grounding line to stop retreating near its present position, after extensive retreat during the Holocene. In addition, the timing of retreat of the calving front of the Ross Ice Shelf exerted major influence on the timing of retreat of the ice stream grounding line.
Air‐ice drag coefficients for first‐year sea ice derived from aircraft measurements
Authors: Walter Bernard A. , Overland James E. , Gilmer Richard O.
Published: February 2008

Turbulent flux measurements were made at four levels (42, 90, 195, and 340 m) by the NOAA P‐3 aircraft over first‐year sea ice in the northern Bering Sea during February 1982. Three profiles of momentum flux and mean wind were used to calculate an air‐ice drag coefficient CD of 3.0 ± .6 × 10−3 referenced to a 10‐m anemometer height. The boundary layer was slightly unstable (zi/L = −1.2, where zi, was the inversion height of 660 m and L the Monin‐Obukhov length). The mean wind speed at the 42‐m height was 17 m/s, and the air temperature was −20°C. From turbulent heat flux measurements the value of the bulk heat transfer coefficient CH was 0.73 ± 1.6 × 10−3, giving a CH/CD of 0.24. The Bowen ratio was greater than 2.8. Comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement, which increases confidence in the calculations. The geostrophic drag coefficient |u*|/|G|, where u* is the friction velocity and G is the geostrophic wind, was 0.047. The turning angle of the surface wind (measured by an anemometer at a height of 3 m on the ice) was 32°, and the ratio of surface wind speed to the geostrophic wind speed was 0.76.
Groups of waves in shallow water
Authors: Elgar Steve , Guza R. T. , Seymour R. J.
Published: February 2008

Wave group statistics predicted by linear theories are compared to numerical simulations, thus determining ranges of spectral shapes for which the theories are valid. It is found that these theories are not generally valid for ocean data because of many assumptions and simplifications beyond linearity and random phase or because their range of applicability does not include the vast majority of ocean conditions. The simulations also provide quantitative information about the variability of linear wave group statistics which is useful when examining ocean field data. The simulation technique is used to show that important ocean gravity wave group statistics are not inconsistent with an underlying wave field composed of linearly superposed random waves. The majority of the field data examined were collected in 10 m depth; significant wave heights varied from about 20 to 200 cm, and the spectral shapes ranged from fairly narrow to broad (1<Qp<6). For the 10–m depth data, the observed mean run length, variance of run length, and probabilities of runs of a given number of waves were statistically consistent with the simulations. In contrast to the apparently linear groups observed in 10 m depth, waves in 2–3 m depth showed marked departures from the linear simulations.
The dynamics of a river‐bay‐delta system
Authors: Wang Flora Chu
Published: February 2008

An analysis has been made to aid our understanding of various phenomena associated with turbulent plane jets that issue from river outlets and discharge into quiescent bays. An integrated form of the hydrodynamic equations of flow continuity and momentum balance, coupled with advective‐diffusion mass transport equations, has been formulated into a two‐dimensional spatial domain. Closed‐form analytical solutions are obtained with the aid of similarity functions for the velocity and sediment concentration profiles. A numerical procedure for estimating the areal and volume deposition of the delta sediments is presented. The Atchafalaya River Delta, a newly developing delta in the south central Louisiana Coast, is used to illustrate analytical techniques. The results of analytical predictions are compared with the results predicted by other statistical and generic approaches; an agreement is found. A sensitivity analysis is performed to assess the relative importance of various parameters in the river‐bay‐delta system.
Production and distributions of sea spray
Authors: Wu Jin , Murray John J. , Lai Ronald J.
Published: February 2008

Sea spray within the lowest meter of the atmospheric surface layer was measured with an optical instrument supported on a raft. Sizes of measured droplets appear to follow a two‐segment equilibrium spectrum; the division of two size regions within the production zone (the ejection range of jet drops), however, differs from that outside. Vertical distributions of droplet concentrations vary greatly with the droplet size; critical diameters for the droplet suspension under various wind velocities are determined. The mass concentrations of droplets at various elevations were also obtained. Longitudinally, the droplets are distributed in patches, whose occurrence appears to correlate well with the frequency of dominant waves.
The slope of sea level along the equator during the 1982/1983 El Niño
Authors: Wyrtki Klaus
Published: February 2008

Observed deviations of monthly mean sea level at seven island stations along the equator in the Pacific have been superimposed on the mean dynamic topography to determine the variations of the east‐west slope of sea surface topography during the 1982/1983 El Niño. The normal east‐west slope is eliminated in January 1983 when the bulk of warm water flowing eastward has reached the coast of South America. The sea surface remains essentially flat from January to June 1983, although zonal winds are very weak until April only. The slope requires several months to be reestablished, and in October and November, sea level along the entire equator is 10 cm or more below normal, indicating a net loss of warm water from the equatorial Pacific.
The sensitivity of a one‐dimensional thermodynamic sea ice model to changes in cloudiness
Authors: Shine K. P. , Crane R. G.
Published: February 2008

A thermodynamic sea ice‐lead model is used to assess the importance of cloud cover changes to modeled ice thickness. For regions of either permanent multiyear ice or seasonal sea ice, the cloud amount variations have relatively little impact. However, for regions where the presence of summer ice is variable from year to year, the predicted ice thickness is strongly dependent on cloud cover. In general, with a snow covered surface, decreased cloud leads to surface cooling while increased cloud gives rise to a surface warming. For a melting bare ice surface, the reverse occurs. The ice model response time is too long for interannual variations in cloud amount to explain interannual variations in ice thickness and extent. Nevertheless, the implication of the results is that numerical modeling of sea ice distribution requires accurate cloud data or cloud prediction and that trends in cloud cover may lead to significant perturbations in sea ice extent and thickness.
A coupled ice‐ocean model of ice breakup and banding in the marginal ice zone
Authors: Smedstad Ole Martin , Røed Lars Petter
Published: February 2008

A coupled ice‐ocean numerical model for the marginal ice zone is considered. The model consists of a nonlinear sea ice model and a two‐layer (reduced gravity) ocean model. The dependence of the upwelling response on wind stress direction is discussed. The results confirm earlier analytical work. It is shown that there exist directions for which there is no upwelling, while other directions give maximum upwelling in terms of the volume of uplifted water. The ice and ocean is coupled directly through the stress at the ice‐ocean interface. An interesting consequence of the coupling is found in cases when the ice edge is almost stationary. In these cases the ice tends to break up a few tenths of kilometers inside of the ice edge.
A comparison of in situ and airborne radar observations of ocean wave directionality
Authors: Jackson Frederick C. , Walton W. Travis , Peng Chich Y.
Published: February 2008

The directional spectrum of a fully arisen ∼3 m sea as measured by an experimental airborne radar, the NASA Ku‐band radar ocean wave spectrometer (ROWS), is compared to reference pitch‐roll buoy data and to the classical SWOP (stereo wave observation project) spectrum for fully developed conditions. The ROWS spectrum, inferred indirectly from backscattered power measurements at 5‐km altitude, is shown to be in excellent agreement with the buoy spectrum. Specifically, excellent agreement is found between the two nondirectional height spectra, and mean wave directions and directional spreads as functions of frequency. This agreement is found despite certain discrepancies between the radar and buoy angular harmonics which are believed to be due to buoy instrumental effects. A comparison of the ROWS and SWOP spectra shows the two spectra to be very similar, in detailed shape as well as in terms of the gross spreading characteristics. Both spectra are seen to exhibit bimodal structures which accord with the Phillips' resonance mechanism. This observation is thus seen to support Phillips' contention that the SWOP modes were indeed resonance modes, not statistical artifacts.
Ice thickness distribution in Davis Strait in February from submarine sonar profiles
Authors: Wadhams Peter , McLaren Alfred S. , Weintraub Ruth
Published: February 2008

A submarine sonar profile obtained in Davis Strait by USS Queenfish in February 1967 has yielded the first quantitative data on ice thickness distribution in the region. Within 50–100 km of the ice edge there is a “marginal ice zone” (MIZ) where the mean draft is 0.25–0.51 m, most of the ice (93–100%) is undeformed, and there are many leads but few ridges, all of them less than 6.1 m in draft. The remainder of the region is an “interior zone” composed mainly of first‐year ice with a mean draft of 0.77–1.66 m, increasing slightly from NE to SW. Level ice is less common than in the MIZ (67–91% of the cover) as are leads. Ridging is more common, with a maximum observed keel draft of 19.56 m. The overall mean ice thickness distribution has a peak at a draft of 1.05 m (1.18 m thickness), identified as the preferred draft of undeformed first‐year ice at this time. Ice draft and keel draft distributions followed a negative exponential distribution at depths beyond 3–4 m, and the distribution of lead widths followed a power law with exponent −2.29.
Vertical profiles of CCl3F (F‐11) and CCl2F2 (F‐12) in the central Arctic Ocean basin
Authors: Wallace Douglas W. R. , Moore Robert M.
Published: February 2008

The anthropogenic chlorofluoro‐methanes CCl3F (F‐11) and CCl2F2 (F‐12) have been measured to depths of 1800 m in the Canada Basin of the Arctic Ocean (approximate position 85°50′N, 108°50′W). The measurements were made as part of the Canadian Expedition to Study the Alpha Ridge (CESAR) during April 1983. Surface layer concentrations beneath the ice were 4.79×10−12 mol/kg (F‐11) and 2.11×10−12 mol/kg (F‐12). Both profiles exhibit a rapid concentration decrease with depth through the halocline and very low, but detectable, concentrations at depths of 350–900 m in the Atlantic Layer. In the Arctic Ocean Deep Water (900–1800 m), concentrations are at or below our practical detection limit of 0.01×10−12 mol/kg. The profiles have been interpreted using two “extreme‐case” lateral ventilation models in order to place bounds on the water column ventilation rates. The “Ventilation age” of the upper portion of the halocline (60–150 m) increases with depth from 4 to 14 years. The core of the Atlantic Layer at this location appears to have been isolated from the surface for at least 30 years.
Introduction: The practice of physical oceanography
Authors: Jennings Feenan D. , Nowlin Worth D.
Published: February 2008

The papers appearing in this special issue of JGR‐Oceans were among approximately 30 presentations made in April 1983 at a symposium honoring Robert O. Reid of Texas A&M University. The authors are his former students and colleagues.

The 2‐day symposium, called the Practice of Physical Oceanography, was convened by Reid's former students to honor him for his “exceptional guidance of graduate students” in his more than 30 years at Texas A&M University. The symposium was planned and organized by Feenan D. Jennings, Executive Director, Office of University Research Services, Texas A&M University; A. D. Kirwan, Jr., University of South Florida,; and William J. Merrell, Jr., and Worth D. Nowlin, Jr., Department of Oceanography, Texas A&M University.
Drifter observations of coastal surface currents during CODE: The statistical and dynamical views
Authors: Davis Russ E.
Published: February 2008

Observations of near‐surface coastal currents were made off the Northern California coast during CODE by using 164 current‐following drifters. These observations are used to describe the two‐dimensional structure of the mean surface flow and the scales of its variability. The mean flow is a broad equatorward current, strongly sheared only within 10 km of the shore, and a mean offshore flow producing an average divergence ∇H·u ≈ 3 × 10−6 s−1. Divergence is uniformly distributed across the shelf, but variation of the alongshore flow causes an upwelling center near Point Arena. The spatial correlation scale is less than 40 km in both the alongshore and across‐shelf directions, even though 55% of the surface kinetic energy is described by a single mode with gradual across‐shelf variation and an alongshore wavelength of the order 200 km. The surface flow is well correlated with flow at 30‐m depth. The Lagrangian time scale (≈1.5 day) is significantly shorter than the Eulerian time scale (≈5 days), indicating that the flow is dominated by highly nonlinear quasi‐stationary eddies. Drifter displacements indicate that the mean lateral eddy transport of passive scalars can be described by an anisotropic and inhomogeneous eddy diffusivity, but this diffusivity cannot be used to relate eddy Reynolds stresses and the mean shear. Analysis of two‐particle separations, which determine the size of dispersing property clouds, shows that dispersal cannot be described by a scale‐dependent diffusivity and indicates the importance of small‐scale convergences in retarding dispersal. Over the entire 100‐km by 50‐km region the surface layer heat budget is dominated by upwelling cooling and surface heating, with onshore eddy heat flux playing a smaller role. Substantial convergence of the alongshore eddy heat flux is apparently required to balance upwelling cooling in the upwelling center. Drifters are found to have a Lagrangian mean acceleration caused by eddy processes. Analysis of this acceleration and of the horizontal flow contributions to the eddy Reynolds stress allows examination of the importance of eddy processes in the mean momentum budget. While the alongshore flow must be in approximate geostrophic balance, there is a clear pattern to the eddy forcing, which appears to be important in the alongshore momentum equation.
Sources and flow patterns of deep‐ocean waters as deduced from potential temperature, salinity, and initial phosphate concentration
Authors: Broecker Wallace S. , Takahashi Taro , Takahashi Timothy
Published: February 2008

Through the deconvolution of ocean chemical data it has been shown that the ratio of O2 utilization to phosphate production in the sea is 175±6 (rather than 138, as proposed by Redfield et al. (1963)). We find no evidence that this ratio changes significantly with location or depth in the sea. We have used this new ratio to calculate the initial phosphate concentrations for the waters sampled during the GEOSECS and TTO programs. The important application of these new results is in constraining the origin and flow patterns of deep waters in the ocean. We believe that a strong case can be made that Antarctic salinity maximum water (i.e., the common water of Montgomery (1958)) is produced by the mixing of waters entering the Antarctic from mid‐depths in the Indian, Pacific, and Atlantic with Weddell Sea bottom water (southern component). Antarctic common water consists of about 45% Weddell Sea bottom water, 30% intermediate waters from the Pacific and Indian oceans, and 25% deep water originating from the northern Atlantic.
Artificial radionuclide tracer supply to the Denmark Strait overflow between 1972 and 1981
Authors: Livingston Hugh D. , Swift James H. , Ostlund H. Gote
Published: February 2008

Measurements of the concentrations of the artificial radionuclides 3H, 137Cs, and 90Sr in the northern Irminger Sea in 1972 and 1981 are reported. In both years, tracer measurements from this area included data from samples of the dense overflow water from the north through Denmark Strait. All three tracers were strongly correlated inversely with salinity in the dense outflows—the tracer maxima being related directly to the salinity minimum. When the tracer characteristics in the outflows in 1972 and 1981 were compared, concentrations of all in 1981 were observed to be about double the 1972 values. The individual tracer concentrations—on a decay‐corrected, density‐normalized basis—were higher in increasing order: 90Sr (+93%) < 3H (+115%) < 137Cs (+150%). The relatively greater increases for 3H and 137Cs were attributed to contributions of new sources of these tracers in northern surface waters: the 3H source is argued to derive from atmospheric hydrological recycling, whereas the 137Cs source is identified as the input to the Greenland and Iceland seas of advected European nuclear fuel reprocessing wastes. Both the tracer and hydrographic data are used to identify northern locations of intermediate water formation capable of supplying the observed dense overflow water characteristics. It is argued, from the time taken for the overflow water to reflect the new surface 137Cs source, that transport from the source to the overflow can be quite rapid (about 2 years).
Formation of ripples in erodible channels
Authors: Kobayashi Nobuhisa , Madsen Ole Secher
Published: February 2008

Formation of ripples and dunes in erodible channels is analyzed by using the hydrodynamic model developed by Kobayashi and Madsen (this issue). Applying the continuity equation of sediment, the propagation velocity of the wavy bed is expressed in terms of the net fluxes of bed load along the wavy bed and suspended sediment out of the bed load transport layer. The spatial variation of the bed load transport rate is derived by analyzing the balance of forces acting on a representative bed load particle on a sloping bed. The net flux of the suspended sediment out of the bed load transport layer is obtained by solving the diffusion equation for the suspended sediment near the bed. The stability analysis predicts that a perturbation that is either fairly short or long relative to the depth of flow will initially grow, depending on whether the flow is hydraulically smooth or fully rough. Thus the model explains why ripples are not observed in experiments involving fairly coarse sediments, since in these cases the flow is rough turbulent.
Advances in satellite sea surface temperature measurement and oceanographic applications
Authors: Njoku E. G. , Barnett T. P. , Laurs R. M. , Vastano A. C.
Published: February 2008

Satellite techniques for measurement of sea surface temperature (SST) are reviewed briefly, and a discussion of satellite SST applications and recent research in oceanography is provided. These applications include the areas of climate, mesoscale oceanography, and fisheries. Examples given focus mainly on the Pacific and California Current regions. Satellite SST data are currently used operationally for fisheries applications and, in conjunction with in situ data, are providing new insights into mesoscale oceanographic phenomena. Requirements for sensor precision and calibration accuracy are more stringent in air‐sea interaction studies and climate research, thus satellite data have gained only qualified acceptance for these applications. Improvements in future satellite instruments, more comprehensive in situ sensor deployments, and better data management procedures should eventually satisfy most oceanography and climate SST requirements.
Large‐scale sea surface temperature variability from satellite and shipboard measurements
Authors: Bernstein R. L. , Chelton D. B.
Published: February 2008

A series of satellite sea surface temperature (SST) intercomparison workshops were conducted under NASA sponsorship at the Jet Propulsion Laboratory. Three different satellite data sets were compared with each other, with routinely collected ship data, and with climatology for the months of November 1979, December 1981, March 1982, and July 1982. The three satellite data sets were (1) AVHRR—SST estimates produced operationally by the National Oceanic and Atmospheric Administration from the advanced very high resolution radiometer aboard the NOAA polar‐orbiting weather satellites; (2) HIRS/MSU—SST estimates produced by a research group at the NASA Goddard Space Flight Center from the 20‐channel high resolution infrared sounder and the 4‐channel microwave sounding unit, also aboard the same NOAA satellites; and (3) SMMR—SST estimates produced by another group at Goddard from the scanning multifrequency microwave radiometer on the NASA research satellite Nimbus 7. The satellite and ship data were differenced against an accepted climatology to produce anomalies, which in turn were spatially and temporally averaged into 2° latitude‐longitude, 1‐month bins. Monthly statistics on the satellite and ship bin average SST yielded rms differences ranging from 0.58° to 1.37°C and mean differences ranging from −0.48° to 0.72°C, varying substantially from month to month and sensor to sensor. The SMMR generally had the largest rms differences and time‐dependent biases, while the AVHRR and HIRS/MSU had smaller more comparable values. The monthly bins were further smoothed spatially to correspond to 600‐km averages to further suppress the noise of individual observations, particularly for the ship data. When this was done the monthly ship data standard deviations about climatology varied between 0.35° and 0.63°C. Taking these values as true SST signal standard deviation levels, and the satellite‐ship rms differences as noise levels, results in signal‐to‐noise variance ratios of about 0.25 for SMMR and 1.0 for AVHRR and HIRS/MSU. Maps of SST anomaly reveal a complex pattern of partial agreement and disagreement between ship and satellite data. Maps of satellite minus ship and satellite minus satellite SST differences were often dominated by coherent large‐scale patterns of obvious geophysical origin related to distributions of surface wind speed, atmospheric water vapor, cloudiness, and stratospheric aerosols. Unfortunately, the spatial scales of these patterns are often quite similar to those associated with actual SST anomalies. Caution must therefore be exercised when dealing with the satellite data so that errors are not misinterpreted as true SST anomalies.
The distribution of diurnal sea surface warming events in the western Sargasso Sea
Authors: Cornillon Peter , Stramma Lothar
Published: February 2008

Large diurnal sea surface warming exceeding 1°C is common in the western North Atlantic Ocean and is often of large horizontal extent. These events correlate closely with very light winds and high insolation. In the area investigated, 17°–40°N and 55°–80°W, the largest warming is found in the western portion of the ridge associated with the Azores‐Bermuda high, where the lowest wind speeds are observed. The distribution of warming events shows that the largest number occur between June and August, when insolation is highest and percent cloud cover and wind speed are low. The most probable latitude of warming events moves north from approximately 25°N in spring to near 30°N in summer, a shift similar to that seen in the minimum of the climatological winds. Local areas have a probability as high as 30% for diurnal warming in excess of 1°C in the summer. The net heat flux into the ocean, calculated by using monthly mean values for low latitudes in the summer, excluding diurnal warming events, is biased consistently high by as much as 5 W/m2 relative to the same values calculated with warming events included.
Covariances and spectra of the kinematics and dynamics of nonlinear waves
Authors: Tung C. C. , Huang N. E.
Published: February 2008

Using the Stokes waves as a model of nonlinear waves and considering the linear component as a narrow‐band Gaussian process, we derive, for points in the vicinity of still water level, the covariances and spectra of velocity and acceleration components and pressure, taking into consideration the effects of free surface fluctuations. The results are compared with those obtained earlier using linear Gaussian waves.
Introduction
Authors: Pierson Willard J. , Katsaros Kristina B.
Published: February 2008

The URSI (International Union of Radio Science) Commission F convened a symposium and workshop in Israel from May 14 to May 23, 1984, entitled “Frontiers of Remote Sensing of the Oceans and Troposphere from Air and Space Platforms.” The areas of research and application covered by this general topic are very active, indeed, and are undergoing intense development. It was, therefore, a very timely meeting to which it seemed most participants came with a certain sense of anticipation. Preprints of the papers to be presented were available in a bound volume before the symposium as NASA Conference Publication 2303.
Synoptic impacts of NOAA 6/TIROS N data on numerical circulation forecasts
Authors: Druyan Leonard M. , Alperson Zvi , Ben‐Amram Tamar
Published: February 2008

Profiles of retrieved satellite observed temperatures provided to the Israel Meteorological Service (IMS) by the National Environmental Satellite Data and Information Service were used to enhance the specification of atmospheric conditions during three winter periods. Introduction of the satellite data was via three alternative schemes, and the enhanced specifications were used to initialize 48‐hour numerical forecasts with the IMS five‐layer primitive equation model; control forecasts were run in parallel from initial conditions without the satellite data. The study selects one forecast from each period for which discernible impacts on forecast synoptic fields can be attributed to the different initializations. The first two case studies examine the results of only one assimilation scheme and the third relates to all three schemes. Verification of the prognostics show the positive impact of including satellite temperatures in the initialization, but there were also examples of negative impact.
Achieving improved frequency response of the rain structure from spaceborne radar altimeters by employing deconvolution methods
Authors: Goldhirsh Julius , Monaldo Frank M.
Published: February 2008

A technique is described for arriving at improved measurements of the rain structure near the earth's surface from satellite‐borne radars. The method uses deconvolution and Fourier transform procedures and assumes a knowledge of the antenna beam pattern. As an example, the method is directed toward the application of future spaceborne radar altimeters that may contain additional range gates to permit the measurement of rain in the lower troposphere. Using a radar‐measured rain reflectivity profile acquired at Wallops Island, Va., in a simulation example, it is specifically demonstrated that improved measurements of the spatial frequency spectrum of the rain structure may be deduced by means of deconvolution methods, as compared to the measured spectrum derived by beam averaging. Rain measurements are considered vital from the standpoint of providing a flag for altimeter data that may be corrupted by rain. Such measurement capabilities should also provide sorely needed data on rain over the oceans where few or no such data are available for the meteorologist or the communicator interested in space diversity communications.
Satellite definition of the bio‐optical and thermal variation of coastal eddies associated with the African Current
Authors: Arnone Robert A. , La Violette Paul E.
Published: February 2008

The circulation of the African Current along the north coasts of Morocco, Algeria, and Tunisia is shown by seasonal satellite imagery to normally consist of a series of complex anticyclonic eddies that propagate eastward. The large surface area associated with the eddy field illustrates significant amounts of coastal and modified Atlantic waters that are entrained, and the eddies compose the bulk of the net eastward transport. Analysis of the satellite imagery indicates that the turbulent shear produced by the current interacting with the African coast results in the advection of coastal waters into the modified Atlantic water already contained in the eddy field. The biological activity and chemical reactions spawned by the resultant mixing is clearly observed in the ocean color variations depicted in Nimbus 7 coastal zone color scanner (CZCS) visible imagery. The extent of the offshore advection is indicated in the imagery by the high suspended sediment concentrations that border the periphery of the eddies. Sea surface temperature shown by both Nimbus 7 CZCS and NOAA 7 AVHRR (advanced very high resolution radiometer) infrared imagery also illustrate complex flow, although in some imagery the ocean color imagery better defines the patterns. Applications of both visible (ocean color) and thermal imagery are suggested as a method of best determining the patterns of regional flow.
Ocean waves and turbulence as observed with an adaptive coherent multifrequency radar
Authors: Gjessing Dag T. , Hjelmstad Jens
Published: February 2008

An adaptive coherent multifrequency radar system has been developed for several applications. By means of this the velocity distribution (Doppler spectrum) and spectral intensity of 15 different irregularity scales (waves and turbulence) can be measured simultaneously. Changing the azimuth angle of the antennas at regular intervals, the direction of the wave/turbulence pattern on the sea surface can also be studied. Using this radar system, series of measurements for different air/sea conditions have been carried out from a coast‐based platform in southern Norway. Experiments in the Atlantic were also performed with the same equipment, making use of the NASA Electra aircraft. There are many air/sea phenomena that play a role in relation to backscattering of radio waves in the microwave region: gravity waves “modulate” the capillary wave structure, overturning wave crests produce focusing effects and also periodic regions of strong turbulence, and the boundary layer wind field with strong turbulence amplified by the ocean waves will conceivably leave a patchy and even periodic footprint on the sea surface. Internal waves originating from density gradients in this ocean further complicates the sea surface irregularity pattern. By virtue of the fact that the multifrequency radar allows one to measure the velocity distribution (“coherent and incoherent component”) associated with 15 different ocean irregularity scales simultaneously for several azimuth directions, it is possible to study the different air/sea mechanisms in some degree of detail.
The climatology of internal waves in a deep temperate lake
Authors: Wiegand Ronald C. , Carmack Eddy C.
Published: February 2008

Kootenay Lake is a long (100 km), deep (140 m), dimictic lake in southeastern British Columbia. Internal waves were observed over an 18‐month period using three thermistor chains moored along the major axis of the lake. To characterize their seasonal aspects, four types of oscillations are recognized: (1) classical seiches with amplitudes of 10–30 m and periods of 1–2 weeks, (2) intrabasin waves with periods of 2–4 days, (3) large‐amplitude waves resembling nonlinear surges, and (4) high‐frequency waves associated with both the internal surge and large‐amplitude internal seiche motions. The periods of the major components of the internal wave field are determined mainly by morphometry but vary seasonally with stratification. Thus the wind, which not only forces internal waves but can also modify stratification, is important. In large lakes like Kootenay, the thermal structure may vary not only spatially but also temporally at periods comparable to those of the internal waves themselves. Hence the shape and frequency of these waves may be altered as they pass through the lake.
Prediction of phytoplankton growth in response to the frictional decay of a warm‐core ring
Authors: Franks Peter J. S. , Wroblewski J. S. , Flierl Glenn R.
Published: February 2008

A modelling study was conducted to examine the question, Is the high phytoplankton biomass which often develops in warm‐core rings of the Gulf Stream a consequence of the circulation associated with the frictional decay of the ring? A time‐dependent, two‐dimensional (r, z, t) model of plankton dynamics in a hypothetical ring similar in features to warm‐core ring 82B generates a lens of high phytoplankton biomass at ring center. Phytoplankton grow on nutrients advected into the euphotic zone as the depressed warm water in the ring's core rebounds and spreads out at the surface. This vertical motion induced as the ring's rate of rotation slows may be an important process maintaining the high production in warm‐core rings.
On narrow‐band representation of ocean waves: 1. Theory
Authors: Tayfun M. Aziz
Published: February 2008

The description of linear random waves in the form of an amplitude‐modulated carrier wave is known as narrow‐band representation. Herewith, the theoretical basis of such a representation is examined in terms of integral properties of surface spectra and criteria governing the statistical and kinematic characteristics of the carrier wave. These considerations are then extended systematically to derive two narrow‐band type representations for nonlinear waves. The nature of these representations and their statistical properties are discussed and compared with other models such as those proposed earlier by Tayfun (1980) and Huang et al. (1983).
Modeling radiotracers in sediments: Comparison with observations in Lakes Huron and Michigan
Authors: Christensen Erik R. , Bhunia Prasanta K.
Published: February 2008

A comprehensive model for the activity of radionuclides in sediments is presented. The model is based on the advection‐diffusion equations for sediment solids and a radioactive tracer. Mixing, caused by deposit feeders, is taken into account by a half‐Gaussian (HG), integrated Gaussian (IG), or exponential (EX) diffusion coefficient with a maximum value D0 at the sediment‐water interface and an effective mixing depth m, where m = σ(HG), zm (IG), or a (EX). Compaction is described by an exponential bulk sediment density. The differential equations are solved by finite differences, in particular, the Crank‐Nicolson method for the time‐dependent case (Cs‐137). Estimation of the mixing parameters D0 and m is carried out efficiently by minimizing chi‐square for measured and calculated steady state Pb‐210 activities. The derived mixing depths of zm = 4.6 ± 0.1 cm (station 14) and a = 0.8 ± 0.1 cm (station 18) for the cores from Lake Huron are in good agreement with the organism distributions. The corresponding D0 values are 12 ± 2 and 1.5 ± 0.5 cm2/yr, respectively, where the latter number is lower than a previous lower limit estimate (≥ 3.3 cm2/yr), based on 1974 data. These diffusion coefficients are in excellent agreement with those inferred from the densities of Pontoporeia and tubificid oligochaetes (9.3 and 1.6 cm2/yr, respectively). Compared with southern Lake Michigan, there appears to be less sediment focusing in northern Lake Michigan, where the ratios of measured to atmospheric Cs‐137 inventories have an average value of 0.89 and range from 0.32 to 1.41 for six cores from the deep basin. When these ratios are used to correct the Pb‐210 fluxes, we obtain an atmospheric Pb‐210 flux of 0.99 ± 0.06 dpm/cm2/yr. Because of its more realistic activity profiles, we consider the present model to be generally better than previous models.
SIR‐B observations of dominant ocean waves near Hurricane Josephine
Authors: Holt Benjamin , Gonzalez F. I.
Published: February 2008

Radar images of ocean surface waves near hurricane Josephine were acquired with the shuttle imaging radar B (SIR‐B) system on October 12, 1984. Fast Fourier transform analyses of the images have been performed along most of the 600‐km image track. These data reveal the presence of at least two dominant wave systems which undergo significant spatial variations in wavelength and direction.
Mapping climatological seasonal variations of surface currents in the tropical Atlantic using ship drifts
Authors: Richardson Philip L. , Walsh David
Published: February 2008

The seasonal variability of current velocities in the tropical Atlantic was studied by grouping ship drift velocity observations into 2° × 5° boxes and calculating monthly mean velocity values. These values were used to calculate and map the annual mean velocity, the seasonal variation about the mean, the annual and semiannual harmonics, and the first two empirical orthogonal functions (EOFs). The seasonal variation is primarily zonal in the equatorial band and in the North Equatorial Countercurrent (NECC) and primarily alongshore near the coast of South America. Maxima of seasonal variation of 23 cm/s are centered in the NECC near 6°N, 42.5°W and in the Gulf of Guinea near 2°N, 7.5°W. Most (∼80%) of the variance in the NECC and along the western boundary of the area studied has an annual period; most of the variance along the equator in the mid‐Atlantic has a semiannual period. Over the whole region, 49% of the seasonal variance is explained by the annual harmonic, and 69% is explained by a combination of the annual and semiannual harmonics. The second EOF contains 29% of the variance of the data set and shows a simultaneous speeding (slowing) of the major equatorial currents (the South Equatorial Current (SEC), the North Brazil Current, the NECC, and the Guinea Current) along their principal axes of variation with a concurrent slowing (speeding) of the Guyana Current and the Brazil Current. The pattern of variation resembles a large equatorial gyre centered along 4°N that flows clockwise from May to September and counterclockwise most of the rest of the year. The first EOF accounts for 35% of the variance and shows a simultaneous speeding (slowing) of eastward velocity from 5°S to 10°N except in the western SEC, the western end of the North Brazil Current, and the Guinea Current. The out‐of‐phase fluctuations apparent in the western SEC near the equator are explained by the slowing and reversal of the South Equatorial Current near 2°N, 40°W between April and June. This slowing of the SEC is associated with the start up of the NECC, which accelerates eastward in May, June, and July and flows eastward across the Atlantic from July through December. The SEC divides seasonally near the eastern tip of Brazil, where residual alongshore velocities are northward for half the year (peaking during May and June) and southward for the other half of the year. A second division can be seen north of the Amazon, where the North Brazil Current continues up the coast into the Guyana Current during the first half of the year but partially retroflects into the NECC during the last half of the year. A fast eastward flow in the NECC coincides with below average velocities in the Guyana Current and above average velocities in the western sections of the North Brazil Current and the SEC (north of the equator).