bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data
Authors: Cavalieri Donald J. , Burns Barbara A. , Onstott Robert G.
Published: February 2008

Active and passive microwave data sets acquired during the 1984 Marginal Ice Zone (MIZ) Experiment aircraft flights in the Fram Strait region are used to examine the effects of ice surface melt on microwave signatures and their resulting error in the calculation of sea ice concentration. Conditions examined with the active‐passive data set include ice floes with moist and dry snow cover and both heavily ponded and ridged surfaces. Passive sensors on the NASA CV‐990 aircraft included the aircraft electrically scanning microwave radiometer (ESMR) operating at 19.4 GHz and aircraft multichannel microwave radiometer (AMMR) operating at 10.7, 18.0, 21.0, and 37.0 GHz. Active microwave sensors flown on the Canadian Centre for Remote Sensing CV‐580 aircraft included the Environmental Research Institute of Michigan synthetic aperture radar (SAR) operating at 1.2 and 9.4 GHz. Coincident AMMR and SAR measurements of individual floes identified in aerial photography are used to describe the effects of surface melt on the calculation of sea ice concentration, and in particular, the response of the passive microwave polarization and spectral gradient characteristics to different stages of surface melt. Although the onset and progression of summer melt are not uniform throughout the Arctic, the stages of summer melt observed in the MIZ are also observed on a large‐scale in the central Arctic. This is demonstrated using Nimbus 7 SMMR data and Arctic Ocean buoy temperature data over one annual cycle. Finally, the potential of optimally combining both active and passive microwave data in an effort to ameliorate these surface melt effects during the summer months is also explored.
Low‐frequency, motionally induced electromagnetic fields in the ocean: 1. Theory
Authors: Chave Alan D. , Luther Douglas S.
Published: February 2008

The theory of electromagnetic induction by motional sources in the ocean is examined from a first principles point of view. The electromagnetic field is expanded mathematically in poloidal and toroidal magnetic modes based on the Helmholtz decomposition. After deriving a set of Green functions for the modes in an unbounded ocean of constant depth and conductivity underlain by an arbitrary one‐dimensional conducting earth, a set of exact integral equations are obtained which describe the induction process in an ocean of vertically varying conductivity. Approximate solutions are constructed for the low‐frequency (subinertial) limit where the horizontal length scale of the flow is large compared to the water depth, the effect of self induction is weak, and the vertical velocity is negligible, explicitly yielding complex relationships between the vertically‐integrated, conductivity‐weighted horizontal water velocity and the horizontal electric and three component magnetic fields and accounting for interactions with the conductive earth. After introducing geophysically reasonable models for the conductivity structures of the ocean and earth, these reduce to a spatially smoothed proportionality between the electromagnetic field components and the vertically‐integrated, conductivity‐weighted horizontal water velocity. An upper bound of a few times the water depth for the lateral averaging scale of the horizontal electric field is derived, and its constant of proportionality is shown to be nearly 1 for most of the deep ocean based on geophysical arguments. The magnetic field is shown to have a similar form but is a relatively weak, larger‐scale average of the velocity field. Because vertical variations in the conductivity of seawater largely reflect its thermal structure and are weak beneath the thermocline, the horizontal electric field is a spatially filtered version of the true water velocity which strongly attenuates the influence of baroclinicity and accentuates the barotropic component. This is quantified using conductivity profiles and velocity information from a variety of locations.
Surface current distributions in the tropical Indian Ocean derived from compilations of surface buoy trajectories
Authors: Molinari Robert L. , Olson Donald , Reverdin Gilles
Published: February 2008

Three different satellite‐tracked drifting buoy data sets are compiled and used to generate a monthly climatology of surface currents in the tropical Indian Ocean. Buoys were deployed between 1975 and 1987. The data density is maximum on and near the equator and decreases poleward. Drift characteristics of the different buoy configurations are compared using a structure function analysis. The differences in windage effects are consistent with the buoy designs and small compared with the signals studied. The currents in the tropical Indian Ocean during boreal winter and spring can be characterized as two counterrotating gyres. A southern clockwise rotating gyre bounded on the south by the South Equatorial Current (SEC) and on the north during winter by the Equatorial Countercurrent (ECC) and during spring by the Equatorial Jet (EJ). A northern counterclockwise rotating gyre is bounded on the south by the ECC and EJ, depending on season, and on the north by the North Equatorial Current (NEC). The two gyre systems break down during boreal summer. During this season, the SEC is located closer to the equator, and the NEC is replaced by the eastward flowing Indian Monsoon Current (IMC). The western boundary circulation becomes more complicated from late spring through early autumn with the observation of two intense smaller scale gyres. The large‐scale southern gyre reappears during boreal autumn with the reappearance of the EJ. The northern gyre begins to reappear in December, with the reversal of the IMC and the reappearance of the NEC. The monthly buoy speeds are compared with a monthly climatology generated from ship drift reports. Differences between the two climatologies are in general small except in regions of few trajectories. The annual cycles in amplitudes and phases of the major currents in the region are thus comparable.
Near‐inertial motions over a mid‐ocean ridge: Effects of topography and hydrothermal plumes
Authors: Thomson Richard E. , Roth Sharon E. , Dymond Jack
Published: February 2008

We investigate the spatial structure of near‐inertial motions in the vicinity of the Endeavour segment of Juan de Fuca Ridge (approximately 48°N, 129°W) in the northeast Pacific Ocean. On the basis of time series current and water property data collected from September 1984 to September 1987, near‐inertial motions are ubiquitous features of the 2200‐m water column, with root‐mean‐square (rms) current speeds comparable to those of the dominant M2 tidal currents. Within the lower 1000 m of the water column where most of the observations were obtained, near‐inertial oscillations have rms current speeds of O(1 cm/s) and vertical isotherm displacements of O(10 m). The fluctuations are confined to the frequency band 0.966–1.079 f(f is the local Coriolis parameter) and have characteristic event durations of 1 week. Although the spectra of subsurface motions are dominated by the “blue‐shifted” superinertial band, significant spectral peaks are found also in the subinertial and inertial frequency bands. Marked alteration of the near‐inertial current amplitudes occurs over two well‐defined depth zones within the study region. Within the 200‐m zone immediately above the 2100‐m ridge crest, current amplitudes are amplified by a factor of 1.2–1.7 because of bottom reflection and/or scattering of the downward propagating energy. Evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross‐slope rotation of the near‐inertial current ellipses with increased proximity to the top of the ridge. Reflection would occur at grazing angles of less than 1° and would be associated with surface‐generated waves originating at distances of over 100 km from the observational site. In contrast to the enhanced amplitudes immediately above the top of the ridge, near‐inertial currents within the 1600‐ to 1800‐m depth range undergo pronounced attenuation and frequency alteration. Amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical‐layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow. The increased shear is most likely associated with buoyancy‐induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest, but it could also be related to bottom‐trapped oscillations over the steep ridge topography. Near‐inertial motions are estimated to have vertical coherence scales of the order of 10–100 m, while horizontal coherence scales exceed the 50‐km separation between the mooring locations. Minimum vertical and horizontal coherences are found for the depth zone 1600–1800 m, while maximum correlation occurs for near‐bottom motions immediately above the crest of the ridge. Weak near‐inertial motions are observed within the 100‐m‐deep axial valley.
Nonlinearity corrections in calibration of advanced very high resolution radiometer infrared channels
Authors: Weinreb Michael P. , Hamilton Gary , Brown Stanley , Koczor Ronald J.
Published: February 2008

The infrared channels of the advanced very high resolution radiometer (AVHRR) are calibrated in‐flight with data acquired when the AVHRR views space and a warm target on board. This determines the two coefficients of a linear calibration equation. However, in its 11‐ and 12‐μm channels the response of the AVHRR is nonlinear. If not accounted for, the nonlinearity could cause errors as large as 2°C in inferred scene temperatures. Therefore NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) computes corrections to the brightness temperatures inferred from the linear calibration. This paper describes how the corrections have been calculated at NESDIS since March 1986 and presents the corrections for the AVHRRs on the NOAA 9, 10, and 11 satellites. The corrections are calculated from results of the prelaunch calibration, in which a calibrated laboratory blackbody illuminates the AVHRR. At NESDIS the calculation of the corrections differs from that of Brown et al. (1985) because NESDIS transfers the calibration of the laboratory blackbody to the internal calibration target of the AVHRR, but Brown et al. do not. The absolute radiometric accuracy of AVHRR data that have been corrected for the nonlinearity is approximately 0.55°C, of which 0.35°C is traceable to the calibration of the laboratory blackbody.
A coupled sea ice‐mixed layer‐pycnocline model for the Weddell Sea
Authors: Lemke P. , Owens W. B. , Hibler W. D.
Published: February 2008

A dynamic‐thermodynamic sea ice model is coupled to a one‐dimensional model of the oceanic mixed layer and pycnocline and is applied to the Weddell Sea. This model prognostically determines the vertical oceanic heat flux from the mixed layer dynamics in contrast to earlier sea ice modeling where the oceanic heat flux was prescribed. In addition to the standard simulation, polynya and paleoclimate experiments were performed to investigate the effects of sea ice dynamics. Furthermore, the mixed layer‐pycnocline model is compared to the original Kraus‐Turner approach.
Global charts of ocean tide loading effects
Authors: Francis O. , Mazzega P.
Published: February 2008

Global ocean tide loading charts of the radial displacement, the potential divided by g (gravity acceleration), and the gravity effect have been computed using the 11 constituents M2, S2, N2, K2, K1, O1, P1, Q1, Mf, Mm, Ssa of Schwiderski's tidal model. These new charts have a resolution of 1° × 1° on the continents as well as on the oceanic area. A description of Farrell's convolution method to compute the loading effects is given, and an estimate of the numerical errors leads to the conclusion that these global charts have a precision better than 2.5% independent of the accuracy of Schwiderski's maps. The current approximation of the loading effects by a proportionality relation with the local oceanic tides is also compared with Farrell's convolution method. Departures of several centimeters systematically appear, in particular over the continental shelves. We then show that the maps of the oceanic tides deduced from satellite altimetry could be corrected for the loading effect by an iterative computational procedure based on our algorithm of Farrell's convolution.
A poleward flow along the Atlantic coast of the Iberian peninsula
Authors: Haynes R. , Barton E. D.
Published: February 2008

Satellite Advanced Very High Resolution Radiometer (AVHRR) imagery and Argos tracked drifters have revealed the existence of a narrow, warm surface poleward current along the Iberian coast during autumn and winter. Six near‐surface drifter tracks indicated a net northward flow between September 1986 and March 1987, although individual drifter trajectories also provided evidence of eddy activity and episodes of equatorward flow. A SeaSoar survey during September 1986 in the region 37°–43°N, 9°–11°W showed that poleward flow at that time was associated with the northward advance of a warm, salty tongue of water throughout the upper 400 m layer. Infra‐red imagery confirmed the northward penetration of the warm current and its progression around Cape Finisterre along the north coast of Spain during the course of the winter. A similar situation is indicated by satellite imagery during other years. Current meter data show that poleward flow occurred along the continental slope down to depths greater than 600 m. Conductivity, temperature, and depth (CTD) casts show the presence of Mediterranean Intermediate Water (MIW) at depths greater than 600 m. The MIW does not flow as a simple northward flowing jet along the continental slope off Iberia, but instead shows evidence of eddies within the flow. The poleward surface current is in the opposite sense to the general summer circulation of the region, when cool upwelled water is advected equatorward. It is postulated that the poleward flow is generated by thermohaline forcing when the southward trade winds, characteristic of the summer months, weaken or reverse. Intermittent poleward flow appears to be a common characteristic of the Eastern Boundary throughout the North Atlantic from West Africa to the Norwegian Sea.
The spatial and temporal variability of sand bar morphology
Authors: Lippmann T. C. , Holman R. A.
Published: February 2008

The spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years. The data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology (Lippmann and Holman, 1989). The morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria. The most frequently observed morphologies are the longshore‐periodic (rhythmic) bars, observed in 68% of the data. Linear bars occur under highest wave conditions
and are unstable (mean residence time ≈ 2 days). Shore‐attached rhythmic bars are the most stable (mean residence time ≈ 11 days) and generally form 5–16 days following peak wave events. Non‐rhythmic, three‐dimensional bars are very transient (mean residence time ≈ 3 days). Eighty‐seven percent of transitions to lower bar types (defined in text) occurred one state at a time, supporting our selection of the ordering of states, and suggesting the suitability of a sequential morphology model. Transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states, with more substantial changes in morphology resulting from larger wave increases. This suggests that up‐state, erosional transitions (based on offshore bar migration) are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state. Time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance. Principal component analysis was used to decompose bar position into two‐dimensional (linear) and three‐dimensional (longshore variable) components. Cross‐shore (linear) bar position ranges ±50 m about the 2‐year mean (27 m standard deviation) and dominates bar variability (74.6%). Three‐dimensional bar structure accounts for ∼14% of the variance (12 m standard deviation). Changes in incident wave height precede cross‐shore bar migration by less than 1 day. Changes in longshore variability are inversely correlated to changing wave conditions, with bar morphology becoming linear rapidly during storms (on time scales of less than 1 day). Evolution to significantly three‐dimensional structure typically occurs over 5–7 days following peak wave events.
On the bulk‐skin temperature difference and its impact on satellite remote sensing of sea surface temperature
Authors: Schluessel Peter , Emery William J. , Grassl Hartmut , Mammen Theodor
Published: February 2008

Satellite infrared sensors only observe the temperature of the skin of the ocean rather than the bulk sea surface temperature (SST) traditionally measured from ships and buoys. In order to examine the differences and similarities between skin and bulk temperatures, radiometric measurements of skin temperature were made in the North Atlantic Ocean from a research vessel along with coincident measurements of subsurface bulk temperatures, radiative fluxes, and meteorological variables. Over the entire 6‐week data set the bulk‐skin temperature differences (ΔT) range between −1.0 and 1.0 K with mean differences of 0.1 to 0.2 K depending on wind and surface heat flux conditions. The bulk‐skin temperature difference varied between day and night (mean differences 0.11 and 0.30 K, respectively) as well as with different cloud conditions, which can mask the horizontal variability of SST in regions of weak horizontal temperature gradients. A coherency analysis reveals strong correlations between skin and bulk temperatures at longer length scales in regions with relatively weak horizontal temperature gradients. The skin‐bulk temperature difference is parameterized in terms of heat and momentum fluxes (or their related variables) with a resulting accuracy of 0.11 K and 0.17 K for night and daytime. A recommendation is made to calibrate satellite derived SST's during night with buoy measurements and the additional aid of meteorological variables to properly handle ΔT variations.
Satellite observations of the ice cover of the Kuril Basin region of the Okhotsk Sea and its relation to the regional oceanography
Authors: Wakatsuchi Masaaki , Martin Seelye
Published: February 2008

For the period 1978–1982, this paper examines the nature of the sea ice which forms over the Kuril Basin of the Okhotsk Sea and describes the impact of this ice on the regional oceanography. The paper compares the oceanographic behavior during the heavy ice season associated with the cold 1979 winter with the behavior during the lighter ice years of 1980 and 1982. Examination of the oceanography in the Okhotsk and the adjacent Pacific shows that the early summer water column structure depends on the heat loss from the Okhotsk during the preceding ice season, the total amount of Okhotsk ice formation, and specifically the amount of ice formation in the Kuril Basin. Following the 1979 ice season, the upper 200–300 m of the Kuril Basin waters were cooler, less saline, and richer in oxygen than for the other years. This modification appears to be a process local to the Kuril Basin, driven by eddy‐induced mixing, local cooling, and ice melting. In the depths 300–1200 m, the water modification is caused by the advection of water from the northern Okhotsk. For 1979, this deeper water is also less saline, colder, and richer in oxygen than for the lighter ice years. The water modified in the Okhotsk enters the adjacent North Pacific through the Bussol' Strait, where for 1979 the adjacent waters are also cooler, less saline, and richer in oxygen down to a depth of 1000 m than for the lighter ice years.
A modified objective mapping technique for scatterometer wind data
Authors: Kelly Kathryn A. , Caruso Michael J.
Published: February 2008

An objective method to generate high resolution wind maps from the irregularly spaced scatterometer data was developed and tested on synthetic data for the northeast Pacific Ocean. Current assimilation methods for atmospheric global circulation models (GCMs) reproduce only the large‐scale features (>600 km) of the wind field. In contrast, this method attempts to retain the high spatial resolution of the scatterometer where there are adequate measurements. To estimate the covariance function and to compute realistic error estimates for the method, a synthetic data set was constructed using wind fields from the European Centre for Medium Range Weather Forecasts. The wave number spectrum of the synthetic data was based on an analysis of Seasat scatterometer data. The patchiness of the scatterometer data caused discontinuities in the objective estimates, which would give unacceptable wind stress curl fields; thus the initial estimates were selectively smoothed using overdetermined biharmonic splines. A constraint on the horizontal divergence of the wind, applied only in regions of large estimated errors, improved the estimates. For the NASA scatterometer this method would produce a wind map every 12 hours with spatial resolution that preserves the small‐scale features of the original data over about half the mapped region and with somewhat decreased resolution and accuracy over the rest of the region.
Oceanographic data interpolation: Objective analysis and splines
Authors: McIntosh Peter C.
Published: February 2008

Two data interpolation methods are reviewed and compared. They are objective analysis (also known as objective mapping, statistical interpolation or Gauss‐Markov interpolation), and spline interpolation. The former is a statistical method based on minimizing the interpolation error variance; the latter is a deterministic method which seeks to obtain the smoothest interpolated field consistent with the data. The two methods are formally equivalent. This means that a single interpolated field may be viewed as deriving from the extremization of either a statistical or a deterministic quantity. This helps to explain why objective analysis remains a useful tool even when the statistics are poorly known. Two types of spline interpolation are considered: “norm splines”, for which smoothness is defined in terms of the field amplitude and curvature, and “semi‐norm splines”, which consider only the field curvature. The objective analysis algorithm may be used to perform norm spline interpolation simply by a suitable choice of covariance function. An example of such a choice is given. The statistical, norm spline, and semi‐norm spline methods are tested on 100 realizations of a random field with known covariance structure. It is shown that the interpolation error is a weak function of the length scale needed by objective analysis and norm splines, but that the statistical error estimate depends strongly on the length scale, and can be quite misleading. The data spacing is shown to have more influence on the interpolation error than does the length scale. Semi‐norm splines are shown to have poor performance near the boundaries of the data set, and do not provide an error estimate. However, they have the advantage of not requiring the specification of a length scale, and provide a more accurate interpolation if a good estimate of the length scale is not available. The objective analysis error estimate does not reflect any error in the estimate of the true mean of the field, a statistic which is required by the method. Fortunately, all the methods appear to be insensitive to errors in estimating the mean, with the exception of objective analysis with an oscillatory covariance function. This result is all the more surprising because the data sets were generated using exactly this covariance function.
The dissolution of atmospheric iron in surface seawater of the open ocean
Authors: Zhuang Guoshun , Duce Robert A. , Kester Dana R.
Published: February 2008

A series of leaching experiments designed to determine the soluble fraction of atmospheric iron in seawater was conducted. Aerosol samples collected in 1986 at four island stations (Midway, Oahu, Enewetak, and Fanning) of SEAREX (Sea‐Air Exchange) and in May 1988 at station 4 (33.3°N, 139.1°W) of VERTEX (Vertical Transport and Exchange) were leached by surface seawater collected from the North Pacific and Sargasso Sea and at a pH range of 3–8. The results from these experiments indicated that for all marine aerosol samples examined, the dissolution of atmospheric iron was limited by a similar saturated concentration range. Using the operationally defined concept of a dissolved fraction that could pass through a 0.4‐μm filter, the “saturated concentration” of dissolved atmospheric iron in seawater was found to be ∼10–17 nmol/kg. If 0.05‐μm Millipore filter was used to separate the soluble fraction from the particulate fraction, the “saturated concentration” of dissolved atmospheric iron in seawater was found to be ∼5–8 nmol/kg. The dissolution of atmospheric iron in seawater takes place within a few minutes. If the total iron concentration was less than 2 nmol/kg (the open Pacific Ocean is in this category), ∼50% of the atmospheric iron dissolved in seawater. A comparison of the atmospheric dissolved iron flux into the North Pacific with the dissolved iron profile in this area suggests that more than 99% of the dissolved iron is provided by atmospheric input.
Evidence of Bragg scattering in microwave Doppler spectra of sea return
Authors: Plant William J. , Keller William C.
Published: February 2008

Microwave signals backscattered from the ocean (and one lake) have been collected at many different windspeeds and fetches. Doppler spectra of some signals obtained at low microwave frequencies exhibit double peaks clearly indicating Bragg scattering. At higher microwave frequencies, high wind speeds, long fetches, or in the presence of substantial swell, these splittings disappear. A model of microwave Doppler spectra based on Bragg‐scattering, composite‐surface theory is developed and used to show that the results obtained in these field studies are compatible with the hypothesis that Bragg scattering dominates microwave backscatter from rough water surfaces under many wind speed and incidence angle conditions. In particular, the model shows double peaks of the proper separation which disappear under the same conditions as those of the actual spectra. Furthermore, Doppler bandwidths given by the model agree with those of the field data under a variety of conditions. A rough angular dependence of the amplitudes of Bragg waves traveling in different directions with respect to the wind is deduced from the measurements. Finally, the implications of these findings for synthetic aperture radar imagery of the ocean are briefly discussed.
Large‐scale meridional transport in the tropical Pacific Ocean during the 1986–1987 El Niño from Geosat
Authors: Miller Laury , Cheney Robert
Published: February 2008

Geosat altimeter data are used to obtain the first detailed basin‐wide measurement of the meridional transport of warm surface water in the tropical Pacific during El Niño. Using a combination of crossover and collinear difference techniques, continuous sea level time series are constructed on a 2°×1° grid covering the Pacific between 20°N and 20°S for the 4‐year period 1985–1989. Zonal integrations of these data are performed over three latitude bands to examine large‐scale sea level changes. Comparison with tide gauge data suggests that these zonal averages have an accuracy of better than 1 cm. The Geosat analyses show a clear pattern of water exchange involving principally the equatorial and north equatorial regions. From the onset of the warm event in late 1986 to the mature phase in mid‐1987, mean sea level in the equatorial region dropped nearly 5 cm while simultaneously in the north equatorial region it increased by about the same amount. These anomalies, equivalent to 2×104 m3 of upper layer water, persisted for nearly 2 years before both regions returned to normal. A similar pattern and amplitude of north‐south water exchange is also observed on the seasonal time scale, consistent with annual variation of the wind stress curl. Water moves northward across 8°N during boreal winter and southward during summer with a net transport of approximately 30 Sv. Thus, in terms of meridional transport, the 1986–1987 El Niño is seen as a low‐frequency modulation of the normal seasonal cycle. In contrast to the widely held view that a surplus of equatorial water is required prior to El Niño, no such buildup was observed prior to the 1986–1987 event.
Sea level variabilities in the Gulf Stream between Cape Hatteras and 50°W: A Geosat study
Authors: Vazquez Jorge , Zlotnicki Victor , Fu Lee‐Lueng
Published: February 2008

Sea level residuals relative to a 2‐year mean sea level in the Gulf Stream downstream of Cape Hatteras (between 80°W and 50°W longitude) are studied using Geosat altimetry between November 1986 and December 1988. Spectral slopes computed at four nominal locations along the Gulf Stream (72°W, 65°W, 60°W, and 55°W) range between −1.5 and −0.9, significantly less steep than the −2.5 spectral slope found at Bermuda. Because of increased short‐wavelength energy, the spectra tend to become more “white” going eastward, but this trend is not statistically significant. Energy at the annual cycle decreases eastward from around 40% of the total variance at 72°W to 20% of the total variance at 55°W. Maximum residual geostrophic sea surface velocities associated with the annual cycle were of the order of 70 cm/s. Comparison between the Gulf Stream path from sea level residual maps and the north wall edge observed from NOAA infrared (IR) imagery shows an rms difference of 49 km between 75°W and 60°W longitude, but not all sea level maps show a clearly defined Gulf Stream. Using the IR estimates for Gulf Stream position, sea level residuals were modeled as the meandering of a sea level front shaped as 0.5 m · tanh {(X–X0)/[50 km · sin (α)]}, with α the angle between the Geosat track and the Gulf Stream edge and X0 is based on the observed IR north wall positions. This showed that the annual signal, in terms of the location and phase of its maxima, is dominated by the meandering of the Gulf Stream.
Surface patterns in temperature, flow, phytoplankton biomass, and species composition in the coastal transition zone off Northern California
Authors: Hood Raleigh R. , Abbott Mark R. , Huyer Adriana , Kosro P. Michael
Published: February 2008

Satellite thermal imagery and in situ biological and physical data are presented that describe the spatial variability of phytoplankton biomass and species composition in relation to the physical structure at the sea surface during persistent upwelling off northern California. Surface patterns in temperature, geostrophic velocity, chlorophyll, and particle size structure show that the coastal zone was dominated by two water masses separated by a well‐defined physical boundary. This boundary is apparent in satellite thermal imagery as a cold front and in dynamic height as a meandering jet in the California Current. On the landward side of the front (jet) we observed cold, coastal water that was relatively enriched in phytoplankton biomass, due to the presence of large diatoms. On the seaward side of the front (jet) we observed relatively warm water where the phytoplankton biomass was low and the diatoms were largely absent. Broad tongues and narrow filaments of cold, chlorophyll‐rich water that extended over 100 km offshore were present in our study area. These features were bounded by the meandering coastal jet. The coldest, most chlorophyll‐rich water in these tongues and filaments was located between the onshore and offshore flows in relatively slow moving water, but entraimnent of coastal water into the jet was apparent.
A Lagrangian description of motion in Northern California coastal transition filaments
Authors: Paduan Jeffrey D. , Niiler Pearn P.
Published: February 2008

Lagrangian drifters deployed during May 1987 as part of the Coastal Transition Zone experiment were used to examine the motion in cold‐water features seen in satellite AVHRR imagery. The drifters were drogued at 15 m depth and had temperature sensors at 0 m, 12 m, and 18 m. Drogue positions were obtained via service ARGOS at an average of 8 times per day. A cluster of nine drifters was deployed on May 18 near the base of a cold‐water feature off Pt. Reyes. Drifter trajectories confirm the presence of strong (> 50 cm s−1) currents along the axis of the feature. Six of the drifters moved northward following a cyclonic circulation pattern between the Pt. Reyes jet and another feature originating near Pt. Arena. The remaining three drifters, together with three more deployed on May 20, moved offshore in the positive vorticity portion of the Reyes jet. Cluster analysis of the northern tracks indicates large convergence (∼0.5f;), but because relative vorticity during the same few‐day period is found to be constant (∼−0.2f), a simple vorticity balance does not emerge. This is attributed to insufficient resolution of divergence of the water parcel by the small number in the cluster. Drifters reside on the negative vorticity side of the jet while the flow is upwind but on the positive vorticity side while the flow is downwind. Such behavior is consistent with the convergence or divergence patterns expected when along‐jet winds blow over such strong and narrow ocean currents producing significant advection of relative vorticity. Temperature‐salinity data from CTD surveys during the experiment show how the jets that were revealed in both the imagery and the drifter trajectories were advecting different water masses. In the nearshore area where the drifters were deployed a column of cold and salty water had upwelled about 80 m since leaving the source region far offshore. Within the offshore extension of the jets as traced by the drifters, this same water is found about 20 m deeper than it is in the nearshore area. We thus observe that cold filaments seen in AVHRR transport upwelled water offshore through the coastal transition zone. That water subducts in the offshore extension of the filaments. Analysis of the high‐frequency motion from a cluster of five drifters in the Reyes jet shows a multitude of mixing scales. For periods shorter than a day, the cluster shows coherent oscillations of tidal/inertial period whose motions lead to excursions on the order of 2 to 4 km. This suggests that motions on these scales are organized and not random or turbulent. Conversely, motions at scales of 1 km and less appear turbulent. Over longer time periods (several days), the particles exchange places over the cross‐jet scale of the feature (10 to 20 km).
The North Atlantic tritium and radiocarbon transients 1972–1983
Authors: Östlund H. Göte , Rooth Claes G. H.
Published: February 2008

Deep ventilation and water mass transformation processes in the North Atlantic, on decadal time scales, are illustrated by the evolving distribution patterns of anthropogenic tritium and radiocarbon. Data from two quasisynoptic surveys of the interior of the North Atlantic, the Geochemical Ocean Sections Study (GEOSECS) and complementary oceanographic observation projects in 1972, and the Transient Tracers in the Oceans (TTO) in 1981 and 1983, are presented in comparative cross sections and maps representing conditions roughly one and two decades, respectively, after the first major tracer injections. The discussion emphasizes comparisons of the decay corrected tritium concentration fields, which show several distinct regimes of transient evolution, including examples of surprising constancy in some regional patterns. While largely supportive of previous qualitative ideas about transport patterns, these results also suggest that the patterns of deep water injection in high latitudes must have undergone a major change around or soon after the time of GEOSECS (1972), involving a major increase in supply of Upper North Atlantic Deep Water. The near‐surface waters show strong signatures of tropical (low tritium) influence in the southwestern and western part of the subtropical gyre, while the northeastern part is influenced by continued tritium input from Arctic surface waters. Strong evidence for distinct sub‐basin‐scale interior circulation domains is found in the fact that the major distribution regime transitions seen in the GEOSECS data are observed again in TTO, and thus maintained through the second decade of the transient. The radiocarbon data set, which reflects the addition to the natural background distribution, supports the significance also on longer time scales of the mid‐depth regime transition around 30°N latitude.
Coupling of coastal zone color scanner data to a physical‐biological model of the southeastern U.S. continental shelf ecosystem: 1. CZCS data description and Lagrangian particle tracing experiments
Authors: Ishizaka Joji
Published: February 2008

Nine Coastal Zone Color Scanner (CZCS) images from the southeastern U.S. continental shelf area during April 1980 were processed, and the resulting chlorophyll distributions were analyzed in conjunction with concurrent flow and temperature fields which were obtained from an optimal interpolation of current meter measurements from 17m. The chlorophyll distributions obtained from the CZCS showed high chlorophyll concentrations over the shelf and low chlorophyll concentrations over the offshore shelf region. The variance of the CZCS‐derived chlorophyll distributions was highest at the shelf break region. The chlorophyll patterns at the shelf break varied with time and space and showed shapes characteristic of typical Gulf Stream frontal eddies, high‐chlorophyll bands that were oriented along‐shelf, isolated high‐chlorophyll patches, and simple waveforms. Each event observed in the chlorophyll patterns corresponded with a Gulf Stream frontal eddy event that could be identified in the optimally interpolated flow and temperature fields. Lagrangian particle tracing experiments were also conducted to track the movement of the features observed in the CZCS images. The particles traced in these experiments showed movement that was consistent with the evolution of the patterns observed in the CZCS chlorophyll distributions. Results of the Lagrangian experiments indicate that the optimal interpolation of the current meter measurements reproduced the flow between successive CZCS images. These experiments provide evidence that the high‐chlorophyll bands seen in the CZCS chlorophyll distributions were produced by the passing of Gulf Stream frontal eddy events.
Reflected solar radiances from broken cloud scenes and the interpretation of scanner measurements
Authors: Davies Roger
Published: February 2008

If an adequate model of the reflection characteristics of a given scene is available, the reflected solar irradiance from the scene may be determined from radiance measurements made by satellite‐borne scanning radiometers. A theoretical analysis of the reflection functions of broken cloud scenes is presented, using Monte Carlo simulations of the radiative transfer in various three‐dimensional geometries. It is shown that the reflection functions of horizontally extensive (stratiform) and horizontally limited (cumuliform) clouds are generally quite different. The differences are greatest for nadir and limb views, but tend to vanish for reflected radiances with a zenith angle of 60°. Applications to satellite observations suggest potential errors of a factor of 2 in the inferred irradiance are likely due to scene misidentification when the radiances are interpreted indiscriminantly. Selection of preferred satellite viewing directions, however, can significantly reduce this error.
Vertical distribution features of atmospheric water vapor in the Mediterranean, Red Sea, and Indian Ocean
Authors: Tomasi Claudio
Published: February 2008

Measurements of total precipitable water w and of water vapor scale height H were obtained from both sun photometer measurements and soundings taken in the Mediterranean, Red Sea, and Indian Ocean during the scientific cruise of the vessel Salernum (January and February 1979). Scale height H was found to assume average values of 1.93 km for the Mediterranean leg of the cruise, 2.33 km for the Indian Ocean, and 2.45 km for the Red Sea and Somalian Coast. Moreover, average vertical distribution curves of air temperature, dew point, and absolute humidity were determined from the soundings taken in an equatorial area of the Indian Ocean. This atmospheric water vapor model gives a value of w = 5.12 g cm−2, while the tropical model proposed by McClatchey et al. (1972) gives w = 4.20 g cm−2. In fact, absolute humidity was found to assume appreciably higher values than those in the tropical model from sea level to about 14 km altitude and considerably smaller values throughout the tropopause region. The measurements also show that the present evaluations of scale height H can be conveniently used to represent the absolute humidity vertical profiles in tropical oceanic areas.
Tropical glaciers: Potential for ice core paleoclimatic reconstructions
Authors: Thompson L. G. , Mosley‐Thompson E. , Grootes P. M. , Pourchet M. , Hastenrath S.
Published: February 2008

The objective of this work is to evaluate the potential of tropical glaciers and ice caps for the reconstruction of past climatic conditions by the analysis of firn and ice cores. Samples were collected in pits and from cores retrieved on three snow fields in the South American Andes: Quelccaya Ice Cap and Huascarán in Peru and Chimborazo in Ecuador. These are compared with results from west Africa and Indonesia. Measurements include the microparticle concentration, oxygen isotopic abundance ratios, and total beta radioactivity, which in polar regions often exhibit seasonal depositional cycles. Annual variations in these three parameters are fairly well defined on Quelccaya and Huascarán and are apparently absent on Chimborazo. The Quelccaya Ice Cap contains the best preserved annual signal for all three parameters and, although in some instances the annual cycle is difficult to distinguish, the measurement of more than one stratigraphic parameter aids in the interpretation of the firn core records. The relatively flat bottom topography under Quelccaya suggests a simple ice flow regime, and depth‐age calculations indicate that an ice core to bedrock should contain a record of 600 to 1300 years. This inference was confirmed by drilling to bedrock in 1983. This investigation of tropical glaciers indicates that the Quelccaya Ice Cap on the eastern edge of the Peruvian Andes has excellent potential to contain a lengthy and interpretable record of climatic conditions within the tropics of South America.
Analyses of monthly mean cloudiness and their influence upon model‐diagnosed radiative fluxes
Authors: Gordon Charles T. , Hovanec Russell D. , Stern William F.
Published: February 2008

Two different monthly mean analyses of low, middle, and high cloud amounts for January 1977 and July 1979 are compared: 3DNEPH is a condensed version (northern hemisphere only) of the Air Force 3D‐Neph analysis, which incorporates satellite data plus surface observations of clouds and auxiliary meteorological data. SFCOBS is objectively analyzed from surface observations of clouds. The SFCOBS and 3DNEPH analyses of low cloud amounts agree qualitatively in the winter extratropics. The 3DNEPH ITCZ is much more sharply defined than the SFCOBS. The sensitivity of radiative fluxes to 3DNEPH, SFCOBS, and zonal mean 3DNEPH clouds is then evaluated. The fluxes are diagnosed by a cloud‐radiation model utilizing “observed” monthly mean temperature and water vapor fields and are verified against satellite data. The outgoing longwave radiative flux clearly verifies best for 3DNEPH clouds and worst for zonal mean 3DNEPH clouds in the tropics. It is predominantly controlled by surface temperature in the winter extratropics. Generally speaking, the shortwave fluxes do not verify as well as the longwave fluxes. Also, outside of the winter extratropics, the net radiative fluxes correlate poorly with observation. Biases in the zonal mean long and shortwave fluxes can be reduced by adjusting other cloud‐related parameters. Based upon the above results, it may be worthwhile to construct a monthly mean cloud climatology from a condensed version of the 3D‐Neph. However, alternative strategies should also be explored, such as the development of cloud analysis schemes that constrain the model‐diagnosed net radiative flux to be consistent with observation.
Mean profiles of trace reactive species in the unpolluted marine surface layer
Authors: Thompson Anne M. , Lenschow Donald H.
Published: February 2008

We have investigated several aspects of trace gas photochemistry in the marine boundary layer using a time‐dependent transport‐kinetics model with one‐dimensional eddy diffusion. The photochemical scheme in the model (Thompson and Cicerone, 1982) is represented by a conventional complement of reactions involving O, H, N, and methane‐derived organic species; boundary conditions are assigned which give low surface mixing ratios of O3 and NOx (Routhier et al., 1980; McFarland et al., 1979) characteristic of the remote marine environment. Altitude dependent eddy diffusion coefficients in the surface layer (1 mm to 100 m) are based on the formulation of Businger et al. (1971) for temperature diffusivity in an unstably stratified surface layer. Diffusion coefficients in the rest of the convective boundary layer (the mixed layer) are taken from Lamb and Durran (1978). The surface is assumed to be the tropical ocean with a steady state mixed layer. In the simulations described here, particular attention has been given to the distribution of odd nitrogen and the NO2‐NO‐O3 photostationary state in the surface boundary layer. Calculated profiles of NO, NO2, O3, and HNO3 show definite gradients in the surface layer. When the ocean is assumed to be a source of NO, mixing ratios on the order of a few parts per trillion can be supported by an upflux of ∼108 cm−2 s−1. If a surface input of NO is not assumed, NOx levels are much lower. This is consistent with measurements in the Equatorial Pacific (McFarland et al., 1979; Zafiriou et al., 1980; Liu et al., 1983) and suggests that NO upwelling may be significant in the local budget of NOx in certain remote marine environments. Calculated values of the O3‐NO‐NO2 photostationary state ratio, Rps, and NO/HNO3 show appreciable variation within the surface layer. The latter ratio is sensitive to the NO upflux and to heterogeneous removal of HNO3. Rps decreases away from the surface and is unity only at one point. Both chemical and micrometeorological factors (Lenschow, 1982) contribute to nonunity values of Rps. Significant departures from a profile characteristic of a nonreactive species are shown to occur in the NO profile as low as 0.2 m above the surface.