bluuebunny/crossref_metadata_2025 huggingface dataset:
Low frequency variability of the 20°C isotherm topography in the western equatorial Indian Ocean
Authors: Quadfasel D. R.
Published: February 2008

Monthly maps of the mean 20°C isotherm topography in the western Indian Ocean have been compiled from historical data. They reveal strong annual and semi‐annual fluctuations. The yearly cycle has significant phase lags across the area investigated that reflects the different circulation patterns during and in between the two monsoon periods. In particular, the different development of the Somali Current north and south of 5°N can be seen in these data. The flow in the southern part reverses 1 month prior to the large scale onset of the SW‐monsoon but otherwise follows the monsoonal windfield. In the northern part southward flow is found only for 2 months during the height of the NE‐monsoon. The Somali eddy spins up immediately after the SW‐monsoon onset but remains strong for 2 months after the winds weaken. The semi‐annual fluctuations are in phase from 10°N to 10°S and can be related to the zonal winds over the equator. Eastward surface currents cause thermocline upwelling during boreal spring and fall which has maxima along the coast and at 5° north and south of the equator. It can feed the currents at a rate of 15×106 m3 s−1 during a 3‐month period.
The residence time of the freshwater component in the Arctic Ocean
Authors: Östlund H. Göte
Published: February 2008

The time function of bomb tritium concentrations in river runoff to the Arctic Ocean has been reconstructed from published data on tritium in precipitation 1959–1975. Tritium measurements on oceanic samples through the halocline exhibit strong linear relationships between tritium concentrations (TU values) and salinity. These waters thus look like binary mixtures of Atlantic source water and freshwater runoff. Combining these data, the vintage of the freshwater component in the Arctic Basin has been determined assuming no other major tritium source. The relation indicates the average age of the freshwater component to be 11±1 years in the Nansen Basin and the outflow and somewhat higher in the Canada Basin. According to tritium/salinity data, a surface layer of 10–60 m is affected by sea ice melting and freezing in the Nansen Basin, and the thickness of this layer increases to 150–170 m toward the Canada Basin. There is tritium also in the deeper waters, the unmixed Atlantic water, which points at residence times for that water not to exceed 17 years.

The appendix is available with the entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J81‐012; $1.00, payment must accompany order.
The relationship between wind vector and normalized radar cross section used to derive SEASAT‐A satellite scatterometer winds
Authors: Schroeder Lyle C. , Boggs Dale H. , Dome George , Halberstam Isadore M. , Jones W. Linwood , Pierson Willard J. , Wentz Frank J.
Published: February 2008

The dependence of ocean normalized radar cross section (NRCS or σ0) on the 19.5 m neutral stability wind vector for the SEASAT‐A Satellite Scatterometer (SASS) is described. For the SASS wind vector algorithm this dependence is specified in the form NRCS = ƒ(θ, χ, U), where θ is the radar incidence angle, χ is the angle between wind direction and radar azimuth, and U is the neutral stability wind speed in meters per second at a height of 19.5 m. The development of models to express this relationship and to provide the basis for inversion of NRCS to SASS winds is traced from its initial form based on aircraft scatterometer measurements through the SEASAT field‐validation experiments (GOASEX, STORMS, and JASIN) to its final form. Comparison of the model NRCS versus surface wind speed with SASS data from these experiments are made.
Description of SEASAT radiometer status and results
Authors: Lipes Richard G.
Published: February 2008

Improved geophysical algorithms are shown to be capable of determining sea surface temperature (SST) to an accuracy of 1°C (1σ) under favorable surface and atmospheric conditions over the SST range of 10–30°C. Under similar conditions the radiometer wind retrievals track the scatterometer winds within a scatter of 2 m/s (1σ) over the wind speed range of 0–25 m/s. These conditions require that contamination from land, sun glint, rain, and radio frequency interference be avoided. Furthermore, water vapor determinations in the midlatitudes and in the tropical Pacific agree with estimates of precipitable water from radiosondes to within 10%.
A ship and satellite view of hydrographic features in the western Gulf of Mexico
Authors: Brooks David A. , Legeckis Richard V.
Published: February 2008

In April 1980, nearly synoptic hydrographic observations were obtained in the western Gulf of Mexico by satellite and ship. A meandering surface thermal front which turned northeastward from the Mexican coast near 23°N was prominent in the satellite infrared observations. The front separated a southern anticyclone and a northern cyclone, both of which had horizontal scales of several 100 km and were prominent in the subsurface hydrographic observations. The eastward geostrophic volume transport in the confluent leg of the two features was roughly equal to that of the Florida Current. A shallow layer of fresh, cool water from the Texas shelf region extended ∼300 km seaward into the cyclone along the northern side of the front. Remnant Subtropical Underwater in the core of the April anticyclone indicates its origin in the eastern Gulf Loop Current.
On the residence time of the Antarctic ice sheet sulfate aerosol
Authors: Shaw Glenn E.
Published: February 2008

Optical extinction caused primarily by light scattering from suspended sulfate particles above Antarctica provides a relative measure of the amount of overlying sulfate mass. It has been found that the optical extinction, and hence the column‐integrated amount of sulfate, varies systematically with altitude, decreasing with increasing heights on the ice sheet, approximately as exp (−h/H) with 3.2 < H < 6.8, with a most probable estimate of 4.05 km. No particular tendency is found for the aerosol to disappear as one moves inland (to South Pole station); this is interpreted with an eddy diffusion model to mean that the SO4= aerosol over the ice sheet has a residence time, TR > 1 month. Other data, notably the shape of the aerosol size spectrum and the observed rate of surface deposition of SO4=, also suggest a long residence time for the SO4= aerosol. It is shown that nucleation of SO2 over the continent is unlikely to contribute substantially to the sulfate aerosol mass. Though it can be concluded that the SO4= aerosol is directly imported to the continent in the form of particles, whether the transport is tropospheric or stratospheric cannot be deduced. It is suggested that 0.1 μm radius particles from growing industrialization are the ones most likely to show an increase in concentration in the future. Though not optically important, such particles may have relevancy in cloud microphysical process on large scales of distances.
Electric fields preceding cloud‐to‐ground lightning flashes
Authors: Beasley William , Uman Martin A. , Rustan P. L.
Published: February 2008

We analyzed in detail the electric field variations preceding the first return strokes of 80 cloud‐to‐ground lightning flashes in nine different storms observed at the NASA Kennedy Space Center during the summers of 1976 and 1977. The electric field variations are best characterized as having two sections: preliminary variations and stepped leader. The stepped‐leader electric‐field change begins during a transition period of a few milliseconds duration marked by characteristic bipolar pulses. The durations of stepped leaders lie most frequently in the range 6–20 milliseconds. We infer from our measurements and critical review of the previous literature that there is only one type of stepped leader, not the two types, α and β, often referred to in the literature.
Lightning return stroke velocities in the thunderstorm research international program (TRIP)
Authors: Idone Vincent P. , Orville Richard E.
Published: February 2008

We have used high‐speed streaking photographic techniques to time‐resolve the luminous components of cloud‐to‐ground lightning flashes. Two‐dimensional return stroke velocities have been measured for 63 strokes representing, we believe, the largest set of return stroke velocity measurements obtained to date. All recordings were made during our participation in the Thunderstorm Reseach International Program conducted at the Kennedy Space Center, Florida, during the summers of 1977 and 1978 and at the Langmuir Laboratory near Socorro, New Mexico, during the summer of 1979. The mean return stroke velocity, near ground (channel length ≤1.3 km), was found to be 11×107 m/s, with a maximum relative error estimate in most cases of 35% or less. The distribution of velocities peaks strongly at approximately 9×107 m/s. Thirty‐two of the 63 values (51%) fall within the interval of 8–12 × 107 m/s. The range of observed velocities spans the interval of 2.9–24×107 m/s. Based on the presence of branches in the time‐resolved recordings, 17 strokes are considered to be first return strokes, with a mean velocity, near ground, of 9.6×107 m/s. The mean velocity for subsequent strokes is 12×107 m/s. A further breakdown of the results for Florida and New Mexico, respectively, reveals mean first return stroke velocities of 6.6×107 m/s and 15 × 107 m/s as well as mean subsequent stroke velocities of 11×107 m/s and 13 × 107 m/s. Velocity variations for 17 of the best events are presented, with the return stroke velocity observed to decrease with height in every case except one. The velocity reduction can be substantial; velocities in upper channel lengths were often reduced by 25% or more relative to velocities near ground, even for subsequent strokes. The variation of velocity between strokes in multistroke flashes was found to be significant in some cases and minor in others. The results of this study are compared with the earlier major works of Schonland and of McEachron; substantial disparities are found and examined. We show, in fact, that Schonland's South African return stroke velocity measurements were obtained, in part, from a lightning storm atypical of the region. It should be noted, however, that our minimum return stroke velocity value of 2.9×107 m/s is in excellent agreement with the results of Schonland and of McEachron, despite the fact that our work, Schonland's, and McEachron's were obtained in widely differing geographical areas by using different instrumentation and spanning a period of 50 years.
Small particles in plumes of Mount St. Helens
Authors: Rose W. I. , Chuan Raymond L. , Woods David C.
Published: February 2008

Particles in the size range of 0.1–25 micrometers were sampled by aircraft carrying a quartz crystal microcascade in the Mount St. Helens plume on three dates in August and September 1980. Two of the sampling dates represented ‘typical’ emissions of the volcano between plinian eruptions. One sampling flight was made 1–4 hours before the small plinian eruption of August 7, 1980, when the plume had become discontinuous and visibly darker. Size distributions were determined, and individual particles were studied by using scanning electron microscopy. The plume sampled on August 7, before the eruption, contained mainly approximately 2 micrometer diameter silicic glass particles, fragments of the Mount St. Helens magma. The ‘typical’ plumes sampled on September 22 and August 6 had much smaller concentrations of particles, trimodal size distributions with peaks at 10, 0.4, and 0.1 micrometers. The particles were largely nonsilicate and apparently represented Cu‐Zn oxide (10 micrometer peak), Al sulfate, chloride and oxide(?), and sulfuric acid (smallest size peak). The characterization of small particles in the plume may give information about approaching activity and possibly about changing conditions in the subsurface magma body.
Water‐soluble material on aerosols collected within volcanic eruption clouds
Authors: Smith David B. , Zielinski Robert A. , Rose W. I. , Huebert B. J.
Published: February 2008

In February and March of 1978, filter samplers mounted on an aircraft were used to collect the aerosol fraction of the eruption clouds from three active Guatemalan volcanoes (Fuego, Pacaya, and Santiaguito). The samples were collected on Teflon (Fluoropore) filters with a nominal pore diameter of 0.5μm. The mass of air sampled by the filters ranged from 0.15 to 6.6 kg. The particulate material collected consisted of fragments of angular silicate ash and droplets of what is interpreted as dilute H2SO4 and HCl. After collection of the samples, each filter was rinsed with 60 ml of distilled‐deionized water. Splits of each extract were centrifuged to remove particles greater than or equal to 0.1 μm in diameter, acidified, and analyzed for B, Ba, Be, Ca, Cd, Co, Cu, Fe, Li, Mg, Mn, Mo, Na, Pb, Si, Sr, V, and Zn by inductively coupled plasma—optical emission spectroscopy. Separate splits were analyzed for F and Cl by specific‐ion‐electrode methods and for U by a fission track technique. The elements dissolved in the aqueous extracts represent components of water‐soluble material either formed directly in the eruption cloud or derived from interaction of ash particles and aerosol components of the plume. Calculations of enrichment factors, based upon concentration ratios, showed the elements most enriched in the extracts relative to bulk ash composition were Cd, Cu, V, F, Cl, Zn, and Pb. These elements represent a subset (with the addition of Cl and F) of elements previously reported enriched in atmospheric aerosols in remote regions as well as in volcanic areas. This suggests that some of the enriched elements were widely dispersed as volatile halides emitted from a volcanic source.
H2O2 levels in rainwater collected in south Florida and the Bahama Islands
Authors: Zika R. , Saltzman E. , Chameides W. L. , Davis D. D.
Published: February 2008

Measurements of H2O2 in rainwater collected in Miami, Florida, and the Bahama Islands area indicate the presence of H2O2 concentration levels ranging from (1–7)×10−5 M. No systematic trends in H2O2 concentration were observed during an individual storm, in marked contrast to the behavior of other anions (e.g., [NO3−], [SO4=], and [Cl−]). The data suggest that a substantial fraction of the H2O2 found in precipitation is generated by aqueous‐phase reactions within the cloudwater rather than via rainout and washout of gaseous H2O2.
Sulfur emissions from Mt. Etna
Authors: Jaeschke Wolfgang , Berresheim Harald , Georgii Hans‐W.
Published: February 2008

In the course of three measuring trips to the Mt. Etna volcano (Sicily), field measurements and measurements by aircraft were carried out in the plume of the volcano to determine the concentration distributions and emission rates for the sulfur compounds H2S, SO2, and SO42−. Furthermore, the removal of H2S and SO2 and the production of SO42− in the dispersing plume were investigated. The dispersion of the plume was studied by simultaneous tracer measurements of the CO2 concentration. H2S was additionally measured at the crater rims of Stromboli and Vulcano. The sulfur source strength of Mt. Etna was considerably dependent on the activity phase which was post‐eruptive and pre‐eruptive, respectively. The emission rates were found to vary between 142–1600 t SO2/d, 1–10 t H2S/d and 182–232 t SO42−/d. Oxidation rates of 1.7–5.0×10−4 s−1 for SO2 and 2.1×10−4 s−1 for H2S could be determined by the application of two different theoretical models which are described in detail.
An objective procedure for detecting and correcting errors in geophysical data: 1. One‐dimensional applications
Authors: Fleming Henry E. , Hill Michael L.
Published: February 2008

An objective procedure is developed for detecting and then correcting errors arising in the measurement of geophysical data sampled at equal increments of time or distance. The errors of interest are those larger in magnitude than the usual background noise level and are analyzed according to whether they occur in isolation or in clusters. Separate techniques are employed for each of these two cases. The concepts behind the procedures are also developed to provide guidance in their application. Errors occurring at and near the boundaries of the data set require special treatment. Two distinct methods for handling this situation are provided. Also discussed is an important extension to our basic error detection and correction procedure that can dramatically improve the performance of the procedure, provided the data are sampled sufficiently often relative to the shape of the underlying data structure. The complete step‐by‐step error detection and correction procedure is discussed and then outlined in a flowchart format. Finally, an example is presented to demonstrate the kinds of improvements that are possible through the implementation of the procedure.
The transient critical‐level interaction in a Boussinesq fluid
Authors: Fritts David C.
Published: February 2008

A numerical model was used to examine the consequences of transience and nonlinearity in the critical‐level interaction of an internal gravity wave. Wave packets in a shear flow were observed to evolve as predicted by the linear, initial‐value results of Booker and Bretherton (1967) until convectively unstable layers evolved. Once formed, such layers were found to break down via a convective instability, presumably resulting in the turbulent dissipation of the incident wave packet. Several simulations were used to illustrate the transient stabilization of, and the Eulerian mean flow accelerations induced by, critical‐level interactions. Other simulations were performed to examine the evolution of a wave packet in a time‐dependent shear flow. The latter suggest that critical‐level absorption and wave action dissipation can be either greatly accelerated or effectively eliminated depending upon the tendency of the mean velocity shear. The implications of these findings for internal gravity wave propagation in the atmosphere and the oceans are discussed.
On the scaling of vertical temperature gradient spectra
Authors: Gibson Carl H.
Published: February 2008

A physical interpretation is proposed for the temperature gradient wave number scaling of Caldwell et al. [1980]. It is shown that kc/kB = (5.5 AT)1/2, where AT is the turbulence activity parameter of Gibson [1980] used to classify fossil turbulence. AT = 1 corresponds to active turbulence in a stratified fluid where the largest eddies are slightly affected by buoyancy, and AT = 1.4 (Pr/C)1/2 corresponds to fossil turbulence in a fluid with nearly saturated internal waves but no active turbulence. The Caldwell et al. [1980] scaling, with kc/kB = 1, is equivalent to AT = 0.18. According to the Gibson [1980] fossil turbulence model, this indicates completely fossil temperature turbulence for Cox number C < 600 and a mixture of active and fossil turbulence for C > 600. The tendency for kc/kB to decrease with increasing C noted by Caldwell et al. [1980] may reflect both the wider range of possible AT values, 1 to 1.4(Pr/C)1/2, for partially fossilized temperature turbulence microstructure with large C, as well as the relatively long persistence times of such remnants of strong mixing events which makes it more likely that such large C microstructure will be encountered in an advanced stage of decay of its fossil phase. Because all the microstructure encountered was fossil to some degree, the turbulent mixing process has apparently been undersampled.
Exchange of sulfur between the free troposphere, marine boundary layer, and the sea surface
Authors: Kritz Mark A.
Published: February 2008

A steady state analysis has been made of the sources and sinks of sulfur in the remote marine atmosphere and of the steady state exhanges of SO2 and (excess) sulfate between the sea, boundary layer, and free troposphere. Two situations were examined: an area of high biological productivity (Gulf of Guinea) and an area of low productivity (tropical Atlantic). The results of the analysis suggest that about one‐third of the ‘background’ concentrations of SO2 and excess sulfate observed in the remote marine atmosphere mixes in from the free troposphere, with the balance, ∼100 μg S m−2 d−1, attributed to the local oxidation of reduced sulfur‐bearing precursors in the boundary layer.
Chemical analysis of cloud water collected over Hawaii
Authors: Parungo F. , Nagamoto C. , Nolt I. , Dias M. , Nickerson E.
Published: February 2008

Two types of cloud water collectors were developed, and the devices were used to collect samples around the Hawaii Islands. The chemical analyses of cloud water showed that Na+, Cl−, and SO4= ion concentrations were approximately 10−4 m; NH4+, NO3−, and Ca+ + were 1 order of magnitude lower. The pH values were in the range of 4–5 regardless of sampling locations. The high acidity of cloud water over Hawaii may originate in the ocean or from long‐range transport of anthropogenic pollution, in addition to local pollution, if present.
Measurements of ozone vertical flux to ocean and forest
Authors: Lenschow Donald H. , Pearson Richard , Stankov B. Boba
Published: February 2008

Ozone flux has been measured from aircraft by the eddy correlation technique over the Gulf of Mexico, the north Pacific Ocean, and a Gulf Coast pine forest. Measurements over the Gulf were obtained in polluted air (which had flowed down the Mississippi valley) over relatively warm water, while the north Pacific observations were obtained in pristine air over relatively cold water with nearly neutral stratification. Values of the surface resistance to ozone were about 1.8×103 s m−1 over both ocean surfaces and 50 s m−1 over the forest, with an accuracy of better than ±15%. Photochemical production of ozone during midmorning with clear skies over the Gulf of Mexico was 0.2–0.3 ng m−3 s−1, which is an order of magnitude less than that observed over northeastern Colorado.
A model for the relationships between precipitation D/H ratios and precipitation intensity
Authors: Yapp Crayton J.
Published: February 2008

A simple quantitative model has been developed which predicts that a parametric correlation between the isotopic composition of precipitation and precipitation intensity can exist as a consequence of the condensation process when certain conditions are met. These conditions include the following: (1) approximate constancy, from one sampling interval to the next, of the initial isotopic composition of the water vapor in precipitation‐producing air masses; (2) approximate constancy of the initial condensation temperature; (3) approximate constancy of the rate of vertical ascent of the precipitating air mass; and (4) approximate constancy of the ratio of condensed water to water vapor. Such conditions are probably rare in nature for the short collection intervals represented by existing samples. However, with the probable exception of condition 3, tropical oceanic islands may satisfy the preceding conditions on the month‐to‐month time scale for which precipitation samples have generally been collected for isotopic analysis. Precipitation samples from Wake and Johnston islands that plot on the meteoric water line were used to compare monthly δD values with corresponding precipitation intensity. In general, there appears to be a convergence of the data at high values of δD (low intensity) and a divergence at low values of δD (high intensity). Such behavior is predicted by the isotopeintensity model largely in terms of variation in the vertical rate of ascent. For Wake Island this divergence of the data appears to be bimodal in character. However, for Johnston Island, there is considerable scatter in the data. This scatter is roughly constrained by the envelope defined by two vertical ascent rates that approximately characterize the presumably bimodal Wake Island trends. Thus much of the scatter in the Johnston Island data may be explained by month‐to‐variability in vertical ascent rates. The data for these two islands suggest that a simple precipitation δD versus intensity correlation is unlikely for monthly sample intervals. However, the issue remains unresolved for longer time scales.
Optimal weighting of data to detect climatic change: Application to the carbon dioxide problem
Authors: Bell Thomas L.
Published: February 2008

Increasing carbon dioxide concentration in the atmosphere is expected to lead to warming of the surface of the earth. Detection of the warming is difficult because it must be distinguished from natural variability of temperatures due to daily weather changes. It is shown that a weighting of surface temperature data using information about the expected level of warming in different seasons and geographical regions and statistical information about the amount of natural variability in surface temperature can improve the chances of early detection of the warming. Surface temperature data are conventionally averaged over the surface of the earth, weighted according to the geographical area represented by the data. A preliminary analysis of the optimal weighting method suggests that it is 25% more effective in revealing a surface warming than the conventional weighting method, in the sense that 25% more data analyzed in the conventional way are needed to have the same chance of detecting the climatic warming. The possibility of detecting the warming in data already available is examined. A rough calculation suggests that the warming ought to have already been detected if the only sources of significant variability in surface temperature had time scales less than 1 year.
Concentration of atmospheric carbon dioxide over Japan
Authors: Tanaka Masayuki , Nakazawa Takakiyo , Aoki Shuhji
Published: February 2008

Aircraft measurements of atmospheric CO2 concentration over Japan have been initiated in January 1979 at the Upper Atmosphere Research Laboratory of the Tohoku University. An average annual increase of CO2 concentration during a period from the beginning to April 1981 is estimated to be 1.5 ppmv/year. Yearly average values for the concentration decrease with increasing height above ground, rapidly in the lowest layer of the tropopsphere, and rather slightly in the layer above it, showing that the ground acts as a CO2 source. The amplitude of the seasonal variation decreases markedly with elevation. The maximum occurs early in May and the minimum early in August at low levels. The phase shift of the seasonal variation between the lowestmost and uppermost parts of the troposphere is about 1 month. Relations between irregular variations in CO2 concentration and characteristic features of weather systems are also discussed.
Detection of seamount signatures in SEASAT altimeter data using matched filters
Authors: White J. V. , Sailor R. V. , Lazarewicz A. R. , Leschack A. R.
Published: February 2008

Matched‐filter techniques are described for the detection of characteristic geoid undulation signatures of seamounts in SEASAT radar altimeter data. The technique requires models of the expected undulation signatures and a statistical description of the background (seamount‐free) data. Examples are given of the detection of 11 known seamounts on four distinct tracks. Further extensions and applications of the matched‐filter methods are discussed.
Analysis and retracking of continental ice sheet radar altimeter waveforms
Authors: Martin Thomas V. , Zwally H. Jay , Brenner Anita C. , Bindschadler Robert A.
Published: February 2008

The SEASAT‐I radar altimeter data set acquired over both the Antarctic and Greenland continental ice sheets is analyzed to obtain corrected ranges to the ice surface. The radar altimeter functional response over the continental ice sheets is considerably more complex than over the oceans. Causal factors identified in this complicated response include sloping surfaces, undulating ice surfaces with characteristic wavelengths on the same spatial scale as the altimeter beam‐limited footprint, off‐track reflections, and dynamic lag of the altimeter tracking circuit. Retracking methods using the altimeter return pulse waveforms give range corrections that are typically several meters. The entire set of SEASAT‐I altimetry over the continental ice sheets is being retracked by fitting a multi‐parameter function to each waveform. Many waveforms have double ramps indicating near‐normal reflections from two distinct portions of the ice surface within the altimeter beam. Two independent range measurements differing by less than 25 m are obtained from retracking the double‐ramp waveforms.
Some examples of detection of oceanic mesoscale eddies by the SEASAT synthetic‐aperture radar
Authors: Fu Lee‐Lueng , Holt Benjamin
Published: February 2008

This note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the SEASAT synthetic‐aperture radar (SAR). South of the Grand Banks of Newfoundland, a cold eddy is observed to form as the result of the southward intrusion of Labrador Sea water, perhaps having led to the birth of a Gulf Stream extension ring. Off the northern coast of California, features resulting from the offshore intrusions of cold upwelling water are observed. Two topographically generated eddies are detected near Misteriosa Bank on the Cayman Ridge in the northwestern Caribbean. Comparisons are made with concurrent NOAA‐5 infrared images whenever the eddies have thermal signatures.
A model function for ocean microwave brightness temperatures
Authors: Wentz F. J.
Published: February 2008

We derive a relatively simple, yet accurate, relationship between the microwave brightness temperature of the ocean and conventional oceanographic and meteorological parameters. To begin with, the brightness temperature of the ocean and the intervening atmosphere is expressed in terms of integrals for the radiative scattering and emission from the sea surface and the radiative absorption and emission by the atmosphere. We then find closed‐form approximations for these integrals and obtain a simplified model for the radiative transfer and scattering. The model is reduced to a function giving brightness temperature in terms of five variables: sea‐surface temperature, sea‐surface friction velocity, atmospheric columnar water vapor content, atmospheric columnar liquid water content, and surface air temperature« In the derivation of the model, the absorption coefficient for rain clouds and the wind‐induced sea‐surface emissivity are found from SEASAT SMMR observations. The remainder of the derivation is based on wellaccepted microwave theory. The model function is referenced to the five frequencies and 49° incidence angle at which the SEASAT and Nimbus 7 SMMR operate. When compared with the more precise integral formulation, the model function accuracy is 0.2 K at 6.6 GHz and gradually degrades to 2.1 K at 37 GHz, horizontal polarization. These accuracies are an average over an ensemble of winds and atmospheres ranging from a specular surface and clear skies to a 21 m/s wind and a very heavy cloud layer containing 60 mg/cm2 of liquid water, but excluding rain. An uncertainty of about 10% in the wind‐induced emissivity introduces some additional error into the model function. Several of the derived model parameters are compared with values obtained in other experiments and theoretical investigations. The frequency ratios of the SMMR‐inferred absorption coefficients for rain clouds are in very close agreement with that given by Mie scattering theory. The large‐scale sea‐surface slope variance found from the SMMR data is consistent with the slope variance computed from a sea wave spectrum, with that inferred from microwave scatterometer measurements at nadir, and with the Cox and Munk value deduced from sun glitter. The SMMR‐inferred foam coverage correlates better with whitecap coverage than streak coverage, indicating that the increase in brightness temperature due to sea foam is more a result of whitecapping than streaking. A layered dielectric model for sea foam predicts the same frequency and polarization variation in the foam reflectivity as observed by the SMMR. The consistency of these results support the premise that the sea‐surface emissivity is accurately represented by a composite model in which the emission from the rough, foam‐free water is given by twoscale scattering theory and the foam emission is given by a layered dielectric theory.
Azimuthal structure of a cyclonic Gulf Stream ring
Authors: Mied Richard P. , Lindemann Gloria J. , Bergin John M.
Published: February 2008

During the period June 8–19, 1979, an intensive expendable bathythermograph survey of a Gulf Stream ring was made. After mapping the irregularly spaced data onto a regular grid, and azimuthally decomposing the temperature field at constant depth into Fourier constituents einθ, we find the n = 2 mode to be the dominant one. We calculate the geostrophic stream function utilizing the hydrostatic equation and the measured temperature/salinity curves. The stream function is expressed in cylindrical polar coordinates (r, θ, z) and decomposed into a steady, azimuthally independent part ψ(r, z) and a temporally varying disturbance part ϕ(r, θ, z, t) with azimuthal dependence. The quasi‐geostrophic energy equation for ϕ contains source terms representing the interaction of the ψ and ϕ fields by baroclinic and barotropic processes. We find that ∼90% of the total disturbance energy flux results from baroclinic processes, and the remainder from the barotropic exchanges. The time scale of this energy flux into the disturbance ϕ is of the order of 16 days, while the time scale of an energy loss from the disturbance is ∼4.5 days.
Phytoplankton and thermal structure in the upper ocean: Consequences of nonuniformity in chlorophyll profile
Authors: Lewis Marlon R. , Cullen John J. , Platt Trevor
Published: February 2008

Solar irradiance absorption in the upper layers of the ocean is influenced by the concentration of phytoplankton. Nonuniformities in vertical chlorophyll (phytoplankton) distributions lead to nonuniformities in absorption and consequently to variations in local heating. Local heating rate tends to decrease monotonically with increasing depth, but certain vertical distributions of chlorophyll lead to a change of sign of the gradient. Data from an oligotrophic ocean station showed a subsurface maximum of chlorophyll intense enough to allow increased heating on the upper slope of the chlorophyll maximum, with a maximum gradient of 0.003°C d−1 m−1. It is suggested that the importance of such subsurface heating for augmenting vertical mixing and influencing mixed layer deepening may be greatest in the optically clear, open ocean regions.
Norwegian Remote Sensing Experiment: Evaluation of the Nimbus 7 scanning multichannel microwave radiometer for sea ice research
Authors: Svendsen E. , Kloster K. , Farrelly B. , Johannessen O. M. , Johannessen J. A. , Campbell W. J. , Gloersen P. , Cavalieri D. , Mätzler C.
Published: February 2008

An algorithm has been developed for estimating total and multiyear sea ice concentration from passive microwave and surface air temperature measurements. The algorithm was made for use with Nimbus 7 scanning multichannel microwave radiometer (SMMR) data. It is based on radiation physics and may thus easily be modified to suit other passive microwave instruments. A comparison between Nimbus 7 SMMR and aircraft microwave measurements indicates that estimates of total ice concentration are accurate to ±3% and those of multiyear ice concentration to ±10%. These accuracies are not valid during the melt season when the snow on the ice is wet. For the first time such a comparison of independent estimates has been performed to validate the capability of measuring sea ice coverage from space. The ability of the SMMR to follow moving patches of multiyear ice and of rain/wet snow areas has been demonstrated. From the concentration estimates the sharpness of the ice edge can be estimated. The need for accurate concentration estimates for reliable heat budget estimates in the Arctic is also discussed.
An investigation of a polynya in the Canadian Archipelago: 1. Introduction and oceanography
Authors: Topham D. R. , Perkin R. G. , Smith S. D. , Anderson R. J. , Hartog G. Den
Published: February 2008

In certain parts of the Canadian Archipelago, small localized areas of water remain ice free throughout the winter, despite the extreme temperature differences between the atmosphere and the ocean surface. One such area, close to Dundas Island, has been studied in detail, both from the point of view of the atmospheric/oceanic heat exchange over the open water and its local geographic and oceanographic context. This paper describes the oceanography of the area and local weather and tidal flow conditions. A significant feature of the oceanographic records is a strong modulation of near‐surface ocean temperature at tidal frequencies involving temperature differences as great as 0.2°C within a single tidal cycle. For the most part, the surface waters are 0.1° to 0.2°C above freezing. The presence of this relatively warm surface water is thought to be due to upward mixing occasioned by fast tidal flows across the shallow sill connecting Dundas and Devon islands. Historical records of water properties in the Sverdrup Basin lying to the north of the polynya area show temperatures substantially above freezing point at depths of 50 m and below. This readily accessible body of warm water is thought to be the source of the sensible heat required for the existence of the polynya. This is supported by existing current measurements which suggest a mean southerly transport in the channels leading into and out of the region of the polynya site. A tentative application of the atmospheric heat flux measurements to the whole Dundas Island‐Bailey Hamilton Island area suggests that sufficient heat may be lost to affect significantly the water column further south in Crozier Strait and Wellington Channel. The limited information available shows the more southerly waters of these passages to be relatively well mixed and cooled relative to the water of the Sverdrup Basin, just to the north of the Dundas polynya area.
Tracing bomb 14C in the atmosphere 1962–1980
Authors: Nydal Reidar , Lövseth Knut
Published: February 2008

When the ever greater series of nuclear tests were exposed to the atmosphere at higher northern latitudes during 1961 and 1962, an attempt was made at this laboratory to trace the distribution of bomb‐produced 14C down to lower latitudes and into the ocean surface. Several ground level stations were established for this purpose in the early 1960's, from Spitsbergen (78°N) to Madagascar (21°S) Measurements were also gradually extended to the ocean surface. The tropospheric measurements which partly have been performed during the last 18 years have proved to be important for testing exchange models for industrial CO2 in the atmosphere and more generally for studying the carbon cycle in nature. The present paper includes tables of all the atmospheric 14C data measured at this laboratory during 18 years. Several graphs are also included and a description of sampling locations and contamination problems. The paper is an answer to those who want to use the data in their own modeling research.
Stratospheric N2O, CF2Cl2, and CFCl3 composition studies utilizing in situ cryogenic, whole air sampling methods
Authors: Gallagher Charles C. , Forsberg Charles A. , Fieri Robert V.
Published: February 2008

The fluorocarbon and nitrous oxide content of the stratosphere have been studied as a function of altitude, latitude, and time. Whole air samples have been gathered from a balloon platform, primarily through use of a cryogenic sampler. Twenty‐two flights were conducted between 1975 and 1980, and gas chromatography was utilized to determine species mixing ratios in the retrieved samples. Results are evaluated in terms of various stratosphere models.
Mid‐latitude lidar observations of planetary waves in the middle atmosphere during the winter of 1981–1982
Authors: Hauchecorne A. , Chanin M. L.
Published: February 2008

A quasi‐continuous survey of the stratospheric and mesospheric temperature was performed, between June 1981 and April 1982, using the lidar station of the Observatory of Haute‐Provence (44°N, 6°E). During the period of easterly winds in the lower stratosphere (i.e., from June to September), the variability of the temperature is observed to be very low. As long as prevailing winds are westerlies, from October to March, temperature profiles are continuously perturbed by planetary waves, with a maximum of amplitude in January 1982, before the ‘strong minor warning’ of the winter. Spectral analysis of the data indicates the presence of a well‐defined 18‐day wave interpreted as a free Rossby wave and the existence of large perturbations with periods of 25 to 40 days which are tentatively explained as a succession of minor upper stratospheric warmings due to the interference of the 18 day traveling Rossby wave and a stationary wave.
The sampling variability of estimates of spectra of wind‐generated gravity waves
Authors: Donelan Mark , Pierson Willard J.
Published: February 2008

The sampling variability of spectra of wind‐generated waves is tested against the predictions of the theory of waves as a stationary random quasi‐Gaussian process. Both laboratory data, in which stationarity was prescribed, and field data, in which the external conditions were remarkably steady, were treated in the same way. It is demonstrated that the theory of stationary Gaussian processes provides accurate estimates of the sampling variability. For a record length of 17 min, commonly used in wave monitoring at sea, the uncertainties in the significant height and peak frequency estimates are approximately ±12% and ±5% respectively at the 90% confidence level. Furthermore, the height of the peak of the spectrum is generally overestimated.
Cape Romain and the Charleston Bump: Historical and recent hydrographic observations
Authors: Singer J. J. , Atkinson L. P. , Blanton J. O. , Yoder J. A.
Published: February 2008

A review and analysis of historical and new hydrographic data are presented for the Charleston Bump region. An area of doming isotherms is identified primarily between 31.5° and 34.5°N and the 200 and 400 m isobaths. The highest incidences of doming are found off Long Bay (86%), Cape Fear (38%),and Cape Romain (25%). Evidence suggests that low salinity shelf water collects in the doming area off Long Bay in July and that seasonal fluctuations in the depth of the main thermocline layer in this area are linked to Gulf Stream transport and local winds. At times there is a gradual offshore‐onshore movement of the Gulf Stream opposite Long Bay roughly following the 400 m isobath and at other times an abrupt eastward movement near 32°N. Much of the time there appears to be a direct seasonal relationship between historical seasonal velocity fields and offshore deflection with higher (lower) velocities corresponding to greater (lesser) deflection.
On the distribution of nitrogen dioxide in the high‐latitude stratosphere
Authors: Solomon Susan , Garcia Rolando R.
Published: February 2008

A time dependent two‐dimensional model has been used to study the behavior of nitrogen species in the atmosphere. The model employs a residual mean meridional circulation for the transport of photochemical species, and this transport yields large column abundances for NOx (N + NO + NO2 + NO3 + 2 × N2O5 + HNO4) at high latitudes, with the altitude of maximum density occurring in the lower stratosphere. New temperature dependent absorption cross sections are employed for N2O5. It is shown that this photochemical‐dynamical formulation results in the conversion of most of the stratospheric NOx to N2O5 at high latitudes in winter, yielding low NO2 column abundances there, in agreement with observations. Calculated seasonal and diurnal variations in NO2 are also shown to be comparable to observations, even at high latitudes. The effects of departures from zonally symmetric flow on NO2 abundance are examined and found to be consistent with observations.
Effects of weak bed load on the Universal Law of the Wall
Authors: Gust Giselher , Southard John B.
Published: February 2008

Two‐dimensional equilibrium boundary‐layer flows were investigated in an open water channel with a width/depth ratio of 6 for a smooth bed of 0.16 mm quartz grains (d50) and compared with those of an immobile smooth cemented bed with the same sand roughness. For flows at Reynolds numbers between 20,000, representing onset of erosion, and 28,000, before appearance of rhomboid ripples, quartz grains rolled over an otherwise smooth sand bed with a density of ≤40 grains cm−1 s−1. Then the universal law of the wall, as obtained for the fixed, smooth sand bed, could not be confirmed by the data. Instead, (1) a logarithmic layer was found that extended further into the wake region and had a reduced value of von Karman's constant κ = 0.32 ± 0.04, (2) the friction diagram indicated Reynolds number dependent drag reduction, and (3) the logarithmic layer extended down to the top of the rolling grains at ReU >25,000. These results are interpreted as a new class of wall‐bounded shear flow with different momentum transfer processes and a velocity‐defect law throughout the flow down to the top of the rolling grains. Some conclusions are discussed for sedimentological and engineering problems in which this type of flow is the rule rather than the exception.
Tides on the Northern Great Barrier Reef Continental Shelf
Authors: Wolanski Eric
Published: February 2008

Sea level and current data are used to show that, at least for the dominant semidiurnal tides, the northern Great Barrier Reef is permeable to tides, the longshore gradients of the phase and amplitude of the tide at the shelf break are very small, and the tidal currents are controlled by the shelf bathymetry. The bulk friction coefficient may be enhanced by the secondary circulation around coral reefs.
Sensitivity studies with a coupled ice‐ocean model of the marginal ice zone
Authors: Røed Lars Petter
Published: February 2008

An analytical coupled ice‐ocean model is considered which is forced by a specified wind stress acting on the open ocean as well as the ice. The analysis supports the conjecture that the upwelling dynamics at ice edges can be understood by means of a simple analytical model. In similarity with coastal problems it is shown that the ice edge upwelling is determined by the net mass flux at the boundaries of the considered region. The model is used to study the sensitivity of the upwelling dynamics in the marginal ice zone to variation in the controlling parameters. These parameters consist of combinations of the drag coefficients used in the parameterization of the stresses on the three interfaces atmosphere‐ice, atmosphere‐ocean, and ice‐ocean. The response is shown to be sensitive to variations in these parameters in that one set of parameters may give upwelling while a slightly different set of parameters may give downwelling.
Positive cloud to ground lightning return strokes
Authors: Beasley William H. , Uman Martin A. , Jordan Douglas M. , Ganesh Chidambar
Published: February 2008

Several recent papers have reported positive cloud‐to‐ground lightning, but, in our opinion, none provides sufficiently direct evidence that positive return strokes occurred in any given case. Here we present observations that plainly demonstrate the occurrence of positive return strokes in a convective thunderstorm in Florida in August 1982. These observations consist of waveforms of electric field correlated in time with light pulses received through a narrow collimated slit aimed about 1.2 degrees above a level plane and with videotape records of lightning channels. We studied lightning during one 15‐min interval at a range of 20–40 km. During this period we recorded time‐correlated waveforms from three positive return strokes. The 10–90% rise times of the electric fields, 1–5 μs, and of the light pulses, 3–6 μs, were similar to those of negative return strokes in the same storm. The light signals of the positive return strokes began 2–8 μs after the electric fields, consistent with return‐stroke speeds of about 108 m s−1, a value comparable to speeds of ordinary negative return strokes.