bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum multiparameter analysis of mixing in the thermocline of the eastern Indian Ocean
Authors: Tomczak Matthias , Large Daniel G. B.
Published: February 2008

A method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations. It requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types. The procedure to establish the water types, find the correct weights for the parameters, and solve the mixing equations through minimization of the residuals is described in detail. The method is applied to a data set from the eastern Indian Ocean, where Indian Central Water and Australasian Mediterranean Water meet to produce a strong front in the thermocline. It is shown that although most of the water from the Indonesian archipelago is carried westward north of 11°S, contributions from the Australasian Mediterranean Water are found as far south as 25°S, particularly along the Australian shelf as a result of advection with the Leeuwin Current.
Characteristics of the active layer and shallow subsea permafrost
Authors: Osterkamp T. E. , Baker G. C. , Harrison W. D. , Matava T.
Published: February 2008

A seasonal active layer associated with subsea permafrost was found in the sediments near the seabed of the Beaufort Sea near Prudhoe Bay, Alaska. The active layer existed where sea ice was frozen to the seabed and also in shallow water where the under‐ice seawater salinities exceeded open‐water values. Initial freezing of the active layer was about coincident with the formation of new sea ice. Within 400 m of shore, it appeared to freeze to an underlying ice‐bonded permafrost table (IBPT). Farther offshore, where this table is deeper, the active layer thickness decreased with distance offshore, and the layer was underlain by a talik. Relative ice contents in the active layer generally decreased with distance offshore, were a few hundred parts per thousand (ppt) in the fall, and ranged to more than 800 ppt in the spring. Seasonal changes in the bulk soil solution salinity showed that the partially frozen active layer redistributed salts during freezing, was infiltrated by concentrated brines derived from the growth of sea ice, and affected the timing of brine drainage to lower depths in the sediments. These brines provide the salts required for thawing the underlying subsea permafrost in the presence of negative sediment temperatures. The region near shore had a partially frozen transition layer just above the IBPT where the ice content increased and the brine content decreased with depth. Temperature at the IBPT is nearly constant beyond about 412 m to at least 3.5 km offshore at about −2.41°C, implying relatively constant soil solution salinities there.
Shear instabilities of the mean longshore current: 1. Theory
Authors: Bowen A. J. , Holman R. A.
Published: February 2008

A new class of nearshore waves based on the shear instability of a steady longshore current is discussed. The dynamics depend on the conservation of potential vorticity but with the background vorticity field, traditionally the role of Coriolis in larger scale flows, supplied by the shear structure of the longshore current. The resulting vorticity waves are longshore‐progressive with celerities roughly equal to V0/3, where V0 is the peak longshore current velocity. A natural frequency scaling for the problem is fs, the shear of the seaward face of the longshore current. While the instability can span a range of frequencies and wavenumbers, a representative frequency is given by 0.07fs, typically in the range of 10−3–10−2 Hz (called the Far Infragravity, or FIG, band because frequencies are just below those of the infragravity band). Wavelengths are of the order of 2x0, where x0 is the width of the longshore current. Growth is exponential with an e‐folding time that is typically half of a wave period. Field data, presented in the companion paper [Oltman‐Shay et al., this issue], demonstrate the presence of energetic motions from a natural beach whose behavior matches the theory in many aspects. Results from the model suggest that shear instability will be more important on barred, rather than monotonic beach profiles, a result of the stronger shears expected over the bar crest. Since vorticity waves will probably have a profound effect on cross‐shore mixing as well as longshore current dissipation, we expect the dynamics of barred and monotonic beaches to show fundamental differences.
Shear instabilities of the mean longshore current: 2. Field observations
Authors: Oltman‐Shay Joan , Howd P. A. , Birkemeier W. A.
Published: February 2008

A new type of alongshore progressive wave with periods and alongshore wavelengths of the order of 102 seconds and meters, respectively, has been observed in the surf zone. These periods fall into the lower end of the much studied infragravity frequency band previously shown to contain surface gravity edge and leaky waves. However, their short wavelengths (more than an order of magnitude smaller than the mode 0 edge wave) distinguish these new waves from surface gravity waves. In addition, they are only observed in the presence of mean longshore current and they change celerity (O(1 m/s)) and direction with the mean current. Alongshore wavenumber‐frequency spectra clearly identify these waves, distinct from edge and leaky waves, by their approximately linear dispersion line at wavenumbers greater than the mode 0 edge wave dispersion curve. Their rms horizontal velocities can exceed 30 cm/s. These waves are shown to be consistent with a model [Bowen and Holman, this issue] of vorticity waves generated by the shear instability of the mean longshore current.
Water mass structure and boundaries in the Mackenzie shelf estuary
Authors: Carmack E. C. , Macdonald R. W. , Papadakis J. E.
Published: February 2008

The Mackenzie shelf is a broad, estuarine region bordering the southeastern Beaufort Sea in the Arctic Ocean. Its fields of temperature and salinity result from the modification of offshore water masses by river inflow, ice melting and freezing, solar insolation, and air‐sea exchange. We here relate water masses resident on the Mackenzie shelf to the large‐scale oceanography of the Arctic mediterranean. The summertime exchange between the shelf and open ocean is largely confined to waters lying above the main halocline (S<32.3 psu), thus excluding underlying offshore waters from the nutrient maximum layer (S ≈ 33.1 psu) and Atlantic layer (S>34.2 psu). Cross‐shelf property distributions show that individual water masses maintain their structural identity (i.e., core properties and buoyancy frequency) as they move across the shelf and participate in the estuarine circulation. Shelf waters are strongly influenced by river inflow; however, the concept of a single “plume” issuing from the incoming river and forming a strictly two‐layered structure over uniform shelf water is misleading, since a variety of temperature, salinity, and turbidity fronts co‐exist on the shelf at any given time.
The intrusion of water masses into the sea southwest of Taiwan
Authors: Shaw Ping‐Tung
Published: February 2008

Characteristics of water masses were analyzed to study the Kuroshio intrusion into the sea southwest of Taiwan. Hydrographic data were obtained from CTD (conductivity, temperature, and depth) casts during two cruises in May and August 1986. In May, remnants of water intruding from the Kuroshio were found on the continental slope south of the Penghu Channel. By August, these were replaced by water from the South China Sea. During this period, water from the Kuroshio also appeared near the southern tip of Taiwan. The intrusion current reached a depth of at least 500 m and was probably part of a cyclonic circulation in the northern South China Sea. The results support the hypothesis of a seasonal pattern of the intrusion process: intrusion of water from the Kuroshio begins in late summer, intensifies in winter, and ceases by late spring when South China Sea waters again enter this region.
Geostrophic transport variability along the Aves Ridge in the eastern Caribbean Sea during 1985–1986
Authors: Morrison John M. , Smith Orson P.
Published: February 2008

Data from five cruises during 1985–1986 along 63.55°W, across the eastern Caribbean Sea, are examined for seasonal variability of gcostrophic transport. A biannual maximum transport signal appears to correspond to that measured in the Florida Straits as well as to variations in the regional wind stress curl. Similar seasonal variations in the properties of water masses, entering the eastern margin of the basin and concentrated through the passages of the Lesser Antilles, are also indicated. A permanent system of strong westward flowing streams, interspersed by weaker eastward flowing streams, is shown to exist.
Gulf Stream path analysis near the New England Seamounts
Authors: Teague William J. , Hallock Zachariah R.
Published: February 2008

As part of the Naval Ocean Research and Development Activity's Regional Energetics Experiment, 12 inverted echo sounders (IESs) were deployed from June 1985 to July 1986 in two arrays across the historical mean path of the Gulf Stream near 67°W and 58°W, slightly upstream and downstream of the New England Seamount chain. Gulf Stream positions and directions were computed at half‐day intervals for adjacent IES pairs. Levels of variability at the two array locations were similar, but the characteristics of the meanders, in terms of propagation and current direction, were quite different. Evidence was found for a quasi‐stationary meander near 58°W. Features deduced from IES measurements are compared with concurrent infrared, air‐dropped expendable bathythermograph, and Geosat altimetry observations.
Geosat: Beginning a new era in satellite oceanography
Authors: Douglas Bruce C. , Cheney Robert E.
Published: February 2008

The U.S. Navy satellite Geosat has provided the first altimeter data set that is both long term and global in coverage. This special issue of JGR‐Oceans demonstrates the high level of interest in this unprecedented data stream. Geosat data contain information on sea surface topography, sea state, and wind speed. Also present in the sea level data are systematic errors arising from propagation effects and uncertainty in the satellite ephemeris. A major effort of the community that uses altimeter data is to understand the limitations of Geosat data arising from these errors and devise means to overcome them. Thus many papers in this special issue deal with algorithms and verification in an effort to establish the scale of the problems to which Geosat data can be applied both now and with future improvements. The scientific results presented here amply illustrate the value of the data already released. Another facet of Geosat not reported in any paper has been the unselfish cooperation of the satellite geodesy‐altimetry community. Investigators in the United States and abroad are freely sharing their results, ideas, and computer programs on an open basis, making participation in the Geosat effort a great pleasure as well as professionally rewarding.
Impact of phytoplankton‐generated surfactants on air‐sea gas exchange
Authors: Frew Nelson M. , Goldman Joel C. , Dennett Mark R. , Johnson A. Sherwood
Published: February 2008

The effect of surface‐active organic matter generated by seven common species of marine phytoplankton on gas exchange rates under turbulent conditions at the air‐water interface was determined. Reductions in oxygen evasion rates ranging from 5 to 50% were observed relative to clean seawater controls. Relative oxygen exchange coefficients (expressed asR=Kw[sample]/Kw[control]) were shown to be sensitive to small changes in total dissolved carbohydrate at concentrations <1 mg C (carbon) L−1and to asymptotically decrease to a lower limit (R= 55–70%) at concentrations between 2 and 6 mg C L−1. A corresponding relationship was observed in whichRdecreased with increasing relative surfactant amounts derived from surface pressure‐area measurements. However, gas exchange reductions were significant for plankton exudate samples displaying surface pressures ≲1 mN m−1. It thus seems that condensed monolayer films are not a prerequisite for reduced gas exchange and that relatively soluble surfactants derived from phytoplankton can strongly affect the dissipation of near‐surface turbulence and lead to changes in the Schmidt number dependency ofKw. Based on detailed analyses of carbohydrate‐containing surface‐active exudates isolated by solid phase extraction from one of the species,Phaeodactylum tricornutum, it appears that small glucans and heteropolysaccharides associated with proteins and possibly lipids were responsible for the observed reductions inR.
Aluminium in the South Atlantic: Steady state distribution of a short residence time element
Authors: Measures C. I. , Edmond J. M.
Published: February 2008

The aluminium concentrations of water samples from 18 hydrographic profiles and 35 surface samples in the South Atlantic were determined on board ship during leg III of the South Atlantic Ventilation Experiment (SAVE). The observed surface water distributions (range 0.5 to 57 nM) are thought to arise from the partial dissolution of eoliantransported continental dusts coupled with limited lateral transport by prevailing surface currents. In the deep water the greatest enrichments are observed coincident with the depth of the lower North Atlantic Deep Water. The similarity between the Al∶Si ratios in this water mass in both the south and north Atlantic is taken as evidence that no significant Al additions are being made to this water during its transit. The lower Al concentrations observed in the water masses of Antarctic origin (∼3 nM) are consistent with their formation in areas of limited dust input. The somewhat higher values observed in the Antarctic Bottom Water suggest that the shelf component of this water mass may have elevated Al concentrations.
Polynyas and leads: An overview of physical processes and environment
Authors: Smith Stuart D. , Muench Robin D. , Pease Carol H.
Published: February 2008

Polynyas and leads are openings in pack ice due to divergences in ice drift and to local melting. They are the vents and windows to the polar oceans. In winter they are a major source of brine during freezing and a locus for gas exchange. Large sensible heat fluxes, together with evaporation and longwave radiation from a very small percentage of open water and thin ice, dominate regional heat budgets. In summer, solar radiation is absorbed by open water but is reflected from snow‐covered pack ice. Experiments and models describing these processes are reviewed.
Altimeter data assimilation into an ocean circulation model: Sensitivity to orbital parameters
Authors: Verron Jacques
Published: February 2008

Different orbital scenarios for satellite missions are evaluated with respect to their ability to provide a satisfactory altimeter data set as input into an assimilation procedure. The assimilation is realized, using the technique of “nudging” (Anthes, 1974), into a numerical simulation of the general oceanic circulation at mid‐latitudes involving strong variability fields of the Gulf‐Stream‐like jet stream. The numerical model is multilayered and quasi‐geostrophic, and it considers basin‐scale circulation with high resolution. The basic orbital scenarios under consideration are four in number: the two ERS 1 and Topex/Poseidon nominal mission parameters (with 3‐ and 10‐day orbital periods, respectively) and two extra possibilities for Topex/Poseidon: a 17‐day orbital period scenario (close to the Geosat parameters) and a 29‐day orbital period scenario. All four cases are compared for assimilation experiments realized under identical conditions. The criterion of efficiency is to ensure that model flows converge toward observations, i.e., the fact that surface information is sufficient to recreate via the model the realistic three‐dimensional ocean circulation. In the conditions of experiments, results show that the 10‐ to 17‐day range is able to satisfy the convergence condition to some extent. This is not the case for the two scenarios outside this range. The effects of subsequent undersampling (subcycles) are examined in the 10‐day case and found to be of little importance as long as sampling is sufficiently regular. Preliminary tests to take into account data and model inaccuracy are reported.
Thermal forcing on the tropical Pacific from satellite data
Authors: Liu W. Timothy , Gautier Catherine
Published: February 2008

Monthly fields of latent heat flux and surface solar irradiance derived from spaceborne sensors were combined to estimate the surface thermal forcing on the tropical Pacific from 1980 to 1983. The annual cycle and the anomalies associated with 1982–1983 El Niño‐Southern Oscillation episode were examined. Along the equator and during the early phase of the episode the reduction of solar irradiance into the ocean is found to be compensated to some extent by the decrease in evaporative cooling. The distribution of correlation coefficients demonstrated that outside the equatorial waveguides, surface thermal forcing plays a significant role in the seasonal change of sea surface temperature and surface solar irradiance is main driving force. Significant correlation is also found between anomalous latent heat flux and anomalous change of sea surface temperature over a broad area in the equatorial and southern tropical Pacific, indicating that surface thermal forcing may play a larger role than expected in the anomalous sea surface temperature change, particularly in the reestablishment of the cold tongue at end of the episode.
Neutral surfaces and potential vorticity in the world's oceans
Authors: You Yuzhu , McDougall Trevor J.
Published: February 2008

Several neutral surfaces are mapped in this paper and their properties are contrasted with those of potential density surfaces. It is shown that the Pacific is relatively forgiving to the use of potential density, while more care must be taken in the Atlantic and Indian oceans because of the larger compensating lateral gradients of potential temperature and salinity along neutral surfaces in these oceans. The dynamically important tracer, neutral‐surface potential vorticity (NSPV), defined to be proportional to f/h (where f is the Coriolis frequency and h is the height between two neutral surfaces), is mapped on several neutral surfaces in each of the world's oceans. At a depth of 1000m in the Atlantic and Indian oceans, the epineutral gradient of NSPV is different to the isopycnal variations of fN2 by as much as a factor of two (here N is the buoyancy frequency). Maps of isopycnal potential vorticity (IPV) resemble those of fN2, but the values of IPV are less by the simple factor μ, defined by μ = c[Rρ−1]/[Rρ−c], where Rρ is the stability ratio of the water column and c is the ratio of the values of α/β at the in situ pressure to that at the reference pressure (α and β being the thermal expansion and saline contraction coefficients, respectively). Layered models of the ocean circulation often take the vertical shear between layers (the thermal wind) to be given by the product of the interface slope and the contrast of potential density across the interface. The true thermal wind equation involves the interfaeial difference of in situ density, which is larger than the corresponding difference of potential density by the factor μ that is mapped in this paper, taking values up to 1.25 at a depth of 1000 m. This implies that the thermal wind is currently underestimated by up to 25% in layered ocean models. The differences between the slopes of neutral surfaces and potential density surfaces can be quantified Using the factory μ. The magnitudes of these slopes are illustrated here with contour maps and with vertical profiles, One would think that by choosing the reference pressure of potential density to be at the central pressure of a data set, the conservation equation of potential vorticity could be expressed with respect to these potential density surfaces with sufficient accuracy. Here it is shown that even the best potential density variable is significantly in error at thermoclinic frontal regions. This is linked to the fact that diapycnal velocities are not simply due to vertical mixing processes, but are also partly caused by epineutral mixing.
Arctic multiyear ice classification and summer ice cover using passive microwave satellite data
Authors: Comiso J. C.
Published: February 2008

The ability to classify and monitor Arctic multiyear sea ice cover using multispectral passive microwave data is studied. Sea ice concentration maps during several summer minima have been analyzed to obtain estimates of ice surviving the summer. The results are compared with multiyear ice concentrations derived from data the following winter, using an algorithm that assumes a certain emissivity for multiyear ice. The multiyear ice cover inferred from the winter data is approximately 25 to 40% less than the summer ice cover minimum, suggesting that even during winter when the emissivity of sea ice is most stable, passive microwave data may account for only a fraction of the total multiyear ice cover. The difference of about 2×106 km2 is considerably more than estimates of advection through Fram Strait during the intervening period. It appears that as in the Antarctic, some multiyear ice floes in the Arctic, especially those near the summer marginal ice zone, have first‐year ice or intermediate signatures in the subsequent winter. A likely mechanism for this is the intrusion of seawater into the snow‐ice interface, which often occurs near the marginal ice zone or in areas where snow load is heavy. Spatial variations in melt and melt ponding effects also contribute to the complexity of the microwave emissivity of multiyear ice. Hence the multiyear ice data should be studied in conjunction with the previous summer ice data to obtain a more complete characterization of the state of the Arctic ice cover. The total extent and actual areas of the summertime Arctic pack ice were estimated to be 8.4×106 km2 and 6.2×106 km2, respectively, and exhibit small interannual variability during the years 1979 through 1985, suggesting a relatively stable ice cover.
Do we really know how to scale the turbulent kinetic energy dissipation rate ε due to breaking of oceanic internal waves?
Authors: Gargett Ann E.
Published: February 2008

This paper questions a recent claim (Gregg, 1989) that a first‐order understanding of the link between internal waves and turbulence has been achieved. It is demonstrated that (1) the theoretical basis of this result is extremely sensitive to an ad hoc assumption about the nature of the wavelength at which wave energy is delivered to dissipation (turbulence), (2) the method used by Gregg (1989) to calculate instantaneous wave field energy level E is incorrect and will seriously underestimate E in cases where E is greater than EGM, the energy level of the GM (Garrett and Munk, 1975) canonical internal wave field, and (3) the range of variation of E and buoyancy frequency N in the data sets reported by Gregg (1989) is not sufficient to rule out alternative scalings.
The determination of the latent and sensible heat fluxes at the sea surface viewed as an inverse problem
Authors: Gaspar Philippe , André Jean‐Claude , Lefevre Jean‐Michel
Published: February 2008

The determination of the latent and sensible heat fluxes at the air‐sea interface is formulated here as an inverse problem: given an upper ocean model, one seeks the successive values of the “nonsolar” surface heat flux Fnsol (sum of the latent, sensible, and net infrared fluxes) that yield a nearly exact simulation of the observed evolution of the sea surface temperature (SST). The model is otherwise forced by surface insolation and wind stress data. Provided that an estimate of the infrared flux is available, the sum of the latent and sensible heat fluxes is directly obtained as the difference between Fnsol and the infrared flux. A major interest of this approach is that all surface inputs (stress, SST, long‐wave and shortwave radiation) can be measured from a satellite. In this preliminary exploration of the inverse flux estimation technique, attention is restricted to situations where the oceanic advection is weak so that a one‐dimensional ocean model can be used. The inverse problem, in a rudimentary form, is solved using a simple iterative shooting method. The inverse flux estimation technique is tested using a 2‐year data set from station P, in the Gulf of Alaska, and a 2‐week data set from the Long‐Term Upper Ocean Study (LOTUS) experiment, in the Sargasso Sea. The first tests are performed using regularly sampled in situ measurements of the stress, SST, and insolation, rather than actual satellite data. At both test sites the inverse‐derived estimates of Fnsol prove to be consistent with the observed changes of the upper ocean heat content over periods of a few days. On the other hand, the inverse‐derived heat fluxes exhibit a large diurnal variability that is not present in classical bulk‐derived estimates. This difference in the short‐term variability of the two flux estimates is as yet unexplained. The final tests at LOTUS involve actual satellite data for the isolation and SST. Using the few available satellite measurements, the inverse technique still provides a realistic mean flux estimate. The simulated evolution of the SST in between the satellite observations agrees well with in situ observations, and a fair simulation of the deeper temperatures is obtained.
Thorium isotopes, particle cycling models, and inverse calculations of model rate constants
Authors: Murnane Richard J. , Sarmiento Jorge L. , Bacon Michael P.
Published: February 2008

Generalized models of thorium and particle cycling, data from Station P, and an inversion technique are used to obtain rate estimates of important biological and chemical transformations occurring in the water column. We first verify the inversion technique using an idealized data set generated by a finite difference model, and then apply the inversion technique to data from Station P. With the Station P data, predicted rate constants for adsorption and release of thorium between the dissolved and small particle phases are consistent with the results from other workers. The predicted rate constants for the interaction between small and large particles are smaller than previous estimates. The predicted concentration of large rapidly sinking particles is greater than the concentration of suspended non‐sinking particles, whereas the reverse is usually assumed to be the case. The calculated sinking rate for the large particles is 20 m d−1. This sinking rate is an order of magnitude smaller than the large particle sinking rate inferred from sediment trap mass fluxes at two levels in the water column. The reason we predict a high large particle concentration and slow settling velocity has not been uniquely determined. Possible modifications of the current model that could help to reconcile the differences between observations and model predictions include: 1) two classes of rapidly sinking particles or rate constants that change with depth, 2) direct interactions between the large particle and dissolved phases, and 3) incorporation of a continuous distribution of particle size and settling velocity.
Models for synthetic aperture radar imaging of the ocean: A comparison
Authors: Kasilingam Dayalan P. , Shemdin Omar H.
Published: February 2008

Theoretical comparisons are made of different models for synthetic aperture radar (SAR) imaging of ocean waves. The velocity bunching model, distributed surface model, Lyzenga model, Canadian Center for Remote Sensing/Radarsat (CCRS/RADARSAT) model, and the Ocean Research and Engineering (ORE) model are compared analytically with respect to their description of the SAR imaging process and the radar backscatter process. The study concentrates on the temporal description of the backscatter process and its impact on SAR imaging of the ocean. Sample simulations are conducted so as to quantify some of the similarities and differences of the aforementioned models. Other SAR imaging models are discussed, as they pertain to the comparisons noted above. The analytical and numerical simulations show that the Lyzenga model, the CCRS/RADARSAT, model and the ORE model are similar for most commonly occurring sea states. The velocity bunching model is similar to these models when the SAR integration time is small, but it tends to deviate for long integration times. The distributed surface model is shown to describe the imaging process adequately when the radar backscatter is highly correlated in space and time.
Geosat altimeter observations of the surface circulation of the Southern Ocean
Authors: Chelton Dudley B. , Schlax Michael G. , Witter Donna L. , Richman James G.
Published: February 2008

The variability of sea level and surface geostrophic currents in the Southern Ocean is investigated from the first 26 months of unclassified Geosat altimeter data (November 1986 to December 1988). Because of problems unique to Geosat, it has been necessary to develop new techniques for analyzing the height data. These techniques are presented here, and the processed Geosat data are used to examine the relation between mesoscale variability and the mean circulation (as determined from historical hydrographic data). The two are shown to be significantly correlated, implicating the importance of hydrodynamic instabilities in the Antarctic Circumpolar Current. The geographical patterns of both the mean flow and the mesoscale variability are shown to be controlled by the bathymetry. An efficient objective analysis algorithm is introduced for generating smoothed fields from observations randomly distributed in time and two space dimensions. The algorithm is applied to the 26 months of Geosat data, and the smoothed fields are used to investigate the large‐scale, low‐frequency variability of sea level and surface geostrophic velocity in the Southern Ocean. Approximately 33% of the variance is accounted for by the first three empirical orthogonal functions (EOFs) of sea level variability. These three modes describe variability over seasonal time scales and separate into an annual cycle (mode 1), a semiannual cycle (mode 2) and a mode which describes year‐to‐year variability in the seasonal cycles for 1987 and 1988 (mode 3). The complexity of the spatial patterns of the second‐ and higher‐order modes and the small percentages of variance accounted for by the first three modes (15%, 10% and 8%, respectively) reflect the generally regional, as opposed to coherent circumpolar, nature of sea level variability in the Southern Ocean. The inherent weak zonal coherence of the variability is further emphasized by EOF analysis separately within each basin of the Southern Ocean.
Arctic ocean‐shelf exchange: Measurements in Barrow Canyon
Authors: Aagaard K. , Roach A. T.
Published: February 2008

Two closely instrumented arrays were deployed within Barrow Canyon during 1986–1987 in an attempt to measure the outflow of dense, hypersaline plumes created during sea ice formation along the Alaskan coast. However, no hypersaline plumes were observed. Rather, we found cold, relatively fresh waters advected downcanyon by the mean flow alternating with upcanyon flow of warm and saline water upwelled onto the shelf. Upwelling was most frequent in the fall, and upcanyon speeds reached 60 cm s−1. At times the resulting onshore heat and salt fluxes were large enough to be of possible local significance, for example, to the surface heat budget. Contrary to earlier findings, the flow was only weakly correlated with the wind and the atmospheric pressure gradient. Instead, we found both upwelling and flow reversals to be coherent along the coast at sites 400 km apart, with phase differences corresponding to a typical speed of 2.3 m s−1. We suggest that the majority of these events are manifestations of shelf waves propagating eastward along the Arctic Ocean margin.
The angular distribution of infrared radiances emerging from broken fields of cumulus clouds
Authors: Naber P. S. , Weinman J. A.
Published: February 2008

Infrared radiances were simultaneously measured from broken cloud fields over the eastern Pacific Ocean by means of the eastern and western geostationary satellites. The measurements were compared with the results of models that characterized the clouds as black circular cylinders disposed randomly on a plane and as black cuboids disposed in regular and in shifted periodic arrays. The data were also compared with the results obtained from a radiative transfer model that considered emission and scattering by a regular array of periodic cuboidal clouds. It was found that the radiances did not depend significantly on the azimuth angle; this suggested that the observed cloud fields were not regular periodic arrays. However, the dependence on zenith angle suggested that the clouds were not disposed randomly either. The implication of these measurements on the understanding of the transfer of infrared radiances through broken cloud fields is considered.
The role of geographic variables in explaining paleoclimates: Results from Cretaceous climate model sensitivity studies
Authors: Barron Eric J. , Washington Warren M.
Published: February 2008

Changes in geography (topography, continental positions and sea level) are one of the most frequently cited mechanisms of climatic change on geologic time scales. The role of geographic variables in paleoclimatology is investigated through a series of climate model sensitivity studies using a version of the National Center for Atmospheric Research spectral GCM and specified Cretaceous (≈ 100 million years ago) geography. The Cretaceous is investigated because it was both a large geographic and climatic contrast from the present day. The model simulations demonstrate that paleogeography was a substantial climatic forcing factor (4.8°K increase in globally averaged surface temperature compared with a present‐day control). However, the warming is insufficient to explain fully the paleoclimatic data. In addition, the model is insensitive to global sea level variations (related to tectonics and not ice volume) which are well correlated with paleoclimatic data. Additional climatic forcing factors, such as increased atmospheric CO2 correlated with these sea level variations, may be required to explain the Cretaceous climate.
Diurnal and longer‐term temporal changes in the composition of atmospheric particles at Mauna Loa, Hawaii
Authors: Parrington Josef R. , Zoller William H.
Published: February 2008

The collection of midtropospheric atmospheric particulate matter during upslope and downslope mountain winds was accomplished by using two types of sector controllers between February 1979 and April 1982 at Mauna Loa Observatory (MLO) on the island of Hawaii. Initially, a simple time‐of‐day system was used for sampling. This was replaced in May 1980 by a digital system which monitors meteorological conditions, aerosol data, as well as time of day to differentiate between upslope and downslope winds. Particles derived from the marine environment were found to be much lower in concentration during downslope winds than upslope winds (15 ng/m3, σg = 4.0 versus 270 ng/m3, σg = 2.5). The mean ratio was 14 with simple time‐of‐day control and 21 with the improved and more discriminating digital sector controller. Crustal‐derived particles were 2.4 times lower in concentration in downslope winds. The presence of particles of Hawaiian basalt was determined by noting its quite different chemical composition as compared with dust transported from continents, over long distances into the area. Local basalts appear to be a minor source of crustal particles with concentrations of local basalt at MLO estimated to be 15 ng/m3 (σg = 3.3) in downslope winds versus 87 ng/m3 (σg = 2.6) in samples collected under upslope conditions. After correction for this local crustal material, the upslope/downslope crustal dust ratio still remained high (2.2) and exhibited strong seasonal variations, being much lower between mid‐February to July (1.2) when high concentrations of dust are transported from Asian deserts to Hawaii, than during the remainder of the year (3.2). Upslope sulfate concentrations averaged 1.7 times higher than downslope conditions at MLO (530 ng/m3, σg = 1.9, versus 340 ng/m3, σg = 2.0).
Effects of stratospheric aerosol on measured short‐wave radiation incident at the ground
Authors: Carroll John J.
Published: February 2008

Solar radiation measurements taken at Davis, California (38.5°N, 121.8°W, 18 m above mean sea level), are analyzed for the effects of known stratospheric aerosol variation. The data are selected for cloud free periods with high global transmissivity and for zenith angles of 60°±2°. These data include the normal incidence direct and the diffuse and the global components in the spectral intervals 295–3000 nm and 630–3000 nm. Global radiation in the near ultraviolet (295–400 nm) is also analyzed. The data set begins in April 1979 and is analyzed through June 1983. Variations of these data from 3‐year averages are compared with observed middle northern latitude stratospheric aerosol variations. The results are that the global UV radiation shows short‐period reductions of 10–15% associated with increased stratospheric aerosol. A decrease in the maximum received UV in the fourth quarter of each year is also evident at about 4% per year. The direct components show 7–25% decreases at all wavelengths during periods of increased stratospheric aerosol. The decrease is more persistant at the shorter wavelengths (λ≤630 nm) than for the red and near‐IR region. Conversely, the longer‐wavelength diffuse components are affected the most by the presence of stratospheric aerosol, with increase of 70–140% over their earlier 3‐year mean observed in 1982 and 1983. The global radiation shows relatively small changes with the presence of stratospheric particles. Through most of the observational period, variability in global radiation with stratospheric aerosol variability is comparable to the apparent seasonal variation. However, in 1983, the first quarter global radiation is 12% lower than its preeruption value, and the global transmissivity for the first half of 1983 is nearly 4% lower than its average for the first half of the preceding 3‐years. The selective attenuation of direct radiation and the long‐term reduction in the shorter‐wavelength spectral region imply reduced efficiences in high‐temperature solar to thermal energy applications and to photovoltaic electrical power generation.
Remote sensing of weather and climate parameters from HIRS2/MSU on TIROS‐N
Authors: Susskind J. , Rosenfield J. , Reuter D. , Chahine M. T.
Published: February 2008

At the Goddard Laboratory for Atmospheric Sciences (GLAS) we have developed a physically based satellite temperature sounding retrieval system, involving the simultaneous analysis of HIRS2 and MSU sounding data, for determining atmospheric and surface conditions which are consistent with the observed radiances. In addition to determining accurate atmospheric temperature profiles even in the presence of cloud contamination, the system provides global estimates of day and night sea or land surface temperatures, snow and ice cover, and parameters related to cloud cover. The inverse radiative transfer equation approach to the multi‐spectral analysis of the data, and details of its implementation, are described. Ice, snow, and cloud fields derived for January 1979 are consistent with other measures of similar parameters obtained from AVHRR and SMMR. Monthly mean sea‐surface temperature fields agree with those derived from ship and buoy measurements to 0.5°C.
Effects of dynamical heat fluxes on model climate sensitivity
Authors: Wang Wei‐Chyung , Molnar Gyula , Mitchell Todd P. , Stone Peter H.
Published: February 2008

The effect of the meridional and vertical dynamical heat fluxes on climate sensitivity is investigated using an annual mean coupled high and low latitude radiative‐dynamical model of the northern hemisphere. The model was constructed by incorporating a meridional (atmosphere and ocean) dynamical heat flux parameterization into a two‐zone (low latitude 0°–30°N and high latitude 30°–90°N) version of the vertical radiative‐convective model. The atmospheric vertical dynamical heat flux is parameterized through the convective adjustment with two critical lapse rates: the moist adiabatic lapse rate and the critical value for baroclinic adjustment. The meridional dynamical heat flux is related to the meridional temperature gradient empirically. Cloud covers and altitudes and relative humidity are fixed. Ice albedo‐temperature feedback is included. The feedback in the dynamical heat fluxes is found to produce a strong stabilizing effect on climate. The warming of the hemispheric mean surface temperature induced by a 2% increase in solar constant and a doubling of carbon dioxide concentration could be increased by as much as a factor of 4 if the feedbacks from the meridional and vertical dynamical heat fluxes were both eliminated. The coupling effect of the vertical and meridional heat fluxes is also calculated to be very strong (i.e., the vertical flux feedback is strongly stabilizing in the presence of meridional flux feedback but destabilizing in its absence. In fact, the model's current climate is unstable in the latter case.) The interactions of the dynamical heat flux with other temperature‐dependent feedbacks such as radiation, ice albedo, and humidity and their subsequent effects on climate are also studied.
Analysis of upper stratospheric Umkehr ozone profile data for trends and the effects of stratospheric aerosols
Authors: Reinsel Gregory C. , Tiao George C. , DeLuisi John J. , Mateer Carl L. , Miller Alvin J. , Frederick John E.
Published: February 2008

A statistical analysis of stratospheric ozone profile data from the Umkehr method is considered for the detection of trends which may be associated with the release of chlorofluoromethanes (CFMs), where possible effects of atmospheric aerosols on the Umkehr measurements are also taken into account. In the statistical trend analysis, time series models have been estimated using monthly averages of Umkehr data over the past 15 to 20 years through 1980 at each of 13 Umkehr stations and at each of the five highest Umkehr layers, 5–9, which cover an altitude range of approximately 24–48 km. The time series regression models incorporate seasonal, trend, and noise factors and an additional factor to explicitly account for the effects of atmospheric aerosols on the Umkehr measurements. At each Umkehr station, the explanatory series used in the statistical model to account for the aerosol effect is a 5 month running average of the monthly atmospheric transmission data at Mauna Loa, Hawaii, the only long running aerosol data available. A random effects model is used to combine the 13 individual station trend estimates from the time series models to form an overall estimate of trend for each Umkehr layer. The analysis indicates statistically significant trends in the upper Umkehr layers 7 and 8 of the order of −0.2 to −0.3% per year over the period 1970–1980, with little trend in the lower layers 5 and 6. The results of the estimation of trends as well as aerosol effects for the Umkehr data are compared with recent corresponding theoretical predictions.
Some features of stroke occurrence in Florida lightning flashes
Authors: Thomson E. M. , Galib M. A. , Uman M. A. , Beasley W. H. , Master M. J.
Published: February 2008

Characteristics of stroke occurrence are investigated for lightning to ground observed near Tampa, Florida (latitude = 27.4°N, longitude = 82.2°W) during three days of convective thunderstorm activity in July 1979. Strokes were identified from both wideband (0.2 Hz to 1.5 MHz) electric field records and simultaneous video tape recordings from a network of TV cameras. The average number of strokes per flash was 4.0 for 105 flashes and the average number of channels per flash was 1.6 for 78 multiple‐stroke flashes. Interstroke intervals were distributed according to a lognormal rather than a normal distribution with a geometric mean of 69 ms and standard deviation of 0.32 decades in the logarithmic distribution for 310 intervals. Interstroke intervals preceding new channels had a geometric mean of 83 ms and standard deviation of 0.33 decades in the logarithmic distribution for 28 intervals. By comparing our results with others in Florida and New Mexico, we could find no obvious relationship between these intervals and channel length. Histograms of interstroke interval plotted as a function of stroke order did not appear to reveal the systematic increase noted by workers in Japan. This conclusion is corroborated here on the basis of the same statistical tests used by the Japanese workers. The effectiveness of videotape records for determining stroke occurrence in daytime lightning is considered: although 82% of strokes were detected on the videotape record, for ground flashes with at least one stroke visible on TV, there was a significant difference at the 1% confidence level for the t test between the interstroke interval distribution obtained using both wideband electric field and videotape records and that obtained using only videotape records.
High‐precision atmospheric ozone measurements using wavelengths between 290 and 305 nm
Authors: Saunders R. D. , Kostkowski H. J. , Green A. E. S. , Ward J. F. , Popenoe C. H.
Published: February 2008

It is shown theoretically that many errors are significantly less when determining atmospheric ozone thicknesses from measurements of solar terrestrial spectral irradiance in the wavelength region between 290 and 305 nm as compared to the 305‐ to 340‐nm region employed by the Dobson spectrophotometer. In order to test this conclusion experimentally, an elaborate set of state‐of‐the‐art measurements have been made in the shorter wavelength region in Gainesville, Florida, between June 13 and June 18, 1980. Details of these measurements, including an extensive error analysis, are presented and indicate that such short‐wavelength measurements, particularly between 295 and 305 nm, can be used to detect long‐term changes of atmospheric ozone with an uncertainty not exceeding 1%. Observing conditions restricted the Gainesville measurements to zenith angles of less than 35°. Further investigations are required to determine the shortest wavelength that can be used at significantly greater zenith angles.
Some aspects of the design and behavior of the stratospheric and mesospheric sounder
Authors: Wale M. J. , Peskett G. D.
Published: February 2008

The measuring task, the engineering constraints, and the resulting design of the stratospheric and mesospheric sounder are described in broad terms. The calibration system and its performance are discussed in more detail. One significant side effect in the design and its impact on the fields of view is also discussed. The major lessons for future pressure modulator radiometer designs are summarized.
Solar reflection from interacting and shadowing cloud elements
Authors: Harshvardhan  , Thomas Robert W. L.
Published: February 2008

The parameterization of solar reflection from clouds used in climate and general circulation models is based on radiative transfer theory appropriate for plane parallel clouds. We have attempted to relate the reflection from a broken cloud field to that from a plane parallel cloud of the same optical properties by using Monte Carlo simulations for a very simple model of an array of regularly spaced, infinitely long bar clouds. Reflection from the array is represented by an effective cloud fraction, and it is shown that for many cases this may be obtained by treating the cloud elements to be noninteracting azimuthally symmetric reflectors. The effective cloud fraction is a function of solar zenith angle, the aspect ratio of the individual cloud elements, and the normal or zenith cloud fraction of the array. Model computations for reflection from an array of randomly distributed identical cylinders are also presented as an example of a possible application of this technique.