bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling deep convection in the Greenland Sea
Authors: Hakkinen S. , Mellor G. L. , Kantha L. H.
Published: February 2008

The development of deep convective events in the high‐latitude ocean is studied using a three‐dimensional, coupled ice‐ocean model. Oceanic mixing is described according to the level 2.5 turbulence closure scheme in which convection occurs in a continuous way, i.e., convective adjustment is not invoked. The model is forced by strong winds and surface cooling. Strong upwelling at the multiyear ice edge and consequent entrainment of warm Atlantic waters into the mixed layer is produced by winds parallel to the ice edge. Concomitant cooling drives deep convection and produces chimneylike structures. Inclusion of a barotropic mean flow over topography to the model provides important preconditioning and selects the location of deep convection. The most efficient preconditioning occurs at locations where the flow ascends a slope. In a stratified environment similar to the Greenland Sea with a 12 m s−1 wind the model simulations show that localized deep convection takes place after about 10 days to depths of 1000 m.
Measurements of the effects of surface winds on ocean currents with a stepped‐frequency ΔK radar system
Authors: Popstefanija Ivan , McIntosh Robert E.
Published: February 2008

A frequency‐agile C band ΔK radar system was used to measure ocean surface currents during the SAXON‐Chesapeake Light Tower experiment. Surface currents were measured with the radar approximately 80% of the time from September 20 to October 14, 1988. In this paper these measurements are compared with in situ current and wind probe measurements. We find the agreement between the radar and current probe measurements to be very good during periods when the wind‐ and wave‐driven currents are negligible in the radar‐viewing direction. During other times, we find that the radar measurements are approximated by the Weber model.
The barotropic electromagnetic and pressure experiment: 1. Barotropic current response to atmospheric forcing
Authors: Chave Alan D. , Luther Douglas S. , Filloux Jean H.
Published: February 2008

During 1986–1987, an array of horizontal electrometers (which measure the subinertial barotropic velocity) was deployed for 11 months in the central North Pacific to study atmospherically forced motions in a low eddy kinetic energy region. Significant coherence is found to be ubiquitous between the barotropic velocity and one or more surface atmospheric variables over the North Pacific. The maximum squared coherence between currents and wind stress curl at all periods greater than 3 days is typically 0.6, rarely below 0.4, and occasionally above 0.8, and is dominantly nonlocal, although local coherence is seen at some sites, especially at the shorter periods. Both the coherence and the intersite pattern similarity are strongest at the periods of relative maxima in the barotropic current autospectra (e.g., at 6–8, 10–14, and 20–50 days). The locations at which the wind stress curl forces the motions at each site and for each period have been determined. While there is substantial intersite variability, some of the observed patterns of squared coherence over the North Pacific are very similar to those predicted by simple, linear, smooth‐bottomed, quasi‐geostrophic models of atmospherically forced barotropic currents. The forcing location is occasionally found to be the same spot for all oceanic instruments, especially at the autospectral maxima in barotropic current. More commonly, distinct forcing locations are found for each instrument even when closely spaced, suggesting topographic influence. In other cases, multiple forcing locations are implicated for the motions at a single station. All of this site‐ and period‐dependent variability of the forcing location is incompatible with the simple models and is due either to the known spatial inhomogeneity of the curl forcing field or to topographic effects. The importance of the former is emphasized using simple arguments based on analytic transfer functions between the atmospheric and oceanic variables and on observed wavenumber spectra for wind stress curl. Quantitative assessment of topographic effects must await suitable numerical models. In addition, maximum likelihood wavenumber spectra of the barotropic currents have been estimated in those bands with an adequate number of coherent sensors. The wavenumbers at the spectral peaks are compatible with the dispersion relation for Rossby waves modified by the observed, large‐scale, linearly sloping topography which shoals to the northeast. The observed group velocities are in general quite consistent with the inferred forcing locations based on the ocean‐atmosphere coherences.
Internal wave observations from the Arctic environmental drifting buoy
Authors: Plueddemann Albert J.
Published: February 2008

A free‐drifting buoy serving as an ice anchor and flotation sphere for a 125‐m instrumented mooring line was deployed in the Arctic pack ice by the R/V Polarstern in August 1987 at the northernmost point achieved by the Arktis IV expedition. Current measurements were made from this Arctic environmental drifting buoy (AEDB) using a 150‐kHz acoustic Doppler current profiler (ADCP) attached to the mooring line at a depth of 16 m below the flotation sphere with the transducers facing downward. Velocity profiles spanning depths between 35 and 327 m with 15‐m resolution were collected at half‐hour intervals over a period of 216 days while the buoy drifted from its starting point near 86°N, 22°E to about 70°N, 16°W. The full experimental record was separated into three sections corresponding to periods of the drift spent in the Nansen Basin, over the Yermak Plateau, and in the Greenland Sea. Velocity time series and spectra were computed, and results for the three analysis sections were compared. Spectra in the Nansen Basin were found to have energy levels significantly less than those typical for mid‐latitudes, roughly one third of the canonical Garrett‐Munk (GM) level, and a spectral slope between ƒ and 2.5ƒ that was significantly flatter than that expected from the GM model. Between 83°N and 81°N, as the buoy passed over the Yermak Plateau, internal wave energy increased to levels comparable to GM. Isolated, energetic near‐inertial wave packets with upward group velocity were observed in this portion of the record, presumably generated by interaction of the barotropic tide with the bottom topography of the plateau. Estimates of the upward energy flux from these near‐inertial packets were comparable to the downward fluxes from typical surface sources. Interpretation of the Greenland Sea section was complicated by ADCP sampling problems and a lack of Argos fixes, but the available data showed internal wave spectral levels that were intermediate between those of the Nansen Basin and Yermak Plateau and no evidence of upward‐propagating near‐inertial energy.
Global sea level acceleration
Authors: Douglas Bruce C.
Published: February 2008

Greenhouse warming scenarios commonly forecast an acceleration of sea level rise in the next 5 or 6+ decades in the range 0.1–0.2 mm/yr2. Long tide gauge records (75 years minimum) have been examined for past apparent sea level acceleration (i.e., deviation from a purely linear rise) and for indication of how long it might take to detect or verify a predicted future acceleration. For the 80‐year period 1905–1985, 23 essentially complete tide gauge records in 10 geographic groups are available for analysis. These yielded the apparent global acceleration −0.011 (±0.012) mm/yr2. A larger, less uniform set of 37 records in the same 10 groups with 92 years average length covering the 141 years from 1850 to 1991 gave for acceleration 0.001 (±0.008) mm/yr2. Thus there is no evidence for an apparent acceleration in the past 100+ years that is significant either statistically, or in comparison to values associated with global warming. Estimating how well a global acceleration parameter could be determined in a relatively short time was accomplished by dividing the 1905–1985 data set into four equal time spans. The formal 1σ uncertainty (about 0.2 mm/yr2) of global acceleration from these 20‐year periods is more than an order of magnitude larger than for the 80‐ and 141‐year cases owing to the existence of large interdecadal and longer variations of sea level. This means that tide gauges alone cannot serve as a leading indicator of climate change in less than at least several decades. Confirming the prediction of a particular model at the 95% confidence level or differentiating between model predictions will take much longer. The time required can be significantly reduced if the interdecadal fluctuations of sea level can be understood in terms of their forcing mechanisms and then removed from the tide gauge records.
Augmented gas exchange across wind‐sheared and shear‐free air‐water interfaces
Authors: Khoo B. C. , Sonin A. A.
Published: February 2008

Wind‐sheared gas absorption rate correlations have shown a break point at a certain turbulence intensity which signals a change to a higher mass transfer mode. This has been attributed to wave breaking and bubble entrainment. A similar break point is, however, observed with shear‐free interfaces where there is no wave breaking and no bubble entrainment, which suggests that an alternative mechanism might play a role in the mode change.
Evaluating the information content of tomographic data: Application to mesoscale observations
Authors: Gaillard Fabienne
Published: February 2008

Integrating tomography in the design of future experiments requires knowledge of the information content of this type of data. The case of mesoscale observations is examined here. The evaluation of the performances of tomography, as the only data type available, is done by simulating acoustic transmissions in a quasi‐geostrophic model during a period of 106 geophysical days. A linear inversion is then applied to recover the stream function field. The linear hypothesis is validated for that particular scale and type of oceanic perturbation, as is the robustness to erroneous data. The full three‐dimensional stream function fields are reconstructed. Information brought by tomography varies according to the mode: the first baroclinic mode is well estimated, the barotropic mode is partially estimated (only one component of the current is felt), and higher modes are not resolved. The relative vorticity is assessed with horizontal resolution at the scale of the elementary cells defined by the tomographic array; it is compared to direct triangular computations. The original contribution of tomography is in the simultaneous time and space dimensions, complementary to the classical point measurements.
Toward altimetric data assimilation in a tropical Atlantic model
Authors: Bourles Bernard , Arnault Sabine , Provost Christine
Published: February 2008

We present three types of experiments of sequential assimilation of altimetric data in a linear tropical Atlantic model, using an analysis technique we developed. In the first experiments we assimilate dynamic height fields calculated from simulated data in order to study the impacts of assimilations. In the second ones we assimilate dynamic height anomaly fields calculated from simulated data, and finally, in the third ones we use sea level anomaly fields obtained from altimetric data from Geosat. Perturbations are observed in the eastern part of the basin, due to Kelvin waves artificially generated in the west equatorial basin. However, we show that altimetric data may be very useful for improving model simulations in the tropics when appropriate assimilation techniques are used.
Analysis of satellite sea surface temperature time series in the Brazil‐Malvinas Current Confluence region: Dominance of the annual and semiannual periods
Authors: Provost Christine , Garcia Omar , Garçon Véronique
Published: February 2008

We study the dominant periodic variations of sea surface temperature (SST) in the Brazil‐Malvinas Confluence region from a satellite‐derived data set compiled by Olson et al. (1988). This data set is composed of 202 sea surface temperature images with a 4 × 4 km resolution and extends over 3 years (from July 1984 to July 1987). Each image is a 5‐day composite. The dominant signal, as already observed by Podesta et al. (1991), has a 1‐year period. We first fit a single‐frequency sinusoidal model of the annual cycle in order to estimate mean temperature, amplitude, and phase at 159 points uniformly distributed over the region. The residuals are generally small (less than 2°C). The largest departures from this cycle are located either in the Brazil‐Malvinas frontal region or in the southeastern part of the region. Other periods in SST variations are identified by means of periodograms of the 159 residual time series in which the annual cycle has been substracted. The periodograms show that a semiannual frequency signal is present at almost every location. The ratio of the semiannual amplitude to the annual amplitude increases southward from 0% at 30°S to reach up to 45% at 50°S. In the south the semiannual signal creates an asymmetry, and the resulting (total) annual cycle has a cold period (winter) longer than the warm one (summer). In the frontal region the annual and semiannual signals have an important interannual variation. This semiannual frequency is associated with the semiannual wave present in the atmospheric forcing of the southern hemisphere. Differential heating over the mid‐latitude oceans and the high‐latitude ice‐covered Antarctic Continent has been suggested as the cause of this semiannual wave (Van Loon, 1967).
On the deep and bottom waters of the Greenland Sea from summer 1989 and 1990 data
Authors: Bourke R. H. , Paquette R. G. , Blythe R. F. , Stone M. D.
Published: February 2008

The deep waters of the central and southern Greenland Sea are examined using Bartlett 1989 and 1990 summer data displayed at very high temperature and salinity resolutions. The mixing of Arctic Ocean Deep Water (AODW) with Greenland Sea Deep Water (GSDW) in proportions of about 1:1 to form “new” Norwegian Sea Deep Water (NSDW) is confirmed. However, the previously accepted route of this new NSDW through the ridge system into the Norwegian Sea, the Jan Mayen Channel, is shown to pass deep water only intermittently; a passage through Mohn's Ridge farther north, beginning near 72°06′N, 2°W, is identified as a more likely route. Part of the ultimate AODW‐GSDW mixture is shown to continue on along the Greenland continental slope into the Iceland Sea. A peculiar isothermal condition was found in the deeper parts of the GSDW. This is postulated to result from upward diffusion of temperature from a layer initially having the adiabatic temperature gradient. Above the isothermal layer is one of warming and decreasing salinity, the result of recent successive deep convections to different depths.
Microwave brightness temperatures of laboratory‐grown undeformed first‐year ice with an evolving snow cover
Authors: Lohanick A. W.
Published: February 2008

A laboratory experiment was performed to study a case in which a snow cover introduced on an established saline ice sheet resulted in physical processes that significantly affected the microwave brightness temperature over a period of a few weeks. Saline ice was grown to a thickness of 240 mm in an outdoor pool at ambient air temperatures. Precipitation, was allowed by use of a movable roof. Brightness temperatures were measured at 10 and 85 GHz before and for several weeks after one snowfall. During the same period, the vertical temperature profile and crystallography of the snow column, as well as ice structure and salinity at the original ice surface, were monitored. The 10‐GHz brightness temperature dropped by as much as 100 K from bare ice values during the first few days after the snow fell, because of a saline slush layer which formed at the bottom of the snow. The saline water in the slush layer apparently was forced up through the unbroken ice by the added snow load. The slush layer eventually froze into an added highly emissive frazil ice layer which raised the 10‐GHz brightness temperature to above its bare ice values. The frazil ice layer was similar to superimposed frazil ice observed on freezing leads in high‐latitude ice packs. The 85‐GHz brightness temperature did not change from bare ice values soon after the snowfall but dropped by about 40 K over the following 20 days. We use a simple dielectric model to qualitatively test the dependence of 10‐GHz brightness temperature on relevant physical conditions at the bottom of the snow. At 85 GHz the snow layer was optically thick, and the brightness temperature drop was probably the result of increased volume scatter from the growing snow grains.
Deep currents and the eastward salinity tongue in the equatorial Atlantic: Results from an eddy‐resolving, primitive equation model
Authors: Böning Claus W. , Schott Friedrich A.
Published: February 2008

The high‐resolution model of the wind‐driven and thermohaline circulation in the Atlantic Ocean developed in recent years as a “community modeling effort” for the World Ocean Circulation Experiment is examined for the temporal and spatial structure of the deep equatorial current field and its effect on the spreading of North Atlantic Deep Water (NADW). Under seasonally varying wind forcing, the model reveals a system of basin‐wide zonal currents of O(5 cm s−1), alternating east‐west, and oscillating at an annual period. The current fluctuations are induced by the seasonal cycle of the wind stress in the equatorial Atlantic and show characteristics of long equatorial Rossby waves with westward phase propagation of about 15 cm s−1. The mean flow in the deep western tropical Atlantic is governed by a deep western boundary current (DWBC) with core velocities of more than 10 cm s−1. Only a small fraction of the DWBC branches off at the equator, with correspondingly low mean eastward currents of only about 1 cm s−1. Despite this weak advection along the equator, a well‐developed salinity tongue is observed in the model, which is reminiscent of observed property distributions at the upper NADW level. The model evaluation indicates the salinity pattern to be a result of a balance between mean zonal advection and meridional diffusion of salt. The presence of the zonal current oscillations appears to have no significance for the existence of the salinity tongue.
A modified Galerkin‐Spectral model for three‐dimensional, barotropic, wind‐driven shelf circulation
Authors: Sheng Jinyu , Thompson Keith R.
Published: February 2008

We describe an efficient numerical scheme for calculating wind‐driven currents on the continental shelf. Our scheme is based on the spectral approach introduced by Heaps and subsequently modified by Lardner. The basic idea behind Heaps' approach is to express the horizontal flow, u(x, y, z, t), as a linear combination of vertical structure functions, ϕr(z), and then solve numerically for the temporally and horizontally varying coefficients. To obtain an accurate representation of wind‐driven flow, many ϕr are often required. Following Lardner, we reduce this number by subtracting from u an analytically defined flow field, uP, prior to its expansion in terms of the ϕr. Our choice of uP is steady Ekman flow in water of finite depth. This particular choice includes, as a special case, the uP used by Lardner. Using an idealized basin and time‐harmonic wind forcing, we compare the convergence rate of the expansion of u − uP with uP taken to be (1) zero, corresponding to Heaps' approach, (2) flow with constant horizontal shear stress through the vertical, corresponding to Lardner's recent suggestion, and (3) steady Ekman flow. We find that removal of steady Ekman flow generally leads to the most rapid convergence, particularly when the water depth is much greater than the Ekman depth, a condition often found on the middle and outer continental shelf.
A global analysis of the ozone deficit in the upper stratosphere and lower mesosphere
Authors: Eluszkiewicz Janusz , Allen Mark
Published: February 2008

The global measurements of temperature, ozone, water vapor, and nitrogen dioxide acquired by the Limb Infrared Monitor of the Stratosphere (LIMS), supplemented by a precompiled distribution of chlorine monoxide, are used to test the balance between odd oxygen production and loss in the upper stratosphere and lower mesosphere. An efficient photochemical equilibrium model, whose validity is ascertained by comparison with the results from a fully time‐dependent one‐dimensional model at selected latitudes, is used in the calculations. The computed ozone abundances are systematically lower than observations for May 1–7, 1979, which suggests, contrary to the conclusions of other recent studies, a real problem in model simulations of stratospheric ozone. The “ozone deficit” at 30°N is smaller than previous analyses of LIMS data have indicated. In the stratosphere, this reduction in the deficit is due to the fact that ClO abundances for the 1979 period utilized in this study are much lower than in earlier work, mainly as a result of lower Cly concentrations. In the mesosphere, a correlation of the ozone deficit with the distribution of water vapor is indicated. The ozone deficit in the stratosphere can be eliminated by modifying only one model reaction rate: either by decreasing the rate of odd oxygen loss (e.g., by decreasing the abundances of atomic oxygen through an increase in the rate of the reaction O + O2 + M→ O3 + M within the recommended uncertainties) or by increasing the rate of odd oxygen production (by increasing the photodissociation rate of molecular oxygen primarily in the Herzberg continuum and/or invoking photolysis of vibrationally excited molecular oxygen). With the ozone abundances thus increased, a small residual deficit in the lower mesophere can be eliminated by reducing, within the recommended kinetic uncertainties, the efficiency of odd hydrogen‐catalyzed odd oxygen loss. With the adjusted model, the calculated ozone abundances for the week of January 1–7, 1979, outside of winter latitudes, also agree with the LIMS observations to within 10%.
Annual variations of water vapor in the stratosphere and upper troposphere observed by the Stratospheric Aerosol and Gas Experiment II
Authors: McCormick M. P. , Chiou E. W. , McMaster L. R. , Chu W. P. , Larsen J. C. , Rind D. , Oltmans S.
Published: February 2008

This paper presents a description of the annual variations of water vapor in the stratosphere and the upper troposphere derived from observations of the Stratospheric Aerosol and Gas Experiment II (SAGE II). The altitude‐time cross sections exhibit annually repeatable patterns in both hemispheres. The appearance of a yearly minimum in water vapor in both hemispheres at approximately the same time supports the idea of a common source(s) for stratospheric dry air. Annual patterns observed at northern mid‐latitudes, like the appearance of a hygropause in winter and the weakening and upward shifting of the hygropause from January to May, agree with in situ balloon observations previously obtained over Boulder and Washington, D.C. An increase in water vapor with altitude in the tropics is consistent with methane oxidation in the upper stratosphere to lower mesosphere as a source for water vapor. A poleward gradient is also shown as expected based on a Lagrangian mean circulation. A linear regression analysis using SAGE II data from January 1986 to December 1988 shows that little annual variation occurs in the middle and upper stratosphere with the region of large annual variability near the tropopause. The semi‐annual variability is relatively marked at altitudes of 24 and 40 km in the tropics.
A modified K model for chemically reactive species in the planetary boundary layer
Authors: Hamba Fujihiro
Published: February 2008

A modified K model is proposed for the diffusion of chemically reactive species. Eddy diffusivity is modified due to chemical reactions. The effect of cross diffusion is introduced; that is, the scalar flux of a species depends on the scalar gradients of other species. One‐dimensional calculations are carried out for the convective boundary layer by using a K model, a modified K model, and a second‐order model. Three types of simple chemical reactions are investigated. It is shown that results of the modified K model agree well with those of the second‐order model. Profiles of mean mixing ratios and scalar fluxes are compared between the K model and the modified K model. For the simplest chemical reaction the difference between the two models is large when the chemical reaction time scale is shorter than the turbulent time scale. For the reaction of NO‐NO2‐O3 triad, profiles of the scalar fluxes are shown to be very different between the two models.
New parameterizations and sensitivities for simple climate models
Authors: Graves Charles E. , Lee Wan‐Ho , North Gerald R.
Published: February 2008

This paper presents a reexamination of the Earth radiation budget parameterization of energy balance climate models in light of data collected over the last 12 years. The study consists of three parts: (1) an examination of the infrared terrestrial radiation to space and its relationship to the surface temperature field on time scales from 1 month to 10 years; 2) an examination of the albedo of the Earth with special attention to the seasonal cycle of snow and clouds; (3) solutions for the seasonal cycle using the new parameterizations with special attention to changes in sensitivity. While the infrared parameterization is not dramatically different from that used in the past, the albedo in the new data suggest that a stronger latitude dependence be employed. After retuning the diffusion coefficient the simulation results for the present climate generally show only a slight dependence on the new parameters. Also, the sensitivity parameter for the model is still about the same (1.25°C for a 1% increase of solar constant) for the linear models and for the nonlinear models that include a seasonal snow line albedo feedback (1.34°C). One interesting feature is that a clear‐sky planet with a snow line albedo feedback has a significantly higher sensitivity (2.57°C) due to the absence of smoothing normally occurring in the presence of average cloud cover.
Incorporating landscape heterogeneity in land surface albedo models
Authors: Rowe Clinton M.
Published: February 2008

The importance of incorporating landscape heterogeneity into climate models has been recognized by a number of researchers. However, attempts to relax the assumption of uniform, homogeneous and complete vegetation cover have generally been limited to modeling each component of the landscape (e.g., trees, grasses, shrubs) as a homogeneous unit and then combining the results for each type, weighted by the percentage of ground area it covers (i.e., an area‐weighted average is computed).

The purpose of this paper is to demonstrate that substantial errors in the representation of vegetation‐atmosphere interactions can arise from the assumption of landscape homogeneity. Even when weighted averages are employed as a first attempt to consider landscape heterogeneity, the underlying assumption of homogeneity of the vegetation patches can lean to significant errors. To demonstrate an example of how this can occur, vegetation canopy albedo derived from weighted averages is compared to that computed with explicit consideration of canopy heterogeneity.
Quasi‐decadal modulation of the influence of the equatorial quasi‐biennial oscillation on the north polar stratospheric temperatures
Authors: Kodera Kunihiko
Published: February 2008

Low‐frequency variations, produced by stratifying north polar temperature data according to the phase of the equatorial quasi‐biennial oscillation, have been suggested by several authors to aliasing effects resulting from an undersampling. However, similar low‐frequency quasi‐decadal variations correlated with the solar cycle can be found by calculating a running correlation between the equatorial zonal winds and the north polar temperatures without decreasing the sampling frequency of the original signal. This clearly shows that the undersampling is not an essential feature of the present problem, but changes in the relationship between the equatorial and polar regions on the decadal time scale are fundamental aspects.
Further analysis of the relationship between circulation anomaly patterns and tropical convection
Authors: Mo Kingtse C. , Kousky Vernon E.
Published: February 2008

Tropical‐extratropical connections are investigated for 250‐mbar stream function fluctuations in both intraseasonal and interannual bands. The principal modes of anomalous 250‐mbar stream function are computed and related to anomalous outgoing longwave radiation (OLR), which is used as a proxy for deep tropical convection. The leading mode for both boreal winter and summer displays a large zonally symmetric component, which appears in both the intraseasonal (IS) and interannual (IA) bands. In the IS band, the dominant mode is an oscillation with a period of 48 days. Correlations between the principal component of this mode and OLR anomalies indicate that this pattern is directly related to convection in the tropical Pacific. The second mode for the boreal winter consists of a wave train from the Pacific Ocean east‐northeastward to western North America and then east‐southeast ward to the subtropical Atlantic Ocean. This mode also exists in both IA and IS bands. Simultaneous and lagged correlations between the amplitude time series of this mode and OLR anomalies indicate that extreme amplitudes of this wave train are preceded by extremes in the OLR anomalies (cloud band activity) in the subtropical North Pacific. Enhanced cloud band activity in the vicinity of Hawaii, associated with an anomalous cyclonic 250‐mbar circulation in the same region precedes the maximum development of a 250‐mbar ridge south of the Aleutian Islands, trough over western North America and another ridge along the east coast of the United States. The second mode for boreal summer (June‐August) is associated with variations of the Asian monsoon.
The ferroan‐anorthositic suite, the extent of primordial lunar melting, and the bulk composition of the Moon
Authors: Warren Paul H. , Kallemeyn Gregory W.
Published: February 2008

The geochemical bimodality among compositionally pristine lunar rocks is strong evidence that a major component of the Moon's crust is fundamentally unrelated to the plagioclase flotation crust that accumulated over the primordial magma ocean. The ferroan anorthositic suite (FAS) has all the characteristics expected for a series of magma ocean plagioclase flotation cumulates, but we estimate, based on mass balance for Al2O3, that ∼ 30 wt% of the crust, and 20 wt% of the crust's total Al2O3 (or roughly 15% of the bulk‐Moon Al2O3 content, assumed to be 3–4 wt%), was emplaced by postmagma ocean, Mg‐suite “serial” magmatism. Remelting of plagioclase‐bearing magma ocean cumulates cannot plausibly account for the “late” emplacement of Al2O3, because the only plagioclase‐rich cumulates produced by a deep, ultramafic magma ocean would have mg ratios too low to engender the Mg‐suite. Conceivably, remelting of garnet‐rich magma ocean cumulates supplied the late Al2O3, but only if the bulk‐Moon Al2O3 content is substantially higher than generally assumed. High pressures in the magma ocean acted to enhance the py (pyroxene/(pyroxene+olivine)) ratio of the MO cumulates, and the Al2O3 content of whatever pyroxene formed. Remelting of pyroxene‐rich MO cumulates could conceivably have supplied the late Mg‐suite Al2O3 to the crust. The source region would have to encompass roughly 40 wt% of the mantle. Another possible source for late Al2O3 addition is a large portion of the deepest mantle that avoided more than a slight degree of partial melting, and thus remained Al‐rich, during formation of the magma ocean. The source region would have to encompass 20–30 wt% of the mantle. Ascent of diapiric masses from the lowermost mantle would likely coincide with (trigger, or be triggered by) a large‐scale overturn of the gravitationally unstable MO cumulate pile, with concomitant pressure‐release melting, in which case the Mg‐suite parental melts would be derived from a mix of deepest MO cumulates and the even deeper primitive mantle. The popular giant impact hypothesis of lunar origin implies an extremely hot beginning for the Moon, suggesting that the deep interior was either molten or depleted in Al2O3 (by differentiation in hot protomoons) as it formed. Origin of ∼ 30 wt% of the Moon's crust by postmagma ocean, serial magmatism is more consistent with coaccretion models that form the Moon without a giant, hot impact. In any scenario with a large fraction of the crust originating by partial remelting of deep magma ocean cumulates, mass balance for Al2O3 implies that the bulk‐Moon normative py ratio must be greater than roughly 0.5, i.e., significantly higher than generally estimated. In this respect, the Moon appears more compositionally similar to chondritic silicates than to the Earth's upper mantle.
Absolutely calibrated CCD images of Saturn at methane band and continuum wavelengths during its 1991 opposition
Authors: Ortiz J. L. , Moreno F. , Molina A.
Published: February 2008

Ground‐based charge‐coupled device images of Saturn were obtained at the Cassegrain focus of the 1.52‐m telescope at the Calar Alto Observatory (Andalucía, Spain) during the 1991 opposition. The images were obtained in and out of the absorption methane bands at 6190, 7250, and 8900 Å under very good seeing conditions. A Bayesian deconvolution technique was employed in the restoration procedure. The derived absolute reflectivities and band depths at some locations of the disk are provided in tables appropriate for analysis in terms of scattering models. Possible temporal variations between the reflectivities found here and those reported by West et al. (1982) are discussed. No longitudinal variations in reflectivity larger than a 4% level were found. Some images showed bright spot activity at the equatorial region.
Small‐scale density irregularities in the nightside Venus ionosphere: Comparison of theory and observations
Authors: Huba J. D. , Grebowsky J. M.
Published: February 2008

The lower‐hybrid‐drift instability has been proposed as a mechanism to generate small‐scale density and 100 Hz electric field fluctuations in the nightside Venus ionosphere [Huba, 1992]. The primary purpose of this paper is to compare this theory with observations of density irregularities. Marginal stability boundaries (γ = 0) for the lower‐hybrid‐drift instability and the occurrence of small‐scale density fluctuations are presented as a function of magnetic field B and density n. For density gradient scale lengths in the range 2–10 km, 80–85% of the density fluctuations lie in the unstable B/n parameter regime (γ > 0). A secondary purpose of the paper is to present stability boundaries for the onset of instability at a wavelength for which the Pioneer Venus Orbiter (PVO) could measure a Doppler‐shifted frequency of 100 Hz. The conditions on B and n for instability in this situation are more stringent than those for marginal stability, especially at low densities (n ≤ 5 × 103 cm−3). In general, the instability is most likely to be generated in regions of low β: high magnetic field strength and low density, as found in ionospheric holes or troughs.
Introduction to special section on laboratory research for planetary atmospheres
Authors: Fox Kenneth
Published: February 2008

The Third International Conference on Laboratory Research for Planetary Atmospheres (3rd ICLRPA) was held in Palo Alto, California, on November 3, 1991, preceding the 23rd Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society (DPS/AAS). These conferences continue to highlight important progress in laboratory studies with an emphasis on their relationships to models and theories of planetary atmospheres, and importantly, with a focus on those needs for data most critical both to the analyses of ground‐based and spacecraft measurements, and to the planning of new missions. This special section of the Journal of Geophysical Research‐Planets (JGR‐Planets) includes several invited and contributed papers originally presented at the 3rd ICLRPA.

I. de Pater and D. Mitchell (University of California, Berkeley) discussed radio observations of planetary atmospheres and solid surfaces, and explained the role of laboratory data in the analysis of these astronomical observations. They also noted the absence of certain relevant laboratory results needed to further develop our understanding of physical properties of planets. D.C. Reuter and J.M. Sirota (NASA Goddard Space Flight Center, Greenbelt, Maryland) discussed the utility of a spectroscopic system consisting of tunable diode lasers at wavelengths out to 28 microns; a liquid helium‐4 cooled, back‐illuminated, bounded impurity‐band (BIBIB) detector; and a 100‐m White cell to measure infrared transitions in molecules of planetary interest at very high spectral resolution and detectivity. B. Bezard (Observatory of Paris, Meudon, France) considered molecular spectra for Titan to be measured from the Infrared Space Observatory and the Cassini mission over a great range of wavelengths, from the infrared to the submillimeter, with high spectral resolution. He discussed the detectability of certain hydrocarbons and nitriles, and the corresponding need for spectroscopic measurements in the laboratory. H.A. Weaver (Space Telescope Science Institute, Baltimore, Maryland) reviewed the physical and chemical nature of cometary comae, and the connection of molecules and atoms therein with the composition of cometary nuclei. P.J. Gierasch (Cornell University, Ithaca, New York) reviewed the dynamics and thermal structure of the atmospheres of the outer planets, summarizing important measurements that are feasible with remote‐sensing spectroscopic techniques. He discussed precise observations of temperatures, velocities, and abundances to determine seasonal variations in global stratospheric circulations, winds, wave phenomena, and global oscillations. W.T. Huntress (NASA Headquarters, Washington, D.C.) introduced a program for state‐of‐the‐art, integrated systems of laboratory instruments designed for planetary applications. He noted that the establishment of these Centers for Laboratory Planetary Science Studies would facilitate, for all qualified experimentalists, the complex analytical studies needed to support planetary space missions.
The hemispherical asymmetry in the Martian polar caps
Authors: Lindner Bernhard Lee
Published: February 2008

An energy balance model is used to study the behavior of CO2 ice on Mars. The effect of the solar zenith angle dependence of albedo is to lengthen CO2 ice lifetimes at the poles. Hemispherical asymmetries in cloud and dust abundance could result in the survival of seasonal CO2 ice through summer in the south and not in the north, in agreement with observations. CO2 ice observed in the summertime polar cap in the south could be of recent origin, although a permanent CO2 polar cap cannot be ruled out.
Glacial‐Holocene Biogenic Sedimentation Patterns in the South China Sea: Productivity Variations and Surface Water pCO2
Authors: Thunell R. C. , Qingmin Miao , Calvert S. E. , Pedersen T. F.
Published: February 2008

A bathymetric transect of cores in the South China Sea extending from 4200‐m to less than 1000‐m water depth has been examined for glacial‐interglacial changes in carbonate and organic carbon sedimentation. Typical “Pacific carbonate cycles” (high carbonate content during glacials and low carbonate content during interglacials) characterize cores from water depths deeper than 3500 m. In contrast, “Atlantic carbonate cycles” (low carbonate during glacials and high carbonate during interglacials) are observed in cores from depths shallower than 3000 m as a result of increased dilution of carbonate by terrigenous material during glacial low stands of sea level. Glacial‐interglacial changes in the carbonate chemistry of South China Sea intermediate and deep waters resulted in significant changes in the positions of the carbonate compensation depth (CCD) and the aragonite compensation depth (ACD). During the last glacial the CCD and ACD were at least 400 and 1200 m deeper, respectively, than at present. Organic carbon accumulation rates in the South China Sea were approximately 2 times higher during the last glacial than the Holocene. Carbon isotopic analyses and C/N ratios of the organic matter indicate that only a small fraction of the increase in glacial organic carbon accumulation can be attributed to input of terrestrial carbon. On the basis of this we conclude that surface water productivity in the South China Sea was approximately 2 times higher during the last glacial maximum. This is consistent with previous studies which have demonstrated that glacial productivity was higher in low‐ to mid‐latitude regions of the Atlantic and eastern Pacific. The deglacial decrease in organic carbon accumulation is accompanied by a decrease in δ13Corg. Using the relationship between δ13Corg and [CO2](aq) developed by Popp et al. [1989], we estimate that surface water pCO2 values in the South China Sea during the last 25,000 years were very similar to atmospheric CO2 concentrations.
Planktonic foraminifers as tracers of ocean currents in the eastern South Atlantic
Authors: Oberhänsli H. , Bénier C. , Meinecke G. , Schmidt H. , Schneider R. , Wefer G.
Published: February 2008

The standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals (0–25 m, 25–50 m, 50–100 m, 100–150 m, and 150–300 m). The assemblages document the status of populations in the surface and subsurface waters of the Southeast Atlantic during February/March 1988. Standing crops document hydrographic conditions in the coastal and geostrophic branch of the Benguela Current, the Angola Current, the Tropical Cyclonic Gyre, and the South Equatorial Current. Standing stocks are highest when primary production is intermediate. Very high primary production reduces foraminiferal crops significantly. Eleven species occur abundantly (average >10% of the total standing stock). A few species (G. glutinata, G. quinqueloba/G. clarkei) are abundant at each station whereas the occurrence of other species (G. ruber, G. sacculifer, G. scitula, G. menardii, G. crassaformis, N. incompta, N. dutertrei) is spatially restricted. G. ruber, G. rubescens, and G. glutinata are abundant in high‐salinity surface water. Also, G. ruber is abundant within the Equatorial Undercurrent water, when this water is brought to the surface. High concentrations of N. incompta and G. bulloides are observed in the Angola Benguela Front when nutrient concentration is moderately elevated in surface and subsurface water (upper part of the thermocline). G. crassaformis becomes abundant in the subsurface water of the Angola Benguela Front. This species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the Angola Current. G. menardii is considered as an indicator for the Equatorial Undercurrent below the mixed layer, whereas G. scitula most probably points to an admixture of water transported by the northward flowing Benguela Current. High abundances of G. quinqueloba/G. clarkei in the surface and subsurface waters reflect favorable nutrient conditions, like those present in the geostrophic Benguela Current and in the equatorial divergence zone. G. falconensis, N. dutertrei, and G. siphonifera appear to trace the Southern Equatorial Current.
Boundary Scavenging and Deep‐Sea Sediment Dating: Constraints from Excess 230Th and 231Pa
Authors: Lao Yong , Anderson Robert F. , Broecker Wallace S.
Published: February 2008

Apparent sedimentation rates derived from excess 230Th and 231Pa in deep‐sea sediments accumulated during the last 25,000 years in the Pacific Ocean are mostly lower than the average rates determined by other independent (such as 14C and ∂18O) dating methods, which may be a consequence of generally higher accumulation rates of aluminosilicate and carbonate during the last glacial that diluted the excess 230Th and 231Pa activities in glacial sediments. The pattern of enhanced scavenging of nuclides in ocean margin areas (i.e., boundary scavenging) also changed from the glacial to the Holocene. Fluxes of 230Th and 231Pa throughout the ocean varied over time responding to changes in the nature and intensity of boundary scavenging which, in turn, were influenced by changes in particle flux and particle composition. The lower intensity of boundary scavenging of 231Pa during the last glacial may also have contributed to the lower apparent sediment accumulation rates based on excess 231Pa for cores in ocean margin areas.
Modeling the Late Quaternary Indian Ocean Circulation
Authors: Bigg Grant R. , Jiang Dongxiang
Published: February 2008

An ocean general circulation model (OGCM) of the Indian Ocean is forced by paleoclimate simulations for five time slices over the last 126,000 years. Using an annual period sinusoidal fit to the perpetual January and July paleoclimatic model forcing, the OGCM produces seasonal cycles in velocity fields, both vertical and horizontal, and temperature/salinity fields at these five times. The simulations indicate that the southern hemisphere upper ocean circulation of the Indian Ocean is essentially/invariant to climatic fluctuation on this time scale. They also suggest that the low‐insolation (18,000 years B.P.) northern hemisphere upper ocean summer circulation was very much weaker compared to high‐insolation periods (such as 9000 years B.P. and 126,000 years B.P.), by perhaps an order of magnitude. By contrast, the simulated low‐insolation winter northern hemisphere upper ocean circulation was substantially stronger than during high insolation periods. Equatorial upwelling, as simulated, is shown to be a mainly boreal summer event, reduced by an order of magnitude during low‐insolation conditions. A similar reduction in upwelling is seen along the Arabian coast, but a less severe decrease along the Somalian coast. The model simulation of February and August sea surface temperature at 18,000 years B.P., the height of the last glaciation, is generally within 1°–2°C of paleoclimate reconstructions. The effect of lower glacial sea level on the circulation is shown to be only local.