bluuebunny/crossref_metadata_2025 huggingface dataset:
Climate and litter quality controls on decomposition: An analysis of modeling approaches
Authors: Moorhead D. L. , Currie W. S. , Rastetter E. B. , Parton W. J. , Harmon M. E.
Published: December 2003

Four mathematical models simulated decay of two litter types of contrasting quality over a 2‐year period at four sites in North America. The litter types were Drypetes glauca and Triticum aestivum, representing litter with high and low nitrogen:lignin ratios, respectively. The field sites were an Arctic tussock tundra (Alaska, United States), a warm desert (New Mexico, United States), a temperate deciduous forest (New York, United States) and a tropical rain forest (Puerto Rico). Models captured the overall patterns of site and litter quality controls on decomposition; both simulated and observed mass losses were higher in warm, moist environments (both forests) than in cold (tundra) or dry sites (desert), and simulated and observed decay was more rapid for Drypetes than Triticum. However, predictions tended to underestimate litter mass loss in the tropical forest and overestimate decay in the desert and tundra, suggesting that site controls in model formulations require refinement for use under such a broad range of conditions. Also, predicted nitrogen content of litter residues was lower than observed in Drypetes litter and higher than observed for Triticum. Thus mechanisms describing loss of nitrogen from high‐quality litter and nitrogen immobilization by low‐quality litter were not captured by model structure. Individual model behaviors revealed different sensitivities to controlling factors that were related to differences in model formulation. As these models represent working hypotheses regarding the process of litter decay, results emphasize the need for greater resolution of climate and litter quality controls. Results also demonstrate the need for finer resolution of the relationships between carbon and nitrogen dynamics during decomposition.
Long‐term greenhouse gas emissions from hydroelectric reservoirs in tropical forest regions
Authors: Galy‐Lacaux Corinne , Delmas Robert , Kouadio Georges , Richard Sandrine , Gosse Philippe
Published: December 2003

The objective of this work is to quantify long‐term emissions of two major greenhouse gases, CO2 and CH4, produced by the decomposition of the flooded organic matter in tropical artificial reservoirs. In a previous paper [Galy‐Lacaux et al., 1997], gas emissions from the tropical reservoir of Petit Saut (French Guiana) were quantified over the first two years after impounding. This work presents emission fluxes and distributions of dissolved methane and carbon dioxide measured in the reservoir of Petit Saut over three and a half years, since the beginning of impounding (1994) and during operation (1995–1997). To assess long term emissions, an experimental campaign was conducted on four hydroelectric reservoirs (Taabo, Buyo, and Ayame I and II) built between 1960 and 1980 in the Ivory Coast. Average dissolved CH4 concentration in the water column of the Petit Saut reservoir first increased, up to a maximum of 14 mg L−1, in May 1995. Then the time course of dissolved CH4 over the three and a half year period, showed periodical variations. These changes were related to changes in the inlet water flow and the residence time of water in the reservoir. In the older African reservoirs, average dissolved methane concentrations were lower and ranged between 0.20 and 0.32 mg L−1. The whole data set allows us to propose an analytical algorithm in order to predict the time course of dissolved CH4 concentration in the Petit Saut reservoir. Temporal variations of total CH4 and CO2 emissions from the reservoir over three and a half years were extrapolated with this algorithm to calculate long term carbon losses. Over a 20‐year period the estimated carbon losses in the form of CO2 and CH4 were dominated by the outlet fluxes of dissolved gases (2160 ± 400 Gg (C)), and they correspond to a total net carbon loss of 3.2 Tg (C). The contribution of the Petit Saut reservoir to greenhouse gas emission, over 20 years, is estimated to be 66 ± 20 Tg of CO2 equivalent (56 Tg as CH4 and 9.7 Tg as CO2).
Site variation in methane oxidation as affected by atmospheric deposition and type of temperate forest ecosystem
Authors: Brumme Rainer , Borken Werner
Published: December 2003

Factors controlling methane oxidation were analyzed along a soil acidity gradient (pH(H2O) 3.9 to 5.2) under beech and spruce forests in Germany. Mean annual methane oxidation ranged from 0.1 to 2.5 kg CH4 ha−1 yr−1 and was correlated with base saturation (r2 = 0.88), soil pH (r2 = 0.77), total nitrogen (r2 = 0.71), amount of the organic surface horizon (r2 = 0.49) and bulk density of the mineral soil (r2 = 0.43). At lower pHs the formation of an organic surface horizon was promoted. This horizon did not have any methane oxidation capacity and acted like a gas diffusion barrier, which decreased the methane oxidation capacity of the soil. In contrast, on sites at the higher end of the pH range, higher burrowing activity of earthworms increased macroporosity and thereby gas diffusivity and methane oxidation. Gas diffusivity was also affected by litter shape: broad beech leaves reduced methane oxidation more than spruce needles. An increase in methane oxidation of most soil samples following sieving indicates that diffusion is the main limiting factor for methane oxidation. However, this “sieving effect” was less in soils with a pH below 5 than in soils with a pH above 5, which we attribute to a direct effect of soil acidity. We discuss our results using a hierarchical concept for the “short‐term” and “long‐term” controls on methane oxidation in forest ecosystems.
Mathematical modeling of nitrous oxide emissions from an agricultural field during spring thaw
Authors: Grant R. F. , Pattey E.
Published: December 2003

Confidence in regional estimates of N2O emissions used in national greenhouse gas inventories could be improved by using mathematical models of the biological and physical processes by which these emissions are known to be controlled. However these models must first be rigorously tested against field measurements of N2O fluxes under well documented site conditions. Spring thaw is an active period Of N2O emission in northern ecosystems and thus presents conditions well suited to model testing. The mathematical model ecosys, in which the biological and physical processes that control N2O emissions are explicitly represented, was tested against N2O and CO2 fluxes measured continuously during winter and spring thaw using gradient and eddy covariance techniques. In the model, ice formation at the soil surface constrained soil‐atmosphere gas exchange during the winter, causing low soil O2 concentrations and consequent accumulation of denitrification products in the soil profile. The removal of this constraint to gas exchange during spring thaw caused episodic emissions of N2O and CO2, the timing and intensities of which were similar to those measured in the field. Temporal variation in these emissions, both simulated and measured, was high, with those of N2O ranging from near zero to as much as 0.8 mg N m−2 h−1 within a few hours. Such variation should be accounted for in ecosystem models used for temporal integration of N2O fluxes when making long‐term estimates of N2O emissions.
Role of regional bioproductivity in atmospheric CO2 changes
Authors: Rich Jonathan J. , Hollander David , Birchfield G. Edward
Published: December 2003

One process that has been proposed to explain the glacial‐interglacial change in atmospheric CO2 is a change in the strength of the ocean's biological pump, that is, changes in ocean export bioproductivity. Using a coupled ocean‐atmosphere box model that incorporates carbon chemistry and a nutrient budget, we investigate the effect on atmospheric CO2 levels of changes to ocean export productivity in different regions. The primary discovery is the role of water column stratification in controlling the extent to which atmospheric CO2 is affected by regional changes in the biological pump. Stratification manifests itself in two competing ways. On the one hand, increasing stratification causes an increase in atmospheric CO2 sensitivity to export bioproductivity. This results in modeled CO2 being almost an order of magnitude more sensitive to low‐latitude bioproductivity changes than it is to high‐latitude changes. On the other hand, increasing stratification decreases the rate at which nutrients mix up into the surface layer, thereby setting a limit on the overall magnitude of bioproductivity increase and atmosphere CO2 decrease that is possible in stratified ocean regions. One of the implications of this work is to point to the potential importance of changes in the strength of low‐latitude ocean bioproductivity as a cause of the glacial‐interglacial atmospheric CO2 change.
Depth ranges of alkenone production in the central Pacific Ocean
Authors: Ohkouchi N. , Kawamura K. , Kawahata H. , Okada H.
Published: December 2003

We report analytical results of long‐chain (C37−C39) alkenones in the surface sediments taken along a latitudinal transect at 175°E from 48°N to 15°S. Unsaturation degree of C37alkenones (Uk′37) indicated that alkenone temperature is the highest (about 28.3°C) in the tropical Pacific and decreases toward 48°N (about 10.1°C). Although the latitudinal trend of the alkenone temperature is generally similar to that of the observed sea surface temperature of the surface mixed layer, the former exhibits markedly lower values than the latter does in the midlatitude (35°−19°N). On the basis of the comparisons between water column temperatures and alkenone temperatures in the surface sediments, we estimated that in the midlatitudes alkenones are produced in the thermocline waters, whereas in the high (48°−40°N) and low (10°N−2°S) latitudes they are produced in the surface mixed layer. This result is supported by the depth distribution ofEmiliania huxleyiandGephyrocapsa oceanicaalong a 155°W transect in the central Pacific. The latitudinal distribution of the alkenone production layers estimated from UK′37is found to be consistent with that of the nitrate, suggesting that the depth of alkenone production is mainly controlled by the nutrient supply from deeper waters. Alkenones in the sediments exhibited relatively large abundances in 43°−27°N with a maximum at 30°N, which may be explained by high productivity of haptophyte algae in Kuroshio Extension.
Role of sea‐surface temperature and ocean circulation changes in the reorganization of the global carbon cycle at the Last Glacial Termination
Authors: Hausman Ezra Daskal , McElroy Michael B.
Published: December 2003

The increase in atmospheric CO2 mixing ratio at the close of the Pleistocene epoch was part of a larger reorganization of the global carbon cycle that involved the regrowth of the terrestrial biosphere and soil reservoirs, changes in the circulation and surface temperature of the oceans, and possibly changes in oceanic productivity and the throughput of oceanic alkalinity. Here we use a box model of the global carbon cycle to highlight and investigate the role that two of these mechanisms played in distinguishing the carbon dioxide and carbon isotope budgets of glacial versus interglacial conditions: the increase in ocean surface temperature and the circulation‐driven change in export productivity as the last glacial period came to a close. The first of these is shown to explain the otherwise paradoxical isotopic lightening of atmospheric CO2 despite the enhanced sequestration of organic carbon in the deep ocean under glacial conditions. The second provides a new mechanism for increasing whole‐ocean carbonate ion activity, with the expected effect of chemically decreasing CO2 partial pressure in the surface ocean. It is argued that the implied reorganization of the oceanic carbon budget is consistent with both the steady state and the transient features of deglacial carbon cycle history, as well as with the timescale for the atmospheric CO2 increase at glacial termination.
Limitation of algal growth by iron deficiency in the Australian Subantarctic Region
Authors: Sedwick Peter N. , DiTullio Giacomo R. , Hutchins David A. , Boyd Philip W. , Griffiths F. Brian , Crossley A. Clive , Trull Thomas W. , Quéguiner Bernard
Published: December 2003

In March 1998 we measured iron in the upper water column and conducted iron‐ and nutrient‐enrichment bottle‐incubation experiments in the open‐ocean Subantarctic region southwest of Tasmania, Australia. In the Subtropical Convergence Zone (∼42°S, 142°E), silicic acid concentrations were low (< 1.5 µM) in the upper water column, whereas pronounced vertical gradients in dissolved iron concentration (0.12‐0.84 nM) were observed, presumably reflecting the interleaving of Subtropical and Subantarctic waters, and mineral aerosol input. Results of a bottle‐incubation experiment performed at this location indicate that phytoplankton growth rates were limited by iron deficiency within the iron‐poor layer of the euphotic zone. In the Subantarctic water mass (∼46.8°S, 142°E), low concentrations of dissolved iron (0.05‐0.11 nM) and silicic acid (< 1 µM) were measured throughout the upper water column, and our experimental results indicate that algal growth was limited by iron deficiency. These observations suggest that availability of dissolved iron is a primary factor limiting phytoplankton growth over much of the Subantarctic Southern Ocean in the late summer and autumn.
Water injection experiments and discharge changes at the Nojima Fault in Awaji Island, Japan
Authors: Kitagawa Yuuichi , Koizumi Naoji , Notsu Kenji , Igarashi George
Published: December 2003

Three boreholes (500, 800, and 1800 m) were drilled near the Nojima Fault, which is one of the Hyogoken‐Nanbu Earthquake faults. Water injection experiments were conducted from the 1800‐m borehole over three periods (1997/2/9–11, 2/12–13, 3/16–25). Groundwater discharge increased at the 800‐m borehole during the water injections. The discharge started to increase at between one‐half to one full day after the beginning of the injections and decreased substantially just after the stop of the injections. One day after the injections were stopped, their effects on the discharge roughly disappeared. It appeared that these changes in discharge were due to changes in pore water pressure changes induced by the water injections. Therefore, by means of a simple numerical simulation, we analyzed the correlation between the pore water pressure changes and the water injections. In the case of a permeable stratum with a hydraulic diffusivity of 1.0–2.0 km²/day, which is equivalent to 0.08–0.47 darcy on the assumption that the porosity of the stratum is 0.01∼0.1, the calculated pore water pressure changes were highly similar to the observed discharge changes.
Numerical model of the selectivity effect and the ΔV/L criterion
Authors: Sarlis N. , Lazaridou M. , Kapiris P. , Varotsos P.
Published: December 2003

Numerical solutions of Maxwell equations for a model earth with a reasonably conducting channel indicate that the electric field values are intensified within a certain region only (i.e., above the end of the channel), thus explaining the observed selectivity effect. In this region, the electric field may reach detectable values (5–10mV/km), while the magnetic field still remains low (10−2nT). The results are compatible with those obtained recently by analytical solutions (Varotsos et al. [1998]). Both the numerical and the analytical solutions lead to a natural explanation of the ΔV/L≈const criterion. This criterion, however, should not be applied over an area with strongly inhomogeneous electrical structure.
Explosion‐seismic tomography of a magmatic body beneath Etna: Volatile discharge and tectonic control of volcanism
Authors: Laigle Mireille , Hirn Alfred
Published: December 2003

To constrain the upper depth range of lateral heterogeneities beneath Mt Etna, a seismic tomography method with artificial sources is designed to undershoot the target and restrict the depth of seismic propagation by reflection at the top of the basement. A strong high velocity anomaly thus imaged southeast of the summit, interpreted as a magmatic body, is reliably constrained to reach at least as shallow as 2 km depth where exsolution of SO2 from magma may occur. The high gas output rate of Etna [Allard, 1997] hence appears as the normal complement of the huge magma body seismically imaged. This magma body is located beneath the volcanic edifice rather than within, which attests to the control of volcanism by extension. These volatile output and internal structure distinguish Mt Etna volcanism among current types and may relate to the peculiar context of a recent regional change from subduction‐related compression to extension.
Defocusing of teleseismic P‐waves by the Tonga‐Kermadec Slab
Authors: Suetsugu Daisuke
Published: December 2003

We analyze P‐wave amplitude reduction for Tonga earthquakes observed at the SKIPPY broadband seismograph network in Australia. The negative amplitude anomaly diminishes with a focal depth, suggesting that the anomaly is due to defocusing caused by the fast Tonga slab. The SKIPPY network covers the distance range where the effect of the Tonga slab is most pronounced. We calculate theoretical amplitudes using simplified slab models based on previous delay time tomography, and show that the theoretical amplitude anomaly reproduces the observations reasonably well. A 100‐km thick slab provides a better fit to the data than a 50‐km thick slab. A thin slab penetrating deep into the lower mantle is inconsistent with the pattern of amplitude variation with distance.
Infrasonic precursors to a Vulcanian Eruption at Sakurajima Volcano, Japan
Authors: Garcés Milton , Iguchi M. , Ishihara K. , Morrissey M. , Sudo Y. , Tsutsui T.
Published: December 2003

The May 1998 eruption sequence of Sakurajima Volcano was monitored by ten infrasonic stations, ten seismometers, and a video camera. During this seismo‐acoustic experiment, we recorded hundreds of infrasonic tremor and long‐period events associated with seismic signals, and observed a progression from relative quiescence to a Vulcanian eruption. The number of infrasonic events increased with escalating volcanic activity, and the dominant character of the infrasonic signals changed from impulsive to emergent. At 22:17 of May 19, Sakurajima released ash and gases to a height of 2 km above the vent, an event that was recorded continuously by one infrasonic and two seismic stations. We present the experimental setup as well as a procedure through which infrasonic signals may be incorporated into future eruption monitoring and forecasting algorithms for open‐vent volcanic systems. In addition, our recordings suggest that infrasonic signals are more representative of processes occurring within the volcanic interior than are seismic signals, which are strongly altered by diffraction and scattering in the volcanic edifice.
Enhanced velocity tomography: Practical method of combining velocity and attenuation parameters
Authors: Debski W. , Young R. P.
Published: December 2003

Acoustic (ultrasonic) tomography is now a well acepted method for investigating the internal structure of rock samples and rock masses. In this article we describe a new parameter to be imaged, which combines the robustness of velocity tomography and the sensitivity of attenuation tomography resulting in Enhanced Velocity Tomography. The theoretical considerations are illustrated by a computer simulation and then by application to data from a granite sample subjected to induced damage by heating. In both cases the Enhanced Velocity Tomography is found to be more sensitive to the internal rock structure than classical velocity tomography and overcomes instability problems characteristic of attenuation tomography.
First results of the TRMM Microwave Imager (TMI) monthly oceanic rain rate: comparison with SSM/I
Authors: Chang A. T. C. , Chiu L. S. , Kummerow C. , Meng J. , Wilheit T. T.
Published: December 2003

We evaluated the performance of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) at‐launch algorithm for monthly oceanic rain rate using six months (January–June 1998) of TMI data. Comparison with oceanic monthly rain rates derived from the Special Sensor Microwave Imager (SSM/I) data shows statistically significant differences. The TMI rain rates are lower than the SSM/I rain rates by about 10% overall, except for rain rates lower than 1.4 mm/day. The low TMI bias may be due to an overestimate of the columnar water vapor as indicated by the estimated rain layer thickness. The superior sampling by the TMI improves the algorithm statistics at the low rain rates. The averaged monthly rain rates over the latitudes between 40°S and 40°N are 2.78 and 3.17 mm/day, respectively for TMI and SSM/I, with RMS difference of 1.35 mm/day and correlation coefficient of 0.94.
Effects of the crustal stress on the growth of dikes: Conditions of intrusion and extrusion of magma
Authors: Ida Yoshiaki
Published: December 2003

Dike growth is analyzed, on the basis of the fluid‐dynamical behavior of incompressible, Newtonian magma in a spatially uniform fissure of temporally variable width. The length and width of the dike vary with the magma pressure at the dike entrance connected to the magma chamber and with the mean stress working normal to the dike walls. The mean stress consists of the regional crustal stress and the mean elastic stress, which is approximately evaluated using an analytic solution of the crack with a constant aperture. The length and width of the dike are determined as a function of time by simple ordinary differential equations. The dike can grow when the initial pressure of the entering magma is above the lithostatic pressure and high enough to suppress compression of the crustal stress. The assumed size of the initial crack affects the growth only in the duration needed for an initial adjustment stage. After this stage the width and length first grow exponentially, and then the growth slows as magma is released from the chamber. The growth in the later stage is classified into two types. When the initial magma pressure is high enough, the dike elongates unlimitedly while the width finally decreases. This “extrusive growth” is likely to lead to eruptions. The other “intrusive growth,” in which the dike finally stops its growth with a finite length and width, occurs when the crustal stress component normal to the fissure is of sufficiently strong extension. Buoyancy of magma is not very effective in the earlier growth stage, but it shifts the marginal condition separating the extrusive and intrusive growths. The extrusive and intrusive events that recently happened in Izu‐Oshima volcano and Izu‐Tobu volcano group, Japan, are interpreted as the examples of these two growth types.
Numerical evaluation of mantle plume spacing, size, flow rates, and unsteadiness
Authors: Wüllner Ursula , Davies Geoffrey F.
Published: December 2003

Predictions of several characteristics of mantle plumes from boundary layer theory have been tested and calibrated with numerical models in cylindrical coordinates. Instability spacing in the initial stages of the numerical models is well predicted as are the lift‐off time of plume heads, the size of plume heads at lift‐off, and the heat flow of individual plume tails. However, since the prediction quality for the instability spacing and the lift‐off time of plume heads deteriorates in the presence of larger heterogeneities in the thermal boundary layer, these predictions seem not very useful for mantle plumes. Predictions for the plume head size at lift‐off appear to be largely independent of the degree of boundary layer heterogeneity and therefore may provide reasonable estimates for mantle plumes. The predictions for the heat flow of a plume tail seem to yield usable results for both stationary plume tails and those that show at least periods of quasi‐stationary heat flow. Assuming that mantle plumes are reasonably steady, the prediction formula is used to derive estimates for the temperature difference ΔT′ across the thermal boundary layer at the core‐mantle boundary. This depends on the fraction of the core surface that is presumed to be occupied by plume feeding areas. Taking this fraction to be greater than 1/2 yields ΔT′ < 400°C, too low to be compatible with petrological constraints on plumes. Smaller fractions yield larger ΔT′, but this seems to be incompatible with the geophysical distribution of hotspots.
Barents Sea seasonal ice zone features and processes from ERS 1 synthetic aperture radar: Seasonal Ice Zone Experiment 1992
Authors: Sandven Stein , Johannessen Ola M. , Miles Martin W. , Pettersson Lasse H. , Kloster Kjell
Published: December 2003

Sea ice features and processes in the Barents Sea were studied during the Seasonal Ice Zone Experiment 1992 (SIZEX92), a dedicated ERS 1 satellite synthetic aperture radar (SAR) field campaign carried out in March 1992. SIZEX92 was based around the research vesselsPolarsyssel and Håkon Mosby. In situ oceanographic, meteorological, and ice measurements were made, coordinated with low‐altitude aerial observations and ERS 1 SAR data acquired in near real time. Fifty‐eight low‐and full‐resolution SAR scenes were obtained during SIZEX92, which provided a validation data set for ERS 1 SAR backscatter under winter conditions in the Barents Sea. Analysis of SIZEX92 data has provided geophysical insights, including a better understanding of Barents Sea ice edge freezing processes and ice edge development in response to atmospheric forcings. In particular, areas of new ice formation were found to be related to bathymetric features through their influence on the circulation of Arctic and Atlantic water masses. ERS 1 SAR image sequences revealed rapid, mesoscale variations in new ice areas and the ice edge in response to wind conditions. In addition to geophysical insight, SIZEX92 demonstrated some of the technical capabilities and limitations of ERS 1 SAR to identify new ice areas, the ice edge, ice floes, and ice types. Mapping new ice areas using satellite SAR data may be considered the most promising new application. The limitations of ERS‐1 SAR‐derived ice classification and ice motion estimates in the marginal ice zone are identified.
Fractionally modified flow in a deep ocean channel: Application to the Vema Channel
Authors: Jungclaus Johann H. , Vanicek Michael
Published: December 2003

The modification of the exchange flow in a deep southern hemisphere passage, resembling the Vema Channel, by frictionally induced secondary circulation is investigated numerically. The hydrostatic primitive equation model is a two‐dimensional version of the sigma‐coordinate Princeton Ocean Model. The time dependent response of a stratified along‐channel flow, forced by barotropic or baroclinic pressure gradients, is examined. Near the bottom, where the along‐channel flow is retarded, there is cross‐channel Ekman flux that is associated with downwelling on the eastern side and upwelling on the western side of the channel. In the presence of stratification the cross‐channel flow rearranges the density structure, which in turn acts on the along‐channel velocity via the thermal wind relation. Eventually the cross‐isobath Ekman flux is shut down. In the case of baroclinically driven flow of Antarctic Bottom Water through the Vema Channel the model reproduces the observed shape of the deep temperature profiles and their cross‐channel asymmetry. The model offers an explanation that is alternative or supplementary to inviscid multilayer hydraulic theory that was proposed in earlier studies. It explains the extremely thick bottom boundary layers in the center and on the western slope of the channel. The deep thermocline is spread out in the west and sharpened in the east, and the coldest water is found on the eastern side of the deep trough. The modified density field reduces the along‐channel flow near the bottom and focuses it into a narrow jet on the eastern side of the channel.
Analysis of Legeckis eddies in the near‐equatorial Pacific
Authors: Weidman P. D. , Mickler David L. , Dayyani B. , Born G. H.
Published: December 2003

A study of Legeckis eddies in the equatorial Pacific during seasonal periods of high zonal shear between the Southern Equatorial Current and the Northern Equatorial Counter Current is undertaken. We use both Geosat and TOPEX altimetry data, in combination with advanced very high resolution radiometer (AVHRR) temperature fields and numerical results generated by the Parallel Ocean Climate Model (POCM). Geosat data analyzed using the Marquardt‐Levenberg Fourier series algorithm [Dayyani et al., 1996], exhibit eddy features in good qualitative agreement with both linear stability theory of the zonal barotropic flow and with other independent field and satellite observations. A comparison of sea surface height (SSH) and sea surface temperature (SST) anomaly fields suggests that the phase relation between them may be explained in a first approximation by simple cat's‐eye kinematics [Musman, 1989]. This is explored further using the POCM, TOPEX, and AVHRR data. The POCM time series of SST and SSH anomalies obtained during a time of quasi‐steady eddy propagation clearly show that the phase ϕ between their respective minima varies continuously with latitude, ranging from near zero at latitudes well below the separatrix of the cat's eye to values approaching π radians at latitudes near the critical layer of the cat's eye. The unsteady wave systems observed in both the Geosat and TOPEX SSH anomaly data show the birth and death of individual eddies, with a fairly clear trend that births occur 1°N of the zonal wave train while deaths occur only in the latitude of the mature wave train.
On the sea surface temperature high in the Lakshadweep Sea before the onset of the southwest monsoon
Authors: Shenoi S. S. C. , Shankar D. , Shetye S. R.
Published: December 2003

The north Indian Ocean becomes the warmest area of the world oceans prior to the onset of southwest monsoon in June. During this period a zonal band of high sea surface temperature (SST), the “thermal equator” (TE), moves over this region concurrently with the Intertropical Convergence Zone (ITCZ). Using a weekly SST data set, we show that another SST high develops off southwest India in the Lakshadweep Sea in March, well before the TE moves in to the area, and that it continues to retain its identity until the onset of monsoon. The SST high has its genesis about 6 months earlier in the Bay of Bengal. The collapse of the southwest monsoon in October and the onset of the northeast monsoon trigger down welling coastal Kelvin waves that propagate along the periphery of the Bay of Bengal, forcing an equatorward East India Coastal Current, which brings low‐salinity water from the bay to the southeastern Arabian Sea during the northeast monsoon (November‐January). As the Kelvin waves propagate poleward along the west coast of India after turning around Sri Lanka, they radiate downwelling Rossby waves that produce a “high” in sea level off southwest India. The downwelling and the surface layer of low‐salinity water provide a breeding ground for the formation of a SST high in January. By March, with the increase in solar insolation due to the northward march of the Sun and the deep stable surface layer, the high reaches a mature phase clearly evident in the Lakshadweep Sea. By May, when the thermal equator and ITCZ move over the region, the high can be seen embedded in the TE. We speculate that at this time the high helps in producing conditions that are conducive for genesis of the monsoon onset vortex.
Indian‐Atlantic interocean exchange: Dynamics, estimation and impact
Authors: de Ruijter W. P. M. , Biastoch A. , Drijfhout S. S. , Lutjeharms J. R. E. , Matano R. P. , Pichevin T. , van Leeuwen P. J. , Weijer W.
Published: December 2003

Interocean exchange of heat and salt around South Africa is thought to be a key link in the maintenance of the global overturning circulation of the ocean. It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean. This makes it extremely hard to estimate the inter ocean fluxes. Estimates of direct Agulhas leakage from hydrographic and tracer data range between 2 and 10 Sv (1 Sv = 106 m3 s−1). The average ring shedding frequency, determined from satellite information, is approximately six rings per year. Their associated interocean volume transport is between 0.5 and 1.5 Sv per ring. A number of Agulhas rings have been observed to cross the South Atlantic. They decay exponentially to less than half their initial size (measured by their available potential energy) within 1000 km from the shedding region. Consequently, most of their properties mix into the surroundings of the Benguela region, probably feeding directly into the upper (warm) limb of the global thermohaline circulation. The most recent observations suggest that in the present situation Agulhas water and Antarctic Intermediate Water are about equally important sources for the Benguela Current. Variations in the strength of these may lead to anomalous stratification and stability of the Atlantic at decadal and longer timescales. Modeling studies suggest that the Indian‐Atlantic interocean exchange is strongly related to the structure of the wind field over the South Indian Ocean. This leads in the mean to a subtropical supergyre wrapping around the subtropical gyres of the South Indian and Atlantic Oceans. However, local dynamical processes in the highly nonlinear regime around South Africa play a crucial role in inhibiting the connection between the two oceans. The regional bottom topography also seems to play an important role in locking the Agulhas Currents' retroflection. State‐of‐the‐art global and regional “eddy‐permitting” models show a reasonably realistic representation of the mean Agulhas system; but the mesoscale variability and the local geometrical and topographic features that determine largely the interocean fluxes still need considerable improvement. In this article we present a review of the above mentioned aspects of the interocean exchange around South Africa: the estimation of the fluxes into the South Atlantic from different types of observations, our present level of understanding of the exchanges dynamics and forcing, its representation in state‐of‐the‐art models, and, finally, the impact of the Indian‐Atlantic fluxes on regional and global scale both within the Atlantic Ocean and in interaction with the overlying atmosphere.
The role of the alongshore wind stress in the heat budget of the North Carolina inner shelf
Authors: Austin Jay A.
Published: December 2003

The heat budget of a cross‐shelf section extending 16 km offshore of the outer banks of North Carolina is studied during two time periods: August 1994 and October 1994, using data collected as part of the Coastal Ocean Processes (CoOP) Inner Shelf Study. Heat budgets are computed on two different timescales: monthly averages over August and October, which reflect seasonal variations, and a fluctuation budget, which reflects variation on daily to weekly timescales. During August, a period of strong stratification, the increase in the area‐averaged water temperature (approximately 3.2°C) was due primarily to the surface heat flux. Fluctuations in temperature during August were caused primarily by the cross‐shelf heat flux, due to wind‐driven upwelling and downwelling circulation. In October, the area‐averaged shelf temperature dropped by approximately 3.5°C due to both surface heat loss and the alongshore transport of heat. Weak vertical stratification in October led to small cross‐shelf heat fluxes, and temperature fluctuations in October were due primarily to fluctuations in the surface and alongshore heat fluxes. In both August and October, variation on daily to weekly timescales of the area‐averaged temperature of the shelf was strongly correlated with the alongshore component of the wind stress. In August, alongshore poleward winds caused upwelling and the area‐averaged temperature decreased; conversely, equatorward winds caused downwelling and warming. In October, although the variations in temperature were smaller, alongshore winds were positively correlated with alongshore currents and the surface heat flux (for reasons discussed by Austin and Lentz [this issue]), so that poleward winds resulted in warming; conversely, equatorward winds resulted in cooling. Therefore the dependence of the change in heat content on the alongshore wind stress changed sign between August and October. A simple dynamical model was constructed to relate changes in heat content to the alongshore wind stress. The model results were compared to 12 years of meteorological records from the Coastal Engineering Research Center's Field Research Facility, directly onshore of the experimental site. The results suggest a seasonal cycle in the dominant fluctuating heat balance, consistent with the field results found for August and October 1994. In May through August, cross‐shelf flux dominates variation in the heat content. In October through March, the surface heat flux and alongshore heat flux dominate the variation.
On the structure, paths, and fluxes associated with Agulhas rings
Authors: McDonagh Elaine L. , Heywood Karen J. , Meredith Michael P.
Published: December 2003

In January 1993, two Agulhas rings were sampled in the eastern South Atlantic during the World Ocean Circulation Experiment one‐time hydrographic section A11. The first of these, Ring 1, was sampled at 36°S, 4°E in the Subtropical Frontal Zone and was smaller and less energetic than other, more typical Agulhas rings, owing partly to its interactions with the North Subtropical Front. The other, Ring 2, was sampled at 33°S, 10°E in the subtropics. This ring was average in size and reasonably representative of the rings observed in the southeast Atlantic during the early 1990s. The path of the rings is found to be dominated by advection in the mean flow rather than self‐induced velocities of eddies under the β effect. We observe significant differences in reduced gravity and available heat and salt anomalies in the rings; from these we infer temporal variability in the stratification of rings upon their formation at the Agulhas Retroflection. This temporal variability in the structure of rings will affect the fluxes associated with them. Data collected within Ring 2 show that neglecting consideration of the water beneath the 10°C isotherm underestimates the volume flux by half and the potential temperature and salinity flux by in excess of one third and one half, respectively. Using a base of the 3.5°C isotherm and including the high‐salinity intermediate water from the Indian Ocean is found to be more appropriate. With these conditions, six Agulhas rings per year entering the subtropical South Atlantic would equate to a volume flux of 9 Sv and an absolute potential temperature and salinity flux of 84 Sv°C and 322 Sv psu (1 Sv psu ≈ 106 kg s−1). The significant flux of intermediate water from the Indian Ocean may be as important in the return path of the thermohaline circulation as the intermediate water that enters the South Atlantic through Drake Passage. Further, the water associated with Agulhas rings and cooler than 10°C potentially contributes a larger volume flux to the warm water return path than the corresponding surface and upper thermocline water.
A Monte Carlo uncertainty analysis of ozone trend predictions in a two‐dimensional model
Authors: Considine D. B. , Stolarski R. S. , Hollandsworth S. M. , Jackman C. H. , Fleming E. L.
Published: December 2003

We use Monte Carlo analysis to estimate the uncertainty in predictions of total O3 trends between 1979 and 1995 made by the Goddard Space Flight Center (GSFC) two‐dimensional (2‐D) model of stratospheric photochemistry and dynamics. The uncertainty is caused by gas phase chemical reaction rates, photolysis coefficients, and heterogeneous reaction parameters which are model inputs. The uncertainty represents a lower bound to the total model uncertainty assuming the input parameter uncertainties are characterized correctly. Each of the Monte Carlo runs was initialized in 1970 and integrated for 26 model years through the end of 1995. This was repeated 419 times using input parameter sets generated by Latin hypercube sampling. The standard deviation (σ) of the Monte Carlo ensemble of total O3 trend predictions is used to quantify the model uncertainty. The 34% difference between the model trend in globally and annually averaged total O3 using nominal inputs and atmospheric trends calculated from Nimbus 7 and Meteor 3 total ozone mapping spectrometer (TOMS) version 7 data is less than the 46% calculated 1σ model uncertainty, so there is no significant difference between the modeled and observed trends. In the northern hemisphere midlatitude spring the modeled and observed total O3 trends differ by more than 1σ but less than 2σ, which we refer to as marginal significance. We perform a multiple linear regression analysis of the runs which suggests that only a few of the model reactions contribute significantly to the variance in the model predictions. The lack of significance in these comparisons suggests that they are of questionable use as guides for continuing model development. Large model/measurement differences which are many multiples of the input parameter uncertainty are seen in the meridional gradients of the trend and the peak‐to‐peak variations in the trends over an annual cycle. These discrepancies unambiguously indicate model formulation problems and provide a measure of model performance which can be used in attempts to improve such models.
Simulation of carbon monoxide transport during April 1994
Authors: Faluvegi G. S. , Alapaty K. , Reichle H. G. , Mathur R. , Raman S. , Connors V. S.
Published: December 2003

The Multiscale Air Quality Simulation Platform (MAQSIP) is used to simulate transport of carbon monoxide (CO) as a passive tracer over North America, Europe, and the North Atlantic during the April 1994 Measurement of Air Pollution from Satellites (MAPS) mission. MAQSIP is driven by meteorological fields generated by the Pennsylvania State University/National Center for Atmospheric Research fifth‐generation mesoscale model. Model CO surface emissions from biomass burning, fossil fuel combustion, nonmethane hydrocarbon oxidation, oceans, and soils are based on inventories from the Belgian Institute for Space Aeronomy and the Global Emissions Inventory Activity. Predicted CO mixing ratios are vertically weighted for comparison with MAPS observations. The spread in the mission‐averaged vertically weighted simulated CO mixing ratios (∼38 ppbv, compared to 60 ppbv in the MAPS data) suggests that CO surface emissions significantly affect MAPS observations on a weekly timescale. Good qualitative agreement is found between MAPS observations and model predictions on several temporal and spatial scales. Possible reasons for discrepancies are examined. A simulation without cumulus convection increases CO mixing ratios in the lower model layers and depletes CO above, resulting in a complex pattern of increases and decreases upon vertical weighted integration. Another simulation, which included a diurnal emissions variation, produced significant changes in instantaneous local CO mixing ratios, but had a minimal effect on the mission‐averaged MAPS comparisons.
Long‐range transport of anthropogenic aerosols to the National Oceanic and Atmospheric Administration baseline station at Mauna Loa Observatory, Hawaii
Authors: Perry Kevin D. , Cahill Thomas A. , Schnell Russell C. , Harris Joyce M.
Published: December 2003

Size‐segregated measurements of aerosol mass and composition are used to determine the composition and seasonal variations of natural and anthropogenic aerosols at Mauna Loa Observatory (MLO) from 1993 through 1996. Although the springtime transport of Asian dust to MLO is a well‐documented phenomenon, this study shows that fine anthropogenic aerosols, including sulfur, black carbon, and enriched trace metals such as As, Cu, Pb, and Zn, are also routinely transported to MLO each spring. It is estimated that at least one third of the sulfate measured at MLO during the spring is anthropogenic. In addition, indirect measurements indicate that the organic aerosol concentrations are often comparable to the sulfate concentrations. This study also combines size‐ and time‐resolved aerosol composition measurements with isentropic, backward air‐mass trajectories and gas measurements of 222Rn, CH4, CO, and CO2 to identify some potential source regions of the anthropogenic aerosols. Three types of long‐range transport episodes are identified: (1) anthropogenic aerosols mixed with Asian dust, (2) Asian pollution with relatively small amounts of soil dust, and (3) biomass burning emissions from North America. This study shows that anthropogenic aerosols and gases can be efficiently transported to MLO from both Asia and North America during the spring.
O3 oxidation of SO2 in sea‐salt aerosol water: Size distribution of non‐sea‐salt sulfate during the First Aerosol Characterization Experiment (ACE 1)
Authors: Sievering H. , Lerner B. , Slavich J. , Anderson J. , Posfai M. , Cainey J.
Published: December 2003

Non sea‐salt sulfate (NSS) of 2.2–2.3 nmol m−3 total magnitude in aerosols observed during the First Aerosol Characterization Experiment (ACE‐1) at Cape Grim, Tasmania, was trimodally distributed with ∼1 nmol NSS m−3 in >0.7 μm ambient diameter (diam) coarse sea‐salt mode aerosols; despite this low NSS concentration, [H2SO4(g)] was so low that <1% of this NSS could have been due to H2SO4 scavenging. Ammonium was not associated with these coarse sea‐salt aerosols, suggesting that cloud processing was a minor contributor to the NSS found in >0.7 μm diam aerosols. The mechanism of O3 oxidation of SO2 in sea‐salt aerosol water (SSAW) is assessed for its capability to explain this coarse aerosol NSS. Limitation of this mechanism's NSS contribution is largely due to SSAW's buffering capacity since its reaction rate is reduced by 2 orders of magnitude at pH 6 versus the pH≥8 of unreacted SSAW. However, the buffering capacity of sea‐salt aerosols may have been significantly enhanced over that of bulk seawater alkalinity. This appears to be due to carbonate resulting from small fragments of biogenic CaCO3 in the ocean's surface microlayer. Given the observed nonsoil calcium excess over that in bulk seawater, the estimated actual buffering capacity of sea‐salt aerosols observed during ACE 1 was 50%, or more, enhanced over that due to bulk seawater alkalinity. Considering this enhanced buffering capacity, O3 oxidation of SO2 in SSAW can produce sufficient NSS to explain 70–90% of the ∼1 nmol m−3 found in >0.7 μm diam coarse sea‐salt aerosols with cloud processing and further oxidation of SO2 in SSAW (i.e., pH<6) by other sea‐salt conversion mechanisms contributing the remainder. The amount of NSS produced by sea‐salt conversion mechanisms during the ACE 1 remote Southern Ocean experiment vied with homogeneous and cloud processing in their contribution to the total observed NSS of 2.2–2.3 nmol m−3.