bluuebunny/crossref_metadata_2025 huggingface dataset:
Gradients in H2O, CO2, and exsolved gas in a large‐volume silicic magma system: Interpreting the record preserved in melt inclusions from the Bishop Tuff
Authors: Wallace Paul J. , Anderson Alfred T. , Davis Andrew M.
Published: December 2003

Infrared spectroscopic analyses of ∼140 melt inclusions in quartz phenocrysts from the zoned Bishop rhyolitic tuff demonstrate that systematic gradients in dissolved magmatic H2O and CO2 concentrations were present during preemptive crystallization of the magma body. Melt inclusions from the earliest erupted samples contain lower H2O (5.3±0.4 wt %) and CO2 (62±37 ppm) than inclusions from the middle of the eruption (5.7±0.2 wt % H2O; 120±60 ppm CO2). Melt inclusions from late erupted samples have much lower H2O (4.1±0.3 wt %) and higher and variable CO2 (150–1085 ppm). Trace element analyses of melt inclusions by ion microprobe show that inclusions within single pumice clasts from the early and middle Bishop Tuff have an inverse correlation between CO2 and incompatible elements. This pattern indicates that the magma was gas‐saturated during crystallization, with CO2 partitioning into a coexisting gas phase. Quantitative modeling using H2O‐CO2 solubility relations reveals a preeruptive gradient in exsolved gas, with gas contents varying from ∼1 wt % in the deeper regions of the magma body to nearly 6 wt % near the top. Dissolved Cl, B, Li, and Be in melt inclusions correlate negatively with CO2. Mass balance modeling of Cl loss to exsolving H2O‐rich gas during crystallization provides strong corroborating evidence for the mass fractions of exsolved gas estimated from H2O, CO2, and trace element data. Pressures of quartz crystallization and melt inclusion entrapment calculated from inclusion H2O‐CO2 data are consistent with progressive downward tapping of a zoned magma body during the eruption. Melt inclusion gas saturation pressures, magma volume estimates, and time‐stratigraphic‐compositional relations suggest that early erupted magma was stored at the top of a downward widening magma body. Melt inclusion data and the inferred gradients in dissolved H2O, CO2 and exsolved gas in the Bishop magma body suggest that gas saturation plays an important role in the formation and subsequent preservation of compositional gradients in silicic magma reservoirs.
Sea level comparison between TOPEX/POSEIDON altimetric data and a global ocean general circulation model from an assimilation perspective
Authors: Maes Christophe , Benkiran Mounir , De Mey Pierre
Published: December 2003

The TOPEX/POSEIDON altimetric sea level observations during 1993 are used to validate a simulation made by the Laboratoire d'Océanographie Dynamique et de Climatologie ocean general circulation model (OGCM) at global scales. The forcing fields are provided by the European Centre for Medium‐Range Weather Forecasts reanalysis project. The OGCM is a coarse horizontal resolution model (2° longitude by 1.5° latitude with 31 levels in the vertical), mainly used for climate studies. Horizontal mixing is done along isopycnal surfaces, whereas the parameterization of vertical mixing is based on a local estimate of the turbulent kinetic energy. The comparison is quantitative in the sense that TOPEX/POSEIDON observations are interpolated onto the model grid by an objective interpolation in view of the assimilation case. The model simulation is compared to the observations at large spatial scales of 500 km or more. The basic features of the variability are simulated well by the model, in particular with respect to the annual cycle. Major discrepancies are found in the vicinity of western boundary currents and in the Southern Ocean, due in part to the inadequate horizontal resolution. In anticipation of a future assimilation of the observed sea level a decomposition of the model sea level into baroclinic/barotropic components diagnosed with some dynamical variables of the model is then examined. It is shown that the baroclinic component explains the large seasonal variations confined in the upper layers, whereas the barotropic component is associated with intraseasonal variability. The results of the present study confirm that the model sea level is consistent with the observed large‐scale variability, providing a basis for future assimilation of the data into the OGCM to improve the representation of the ocean state.
Subtropical mode waters in the South Atlantic Ocean
Authors: Provost Christine , Escoffier Christelle , Maamaatuaiahutapu Keitapu , Kartavtseff Annie , Garçon Véronique
Published: December 2003

This systematic study of the subtropical mode waters in the South Atlantic is based on hydrological data (the basin‐wide South Atlantic Ventilation Experiment, Oceanus, and Ajax sections, and the World Ocean Circulation Experiment (WOCE) sections in the Brazil‐Malvinas Confluence region), the WOCE expendable bathythermograph data set, and the atmospheric forcing produced by the National Centers for Environmental Prediction reanalysis. The main ventilation window of the subtropical gyre lies in the southwest and corresponds to the southern part of the recirculation region and to the overshoot of the Brazil Current (BC). Some ventilation occurs along the southern branch of the gyre through deep mixed layers in harsh winters and in the east through the rings shed by the Agulhas Current. However, the ventilation from the eastern border concerns a small volume of water with highly variable characteristics. Three main types of subtropical mode water are observed: the lightest around the 26.2 density surface and the second and third around the 26.5 and 26.7 density surfaces, respectively. The 26.2 subtropical mode water (STMW1) corresponds to potential temperatures between 16° and 18°C and salinities between 35.9 and 36.2. The STMW1 thickness does not exceed 150 m. The volume of the 26.5 mode water (STMW2) is larger. It is produced through the formation of deep mixed layers (reaching 300 m or more) in the active ventilation window over the BC overshoot. Its potential temperature ranges between 14° and 16°C, and its salinity ranges between 35.5 and 35.9. Its thickness can be above 300 m. The last component observed around the 26.7 density surface (STMW3) has a potential temperature between 12° and 14°C and a salinity of about 35.2 to 35.5. It is formed on the eastern flank of the BC overshoot and, during harsh winters, in the center of the southern branch of the gyre. Within the main ventilation window the STMWs exhibit quite a significant variability in characteristics and volume. There is a large interannual variability in the atmospheric forcing over the BC recirculation and BC extension, and the observed variations of the subtropical mode waters are qualitatively correlated to the atmospheric forcing variations.
Simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near‐surface process
Authors: Noh Yign , Jin Kim Hyoung
Published: December 2003

An improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface. In the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified. The parameterization of stratification effects on turbulence is improved, and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer. Evolutions of the profiles of both the dissipation rate and temperature of the observation data Patches Experiment as well as the time series of the sea surface temperature over the observation days, are successfully simulated during a diurnal cycle for the first time. It is also shown that the model reproduces various important features of the oceanic boundary layer, for example, the formation of a diurnal thermocline, the profiles of buoyancy flux, and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline. Performance of the model is compared with that of the widely used Mellor‐Yamada model.
Internal waves in a small reservoir
Authors: Stevens Craig L.
Published: December 2003

Horizontally distributed temperature time series recorded in the thermocline of a small reservoir during autumn are used to identify both basin‐scale and higher‐frequency internal waves. Stationary and nonstationary spectral analyses are used to identify dominant frequencies. The horizontal distribution of data allows a map of the basin‐scale wave energy to be determined. Three‐layer normal mode modeling incorporating damping emulates the basin‐scale behavior well. This provides estimates of velocity shear and hence the internal stability. The nonstationary frequency analysis identifies times of high‐frequency internal wave activity (wave periods of ∼2–10 min). This is definitely linked to the basin‐scale wave‐driven shear and hence, to decreases in stability. Estimates of dissipation for the thermocline and hypolimnion are 3×10−8 and 6×10−9 m2 s−3, respectively. The inferred variability in the hypolimnetic value is demonstrated.
On the crossing of the equator by intermediate water masses in the western Atlantic ocean: Identification and pathways of Antarctic Intermediate Water and Upper Circumpolar Water
Authors: Oudot C. , Ternon J. F. , Andrié C. , Braga E. S. , Morin P.
Published: December 2003

The flow of intermediate water masses across the equator in the Atlantic Ocean is of fundamental interest in the context of the global meridional circulation cell associated with the formation of the North Atlantic Deep Water. This paper describes the flow and pathways of the Antarctic Intermediate Water (AAIW) and the Upper Circumpolar Water (UCPW) at between 500‐ and 1200‐m depths in the western equatorial Atlantic (5°S–7°30′N). These have been deduced from hydrological and geochemical tracer (nutrients and chlorofluorocarbons) data sets from CITHER 1 (R/V L'Atalante, January‐March 1993), ETAMBOT 1 (R/V Le Noroit, September‐October 1995), and ETAMBOT 2 (R/V Edwin Link, April‐May 1996) cruises. Both the AAIW and UCPW enter, on the isopycnals σθ = 27.25 (676±36 dbar) and σθ = 27.40 (919±35 dbar), respectively, the equatorial belt as narrow, northwestward flows around the northeast tip of Brazil near 5°S. During transit within this zone the core properties of UCPW erode more than those of AAIW. Flow patterns of both the water masses show westward spreading and eastward recirculations on either side of the equator. Temporal variations in spreading and recirculation occur at both levels, but they are more pronounced at the AAIW level, in agreement with earlier observations in the upper layers. At the northern boundary of the equatorial belt (7°30'N) the AAIW flows along the western boundary while the UCPW, instead, recirculates into the interior of the ocean.
Combining altimetry with a thermocline model to examine the transport of the North Atlantic
Authors: Williams Richard G. , Pennington Matthew
Published: December 2003

The relationship between sea surface height and transport is explored using a steady, geostrophic, thermocline model. Given an imposed sea surface height (SSH), analytical solutions reveal different patterns for the transport over the interior of a subtropical gyre determined by the background stratification. For no mixed layer or the limit of weak stratification, transport increases more rapidly westward than SSH across a subtropical gyre, whereas in the limit of strong stratification, transport increases linearly with SSH, and streamlines become more orientated from the northwest to southeast. A modified version of the thermocline model is applied to the subtropical gyre of the North Atlantic and uses SSH from TOPEX/Poseidon altimetry and a functional relationship between potential vorticity and density derived from the National Oceanographic Data Center climatology. The model suggests that the transport over the interior of the subtropical gyre reaches 30±13 Sv, which is broadly in accord with the independent Sverdrup estimate from the wind‐stress climatology. The transport pattern includes a north‐south asymmetry, which is consistent with both the mixed layer and background stratification influencing the solution.
Ocean color variability of the tropical Indo‐Pacific basin observed by SeaWiFS during 1997–1998
Authors: Murtugudde Ragu G. , Signorini Sergio R. , Christian James R. , Busalacchi Antonio J. , McClain Charles R. , Picaut Joel
Published: December 2003

High‐quality ocean color data (chlorophyll) provided by the Sea‐viewing Wide Field of view Sensor (SeaWiFS) satellite were analyzed for the first complete year of coverage (October 1997 to September 1998) in the tropical Indo‐Pacific basin. This period coincides with the peak of one of the strongest El Niño events during December 1997 and the La Niña of 1998 that appeared dramatically in less than a month as a sea surface temperature (SST) change of over 6°C in the central equatorial Pacific during June 1998. The tropical Indian Ocean also underwent a highly anomalous series of events with negative SST anomalies (SSTA) of over 3°C in the eastern equatorial and coastal regions during October‐December 1997 and warm SSTA in the west that peaked at over 2°C during February 1998. The ocean color variability is interpreted using other satellite data such as sea level from TOPEX/Poseidon and also in terms of the dynamics and thermodynamics of the region from simulations with an ocean general circulation model. The El Niño‐related reductions in equatorial production and the off‐equatorial increase in biological activity, and their basin scale evolution is clearly seen for the first time. Persistent northerly wind anomalies resulted in a northward shift of the equatorial divergence and the upwelling Kelvin wave which signalled the end of the 1997–1998 El Niño. The anomalous surface chlorophyll associated with this Kelvin wave was also clearly shifted north of the equator by nearly 300 km and appeared more than a month before the negative sea level anomalies seen by TOPEX/Poseidon. On the equator near 165°E, the disappearance of the barrier layer appeared to coincide with a localized bloom that occurred in response to the easterly wind bursts over the western Pacific that lasted from December 1997 through the boreal summer. The ecosystem response to the cold La Niña conditions is clearly seen as elevated chlorophyll during the boreal summer of 1998 in the equatorial Pacific cold tongue region. In the Indian Ocean, an anomalous phytoplankton bloom was observed by SeaWiFS during October‐December 1997 coincident with the anomalous upwelling in the eastern equatorial region and off the coast of Sumatra. A stronger than normal northeast monsoon is seen as higher than climatological values of surface chlorophyll. The open ocean Ekman pumping and the shoaling of the thermocline near 60°E and 10°S and the eastward extension of mixed layer entrainment in the same latitude band is seen as a region of higher biological activity during the boreal summer.
Velocity and transport of the Labrador Current determined from altimetric, hydrographic, and wind data
Authors: Han Guoqi , Tang C. L.
Published: December 2003

Seasonal change of velocity and transport in the Labrador Current is studied using 3.5 years of TOPEX/Poseidon altimeter data, in conjunction with concurrent wind data and climatological density data. A method based on the linearized momentum equation is developed, in which vertically averaged velocities and volume transports normal to selected sections across the Labrador Sea are computed with the sea surface being the level of known motion measured by the altimeter. The three data sources have significantly different temporal and spatial scales, and thus a smoothing technique has been applied to ensure their consistency. Error analyses are performed to estimate the uncertainty in altimetric measurements and geophysical corrections and in density data. The seasonal range of the Labrador Current transport from the 300‐m isobath seaward to the deepest ocean varies from 17 Sv at the Nain Section to 10 Sv at the Hamilton Section and 5 Sv at the northern Newfoundland Section, with a maximum in winter or fall and a minimum in spring. The barotropic effect associated with sea surface slope is most important over the shelf break and upper continental slope at the Nain and Hamilton Sections. At the northern Newfoundland Section the baroclinic effect associated with density gradients has a magnitude comparable with that of the barotropic effect. The largest baroclinic variability occurs offshore of the main density front over the lower continental slope of the Hamilton Section. The Ekman transport variability forced by local wind stress is negligible.
Structure and transports of the East Greenland Current at 75°N from moored current meters
Authors: Woodgate Rebecca A. , Fahrbach Eberhard , Rohardt Gerd
Published: December 2003

The East Greenland Current runs from 80°N to 60°N from the Fram Strait to the Denmark Strait via the Nordic Seas. It transports waters from the Arctic and the Nordic Seas into the Atlantic and also acts as a western‐intensified southward return flow for waters recirculating within the Greenland Sea Gyre, itself an area important for deep water formation. Data from current meters moored across the current at 75°N in 1994–1995 show a large seasonal variation in the current. The annual mean transport is 21±3 Sv (taking 9°W as the eastern boundary), varying from 11 Sv in summer to 37 Sv in winter (errors approximately ±5 Sv). No significant seasonal signal has been observed in the Fram or Denmark Straits, suggesting that the seasonal transport is confined within the Greenland Sea. Using temperature and velocity data, we split the flow at 75°N into two parts, a mainly wind‐driven circulation (annual mean of order 19 Sv), which is trapped within the Greenland Sea Gyre and exhibits a large seasonal cycle, transporting, predominantly, the waters of the Greenland Sea, and a steadier throughflow probably thermohaline‐driven (of order 8 Sv in the annual mean), with very little seasonal variation. Data from previous years, 1987–1994, indicate the interannual variability of the current is low. Assuming a spatially coherent structure to the current, we extend the time series of the transport back to 1991, and suggest it may be possible to monitor the total transport with one suitably placed mooring.
The world's most spectacular marine hydrocarbon seeps (Coal Oil Point, Santa Barbara Channel, California): Quantification of emissions
Authors: Hornafius J. Scott , Quigley Derek , Luyendyk Bruce P.
Published: December 2003

We used 50 kHz sonar data to estimate natural hydrocarbon emission rates from the 18 km2 marine seep field offshore from Coal Oil Point, Santa Barbara, California. The hydrocarbon gas emission rate is 1.7 ± 0.3 × 105 m3 d−1 (including gas captured by a subsea seep containment device) and the associated oil emission rate is 1.6 ± 0.2 × 104 Ld−1 (100 barrels d−1). The nonmethane hydrocarbon emission rate from the gas seepage is 35±7 td−1 and a large source of air pollution in Santa Barbara County. Our estimate is equal to twice the emission rate from all the on‐road vehicle traffic in the county. Our estimated methane emission rate for the Coal Oil Point seeps (80±12 td−1) is 4 times higher than previous estimates. The most intense areas of seepage correspond to structural culminations along anticlinal axes. Seep locations are mostly unchanged from those documented in 1946, 1953, and 1973. An exception is the seepage field that once existed near offshore oil platform Holly. A reduction in seepage within a 1 km radius around this offshore platform is correlated with reduced reservoir pressure beneath the natural seeps due to oil production. Our findings suggest that global emissions of methane from natural marine seepage have been underestimated and may be decreasing because of oil production.
Freshwater sources to the coastal ocean off northeastern North America: Evidence from H218O/H216O
Authors: Khatiwala Samar P. , Fairbanks Richard G. , Houghton Robert W.
Published: December 2003

Oxygen isotope (H218O/H216O)/salinity data identify freshwater sources along the northeastern North American continental margin. The oxygen isotope (δ18O)‐salinity (S) properties of various water types are distinguished. Sea ice formation on the Labrador Shelf is shown to influence δ18O‐S values. It is estimated that 2–3 m of freshwater is extracted from the water column to form sea ice. It is hypothesized that waters on the Scotian Shelf, Gulf of Maine, and the Middle Atlantic Bight are composed of slope water diluted by an upstream low‐salinity source. This upstream source is a mixture of brine‐enriched Labrador Shelf Water and St. Lawrence River water. The δ18O value of the apparent freshwater component (δ18OS=0) of waters on the Scotian Shelf and farther south is ≈−20‰, which has been used to suggest a sole high‐latitude freshwater source. We show instead that the St. Lawrence River contributes ≈35% of the freshwater on the Scotian Shelf, in agreement with the physical oceanographic evidence. The remaining freshwater is supplied by high‐latitude rivers dominated by Arctic runoff. Finally, the isotope evidence identifies Baffin Bay as an important pathway by which freshwater from the Arctic Ocean can reach the Labrador Sea.
Sediment‐induced slope convection: Two‐dimensional numerical case studies
Authors: Kämpf Jochen , Backhaus Jan O. , Fohrmann Hermann
Published: December 2003

The potential role of sediment in oceanic slope convection is examined by means of a rotational numerical model applied in a vertical ocean slice. The model couples the hydrodynamics with transport, settling, deposition, and resuspension of fine‐grained silty muds. Sediment plumes (turbidity currents), descending on an idealized continental slope with constant bottom slope, are driven from an initial density anomaly caused by an assumed suspension of sediment in shelf water. A number of case studies were conducted in order to understand the effects of (1) different suspended sediment concentrations in shelf water as compared to an equivalent salinity anomaly (salt brine release), (2) different oceanic density stratifications, and (3) resuspension of bed sediment. It is demonstrated that sediment plumes may account for a downslope transport of water, which, once void of its sediment load, becomes lighter than water above. Then, sedimentation along the slope, with a maximum adjacent to the foot of the slope, drives vigorous upward convection (parameterized in the model), stirring slope water over a depth range of several hundred meters. This is in agreement with field observations from a tropical ocean. Detrainment associated with sediment settling constitutes an important mechanism inherent in sediment plumes. It not only induces upward convection but also prevents the rapid increase in plume thickness caused by entrainment as compared to “water mass plumes.” Owing to a balance between entrainment and detrainment, the sediment plume, while descending on the slope, attains constant height and bed shear velocities. In order to facilitate the detection of sediment plumes in (historical or future) field data, we describe their simulated traces in terms of water mass properties and flow anomalies.
Impact of mesoscale ocean currents on sea ice in high‐resolution Arctic ice and ocean simulations
Authors: Zhang Yuxia , Maslowski Wieslaw , Semtner Albert J.
Published: December 2003

A high‐resolution sea ice model is designed for simulating the Arctic. The grid resolution is ∼18 km, and the domain contains the main Arctic Ocean, Nordic Seas, Canadian Archipelago, and the subpolar North Atlantic. The model is based on a widely used dynamic and thermodynamic model with more efficient numerics. The oceanic forcing is from an Arctic Ocean model with the same horizontal resolution as the ice model and 30 levels. The atmospheric forcing is from 3‐day average 1990–1994 European Centre for Medium‐Range Weather Forecasts operational data. Results from the ice model are compared against satellite passive‐microwave observations and drifting buoys. The model realistically simulates ice tongues and eddies in the Greenland Sea. The mesoscale ocean eddies along the East Greenland Current (EGC) are demonstrated to be responsible for the presence of ice eddies and tongues out of the Greenland Sea ice edge. Large shear and divergence associated with the mesoscale ice eddies and strong ice drift, such as the one above the EGC, result in thinner and less compact ice. The mesoscale ocean eddies along the Alaskan Chukchi shelf break, the Northwind Ridge, and the Alpha‐Mendeleyev Ridge are major contributors to mesoscale reduction of ice concentration, in addition to atmospheric storms which usually lead to a broad‐scale reduction of ice concentration. The existence of mesoscale ocean eddies greatly increases nonuniformity of ice motion, which means stronger ice deformation and more open water. An eddy‐resolving coupled ice‐ocean model is highly recommended to adequately simulate the small but important percentage of open water in the Arctic pack ice, which can significantly change the heat fluxes from ocean to atmosphere and affect the global climate.
Surface fluxes from satellite winds: Modeling air‐sea flux enhancement from spatial and temporal observations
Authors: Levy Gad , Vickers Dean
Published: December 2003

Scatterometer and buoy observations are collocated at different locations spanning a range of climatic regimes in order to (1) develop a spatiotemporal conversion method that allows synergistic use of satellite and in situ data to estimate flux enhancement due to unresolved wind variability, and (2) formulate a resolution‐dependent velocity‐scale term to incorporate in bulk formulas. The scales found in point 1 above rarely agree with advective scales and are considered as the proper averaging scales for calibration of satellite spatially averaged observations against temporal averages. The flux underestimation due to unresolved directional variability in NASA scatterometer (NSCAT) data varies by region, wind regime, and local conditions. It is most important in the Atlantic due to larger subgrid variability and favorable thermodynamic conditions. It is slightly less important in the Gulf of Mexico locations that experience favorable thermodynamic conditions and more light wind cases but smaller subgrid variability for a given light wind value. Even when small, the flux underestimation of the 50‐km NSCAT data represents a systematic error for which a simple correction exists. A general velocity‐scale formulation for typical model scales is developed based on NSCAT observations. It is consistent with studies that used aircraft flux observations. For typical general circulation model scales of 250 km, the associated heat flux enhancement is as much as 10, 23, and 40 W m−2 for strong, midrange, and light wind regimes, respectively. By inserting a simple velocity‐scale formulation into the bulk aerodynamic relationship, a modeler can effectively account for most of the flux underestimation.
Basin‐scale surface water and energy budgets for the Mississippi from the ECMWF reanalysis
Authors: Betts Alan K. , Ball John H. , Viterbo Pedro
Published: December 2003

This paper compares with observations the energy and water budgets for the subbasins of the Mississippi (the Arkansas‐Red, the upper Missouri, the upper Mississippi, the Ohio, and the lower Mississippi and Tennessee Rivers), which were computed on‐line with an hourly time scale from the European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis from 1985 to 1993. The model has a significant precipitation spin‐up between the analysis cycle and the 12–24 hour forecast, ranging from 24% to about 40% for the drier Missouri basin. The spin‐up of the model “large‐scale” precipitation ranges from 30 to 50%, roughly double that of the spin‐up of the model “convective” precipitation. The model has an erroneous peak in convective precipitation near local noon, but on 2 day and monthly timescales, the 12–24 hour forecast precipitation is only 10 to 20% higher than the observed precipitation for most of the subbasins. The model runoff, which is all deep runoff from the base soil layer, is low on an annual basis, primarily because the model has very little Spring runoff. The nudging of soil water in the analysis cycle, based on 0–6 hour forecast errors in low‐level humidity, plays a major role in the model liquid hydrology. The nudging term has a large annual cycle, positive in summer and negative in winter. Although nudging prevents the downward interannual drift of soil water, associated with a shortfall of precipitation in the analysis cycle, it also attempts to compensate for other errors in the model, such as errors in the seasonal cycle of evaporation and runoff, and may damp the variability of soil water. The model frozen hydrology in winter is not conservative and snowmelt is probably too small. Overall, the ECMWF reanalysis gives a valuable description of the surface energy and water balance of the Mississippi River subbasins on timescales longer than the diurnal, and at the same time, it is clear that improvements in the model physics are needed.
Optimal design of surface networks for observation of soil moisture
Authors: Vinnikov Konstantin Y. , Robock Alan , Qiu Shuang , Entin Jared K.
Published: December 2003

By analyzing in situ soil moisture data, we show that soil moisture variability consists of two components, one of which is related to large‐scale atmospheric forcing, and the other related to small‐scale land surface variability and hydrologic processes. We use empirically estimated spatial autocorrelation functions for Illinois to estimate errors of spatial averaging of soil moisture observations, using the method of statistically optimal averaging of meteorological fields. The estimated dependence of the root‐mean‐square errors of averaging on the soil moisture station network density can be used to analyze existing observational networks and for designing new ones. For the application of providing information on a regular grid for numerical models of weather and climate, we show that the new, relatively high density networks of soil moisture observations in Oklahoma, may not provide estimates with very much more accuracy than the relatively low density currently operational network in Illinois. This prediction must be tested when we receive sufficiently long time series of observations from Oklahoma.
Aspects of soil moisture variability in the Washita '92 study region
Authors: Cosh Michael H. , Brutsaert Wilfried
Published: December 2003

The Washita '92 experiment, which took place in the Little Washita River watershed in Oklahoma, generated maps describing the volumetric surface soil moisture field during an 8‐day drying period. The Little Washita is part of the Red River basin, a major tributary of the Lower Mississippi. A semivariogram analysis revealed that the surface soil moisture field of this 18 km × 25 km study region as a whole was spatially nonstationary and exhibited certain fractal characteristics. However, for smaller subareas within the study region, it was determined that the moisture field could be considered stationary for distances smaller than 5 km, with ranges of approximately 1 km over which surface soil moisture was spatially correlated. A semivariogram analysis for each of the individual soil types over the entire Washita '92 region revealed that surface soil moisture was stationary within each soil type, again with a range of correlation of approximately 1 km. This indicates that soil moisture variability is strongly affected by soil type.
A coarse grid three‐dimensional global inverse model of the atmospheric transport: 2. Inversion of the transport of CO2 in the 1980s
Authors: Kaminski Thomas , Heimann Martin , Giering Ralf
Published: December 2003

Models of atmospheric transport can be used to interpret spatiotemporal differences in the observed concentrations of CO2 in terms of its surface exchange fluxes. Inversion of the atmospheric transport is the systematic search for both a flux field that yields an optimal match between modeled and observed concentrations and, equally importantly, the uncertainties in this inferred flux field. The present inversion study combines observations of the CO2 concentration at the global station network of the NOAA/CMDL in the 1980s with a representation of the atmospheric transport model TM2 by its Jacobian matrix, which has been previously computed by the adjoint model of TM2. This Jacobian matrix maps monthly fluxes on the approximately 8° latitude by 10° longitude horizontal model grid onto the resulting changes in the monthly CO2 concentration at every station. Since the number of observational sites is much smaller than the number of grid cells, the inverse problem is highly underdetermined. A unique solution is determined by including a priori information on the surface exchange fluxes derived from output of high‐resolution models of both the terrestrial biosphere and the ocean, combined with statistics of fossil fuel burning and land use change. Performing a Bayesian synthesis inversion, for a target period in the 1980s, the average seasonal cycle and the mean annual magnitude of CO2 surface fluxes on the TM2 grid are inferred. The resulting simulated concentration compares well with independent observations. On a global scale, an oceanic sink of 1.5±0.4 gigatons of carbon (GtC) is estimated. This sink is stronger in the northern than in the southern hemisphere. On a regional scale, however, the inferred exchange fluxes exhibit high uncertainty, indicating a low capacity of the global observational network to monitor regional trace gas emissions. These findings are relatively insensitive to the year of meteorological driving data, suggesting interannual changes in concentration should primarily result from source not transport changes.
A coarse grid three‐dimensional global inverse model of the atmospheric transport: 1. Adjoint model and Jacobian matrix
Authors: Kaminski Thomas , Heimann Martin , Giering Ralf
Published: December 2003

TM2 is a global three‐dimensional model of the atmospheric transport of passive tracers. The adjoint of TM2 is a model that allows the efficient evaluation of derivatives of the simulated tracer concentration at observational locations with respect to the tracer's sources and sinks. We describe the generation of the adjoint model by applying the Tangent linear and Adjoint Model Compiler in the reverse mode of automatic differentiation to the code of TM2. Using CO2 as an example of a chemically inert tracer, the simulated concentration at observational locations is linear in the surface exchange fluxes, and thus the transport can be represented by the model's Jacobian matrix. In many current inverse modeling studies, such a matrix has been computed by multiple runs of a transport model for a set of prescribed surface flux patterns. The computational cost has been proportional to the number of patterns. In contrast, for differentiation in reverse mode, the cost is independent of the number of flux components. Hence, by a single run of the adjoint model, the Jacobian for the approximately 8° latitude by 10° longitude horizontal resolution of TM2 could be computed efficiently. We quantify this efficiency by comparison with the conventional forward modeling approach. For some prominent observational sites, we present visualizations of the Jacobian matrix by series of illustrative global maps quantifying the impact of potential emissions on the concentration in particular months. Furthermore, we demonstrate how the Jacobian matrix is employed to completely analyze a transport model run: A simulated monthly mean value at a particular station is decomposed into the contributions to this value by all flux components, i.e., the fluxes into every surface model grid cell and month. This technique also results in a series of global maps.
Sensitivity analysis of a land surface scheme using multicriteria methods
Authors: Bastidas L. A. , Gupta H. V. , Sorooshian S. , Shuttleworth W. J. , Yang Z. L.
Published: December 2003

Attempts to model surface‐atmosphere interactions with greater physical realism have resulted in complex land surface schemes (LSS) with large numbers of parameters. A companion paper describes a multicriteria calibration procedure for extracting plot‐scale estimates of the preferred ranges of these parameters from the various observational data sets that are now available. A complementary procedure is presented in this paper that provides an objective determination of the multicriteria sensitivity of the modeled variables to the parameters, thereby allowing the number of calibration parameters and hence the computational effort to be reduced. Two case studies are reported for the BATS model using data sets of typical quality but very different location and climatological regime (ARM‐CART and Tucson). The sensitivity results were found to be consistent with the physical properties of the different environments, thereby supporting the reasonableness of the model formulation. Further, when the insensitive parameters are omitted from the calibration process, there is little degradation in the quality of the model description and little change in the preferred range of the remaining parameters.
Flux estimation of oceanic dimethyl sulfide around North America
Authors: Sharma S. , Barrie L. A. , Plummer D. , McConnell J. C. , Brickell P. C. , Levasseur M. , Gosselin M. , Bates T. S.
Published: December 2003

Simultaneous measurements of atmospheric and surface water dimethyl sulfide (DMS) concentrations were taken aboard the icebreaker USCGC Polar Sea from July to October 1994, as part of a joint Canada/United States circumnavigation of North America, an expedition with a unique Arctic Ocean transect. Atmospheric DMS concentrations around North America varied between 0.25 and 50 nmol m−3 (mean = 5.1 nmol m−3, σ = 8.5 nmol m−3, n = 89) with highest values occurring near (south of) the Arctic ice edge. Surface water DMS concentrations ranged between 0.1 and 12.6 nmol L−1 (mean = 2.2 nmol L−1, σ = 2.7 nmol L−1, n = 46) with highest values in the western Arctic Ocean and off the U.S. east coast, near the Sargasso sea. In the Arctic Ocean, maximum concentrations in air and water were found along the ice edge in the Chukchi Sea region. Atmospheric DMS decay rates of 68% per day and 38% per day were deduced from observations between 70° and 76°N (continental shelf and slope of Chukchi Sea) on the west side and between 80° and 90°N (central Arctic Ocean) for the east side of the Arctic Ocean, respectively. Ocean to atmosphere flux estimates of DMS were determined using the Liss‐Merlivat empirical dependence of exchange coefficient on wind speed, DMS air concentrations, Henry's law constants, and DMS water concentrations. DMS fluxes varied between 0.0017 and 30 μmol m−2 d−1, respectively, with higher fluxes in regions with open water. The Arctic Ocean contributed 0.063 Tg S (DMS) (0.4% of DMS from the world oceans) during the summer of 1994. A simple one‐dimensional (1‐D) photochemical box model, applied to six case studies, showed that the atmospheric lifetime of DMS in the high Arctic was 2.5 to 8 days, whereas at 16°–33°N it was 1 to 2 days. Modeled DMS decay rates for these regions, using the 1‐D model, accounted for only 33% of the measured decay rate. This result also suggests that halogen chemistry, reactions with Br/BrO, may be an important sink for DMS in the Arctic atmosphere.
Evaluation of transport in stratospheric models
Authors: Hall Timothy M. , Waugh Darryn W. , Boering Kristie A. , Plumb R. Alan
Published: December 2003

We evaluate transport characteristics of two‐ and three‐dimensional chemical transport models of the stratosphere by comparing their simulations of the mean age of stratospheric air and the propagation of annually periodic oscillations in tracer mixing ratio at the tropical tropopause into the stratosphere to inferences from in situ and satellite observations of CO2, SF6, and water vapor. The models, participants in the recent NASA “Models and Measurements II” study, display a wide range of performance. Most models propagate annual oscillations too rapidly in the vertical and overattenuate the signal. Most models also significantly underestimate mean age throughout the stratosphere, and most have at least one of several unrealistic features in their mean age contour shapes. In the lower stratosphere, model‐to‐model variation in N2O, NOy, and Cly is well correlated with variation in mean age, and the magnitude of NOy and Cly variation is large. We conclude that model transport inaccuracies significantly affect simulations of important long‐lived chemical species in the lower stratosphere.
The Polar Ozone and Aerosol Measurement (POAM) III instrument and early validation results
Authors: Lucke R. L. , Korwan D. R. , Bevilacqua R. M. , Hornstein J. S. , Shettle E. P. , Chen D. T. , Daehler M. , Lumpe J. D. , Fromm M. D. , Debrestian D. , Neff B. , Squire M. , König‐Langlo G. , Davies J.
Published: December 2003

Polar Ozone and Aerosol Measurement (POAM) III, a follow‐on to the successful POAM II, is a spaceborne experiment designed to measure the vertical profiles of ozone, water vapor, nitrogen dioxide, and aerosol extinction in the polar stratosphere and upper troposphere with a vertical resolution of 1–2 km. Measurements are made by the solar occultation technique. POAM III, now in polar orbit aboard the SPOT 4 satellite, is providing data on north‐ and south‐polar ozone phenomena, including the south‐polar ozone hole, and on the spatial and temporal variability of stratospheric aerosols, polar stratospheric clouds, and polar mesospheric clouds. Differences between the POAM III and POAM II instruments are described. First validations of POAM III data products by comparison with Halogen Occultation Experiment and ozonesonde data are presented.
Diurnal and nocturnal distribution of stratospheric NO2 from solar and stellar occultation measurements in the Arctic vortex: Comparison with models and ILAS satellite measurements
Authors: Payan S. , Camy‐Peyret C. , Jeseck P. , Hawat T. , Pirre M. , Renard J.‐B. , Robert C. , Lefèvre F. , Kanzawa H. , Sasano Y.
Published: December 2003

NO2 mixing ratio profiles were measured at sunset between 14 and 30 km using the Limb Profile Monitor of the Atmosphere (LPMA) experiment and during the night between 13 and 31 km using the Absorption par Minoritaires Ozone et NOx (AMON) experiment inside the Arctic vortex, both on February 26, 1997. Coinciding profiles measured by the Improved Limb Atmospheric Spectrometer (ILAS) instrument on board ADEOS have been used to check the consistency between the satellite and balloon profiles for NO2, O3, and HNO3. A box model has been used for the photochemical correction of the LPMA NO2 profiles at sunset. The resulting NO2 balloon‐borne profiles of LPMA and AMON are compared to each other after accounting for the day/night photochemical variation using the box model initialized with measurements. The comparisons thus performed show an average difference less than 9% between the two measurements (considered to sample similar air masses) when the box model is initialized with little chlorine activation (i.e., when the major burden of chlorine is stored in ClONO2) for a 1 day integration. The comparison with the Reprobus 3‐D chemistry transport model (CTM) seasonal simulations clearly confirms an underestimation of NO2 by the model below 25 km, in the altitude range where aerosols lead to a complete removal of NOx in the model. Recent updates of rate coefficients for conversion of HNO3 into NO2 only slightly improve the NO2 model results in vortex conditions. These results suggest that a source of NO2 is still lacking in the CTM.
A 3‐year continuous record of nitrogen trace gas fluxes from untreated and limed soil of a N‐saturated spruce and beech forest ecosystem in Germany: 1. N2O emissions
Authors: Papen Hans , Butterbach‐Bahl Klaus
Published: December 2003

For 3 years we followed the complete annual cycles of N2O emission rates with 2‐hour resolution in spruce and beech plantations of the Höglwald Forest, Bavaria, Germany, in order to gain detailed information about seasonal and interannual variations of N2O emissions. In addition, microbiological process studies were performed for identification of differences in N turnover rates in the soil of a spruce and a beech site and for estimation of the contribution of nitrification and denitrification to the actual N2O emission. Both pronounced seasonal and extreme interannual variations of N2O emissions were identified. During long‐term frost periods, while the soil was frozen, and during soil thawing, extremely high N2O emissions occurred, contributing up to 73% to the total annual N2O loss. The enormous N2O releases during the long‐term frost period were due to high microbial N turnover rates (tight coupling of ammonification, nitrification, denitrification) in small unfrozen water films of the frozen soil at high concentrations of easily degradable substrates derived from the enormous pool of dead microbial biomass produced during the long‐term frost period. Liming of a spruce site resulted in a significant increase in ammonification, nitrification, and N2O emissions as compared with an untreated spruce control site. The beech control site exhibited 4–5 times higher N2O emissions than the spruce control site, indicating that forest type itself is an important modulator of N2O release from soil. At all sites, nitrification contributed ∼70% to the N2O flux, whereas denitrification contributed markedly less (∼30%). There was a significant positive correlation between amount of in situ N input by wet deposition and magnitude of in situ N2O emissions. At the beech site, 10% of the actual N input was released from the soil in form of N2O, whereas at the spruce site the fraction was 0.5%. N2O emission rates were positively correlated with net nitrification rates. The results demonstrate the need for long‐term measurements over several years for more precise estimates of annual N2O losses from forest ecosystems. On the basis of our results we conclude that the importance of temperate and boreal forests for the global N2O source strength may have been significantly underestimated in the past and that these forests contribute most likely ≫1.0 Tg N2O N.
Analysis of δ18O in tree rings: Wood‐cellulose comparison and method dependent sensitivity
Authors: Borella Silvio , Leuenberger Markus , Saurer Matthias
Published: December 2003

During recent years, new on‐line methods in mass spectrometry have been developed for measuring δ18O in organic material. They allow a much higher sample throughput than off‐line methods with the result that sample preparation becomes the time‐limiting factor. Therefore we tested whether analysis of tree ring samples can be made on whole wood instead of pure cellulose, which until now was commonly used in almost all 18O tree ring studies. Measurements with an on‐line method based on pyrolysis in an elemental analyzer show that the tree ring δ18O time series of wood and cellulose from an oak of the Swiss “Mittelland” are similar (r2 = 0.65). However, there are significant differences, and some climatic information may be lost if bulk wood is analyzed instead of cellulose. This can partly be balanced by an increased sample throughput, resulting in the averaging of more data. Further, we improved an off‐line method (pyrolysis in a nickel tube followed by catalytic CO to CO2 conversion on nickel powder) by adding a CO2 trap to enhance the CO to CO2 conversion. The best reproducibility associated with this method is better than 0.1‰. We also found a strong memory effect linked with this method, causing a dampening of the signal of 30–40%. Therefore published climatic interpretation of δ18O data measured using similar methods may require revision.