bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of coastal nutrient supply for global ocean biogeochemistry
Authors: Giraud Xavier , Le Quéré Corinne , da Cunha Leticia C.
Published: June 2008

The coastal ocean provides nutrients to the open ocean in accounts that are poorly quantified. We use an ocean biogeochemistry model to assess the importance of the coastal nutrient supply to global ocean biogeochemistry. The model includes full cycles of P, Si, and Fe, as well as the representation of two phytoplankton groups, two zooplankton groups, and two organic detritus pools. When coastal mixing is enhanced to reproduce the action of tides and storms, primary production and chlorophyll‐a (Chla) concentrations show a large increase at the coast and a smaller increase in the open ocean. When coastal nutrient supply is enhanced to reproduce sediment resuspension or river supply, both the coastal ocean and the open ocean primary production and Chla concentration increase in comparable amounts. In agreement with the definition of nutrient limitation areas in the model, coastal export of P‐excess impacts mainly the subtropical oligotrophic areas, Si‐excess impacts the Arctic Ocean and some coastal areas, and Fe‐excess impacts the east equatorial Pacific, North Atlantic and North Pacific, and the Southern Ocean. Modeled Chla is closest to observations when the input ratio of Fe to P and Si is enhanced.
The seasonal circulation and volume transport on the northwest European continental shelf: A fine‐resolution model study
Authors: Holt Jason , Proctor Roger
Published: June 2008

In this paper the circulation of the northwest European continental shelf is investigated using the first year‐long density‐evolving simulation at shelf wide scales and sub‐Rossby Radius resolution (∼1.8 km). A series of numerical experiments are conducted to distinguish between the wind‐, density‐, and oceanic‐driven components of the flow. These demonstrate that, while all components have a role throughout the year, the density‐driven component is particularly important during the summer and autumn months. The time evolution of the density field makes a significant contribution to the seasonal variation of volume transport on shelf wide scales and is persistent in direction; whereas the wind‐driven volume transport acts on much shorter timescales and is more variable in direction. The importance of the oceanic forcing is demonstrated, representing tidal residuals and large‐scale oceanic sea level (pressure) variation; this forcing drives a substantial component of the circulation throughout the year. Twenty six satellite tracked drifters deployed in the summer of 2001 are used for a direct validation of the model currents. The model current speeds are found to be accurate to ∼46% when averaged over ∼40 d, but tend to be too slow. The summer volume fluxes are compared with estimates in the literature showing good agreement, although there is a suggestion that the North Sea inflows are overestimated. Comparisons with the coarser resolution model used for boundary conditions demonstrate the importance of fine‐resolution to the details of the frontal currents with consequences for modeling exchange processes and biological activity in these regions.
Determinants influencing seasonal variations of methane emissions from alpine wetlands in Zoige Plateau and their implications
Authors: Chen Huai , Yao Shouping , Wu Ning , Wang Yanfen , Luo Peng , Tian Jianqing , Gao Yongheng , Sun Geng
Published: June 2008

To understand the seasonality of methane flux from alpine wetlands in Zoige Plateau, 30 plots were set to measure the methane emissions in the growing and nongrowing seasons in three environmental types: dry hummock (DH), Carex muliensis (CM), and Eleocharis valleculosa (EV) sites. There were clearly seasonal patterns of methane flux in different environmental types in the growing and nongrowing seasons. Mean methane emission rate was 14.45 mg CH4 m−2 h−1 (0.17 to 86.78 mg CH4 m−2 h−1) in the growing season, and 0.556 mg CH4 m−2 h−1 (0.002 to 6.722 mg CH4 m−2 h−1) in the nongrowing season. In the growing season, the main maximum values of methane flux were found in July and August, except for a peak value in September in CM sites. In the nongrowing season, the similar seasonal variation pattern was shared among all the three sites, in which the methane emissions increased from February to April. In the growing season, the determining factors were surface temperatures (r2 = 0.55, P < 0.05), standing water depths (r2 = 0.32, P < 0.01) and plant community heights (r2 = 0.61, P < 0.01), while in the nongrowing season, ice thickness (r2 = 0.27, P < 0.05; in CM and EV sites) was found most related to flux. In our understanding, the seasonality of methane emissions in our study areas was temperature‐ and‐plant‐growth‐dependent, and the water table position was also very important to shape the temperature‐and‐plant‐growth‐dependent seasonal variation of flux with its vigorous variations in alpine wetland ecosystems. Different environmental types within the wetland also influenced the seasonal pattern of methane flux. For an accurate estimate of the global methane source strength of alpine wetlands, the pronounced seasonal or even temporal variability in methane emission from alpine wetlands should be taken into consideration.
Estimation of large‐scale evaporation fields based on assimilation of remotely sensed land temperature
Authors: Sini F. , Boni G. , Caparrini F. , Entekhabi D.
Published: June 2008

Many Earth system science and environmental applications require knowledge of mapped evaporation. Satellite remote sensing can indirectly provide these measurements with a spatial coverage that is logistically and economically impossible to obtain through ground‐based observation networks. Here a model for surface energy fluxes estimation based on the assimilation of land surface temperature from satellite is presented. The data assimilation scheme provides a useful framework that allows us to combine measurements and models to produce an optimal and dynamically consistent estimate of the evolving state of the system. The assimilation scheme can take advantage of the synergy of multisensor‐multiplatform observations in order to obtain estimations of surface fluxes, flux partitioning, and surface characteristics. The model is based on the surface energy balance and bulk transfer formulation. A simplified soil wetness model, which is a filter of antecedent precipitation, is introduced in order to develop a more robust estimation scheme. This approach is implemented and tested over the Southern Great Plain field experiment domain. Comparisons with observed surface energy fluxes and soil moisture maps have shown that this assimilation system can estimate, when compared with the ground truth observations, the surface energy balance and its partitioning among turbulent heat fluxes. The introduction of the simplified soil wetness model forced by precipitation data improved evaporative fraction estimation. Further research is still required to analyze the reliability of retrieved fluxes in periods where radiation is the limiting factor for latent heat flux.
New airborne laser altimetry over the Thwaites Glacier catchment, West Antarctica
Authors: Young Duncan A. , Kempf Scott D. , Blankenship Donald D. , Holt John W. , Morse David L.
Published: June 2008

A new airborne altimetry data set collected over Thwaites Glacier, one of Antarctica's most active ice streams, demonstrates the improvement in publicly available digital elevation models (DEMs) of the Antarctic ice sheet. The airborne altimetry comprises 35,000 line km sampled at 20 m along track. The full data set has a relative error of ±20 cm; a reference subset has an error of ±8 cm. These data are offset from ICESat observations by +20 cm. We find that a recently released ICESat DEM provides a good model of the surface of Thwaites Glacier, despite cloud cover and wide track spacings. However, the ICESat DEM's accuracy is an order of magnitude less than that of the ICESat profile data. Our airborne data will serve as an additional temporal reference for the evolution of Thwaites Glacier's surface as well as aid the construction of future high‐resolution DEMs.
Latitude and local time dependence of ULF wave power at the magnetopause: A Cluster–Double Star study
Authors: Cornilleau‐Wehrlin N. , Grison B. , Attié D. , Belmont G. , Rezeau L. , Robert P. , Alleyne H. St. C. , Yearby K. , Lucek E. , Carr C.
Published: June 2008

Strong ULF wave activity has been observed at magnetopause crossings over a long time. Those turbulent like waves are possibly one of the contributors to particle penetration from the solar wind to the magnetosphere through the magnetopause. Spatio Temporal Analysis of Field Fluctuations wave experiments onboard Cluster and Double Star TC1 spacecraft permit the comparison of those waves during quasi‐simultaneous magnetopause crossings, some being at the same local time but at different latitude, the TC1 Double Star orbit being nearly equatorial and the Cluster orbit being polar. From a survey of the first half of year 2004 and beginning of 2005 data, 23 coordinated magnetopause crossings have been identified, out of which 11 are at the same local time, for which the wave power density has been calculated. No clear dependence in local time has been found; in particular, the wave power density is not stronger at noon in the vicinity of the subsolar point than at other local times, the morning hour data showing more dispersed values than afternoon ones. For most of the events occurring at the same local time, the wave power density measured by Double Star (at low latitude) is stronger than the one measured by the Cluster spacecraft (at much higher latitude). If those first results were to be confirmed, it could imply a predominant role of the equatorial plane in the solar wind/ magnetosphere coupling via ULF wave turbulence, with no preference for the subsolar region.
Nonlinear evolution of the jet‐flow‐associated Kelvin‐Helmholtz instability in MHD plasmas and the formation of Mach‐cone‐like plane waves
Authors: Lai S. H. , Lyu L. H.
Published: June 2008

Kelvin‐Helmholtz (K‐H) instability triggered by a jet flow along a magnetohydrodynamic (MHD) tangential discontinuity (TD) is studied by means of the two‐dimensional MHD simulations. In addition to the vortex structures and the undulant surface waves, we also found fast‐mode and slow‐mode Mach‐cone‐like plane waves at the saturation stage of the jet‐flow‐associated K‐H instabilities. Fast‐mode Mach‐cone‐like plane waves are launched in pairs from the ridges of the surface waves when the fast‐mode Mach numbers of the surface waves on both sides of the jet flow are greater than one. Slow‐mode Mach‐cone‐like plane waves are found for the first time in a limited range of MSL0y, θ0, and β0, where MSL0y is the slow‐mode Mach number of the surface disturbances observed in the ambient plasma rest frame, θ0 is the angle between the surface wave propagation direction and the direction of the ambient magnetic field, and β0 is the plasma β of the ambient plasma. The flaring angle of the fast‐mode Mach‐cone‐like plane wave is less than or equal to 90°, but the flaring angle of the slow‐mode Mach‐cone‐like plane wave is greater than or equal to 90°. A theoretical model is proposed to explain the formation and the characteristics of the slow‐mode Mach‐cone‐like plane waves. The flaring angles of the slow‐mode Mach‐cone‐like plane waves measured from the simulation results are in good agreement with the flaring angles predicted by the theoretical model. Applications of our results to the observations in the space plasma are discussed.
Model/data comparisons of ionospheric outflow as a function of invariant latitude and magnetic local time
Authors: Winglee R. M. , Peterson W. K. , Yau A. W. , Harnett E. , Stickle A.
Published: June 2008

Globally quantifying ionospheric outflows as a function of local time, invariant latitude and solar wind conditions is the key to determining the mass loading of the magnetosphere, and it subsequent dynamics. This paper provides a first comparison of model predicted outflows with Polar and Akebono outflow measurements for a quiet period that occurred on 18 March 1997. It is shown that that the model is able to account for the H+ fluxes observed on the dayside by Akebono with fluxes of the order of several times 109 ions/cm2/s. H+ fluxes observed by Polar in the midnight auroral zone are lower by an order of magnitude than the model fluxes. The difference is attributed to the presence of a lower energy component below the low energy cutoff of TIMAS. During the geomagnetically quiet conditions considered here, the model underestimates the O+ flux seen by Akebono on the dayside. The model correctly predicts the energetic fluxes of O+ seen on the nightside by Polar at several 107 ions/cm2/s. This calibration of the outflow model predicts the following magnetospheric features: (1) the dayside ionospheric outflows leads to substantial (≳10 cm−3) densities of cold plasma in the vicinity of the magnetopause, particularly on the dusk side during periods of enhanced convection; (2) the composition of the magnetosphere can change over the course of very small IMF changes (±1–2 nT in the present study) with northerly turnings allowing solar wind entry via the low latitude boundary layer, while pressure pulses aid high latitude entry across a magnetopause that is otherwise dominated by ionospheric plasma on the earthward side of the magnetopause; and (3) the calculated changes in the ionospheric outflow rate are sufficiently large that composition of the magnetosphere can change from one that is predominantly ionospheric in origin to one that is primarily of solar wind origin for changes in the IMF as small as ±1 nT.
Combined EISCAT radar and optical multispectral and tomographic observations of black aurora
Authors: Gustavsson B. , Kosch M. J. , Senior A. , Kavanagh A. J. , Brändström B. U. E. , Blixt E. M.
Published: June 2008

Black auroras are recognized as spatially well‐defined regions within a uniform diffuse auroral background where the optical emission is significantly reduced. Black auroras typically appear post‐magnetic midnight and during the substorm recovery phase, but not exclusively so. We report on the first combined multimonochromatic optical imaging, bistatic white‐light TV recordings and incoherent scatter radar observations of black aurora by EISCAT of the phenomenon. From the relatively larger reduction in luminosity at 4278 Å than at 8446 Å we show that nonsheared black auroras are most probably not caused by downward directed electrical fields at low altitude. From the observations, we determine this by relating the height and intensity of the black aurora to precipitating particle energy within the surrounding background diffuse aurora. The observations are more consistent with an energy selective loss cone. Hence the mechanism causing black aurora is most probably active in the magnetosphere rather than close to Earth.
Effect of a compliant fault zone on the inferred earthquake slip distribution
Authors: Barbot Sylvain , Fialko Yuri , Sandwell Dave
Published: June 2008

We present a new semi‐analytic method to evaluate the deformation due to a screw dislocation in arbitrarily heterogeneous and/or anisotropic elastic half plane. The method employs integral transformations to reduce the governing partial differential equations to the integral Fredholm equation of the second kind. Dislocation sources, as well as spatial perturbations in the elastic properties are modeled using equivalent body forces. The solution to the Fredholm equation is obtained in the Fourier domain using a method of successive over‐relaxation, and is mapped into the spatial domain using the inverse Fast Fourier Transform. We apply this method to investigate the effect of a soft damage zone around an earthquake fault on the co‐seismic displacement field, and on the earthquake slip distribution inferred from inversions of geodetic data. In the presence of a kilometer‐wide damage zone with a reduction of the effective shear modulus of a factor of 2, inversions that assume a laterally homogeneous model tend to underestimate the amount of slip in the middle of the seismogenic layer by as much as 20%. This bias may accentuate the inferred maxima in the seismic moment release at depth between 3–6 km suggested by previous studies of large strike‐slip earthquakes.
On the patterns of wing cracks along an outcrop scale flaw: A numerical modeling approach using complementarity
Authors: Mutlu O. , Pollard D. D.
Published: June 2008

The 2D Displacement Discontinuity Method (DDM) is combined with a complementarity algorithm to model the quasi‐static formation and patterns of wing cracks that emanate from regions of stress concentration along a sliding frictional flaw in an otherwise homogeneous and isotropic elastic material. Because stress states and geometry change with sliding on the flaw and wing crack propagation, one cannot specify the boundary conditions a priori. Under these circumstances complementarity is superior to other well‐known contact algorithms. We focus on meter scale phenomena where mineralogical heterogeneity (common to centimeter‐scale laboratory samples) and 3D geometry (common to kilometer‐scale crustal structures) reasonably can be ignored. Analytical solutions to the elastic boundary value problem of the closed sliding flaw include those that assume no friction, uniform friction, and a cohesive end zone (CEZ), and those that assume infinitesimal or straight wing cracks. Here we generalize the problem to consider linearly varying friction in the CEZ and curved wing cracks, and we allow the sliding flaw to open when mechanical interaction with the wing crack dictates that it should. Trace lengths of 135 strike‐slip faults in sandstone are linearly related to wing crack lengths ranging from 0.16 to 72 m and correspond to a range of remote principal stress ratios: 0.06 ≤σ2/σ1≤ 0.2. Opening displacement profiles of wing cracks from the numerical model can be significantly different from analytical solutions. These solutions may produce significant errors in stable crack length for curved propagation paths. The smeared out stress concentration in the CEZ and the heterogeneity in strength of rock suggest that multiple wing cracks may form in one slip event. The mechanical interactions of these cracks leads to kink angles that increase with distance from the flaw tip, a relationship commonly observed in nature.
Diffuse flow hydrothermal manganese mineralization along the active Mariana and southern Izu‐Bonin arc system, western Pacific
Authors: Hein James R. , Schulz Marjorie S. , Dunham Rachel E. , Stern Robert J. , Bloomer Sherman H.
Published: June 2008

Abundant ferromanganese oxides were collected along 1200 km of the active Izu‐Bonin‐Mariana arc system. Chemical compositions and mineralogy show that samples were collected from two deposit types: Fe‐Mn crusts of mixed hydrogenetic/hydrothermal origin and hydrothermal Mn oxide deposits; this paper addresses only the second type. Mn oxides cement volcaniclastic and biogenic sandstone and breccia layers (Mn sandstone) and form discrete dense stratabound layers along bedding planes and within beds (stratabound Mn). The Mn oxide was deposited within coarse‐grained sediments from diffuse flow systems where precipitation occurred below the seafloor. Deposits were exposed at the seabed by faulting, mass wasting, and erosion. Scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 Å and 7 Å manganate minerals, the fundamental chemical difference being high water contents in the amorphous Mn oxides. Alternation of amorphous and crystalline laminae occurs in many samples, which likely resulted from initial rapid precipitation of amorphous Mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages. The chemical composition is characteristic of a hydrothermal origin including strong fractionation between Fe (mean 0.9 wt %) and Mn (mean 48 wt %) for the stratabound Mn, generally low trace metal contents, and very low rare earth element and platinum group element contents. However, Mo, Cd, Zn, Cu, Ni, and Co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits. For the Mn sandstones, Fe (mean 8.4%) and Mn (12.4%) are not significantly fractionated because of high Fe contents in the volcaniclastic material. However, the proportion of hydrothermal Fe (nondetrital Fe) to total Fe is remarkably constant (49–58%) for all the sample groups, regardless of the degree of Mn mineralization. Factor analyses indicate various mixtures of two dominant components: hydrothermal Mn oxide for the stratabound Mn and detrital aluminosilicate for the Mn‐cemented sandstone; and two minor components, hydrothermal Fe oxyhydroxide and biocarbonate/biosilica. Our conceptual model shows that Mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas. The main source of hydrothermal fluid was seawater that penetrated through fractures, faults, and permeable volcanic edifices. The fluids were heated by magma, enriched in metals by leaching of basement rocks and sediments, and mixed with magmatic fluids and gases. Dikes and sills may have been another source of heat that drove small‐scale circulation within sedimentary prisms.
Revisiting heat and salt exchange at the ice‐ocean interface: Ocean flux and modeling considerations
Authors: McPhee M. G. , Morison J. H. , Nilsen F.
Published: June 2008

Properly describing heat and salt flux at the ice/ocean interface is essential for understanding and modeling the energy and mass balance of drifting sea ice. Basal growth or ablation depends on the ratio, R, of the interface heat exchange coefficient to that of salt, such that as R increases so does the rate‐limiting impact of salt diffusion. Observations of relatively slow melt rates in above freezing seawater (plus migration of summer “false bottoms”) suggest by analogy with laboratory studies that double diffusion of heat and salt from the ocean is important during the melting process, with numeric values for R estimated to range from 35 to 70. If the same double‐diffusive principles apply for ice growth as for melting (i.e., if the process is symmetric), supercooling (possibly relieved by frazil crystal production) would occur under rapidly growing ice, yet neither extensive supercooling nor frazil accumulation is found in Arctic pack ice with limited atmospheric contact. Physical properties and turbulent fluxes of heat and salt were measured in the relatively controlled setting of a tidally driven Svalbard fjord, under growing fast ice in late winter. The data failed to show supercooling, frazil production, or enhanced heat flux, suggesting that the double diffusive process is asymmetric. Modeling results compared with measured turbulent fluxes imply that R = 1 when ice freezes; i.e., that double‐diffusive tendencies are relieved at or above the immediate interface. An algorithm for calculating ice/ocean heat and salt flux accommodating the different processes is presented, along with recommended ranges for the interface exchange coefficients.
Summer generation of the Southern Gulf of California eddy train
Authors: Zamudio Luis , Hogan Patrick , Metzger E. Joseph
Published: June 2008

Ocean color and sea surface temperature satellite‐observations show the existence of a series of anticyclonic eddies along the axis of the southern Gulf of California (SGOC). To investigate the summer generation of these eddies, a regional version of the HYbrid Coordinate Ocean Model (HYCOM) has been configured for the GOC and has been nested inside the global model. A suite of experiments, using the nested GOC model, was developed and used to isolate the effects of the local wind and the effects of the oceanic remote forcing on the generation of the SGOC eddies. The results indicate that the local wind is not essential for the generation of these eddies rather it is the oceanic remote forcing. In the SGOC the monthly variability of the currents and sea surface height is mainly due to the deterministic near‐coastal poleward eastern boundary currents (PEBC). The interaction of the PEBC with the topographic irregularities (the capes at Topolobampo and Cabo Lobos and the ridges extending offshore from the entrance of the San Lorenzo and Sinaloa Rivers) generates the SGOC eddies. The northward upper‐ocean transport induced by the PEBC includes two maximums, one in May‐June and the other in December. During the summers of 1999 and 2004 the PEBC were intensified by the arrival of equatorially‐originated downwelling coastally‐trapped‐waves (CTWs), which contributed to the generation of the SGOC eddies. The summer 2004 CTW increased the northward upper‐ocean transport by ∼2 Sv. This particular CTW was measured by several tide gauges located along the coast.
Ocean viscosity and climate
Authors: Jochum M. , Danabasoglu G. , Holland M. , Kwon Y.‐O. , Large W. G.
Published: June 2008

The impacts of parameterized lateral ocean viscosity on climate are explored using three 120‐year integrations of a fully coupled climate model. Reducing viscosity leads to a generally improved ocean circulation at the expense of increased numerical noise. Five domains are discussed in detail: the equatorial Pacific, where the emergence of tropical instability waves reduces the cold tongue bias; the Southern Ocean, where the Antarctic Circumpolar Current increases its kinetic energy but reduces its transport; the Arctic Ocean, where an improved representation of the Atlantic inflow leads to a better sea‐ice distribution; the North Pacific, where the more realistic path of the Kuroshio leads to more realistic temperatures across the midlatitude Pacific; and the northern marginal seas, where stronger boundary currents lead to significantly less sea‐ice. Although the ocean circulation and sea‐ice distribution improve, the oceanic heat uptake, the poleward heat transport, and the large scale atmospheric circulation are not changed significantly. In particular, the improvements to the equatorial cold tongue did not lead to better representation of tropical precipitation or El Niño.
Assessing the globally averaged sea level budget on seasonal to interannual timescales
Authors: Willis Josh K. , Chambers Don P. , Nerem R. Steven
Published: June 2008

Analysis of ocean temperature and salinity data from profiling floats along with satellite measurements of sea surface height and the time variable gravity field are used to investigate the causes of global mean sea level rise between mid‐2003 and mid‐2007. The observed interannual and seasonal fluctuations in sea level can be explained as the sum of a mass component and a steric (or density related) component to within the error bounds of each observing system. During most of 2005, seasonally adjusted sea level was approximately 5 mm higher than in 2004 owing primarily to a sudden increase in ocean mass in late 2004 and early 2005, with a negligible contribution from steric variability. Despite excellent agreement of seasonal and interannual sea level variability, the 4‐year trends do not agree, suggesting that systematic long‐period errors remain in one or more of these observing systems.
A quantitative assessment of uncertainties affecting estimates of global mean OH derived from methyl chloroform observations
Authors: Wang James S. , McElroy Michael B. , Logan Jennifer A. , Palmer Paul I. , Chameides William L. , Wang Yuxuan , Megretskaia Inna A.
Published: June 2008

We estimated the global abundance of OH for the years 1988–1994 by interpreting observations of methyl chloroform (MCF) from two networks using an inverse technique and a 3‐D chemical transport model driven by assimilated meteorology. Our inversion approach optimized both the emissions of MCF and the abundance of OH. Because of an a priori overestimate of the latitudinal gradient of MCF concentration by the model in the standard setup, the inversion lowers global emissions and the global sink due to OH. Optimized emissions are about 10% lower than published inventories on average between 1988 and 1994, and the decrease in the sink suggested by the inversion implies an average lifetime for MCF (with respect to tropospheric OH) of about 6.9 years, 11–21% longer than the 5.7–6.2 years reported in previous optimization studies. Our results are driven by the need to match the observed latitudinal gradient of MCF while balancing the MCF budget. We find that these results depend on the a priori constraint placed on MCF emissions, the rate of interhemispheric mixing in the model, the interhemispheric distribution of OH assumed, and the model simulation of pollution events. Since these factors are highly uncertain, we believe that the level of understanding on global lifetimes of pollutants removed by OH is lower than might be implied by the narrow range of estimates for MCF lifetime in the literature.
Validation of SO2 retrievals from the Ozone Monitoring Instrument over NE China
Authors: Krotkov Nickolay A. , McClure Brittany , Dickerson Russell R. , Carn Simon A. , Li Can , Bhartia Pawan K. , Yang Kai , Krueger Arlin J. , Li Zhanqing , Levelt Pieternel F. , Chen Hongbin , Wang Pucai , Lu Daren
Published: June 2008

The Dutch‐Finnish Ozone Monitoring Instrument (OMI) launched on the NASA Aura satellite in July 2004 offers unprecedented spatial resolution, coupled with contiguous daily global coverage, for space‐based UV measurements of sulfur dioxide (SO2). We present a first validation of the OMI SO2 data with in situ aircraft measurements in NE China in April 2005. The study demonstrates that OMI can distinguish between background SO2 conditions and heavy pollution on a daily basis. The noise (expressed as the standard deviation, σ) is ∼1.5 DU (Dobson units; 1 DU = 2.69 · 1016 molecules/cm2) for instantaneous field of view boundary layer (PBL) SO2 data. Temporal and spatial averaging can reduce the noise to σ ∼ 0.3 DU over a remote region of the South Pacific; the long‐term average over this remote location was within 0.1 DU of zero. Under polluted conditions collection 2 OMI data are higher than aircraft measurements by a factor of two. Improved calibrations of the radiance and irradiance data (collection 3) result in better agreement with aircraft measurements on polluted days. The air mass–corrected collection 3 data still show positive bias and sensitivity to UV absorbing aerosols. The difference between the in situ data and the OMI SO2 measurements within 30 km of the aircraft profiles was about 1 DU, equivalent to ∼5 ppb from 0 to 3000 m altitude. Quantifying the SO2 and aerosol profiles and spectral dependence of aerosol absorption between 310 and 330 nm are critical for an accurate estimate of SO2 from satellite UV measurements.
A size‐resolved model and a four‐mode parameterization of dry deposition of atmospheric aerosols
Authors: Feng Jian
Published: June 2008

To deposit on the ground surface, an airborne aerosol particle needs to pass through an aerodynamic resistance layer and a quasi‐laminar sublayer just adjacent to the surface. Traditionally, it is believed that the main mechanisms through which a particle overcomes the resistance from the quasi‐laminar sublayer are Brownian diffusion, interception, inertial impaction, and gravitational settling. In this study, a size‐resolved dry deposition model is formulated, which includes a new proposed dry deposition mechanism, the burst effect of eddy turbulence. The effects on dry deposition of particles by Brownian diffusion and inertial impaction are parameterized through the Schmidt number and the Stokes number, respectively. On the basis of the similarity between deposition of particles on walls of pipes and deposition of atmospheric particles on the ground surface, the burst effect of eddy turbulence is parameterized with the roughness Reynolds number. Through the roughness Reynolds number the effect on dry deposition by the surface roughness is parameterized into the model. Since the dry deposition velocity depends on particle size strongly, a four‐mode parameterization of dry deposition is proposed for use in atmospheric dispersion models. For each aerosol mode the parameterization of the bulk dry deposition velocity is made up of two terms: the Reynolds term and another term that is a power law function of friction velocity. The dry deposition velocities predicted by the model and the four‐mode parameterization are compared with the measurements reported in the literature, and good agreements are achieved.
Retrieval of from simulated Orbiting Carbon Observatory measurements using the fast linearized R‐2OS radiative transfer model
Authors: Natraj Vijay , Boesch Hartmut , Spurr Robert J. D. , Yung Yuk L.
Published: June 2008

In a recent paper, we introduced a novel technique to compute the polarization in a vertically inhomogeneous, scattering‐absorbing medium using a two orders of scattering (2OS) radiative transfer (RT) model. The 2OS computation is an order of magnitude faster than a full multiple scattering scalar calculation and can be implemented as an auxiliary code to compute polarization in operational retrieval algorithms. In this paper, we employ the 2OS model for polarization in conjunction with a scalar RT model (Radiant) to simulate backscatter measurements in near infrared (NIR) spectral regions by space‐based instruments such as the Orbiting Carbon Observatory (OCO). Computations are performed for six different sites and two seasons, representing a variety of viewing geometries, surface and aerosol types. The aerosol extinction (at 13000 cm−1) was varied from 0 to 0.3. The radiance errors using the Radiant/2OS (R‐2OS) RT model are an order of magnitude (or more) smaller than errors arising from the use of the scalar model alone. In addition, we perform a linear error analysis study to show that the errors in the retrieved column‐averaged dry air mole fraction of CO2 using the R‐2OS model are much lower than the “measurement” noise and smoothing errors appearing in the inverse model. On the other hand, we show that use of the scalar model alone induces errors that could dominate the retrieval error budget.
Comparison of OMI and ground‐based in situ and MAX‐DOAS measurements of tropospheric nitrogen dioxide in an urban area
Authors: Kramer Louisa J. , Leigh Roland J. , Remedios John J. , Monks Paul S.
Published: June 2008

In this paper we compare retrieved tropospheric vertical column densities (VCDs) of nitrogen dioxide (NO2) from the Ozone Monitoring Instrument (OMI) to coincident tropospheric columns retrieved from the Concurrent Multiaxis Differential Optical Absorption Spectroscopy (CMAX‐DOAS) instrument, installed at the University of Leicester (52.38°N, 1.08°W), and in situ near‐surface measurements from chemiluminescence detectors. The results show that tropospheric NO2 columns retrieved from CMAX‐DOAS and OMI correlate well (r = 0.64) when cloud clearing has been applied, and only those pixels that sample at least 90% of the Leicester area were included in the analyses. The correlation of OMI tropospheric VCDs with near‐surface measurements for cloud‐free days in 2005 and 2006 initially showed a strong positive bias in the near‐surface NO2 measurements and scattered points. This was interpreted as being due to the satellite footprint of OMI sampling the NO2 sources from the surrounding area of Leicester as well as emissions from the city. A field‐of‐view (FOV) weighted estimate for the OMI‐equivalent urban NO2 was calculated for each coincidence by including background concentrations from a nearby in situ monitor, situated in a rural area. The subsequent agreement between the OMI tropospheric VCDs and FOV weighted near‐surface measurements is very good for spring (r = 0.83) and summer (r = 0.64) months. Finally, seasonal and weekly cycles of NO2 are produced which show that OMI may be underestimating the amount of NO2 during the winter months. However, all sets of data show expected weekly cycles, with lower values on a Sunday.
Simulation of the 18‐d summer heavy rainfall over East Asia using a regional climate model
Authors: Choi Suk‐Jin , Cha Dong‐Hyun , Lee Dong‐Kyou
Published: June 2008

In this study, an 18‐d‐long heavy‐rainfall event that occurred over the Korean Peninsula in August 1998 was simulated by using the Seoul National University Regional Climate Model (SNURCM) with horizontal resolution of 20 km. In order to determine the potential predictability and the capability of the RCM in the simulation of long‐lasting, extremely heavy rainfall, a time‐lagged ensemble with five different initial conditions of one‐day intervals, and two daily forecast experiments with initial conditions at 00 UTC (24‐h and 48‐h forecasts) were performed. Further, an experiment with high horizontal resolution of 5 km was performed. The ensemble as well as individual runs simulated the evolution and time variation in the convective systems responsible for the heavy rainfall. Somewhat better patterns and magnitudes of precipitation were obtained for the ensemble as compared to those of the individual runs. The continuous integration of the 18‐d heavy rainfall in the ensemble corresponded with the 24‐h and 48‐h forecast experiments that employed the initial data obtained every day during the simulation period. Therefore in the RCM, the daily evolution of the heavy‐rainfall event was reproduced by large‐scale forcing. In the experiment with the 5‐km horizontal resolution, the amount and intensity of heavy precipitation and its diurnal variation were better reproduced by the combined effects of increased horizontal resolution and topography.
Simulated lower stratospheric trends between 1970 and 2005: Identifying the role of climate and composition changes
Authors: Lamarque Jean‐François , Kinnison D. E. , Hess P. G. , Vitt F. M.
Published: June 2008

We have analyzed a set of simulations aimed at understanding the mechanisms that drive observed trends in the lower stratosphere after 1970. The simulations were performed using a version of the Community Atmosphere Model version 3 (CAM3) updated with interactive tropospheric and stratospheric chemistry. Even with a relatively low model top (≈40 km), this model shows good ability at reproducing a variety of large‐scale changes in climate and chemical composition in the stratosphere when forced with the observed sea‐surface temperatures and surface concentrations of long‐lived trace gases and ozone‐depleting substances. We then used the same model framework to differentiate the role of chemically active composition (ozone, methane, and chlorofluorocarbons) and CO2 changes on observed trends in the stratosphere. Among the sensitivity factors analyzed, our simulations indicate that changes in CO2 over the simulated period do not lead to significantly different total ozone trend; however, changes in CO2 lead to important differences in ozone in the upper part of the model. On the other hand, changes in surface methane concentration are shown to play a significant role in driving changes in the globally averaged total ozone column, through a combination of changes in tropospheric and stratospheric ozone columns. We also show that the correlation between a change in tropical mean age of air and in vertical velocity breaks down above 20 hPa, in association with increased isentropic mixing above that level. Finally, we show that our model is capable of reproducing trends in the tropical age of air that were found in other studies; our simulations also indicate a significant impact of keeping methane and ozone‐depleting substances at their 1970 levels, indicating the potentially important role of controlling methane emissions.
Carbonaceous aerosol at two rural locations in New York State: Characterization and behavior
Authors: Sunder Raman Ramya , Hopke Philip K. , Holsen Thomas M.
Published: June 2008

Fine particle samples were collected to determine the chemical constituents in PM2.5 at two rural background sites (Potsdam and Stockton, N. Y.) in the northeastern United States from November 2002 to August 2005. Samples were collected every third day for 24 h with a speciation network sampler. The measured carbonaceous species included thermal‐optical organic carbon (OC), elemental carbon (EC), pyrolytic carbon (OP), black carbon (BC), and water‐soluble, short‐chain (WSSC) organic acids. Concentration time series, autocorrelations, and seasonal variations of the carbonaceous species were examined. During this multiyear period, the contributions of the total carbon (OC + EC) to the measured fine particle mass were 31.2% and 31.1% at Potsdam and Stockton, respectively. The average sum of the WSSC acids carbon accounted for approximately 2.5% of the organic carbon at Potsdam and 3.0% at Stockton. At Potsdam, the seasonal differences in the autocorrelation function (ACF) and partial autocorrelation function (PACF) values for carbonaceous species suggest that secondary formation may be an important contributor to the observed concentrations of species likely to be secondary in origin, particularly during the photochemically active time of the year (May to October). This study also investigated the relationships between carbonaceous species to better understand the behavior of carbonaceous aerosol and to assess the contribution of secondary organic carbon (SOC) to the total organic carbon mass (the EC tracer method was used to estimate SOC). At Potsdam the average SOC contribution to total OC varied between 66% and 72%, while at Stockton it varied between 58% and 64%.
Parameterization of cirrus cloud formation in large‐scale models: Homogeneous nucleation
Authors: Barahona Donifan , Nenes Athanasios
Published: June 2008

This work presents a new physically based parameterization of cirrus cloud formation for use in large‐scale models which is robust, computationally efficient, and links chemical effects (e.g., water activity and water vapor deposition effects) with ice formation via homogenous freezing. The parameterization formulation is based on ascending parcel theory and provides expressions for the ice crystal size distribution and the crystal number concentration, explicitly considering the effects of aerosol size and number, updraft velocity, and deposition coefficient. The parameterization is evaluated against a detailed numerical cirrus cloud parcel model (developed during this study), the equations of which are solved using a novel Lagrangian particle‐tracking scheme. Over a broad range of cirrus‐forming conditions, the parameterization reproduces the results of the parcel model within a factor of 2 and with an average relative error of −15%. If numerical model simulations are used to constrain the parameterization, error further decreases to 1 ± 28%.
Open cellular structure in marine stratocumulus sheets
Authors: Wood R. , Comstock K. K. , Bretherton C. S. , Cornish C. , Tomlinson J. , Collins D. R. , Fairall C.
Published: June 2008

Geostationary and Sun‐synchronous satellite data and in situ observations from ship cruises are used to investigate the formation of open cellular structure in marine stratocumulus clouds over the southeast Pacific (SEP). Open cellular convection either forms spontaneously as pockets of open cells (POCs) within overcast stratocumulus, or is advected into the region from midlatitude regions. POC formation occurs most frequently during the latter part of the night, demonstrating that this transition is not caused by solar absorption‐driven decoupling. The transition preferentially occurs in clouds with low 11–3.9 μm nighttime brightness temperature difference (BTD) which is found to be well correlated with both in situ measured accumulation mode aerosol concentration and cloud droplet concentration estimates derived from MODIS. Besides indicating that nighttime BTD is an excellent proxy for stratocumulus cloud droplet concentration Nd, this also suggests that low aerosol concentrations favor POC formation. Indeed, extremely low accumulation mode aerosol concentrations are found during the passage of open cell events over the ship. Free‐tropospheric moisture is not found to be an important factor in POC formation. Significant subseasonal variability occurs in the fractional coverage of open cellular convection over the broader SEP. This coverage is well correlated with a MODIS‐derived drizzle proxy (MDP) proportional to the ratio of liquid water path (LWP) to Nd for predominantly overcast regions. Both LWP and Nd variability influences the MDP. Periods of low MDP have significant positive large‐scale Nd anomalies and are preceded by offshore winds at 850 hPa, which suggests a potential continental influence upon open cell formation over the SEP. Together, the results suggest important two‐way interactions between aerosols and drizzle in marine stratocumulus and a role for drizzle in modulating the large‐scale albedo of these cloud systems.
Precipitation change from a cumulonimbus cloud downwind of a seeded target area
Authors: Ćurić Mladjen , Janc Dejan , Vučković Vladan
Published: June 2008

A silver‐iodide seeding agent was released, which may have resulted in enhanced precipitation over 100 km downwind from the point of release. This study attempts to determine whether this enhancement occurred. It is not possible to quantify the amount of precipitation that would have been released from an unseeded cloud if it has already been seeded, since no two clouds are alike. As a result, numerical models remain the best tool to investigate the effects of cloud seeding. We use a three‐dimensional mesoscale cloud‐resolving model, and we simulate seeding of a region with temperatures below 0°C in front of a target cloud that might lead to a change in cumulative precipitation far from the initial seeding area. Our model simulations show that this cloud seeding enhances cumulative precipitation 110 km from the center of mass of the initial seeding area by about 50%.