bluuebunny/crossref_metadata_2025_split huggingface dataset:
A two‐layer canopy compensation point model for describing bi‐directional biosphere‐atmosphere exchange of ammonia
Authors: Nemitz Eiko , Milford Celia , Sutton Mark A. 
Published: February 2007

AbstractA new resistance model is described to interpret the biosphere‐atmosphere exchange fluxes of ammonia (NH3) with vegetation, and compared with previous modelling approaches for NH3. The new model constitutes an extension of an existing one‐layer canopy compensation point model: in addition to bi‐directional foliar stomatal exchange and deposition to leaf cuticles, the model treats NH3 emission from a ground layer. This may originate from fertilizer evaporation, the soil or decomposing plant parts. The emission potentials of the foliage and ground surface are given by the NH3 gas concentrations at equilibrium with the ammonium (NH+4) concentration in the apoplastic fluid or soil solution. From these concentrations, as well as the transfer resistances of the different exchange pathways, the net compensation point of the canopy (Xc) may be derived. The net flux is determined by the relative magnitude of Xc and the NH3 air concentration above the vegetation. The two‐layer canopy compensation point is applied to: (i) an oilseed rape canopy, in which NH3 emission from decomposing leaf litter at the ground surface presents a second major source; and (ii) a wheat stubble field, in which emission from the soil contributes significantly to the net exchange. For both canopies, the model performance is contrasted with the single‐layer Xc model, which is not able to reproduce the temporal patterns of exchange. The two‐layer model is proposed as the optimum compromise between simplicity and accuracy, capable of describing bi‐directional NH3 exchange in atmospheric transport models over a very wide range of vegetation types.
Relationship between the Indian monsoon rainfall and the tropospheric temperature over the Eurasian continent
Authors: Liu Xiaodong , Yanai Michio 
Published: February 2007

AbstractBased on climatological data such as the all‐India rainfall (AIR) for 1949–98, air temperatures in the troposphere and at the land surface for 1949–98 as well as precipitation and outgoing long‐wave radiation (OLR) for 1979–98, the statistical relationship between the Indian monsoon rainfall and tropospheric temperature (TT) over the Eurasian continent is examined by using the correlation analysis and singular value decomposition (SVD) analysis methods. The main results are summarized as follows. (1) The June‐September (JJAS) AIR has significant positive correlations with the 200–700 hPa TT averaged for Eurasia in JJAS. The area with the highest simultaneous correlation of upper TT with AIR for JJAS is located in western Eurasia. There is also a region with positive simultaneous correlations in the southern subtropics covering southern Africa. The JJAS AIR also shows significant positive correlations with TT over the Eurasian continent in March‐May (MAM) and with the TT averaged over the Tibetan Plateau in September and October. Although some precursory springtime temperature signals for the anomalous summer monsoon are found in the upper TT over Eurasia, the variation in the upper TT appears mostly independent from that of the land surface temperature. (2) The anomalies of upper TT in JJAS are closely coupled with the variations in OLR related to the monsoon rainfall over tropical Asia and Africa. The spatial structure of the first SVD mode for OLR anomalies shows the coherent variations in convective activity from northern tropical Africa to India, while the pattern of the first SVD mode for 300 hPa temperature anomalies shows a distribution which is nearly symmetric with respect to the equator, with variations of the same sign over subtropical areas in both hemispheres and variations of the opposite sign around equatorial Africa. This pair of coupled patterns suggests that when the monsoon rains from tropical Africa to India become more intense, the upper troposphere from northern Africa to western Asia and over southern Africa becomes warmer. (3) The observed temperature variation in the upper troposphere over the Eurasian continent (especially western Eurasia) during the summer monsoon season is considered to be a result of the anomalous subsidence and thermal advection, dynamically induced by anomalous tropical heating associated with the enhanced monsoon rainfall. This study suggests that the tropical convective activity linked to the Indian monsoon rainfall has an impact on the atmospheric variability on a global scale.
A comparison of extreme European daily precipitation simulated by a global and a regional climate model for present and future climates
Authors: Durman C. F. , Gregory J. M. , Hassell D. C. , Jones R. G. , Murphy J. M. 
Published: February 2007

AbstractThe intensity and distribution of daily precipitation is predicted to change under scenarios of increased greenhouse gases (GHGs). In this paper, we analyse the ability of HadCM2, a general circulation model (GCM), and a high‐resolution regional climate model (RCM), both developed at the Met Office's Hadley Centre, to simulate extreme daily precipitation by reference to observations. A detailed analysis of daily precipitation is made at two UK grid boxes, where probabilities of reaching daily thresholds in the GCM and RCM are compared with observations. We find that the RCM generally overpredicts probabilities of extreme daily precipitation but that, when the GCM and RCM simulated values are scaled to have the same mean as the observations, the RCM captures the upper‐tail distribution more realistically. To compare regional changes in daily precipitation in the GHG‐forced period 2080–2100 in the GCM and the RCM, we develop two methods. The first considers the fractional changes in probability of local daily precipitation reaching or exceeding a fixed 15 mm threshold in the anomaly climate compared with the control. The second method uses the upper one‐percentile of the control at each point as the threshold. Agreement between the models is better in both seasons with the latter method, which we suggest may be more useful when considering larger scale spatial changes. On average, the probability of precipitation exceeding the 1% threshold increases by a factor of 2.5 (GCM and RCM) in winter and by 1.7 (GCM) or 1.3 (RCM) in summer.
Simple adjoint method for three‐dimensional wind retrievals from single‐Doppler radar
Authors: Xu Q. , Gu H. , Yang S. 
Published: February 2007

AbstractA new simple adjoint (SA) method is developed for retrieving three‐dimensional wind from single‐Doppler observations. The method uses the full momentum equations and the mass continuity equation as weak constraints, in addition to the strong constraints of the radial‐wind and reflectivity equations. With these weak constraints, the unknown source term in the previous two‐dimensional SA method is now explicitly estimated in terms of perturbation pressure and buoyancy. This improves the wind retrievals, although the retrieved perturbation pressure and buoyancy may not be accurate. Bi‐spline basis functions are used to express the retrieved fields on coarse finite‐element meshes. The bi‐spline representation filters short‐wave noise and effectively reduces the number of unknowns that need to be retrieved, so the retrievals are further improved. The method is tested with Doppler‐radar data collected during the Phoenix II field experiment. The retrieved winds are very close to the dual‐Doppler observed winds and the difference is about 1.0 m s−1. The retrievals can be further improved by adding smoothness constraints in the cost function, especially when the bi‐spline representation is not used. The robustness of the method is examined in terms of sensitivities to the weights specified for the weak constraints in the cost function.
Evaluation of the mass‐flux approach to parametrizing deep convection
Authors: Swann Hugh 
Published: February 2007

AbstractCloud‐resolving model (CRM) simulations of deep convection in a variety of environmental conditions are used to analyse assumptions in bulk‐updraught convection parametrization schemes, which are commonly employed in climate and weather‐prediction models. It is shown that the mass‐flux approach can faithfully represent the effect of convection on the large‐scale fields, provided that the mass flux and other bulk properties of the updraughts (and downdraughts) are accurately predicted. Entrainment and detrainment (which govern the shape of the mass‐flux profile and the dilution of the bulk updraught with environment air) are calculated from CRM simulations. Limitations in the basic premiss of the classical entraining/detraining plume model are revealed and an alternative method of predicting bulk‐updraught temperature is suggested.
Teleconnections and low‐frequency variability in idealized experiments with two storm tracks
Authors: Franzke Christian , Fraedrich Klaus , Lunkeit Frank 
Published: February 2007

AbstractLow‐frequency variability and teleconnection patterns induced by two storm tracks in idealized experiments depend on their zonal distance. A separation of about 150°, which resembles the northern hemisphere storm‐track distribution, reveals teleconnection patterns which are similar to the Pacific North American (PNA) pattern and the North Atlantic Oscillation (NAO). The NAO‐like structure is associated with retrograde travelling Rossby waves; barotropic stream‐function tendencies show that the interaction of the stationary eddies with the low‐frequency flow and the high‐frequency eddies contribute to the amplification of the pattern. Its decay is due to their interaction with the zonal‐mean flow, and the low‐frequency contribution to the divergence term. The PNA‐like pattern has a longer memory and is linked to a quasi‐stationary wave. The stationary‐wave activity flux shows the dominating influence of baroclinic processes and the other storm track further upstream. The correlation between the teleconnection indices is significant for storm‐track distances between 180° and 160°, and vanishes between 150° and 130°.
Blocking as a local instability to zonally varying flows
Authors: Swanson K. L. 
Published: February 2007

AbstractAn idealized system consisting of a steady‐state, axisymmetric vortex patch with topography forcing variations in the basic‐state flow along the vortex edge is shown to possess local instabilities for a broad range of parameters. One branch of these instabilities corresponds in scale and structure to observed atmospheric blocks. The nonlinear equilibration of these blocking‐type instabilities reproduces many aspects of observed blocking onsets; the potential for rapid non‐modal growth and ready excitation of these local instabilities by transients suggests that this instability may lie at the root of observed blocking onsets.
A scaling hypothesis for moist convective updraughts
Authors: Stiller Olaf , Craig George C. 
Published: February 2007

AbstractThe mixing of air between clouds and their environment is investigated with the help of a simplified model problem that contains only a small number of dynamically relevant parameters whose influence can be systematically explored. The classical model of a buoyant thermal, extensively studied in laboratory experiments, is generalized to include the key moist processes of condensation and re‐evaporation of cloud water. We consider the evolution of an isolated thermal initiated from a spherical warm and moist bubble at rest in a moist neutral sounding. The moist thermal loses buoyancy through mixing with the unsaturated environmental air, and finally collapses. The effect of moist physics on the thermal is shown to be represented by only three scale‐independent parameters. We present large‐eddy simulations that exhibit an approximate dynamical similarity, in that the loss of buoyancy resulting from the mixing process is mainly described by a single scale‐invariant parameter which we call the effective buoyancy, Beff. In order for the thermal to ascend a distance significantly larger than its initial diameter, Beff must be much greater than unity. This implies that the environment must be close to saturation if the bubble has an initial buoyancy that is typical of real clouds. It is also shown that the stratification of the environment induces a length scale, Lbuo, for a thermal with a given buoyancy excess. The resulting scale‐independent parameter Leff = L/Lbuo (where L is the initial bubble radius) is shown to affect the geometry of the thermal. Indeed, the thermal may break up if Leff is too large. These geometrical effects can be explained by relating Lbuo to the depth reached by forced downdraughts, which corresponds to the vertical extent of the largest eddies that entrain unsaturated air into the thermal.
Atmospheric absorption of near infrared and visible solar radiation by the hydrogen bonded water dimer
Authors: Vaida V. , Daniel J. S. , Kjaergaard H. G. , Goss L. M. , Tuck A. F. 
Published: February 2007

AbstractBased on the physico‐chemical properties of water dimers, their near infrared and visible absorption of solar radiation in the earth's atmosphere is calculated. The calculation uses equilibrium constants determined by statistical mechanics, and a vibrational absorption spectrum determined by a coupled oscillator quantum mechanics model and ab initio quantum chemistry. The resulting total atmospheric absorption was calculated using a line‐by‐line radiative‐transfer model, and depends significantly on the dimer abundance, as well as on the frequency and line width given to vibrational transitions. The best estimate achieved for the possible range of total absorption from 400 nm to 5000 nm by water dimer in the tropics is 1.6–3.3 W m−2. In a global‐warming scenario, the increased temperature and water vapour partial pressure result in a nonlinear increase in the absorption of solar radiation by water clusters. Most of the energy from water dimer absorption is deposited in the lower troposphere, particularly in the tropics, tending to make it more convective.
Multi‐year simulations using a regional‐climate model over the Iberian Peninsula: Current climate and doubled CO2scenario
Authors: Gallardo Clemente , Arribas Alberto , Prego Juan A. , Gaertner Miguel A. , De Castro Manuel 
Published: February 2007

AbstractIn order to analyse the regional climate sensitivity in the Iberian Peninsula and surrounding areas to the global change related to an increase of CO2, two simulations (current climate and scenario) are performed using a regional‐climate model (RCM) one‐way nested in a global circulation model (GCM). Both simulations cover a ten‐year period. The results of the control simulation (current climate) are compared to a climatological database. RCM and GCM representations of the climate are realistic, but the RCM shows more detailed results. Following this, a statistical analysis of the differences between current climate and double CO2scenario simulations is carried out considering both 2 m temperature and precipitation. The analysis shows a significant warming in seasonal averages and important differences in the 2 m temperature interannual variability. Especially important is the strong increase in interannual variability of precipitation found in winter and autumn. Relationships between anomalies of general circulation (500 hPa geopotential field) and surface temperature, precipitation and cloudiness are also analysed, showing an important effect of cloud cover anomalies over the 2 m temperature interannual variability.
Ocean‐atmosphere‐land feedbacks in an idealized monsoon
Authors: Chou C. , Neelin J. D. , Su H. 
Published: February 2007

AbstractAn intermediate‐complexity atmospheric model coupled with a simple land‐surface model and a mixed‐layer ocean model is used to investigate the processes involved in an idealized monsoon occurring on a single rectangular continent. Idealized divergences of ocean heat transports are specified as an annual average ‘Q‐flux’. In this simple coupled configuration, the mechanisms that affect land‐ocean contrast and, in turn, the seasonal movement of the continental convergence zones are examined. These include soil‐moisture feedbacks: cooling of tropical oceans by ocean transpoit; ventilation, defined as the import into continental regions of low moist static‐energy air from ocean regions where heat storage opposes summer warming; and the ‘interactive Rodwell‐Hoskins mechanism’, in which Rossby‐wave‐induced subsidence to the west of monsoon heating interacts with the convection zone. The fixed ocean transports have a substantial impact on the continental convection. If Q‐flux is set to zero, subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall. When land hydrology feedbacks are active, the drying of subtropical continents disfavours continental convection even in the tropics. When ocean transports are included, tropical oceans are slightly disfavoured as regions for producing convection which, by contrast, favours continental convection. The monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent. The western portion of the continent tends to have a dry region of characteristic shape. This east‐west asymmetry is partly due to the interactive Rodwell‐Hoskins mechanism. The ventilation is of at least equal importance in producing east‐west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone.
The energetics of an upper tropospheric cyclonic vortex over north‐east Brazil
Authors: Mishra S. K. , Rao V. B. 
Published: February 2007

AbstractThe daily budget of zonal and eddy components of kinetic and available potential energy (APE) including boundary and generation terms are computed for a limited area from 52.5 to 22.5°W and from 20°S to 2.5°N and extending in the vertical from 1000 to 50 hPa, during the period 1–10 January 1993. During the vortex period, 5–10 January, a cyclonic vortex in the upper troposphere with its mean centre at 10°S, 35°W was present. The combined boundary pressure work and dissipation terms of the kinetic energy budget equations, as well as APE generation terms, are computed as residuals. The meridional transports of eddy momentum and sensible heat are also computed.The time‐pressure distributions of the zonal and eddy components of kinetic energy (KZ and KE, respectively) and APE are examined. The upper layer 500–100 hPa is identified as the vertical layer which contains the vortex and its interaction with the ambient flow. A sharp increase of KZ in the upper layer is seen as an important feature of the pre‐vortex period 1–4 January. The role of boundary pressure work in the sharp increase of KZ associated with the development of a strong shear zone before the formation of the vortex is discussed. The vortex formation in the upper layer is associated with a rapid decrease of KZ, a sharp increase of KE and barotropic energy conversion from KZ to KE, the commencement of eddy APE (AE) to KE conversion and the generation of AE. These are identified as the main characteristics of the vortex formation from the time variation of energy variables. The vortex formation is also associated with a large increase of down‐the‐gradient eddy momentum transport.It is found from the vertically integrated mean energy cycle in the upper layer that both the barotropic and AE to KE energy conversions maintain the vortex. However, the former is found to be 0.63 W m−2 and dominates over the latter by a factor of 3.5. A balance between the baroclinic energy conversion and the generation of AE is noted. The system is dynamically (thermally) more active in the vertical layer 350–100 hPa (500–100 hPa) as revealed by the vertical variation of energy variables. The reasonableness of computed energy variables is discussed qualitatively and quantitatively wherever possible.
Kinetics of glycine oxidation by N‐bromophthalimide in the presence of sodium dodecyl sulfate
Authors: Joshi Ghanat K. , Katre Y. R. , Singh Ajaya K. 
Published: February 2007

AbstractThe kinetics of oxidation of glycine by N‐bromophthalimide (NBP) were studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first‐order dependence on [NBP] and fractional‐order dependence on [glycine] and [H+]. The addition of reduced product of the oxidant had no significant effect on the rate of reaction. Increasing [Hg(OAc)2] and [Br−] increased the rate of reaction, whereas a change in ionic strength (μ) of the medium had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. HCN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The index of cooperativity and the micelle binding constant have been calculated.
Novel surfactants for ultralow interfacial tension in a wide range of surfactant concentration and temperature
Authors: Aoudia Mohamed , Al‐Shibli Mohamed Nasser , Al‐Kasimi Liali Hamed , Al‐Maamari Rashid , Al‐bemani Ali 
Published: February 2007

AbstractThis work investigates the possibility of injecting dilute aqueous solutions of novel surfactants into the Yibal field (Sultanate of Oman). This was accomplished through an experimental protocol based on the following criteria: (i) compatibility of the surfactants with the high‐saline reservoir water (∼200 g/L); (ii) low interfacial tension (IFT) between crude oil and reservoir water (less than 10−2 mN m−1); and (iii) maintaining the low IFT behaviour during the entire surfactant flooding. Novel surfactants selected in this study consist of a series of ether sulfonates (AES‐205, AES‐128, AES‐506, and 7–58) and an amphoteric surfactant (6–105). These surfactants were found to be compatible with reservoir water up to 0.1% surfactant concentration, whereas 6–105 and 7–58 showed compatibility within the full range of surfactant concentration investigated (0.001–0.5%). All surfactant systems displayed dynamic IFT behavior, in which ultralow transient minima were observed in the range 10−4–10−3 mN m−1, followed by an increase in the IFT to equilibrium values in the range 10−3–10−1 mN m−1. The results also showed that with respect to concentration (0.05–0.5%) and temperature (45–80°C), AES‐205 and 7–58 surfactants exhibit a wide range of applicability, with the IFT remaining below 10−2 mN m−1, as required for substantial residual oil recovery. In addition, ultralow IFT were obtained at surfactant concentrations as low as 0.001%, making the use of these surfactants in enhanced oil recovery extremely cost‐effective.