Atmospheric Processes (atmospheric + process)

Distribution by Scientific Domains

Selected Abstracts

Continuous, Atmospheric Process to Create Organic Clusters and Nanostructured, Functional Films,

R. Jagannathan
Abstract An atmospheric process based on compressed CO2 is used to create stable clusters of small organic molecules. These clusters, 1,10,nm in size, are used as building blocks to assemble thin films on various substrates. Cluster assembly of these films is verified by using low-angle X-ray diffraction. The surface quality of these cluster-assembled films is similar to that of films usually prepared via the vacuum process. Several functional organic light-emitting diode devices have been prepared, in which only the doped emissive layer has been deposited by our process. The radiometric features and efficiencies of these devices match those of vacuum-built devices. Atomic force microscopy of these molecular clusters reveals that they are liquid-like at standard atmospheric conditions. Coatings of these clusters on cloth and stainless steel have been found to be superhydrophobic in nature. [source]

A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss Alps

Anne Hormes
ABSTRACT. We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid-latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon-dated periods defined with less extensive glaciers coincide with periods of reduced radio-production, pointing to a connection between solar activity and glacier melting processes. Measured long-term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long-term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances. [source]

An Initial Analysis of River Discharge and Rainfall in Coastal New South Wales, Australia Using Wavelet Transforms

H. Kirkup
In many coastal catchments of south eastern New South Wales, Australia, changes in river morphology are a response to human impact superimposed on spatial and temporal patterns of variability in precipitation and discharge. Understanding, and preferably quantifying, spatial and temporal patterns of hydrologic variability are essential to understanding natural changes, and to separate these from artificial changes in river systems. Prediction and management of water resources are also dependent upon this understanding. We assess the variability in precipitation and discharge using the wavelet transform which projects the time series of data into a three dimensional surface of frequency, amplitude and time. The analysis reveals that changes across time often reflect changes in individual seasons and may be linked to changes in particular seasonal atmospheric circulation systems. Strong perturbations in the analysis of one catchment are consistent with documented, geomorphically-effective, flooding sequences. The characteristics of the series in the transformed data reveal interesting differences at certain times and scales which may be a reflection of changes in larger scale atmospheric processes. [source]

Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decomposition

H. J. Curran
Rate coefficients for alkyl and alkoxy radical decomposition are important in combustion, biological, and atmospheric processes. In this paper, rate constant expressions for C1C4 alkyl and alkoxy radicals decomposition via ,-scission are recommended based on the reverse, exothermic reaction, the addition of a hydrogen atom or an alkyl radical to an olefin or carbonyl species with the decomposition reaction calculated using microscopic reversibility. The rate expressions have been estimated based on a wide-range study of available experimental data. Rate coefficients for hydrogen atom and alkyl radical addition to an olefin show a strong temperature curvature. In addition, it is found that there is a correlation between the activation energy for addition and (i) the type of atom undergoing addition and (ii) whether this radical adds to the internal or terminal carbon atom of the olefin. Rate coefficients for alkoxy radical decomposition show a strong correlation to the ionization potential of the alkyl radical leaving group and on the enthalpy of reaction. It is shown that the activation energy for alkyl radical addition to a carbonyl species can be estimated as a function of the alkyl radical ionization potential and enthalpy of reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 250,275, 2006 [source]

Effects of canopy heterogeneity, seed abscission and inertia on wind-driven dispersal kernels of tree seeds

Gil Bohrer
Summary 1Understanding seed dispersal by wind and, in particular, long-distance dispersal (LDD) is needed for management of plant populations and communities, especially in response to changes in climate, land use and natural habitats. Numerical models designed to explore complex, nonlinear atmospheric processes are essential tools for understanding the fundamental mechanisms involved in seed dispersal. Yet, thus far, nearly all such models have not explicitly accounted for the spatial heterogeneity that is a typical feature of all ecosystems. 2The recently developed Regional Atmospheric Modelling System (RAMS)-based Forest Large Eddy Simulation (RAFLES) is used here to explore how within-stand canopy heterogeneity impacts LDD. RAFLES resolves microscale canopy heterogeneity such as small gaps and variable tree heights, and it simulates their impacts on turbulence inside and above the canopy in the atmospheric boundary layer (ABL). For that purpose, an Eulerian,Lagrangian module of seed dispersal is added to RAFLES to simulate seed trajectories. 3Particular attention is paid to the sensitivity of statistical attributes of the dispersal kernels (i.e. mean, mode, variance, tail) to key simplifications common to all seed dispersal models, such as horizontal homogeneity in the canopy and flow field, and the tight coupling between air parcel trajectories and seed trajectories (i.e. neglecting seed inertia). These attributes appear to be sensitive to various factors operating at scales ranging from the seed scale to the ABL scale. 4Simulations with RAFLES show that LDD is characterized by a dispersal kernel with a ,tail', asymptotically approaching a power law decay of ,3/2 (mainly occurring for lighter seeds at high wind speeds). This is consistent with asymptotic predictions from analytical models. The wind speed threshold at which seed abscission occurs, set-up to be twice the standard deviation of the vertical wind speed, is shown to affect short-distance dispersal, but has no significant impact on LDD. Ignoring the effects of seed inertia on the seed trajectory calculations has a minor effect on short-distance dispersal and no effect on the probability of seed uplift. Thus, it has no significant impact on LDD. 5Synthesis. Tree-scale canopy heterogeneity affects the turbulence characteristics inside and above the canopy and, consequently, this affects dispersal kernel statistics. A key finding from this study is that ejection is enhanced above the shorter trees of the canopy. Seeds dispersed above shorter trees have a higher probability of experiencing LDD while their short-distance dispersal remains practically the same. At inter-annual time scales, such interactions could affect species composition. [source]

Introduction to the AMMA Special Issue on ,Advances in understanding atmospheric processes over West Africa through the AMMA field campaign'

J.-P. Lafore
First page of article [source]

Individual and combined influence of El Niño,Southern Oscillation and Indian Ocean Dipole on the Tropospheric Biennial Oscillation

Prasanth A. Pillai
Abstract Tropospheric biennial oscillation (TBO) is the tendency of a strong monsoon to be followed by a weaker one and vice versa. It involves both oceanic and atmospheric processes in the tropical Indian and Pacific Ocean regions. The present study analyses the effect of dynamical processes of the Indian and Pacific Oceans like the Indian Ocean Dipole (IOD) and El Niño,Southern Oscillation (ENSO) on the TBO. The 200 hPa velocity potential, 850 hPa zonal wind and sea-surface temperature datasets obtained from NCEP/NCAR reanalysis for the period 1950,2006 are used for the study of the TBO. The IOD and TBO have both in-phase (positive/negative IOD with positive/negative TBO) and out-of-phase (positive/negative IOD with negative/positive TBO) relationships. On the other hand, La Niña is associated with the positive phase of TBO and El Niño with the negative phase. In the presence of El Niño (La Niña), positive (negative) IOD is associated with negative (positive) TBO and in the absence of ENSO, positive (negative) IOD is associated with positive (negative) phase of TBO. When ENSO is associated with TBO, it tends to dominate the biennial transition irrespective of IOD. In-phase Indian to Australian monsoon transition of TBO is controlled by ENSO. IOD,TBO association is strong and significant in the absence of ENSO only. The biennial reversal is confined to the Indian Ocean in the TBO cycle associated with IOD only. Thus IOD can be considered as the local forcing for the biennial monsoon cycle, and ENSO the remote effect. Copyright © 2010 Royal Meteorological Society [source]

Terrestrial and airborne non-bacterial ice nuclei

S. K. Henderson-Begg
Abstract To freeze above ,36.5 °C, water requires the presence of an ice nucleus (IN). These can be inert particles or living or dead biological material. As they are the most efficient, inducing freezing at up to ,1.8 °C, bacteria are the most widely studied biological IN. Here, we show that there is a huge repository of IN in lichens which comprise a large biomass and are able to become airborne. The lichen IN are similar to those we have detected in urban air, exhibiting heat sensitivity but resistance to lysozyme. This suggests many airborne IN are non-bacterial and that eukaryotic IN may be more important to atmospheric processes than previously thought. Copyright © 2009 Royal Meteorological Society [source]