bluuebunny/crossref_metadata_2025 huggingface dataset:
ON VIBRATION OF FUNCTIONALLY GRADED PLATES ACCORDING TO A REFINED TRIGONOMETRIC PLATE THEORY
Authors: ZENKOUR ASHRAF M.
Published: June 2005

The displacement components are expressed by trigonometric series representation through the plate thickness to develop a two-dimensional theory. This trigonometric shear deformation plate theory is used to perform free-vibration analysis of a simply supported functionally graded thick plate. Lamé's coefficients and density for the material of the plate are assumed to vary in the thickness direction only. Effects of rotatory inertia are considered in the present theory and the vibration natural frequencies are investigated. The results obtained from this theory are compared with those obtained from a 3D elasticity analysis and various equivalent theories that are available. A detailed analysis is carried out to study the various natural frequencies of functionally graded material plates. The influences of the transverse shear deformation, plate aspect ratio, side-to-thickness ratio and volume fraction distributions are investigated.
BIODIVERSITY CONSIDERATIONS IN STRATEGIC ENVIRONMENTAL ASSESSMENT: A CASE STUDY OF THE NEPAL WATER PLAN
Authors: UPRETY BATU KRISHNA
Published: June 2005

Biodiversity conservation has been promoted in Nepal (within and outside protected areas) over the last three decades through relevant policies and legislations. The government has encouraged the participation of people through community user groups in managing the biodiversity and sharing the benefits. About 50 percent of the total revenue generated in protected areas is provided annually to such groups for resource management and community development activities. Forests are also managed by involving community users. Recently, attempts were made to manage biodiversity through an environmental impact assessment (EIA) process. The Nepal Biodiversity Strategy (2002) and Water Resources Strategy (2002), under implementation, recognise the role of EIA in mainstream biodiversity conservation in development programmes. However, biodiversity is under immense pressure due to infrastructure, water resources and socioeconomic development programmes and projects. His Majesty's Government of Nepal has made a policy commitment in its Tenth Plan (2002–2007) to carry out strategic environmental assessment (SEA) of development plans and programmes. Pursuant to this plan, an SEA has been carried out for the 25-year Nepal Water Plan. This plan is designed to, inter alia, promote the development of hydropower, irrigation, water-induced disaster management and drinking water programmes. This paper outlines the general understanding and knowledge of SEA in Nepal and examines how the SEA of the Nepal Water Plan addresses biodiversity aspects. It also outlines problems faced, and challenges and opportunities for strengthening SEA and its use to conserve biodiversity in Nepal.
Hazard and risk assessment of rainfall – induced landsliding along a railway line
Authors: Ko Ko C. , Chowdhury R. , Flentje P.
Published: June 2005

The occurrence of landslides along a transportation route such as a railway line can have severe and even catastrophic consequences. The assessment and management of hazard and risk is, therefore, of paramount importance. This paper introduces an approach for assessing the hazard and risk of rainfall-induced landsliding along a 30 km section of railway track. Careful analysis is made of rainfall data for previous storms, which have led to widespread landsliding. The recurrence interval of a typical landslide triggering rainstorm is estimated. From this the annual probability of widespread landslide occurrence is then calculated. This value combined with information on the frequency of train operations enables the estimation of the annual risk of human casualty. This estimate is then compared with proposed tolerable or acceptable levels. Such a systematic quantitative procedure can facilitate efficient risk management. Moreover, the outcomes of the assessments proposed in this paper can be combined with information and analyses about the relative landslide susceptibility of different section of track based on knowledge of local geology, topography and other factors.
Effectiveness of the Nitrate Sensitive Areas Scheme in reducing groundwater concentrations in England
Authors: Silgram M. , Williams A. , Waring R. , Neumann I. , Hughes A. , Mansour M. , Besien T.
Published: June 2005

The Nitrates Sensitive Areas (NSA) Scheme in England was a voluntary, compensated measure from 1990 to 2003 which aimed to reduce nitrate leaching from agricultural land to vulnerable groundwaters by modifying land use management. Measurements from 22 NSAs introduced in 1994/5 show an overall 34% decrease in the nitrate concentration of water leaching from the soils from 115 mg/l (1994/5-1995/6) to 76 mg/l (1998/9-1999/2000). This study looks at two NSAs in depth. The Old Chalford NSA consists of a small (81 km
2
) catchment with a series of spring sources in the Oolitic Limestone in Oxfordshire, whilst the Pollington NSA is the much larger (358 km
2
) catchment of three large public water supply sources (PWS) in the Sherwood Sandstone of North Yorkshire. Soil leaching model results suggest that the Scheme reduced root zone nitrate concentrations from 98 mg/l in 1994 to 69 mg/l in 1998 at Pollington NSA, and from 43 mg/l in 1990 to 37 mg/l in 1998 at Old Chalford NSA. These data served as inputs into flow modelling to quantify the effect of changes in the soil zone on groundwater concentration. At Old Chalford changes in the soil zone had a measurable effect at abstraction points after only two years, whereas Pollington NSA has shown little effect of the Scheme on abstracted groundwater concentration to date as the geology and geometry of the source catchment zones are expected to lead to a noticeable impact only after 30 years. Although results demonstrate the effectiveness of the Scheme in reducing root zone nitrate leaching, the timescales involved in groundwater responses mean that, in many areas, the impact of such pollution control measures will not be realized for several decades.
Acid sulphate soil remediation techniques on the Shoalhaven River floodplain, Australia
Authors: Indraratna B. , Golab A. , Glamore W. , Blunden B.
Published: June 2005

A commonly used flood mitigation technique in coastal areas of Australia during the late 1960s was the installation of one-way floodgates on flood mitigation drains. In regions affected by acid sulphate soils (the oxidation of pyrite in the soil forms sulphuric acid), the floodgates prevent tidal carbonate/bicarbonate buffering of the drains and thereby create reservoirs of acidic water (pH < 4.5) that discharge during low tide. Several acid sulphate soil remediation techniques have been used in coastal lowland in southeastern NSW, Australia. Following extensive monitoring and finite element modelling of groundwater conditions and quality, fixed level V-notch weirs were installed at three elevations to maintain elevated groundwater levels. The weirs successfully maintained the groundwater level above the acid sulphate soils, preventing additional pyrite oxidation, and reduced the rate of discharge of acid to the drain. Following further monitoring, investigation into anaerobic acid sources, and finite element-based geochemical modelling, modified two-way floodgates that allow tidal ingress were installed. The modified floodgates were successful in buffering the drain water pH before discharging the drain water into adjacent waterways. Numerical analysis based on finite element modelling was extended to illustrate that saline intrusion into the surrounding soil (as a result of tidal ingress and acid buffering in the drains) was not a major concern for the pastureland or other agricultural activities.
Topographic controls on coseismic rock slides during the 1999 Chi-Chi earthquake, Taiwan
Authors: Sepúlveda S.A. , Murphy W. , Petley D.N.
Published: June 2005

Stability back-analyses of sixteen massive, disrupted rock slides triggered by the 1999 Chi-Chi earthquake in the Tachia Valley in Central Taiwan indicated that geological and geotechnical factors alone appear insufficient to explain the distribution of failures under regional shaking. This incidence of landsliding suggests site amplification. A strong topographic effect can be identified when slope morphology and topography are considered in conjunction with strong motion data and theoretical models of topographic amplification to assess the failures and their distribution. The landslides triggered under these conditions are shallow and with a crown located near the crest of the slopes. Slope orientation and slope height provide easily observable field indices that are particularly important, as data suggest that these parameters, together with the wavelength of the seismic waves, control the amplification of ground motions. These observations could provide key inputs to assess unexpectedly high ground accelerations for landslide and seismic hazard studies.
Characterization of sandstone by electrical spectroscopy for stratigraphical and hydrogeological investigations
Authors: Scott J.B.T. , Barker R.D.
Published: June 2005

Electrical spectroscopy is a development of the geophysical techniques of resistivity and induced polarization in which both the in-phase and quadrature components of conductivity are measured over a range of frequencies, in this study between 0.001 and 1000 Hz. Measurements have been made on Permo–Triassic sandstone samples taken from boreholes across the UK and saturated with a synthetic groundwater solution. Some samples were also selected for saturation with different strengths of sodium chloride solution. The lithology of the samples was examined using optical microscopy and parameters such as porosity and pore-throat size have been measured. From this it is clear that the electrical spectra are strongly influenced by many aspects of the sandstone lithology, including carbonate and quartz cementation. Grain and pore-throat size and their distribution are particularly important factors in the frequency dependence of the spectra. Pore surface area is an important influence on the magnitude of the quadrature conductivity. The information contained in the electrical spectra could be a very useful tool for future investigations in geological stratigraphy, hydrogeology and petroleum geology. Electrical spectroscopy can be used in both surface and borehole geophysical measurements.
Volume sensitivity of cation-Cl− cotransporters is modulated by the interaction of two kinases: Ste20-related proline-alanine-rich kinase and WNK4
Authors: Gagnon Kenneth B. E. , England Roger , Delpire Eric
Published: June 2005

In the present study, we have demonstrated functional interaction between Ste20-related proline-alanine-rich kinase (SPAK), WNK4 [with no lysine (K)], and the widely expressed Na+-K+-2Cl− cotransporter type 1 (NKCC1). NKCC1 function, which we measured in Xenopus laevis oocytes under both isosmotic (basal) and hyperosmotic (stimulated) conditions, was unaffected when SPAK and WNK4 were expressed alone. In contrast, expression of both kinases with NKCC1 resulted in a significant increase in cotransporter activity and an insensitivity to external osmolarity or cell volume. NKCC1 activation is dependent on the catalytic activity of SPAK and likely also of WNK4, because mutations in their catalytic domains result in an absence of cotransporter stimulation. The results of our yeast two-hybrid experiments suggest that WNK4 does not interact directly with NKCC1 but does interact with SPAK. Functional experiments demonstrated that the binding of SPAK to WNK4 was also required because a SPAK-interaction-deficient WNK4 mutant (Phe997Ala) did not increase NKCC1 activity. We also have shown that the transport function of K+-Cl− cotransporter type 2 (KCC2), a neuron-specific KCl cotransporter, was diminished by the expression of both kinases under both isosmotic and hyposmotic conditions. Our data are consistent with WNK4 interacting with SPAK, which in turn phosphorylates and activates NKCC1 and phosphorylates and deactivates KCC2.
Calcium adaptation to sodium pump inhibition in a human megakaryocytic cell line
Authors: Kimura Masayuki , Cao Xiaojian , Aviv Abraham
Published: June 2005

The unique characteristics of the platelet Na/Ca exchanger, i.e., its dependence on both transmembrane Na and K gradients, render it highly sensitive to Na pump inhibition. In this project, we observed that the human megakaryocytic cell line CHRF-288 expresses both the α1- and α3-isoforms of the Na-K-ATPase. Inhibition of the Na pump increased the RNA and protein expressions of sarco(endo)plasmic reticulum Ca-ATPase 2b, cytosolic Na and Ca, and the freely exchangeable Ca in the endoplasmic reticulum. These changes occurred in concert with diminished store-operated Ca entry and an increase in the maximal activity of the Na/Ca exchanger. Inhibition of the Na pump by ouabain was more effective in inducing these changes than diminishing medium K. Collectively, these observations point to an integrative effort to counteract the impact of Na pump inhibition by Ca sequestration into the endoplasmic reticulum, diminished Ca entry, and increased activity of the Na/Ca exchanger. The implications of these findings in platelet biology are discussed.
Creatine transporter localization in developing and adult retina: importance of creatine to retinal function
Authors: Acosta Monica L. , Kalloniatis Michael , Christie David L.
Published: June 2005

Creatine and phosphocreatine are required to maintain ATP needed for normal retinal function and development. The aim of the present study was to determine the distribution of the creatine transporter (CRT) to gain insight to how creatine is transported into the retina. An affinity-purified antibody raised against the CRT was applied to adult vertebrate retinas and to mouse retina during development. Confocal microscopy was used to identify the localization pattern as well as co-localization patterns with a range of retinal neurochemical markers. Strong labeling of the CRT was seen in the photoreceptor inner segments in all species studied and labeling of a variety of inner neuronal cells (amacrine, bipolar, and ganglion cells), the retinal nerve fibers and sites of creatine transport into the retina (retinal pigment epithelium, inner retinal blood vessels, and perivascular astrocytes). The CRT was not expressed in Müller cells of any of the species studied. The lack of labeling of Müller cells suggests that neurons are independent of this glial cell in accumulating creatine. During mouse retinal development, expression of the CRT progressively increased throughout the retina until approximately postnatal day 10, with a subsequent decrease. Comparison of the distribution patterns of the CRT in vascular and avascular vertebrate retinas and studies of the mouse retina during development indicate that creatine and phosphocreatine are important for ATP homeostasis.
TGF-β1 stimulates monocyte chemoattractant protein-1 expression in mesangial cells through a phosphodiesterase isoenzyme 4-dependent process
Authors: Cheng Jingfei , Encarnacion Montserrat M. Diaz , Warner Gina M. , Gray Catherine E. , Nath Karl A. , Grande Joseph P.
Published: June 2005

Monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor (TGF)-β1 are critical mediators of renal injury by promoting excessive inflammation and extracellular matrix deposition, thereby contributing to progressive renal disease. In renal disease models, MCP-1 stimulates the production of TGF-β1. However, a potential role for TGF-β1 in the regulation of MCP-1 production by mesangial cells (MCs) has not previously been evaluated. The objectives of this study were to define the role of TGF-β1 in regulation of MCP-1 expression in cultured MCs and to define mechanisms through which rolipram (Rp), a phosphodiesterase isoenzyme 4 (PDE4) inhibitor with anti-inflammatory properties, alters MCP-1 expression. TGF-β1 induced MCP-1 in a time- and dose-dependent manner without increasing transcription of the MCP-1 gene. TGF-β1-mediated induction of MCP-1 occurred without activation of the NF-κB pathway. Rp blocked TGF-β1-stimulated MCP-1 expression via a protein kinase A-dependent process, at least in part, by decreasing MCP-1 message stability. Rp exerted no effect on activation of the Smad pathway by TGF-β1. TGF-β1-mediated induction of MCP-1 required activation of ERK and p38, both of which were suppressed by a PDE4 inhibitor. TGF-β1-stimulated reactive oxygen species (ROS) generation by MCs, and Rp inhibited ROS generation in TGF-β1-stimulated MCs; in addition, both Rp and ROS scavengers blocked TGF-β1-stimulated MCP-1 expression. We conclude that TGF-β1 stimulates MCP-1 expression through pathways involving activation of ERK, p38, and ROS generation. Positive cross-talk between TGF-β1 and MCP-1 signaling in MCs may underlie the development of progressive renal disease. Rp, by preventing TGF-β1-stimulated MCP-1 production, may offer a therapeutic approach in retarding the progression of renal disease.
Inducible expression of Snail selectively increases paracellular ion permeability and differentially modulates tight junction proteins
Authors: Carrozzino Fabio , Soulié Priscilla , Huber Denise , Mensi Noury , Orci Lelio , Cano Amparo , Féraille Eric , Montesano Roberto
Published: June 2005

Constitutive expression of the transcription factor Snail was previously shown to trigger complete epithelial-mesenchymal transition (EMT). The aim of this study was to determine whether inducible expression of Snail could modify epithelial properties without eliciting full mesenchymal conversion. For this purpose, we expressed mouse Snail (mSnail) cDNA in Madin-Darby canine kidney (MDCK) cells under the control of a doxycycline-repressible transactivator. Inducible expression of Snail did not result in overt EMT but induced a number of phenotypic alterations of MDCK cells, the most significant of which was the absence of fluid-filled blisterlike structures called “domes.” To understand the mechanisms responsible for dome suppression, we assessed the effect of mSnail expression on epithelial barrier function. Although mSnail did not alter tight junction (TJ) organization and permeability to uncharged solutes, it markedly decreased transepithelial electrical resistance. In light of these findings, we evaluated the ability of MDCK cell monolayers to maintain ionic gradients and found that expression of mSnail selectively increases Na+ and Cl− permeability. Analysis of the expression of claudins, transmembrane proteins that regulate TJ ionic permeability, showed that mSnail induces a moderate decrease in claudin-2 and a substantial decrease in claudin-4 and -7 expression. Together, these results suggest that induction of mSnail selectively increases the ionic permeability of TJs by differentially modulating the expression of specific claudins.
Maintenance of quantal size and immediately releasable granules in rat chromaffin cells by glucocorticoid
Authors: Xu Jianhua , Tang Kim San , Lu Van B. , Weerasinghe Chandana P. , Tse Amy , Tse Frederick W.
Published: June 2005

Glucocorticoid is reported to regulate catecholamine synthesis and storage. However, it is not clear whether the actual amount of catecholamine released from individual granules (quantal size, Q) in mature chromaffin cells is affected by glucocorticoid. Using carbon fiber amperometry, we found that dexamethasone did not affect mean cellular Q or the proportional release from different populations of granules in rat chromaffin cells cultured for 1 day in a serum-free defined medium. After two extra days of culture in the defined medium, there was a rundown in mean cellular Q, and it was associated with a shift in the proportional release from the different granule populations. This phenomenon could not be rescued by serum supplementation but could be prevented by dexamethasone via an action that was independent of changes in voltage-gated Ca2+ channel (VGCC) density. Using simultaneous measurements of membrane capacitance and cytosolic Ca2+ concentration, we found that for cells cultured in defined medium dexamethasone enhanced the exocytotic response triggered by a brief depolarization (50 ms) without affecting the VGCC density or the fast exocytotic response triggered via flash photolysis of caged Ca2+. Thus glucocorticoid may regulate the number of immediately releasable granules that are in close proximity to a subset of VGCC. Because chromaffin cells in vivo are exposed to high concentrations of glucocorticoid, our findings suggest that the paracrine actions of glucocorticoid maintain the mean catecholamine content in chromaffin cell granules as well as the colocalization of releasable granules with VGCCs.
Dominant-negative PKC-ε impairs apical actin remodeling in parallel with inhibition of carbachol-stimulated secretion in rabbit lacrimal acini
Authors: Jerdeva Galina V. , Yarber Francie A. , Trousdale Melvin D. , Rhodes Christopher J. , Okamoto Curtis T. , Dartt Darlene A. , Hamm-Alvarez Sarah F.
Published: June 2005

We investigated the involvement of PKC-ε in apical actin remodeling in carbachol-stimulated exocytosis in reconstituted rabbit lacrimal acinar cells. Lacrimal acinar PKC-ε cosedimented with actin filaments in an actin filament binding assay. Stimulation of acini with carbachol (100 μM, 2–15 min) significantly ( P ≤ 0.05) increased PKC-ε recovery with actin filaments in two distinct biochemical assays, and confocal fluorescence microscopy showed a significant increase in PKC-ε association with apical actin in stimulated acini as evidenced by quantitative colocalization analysis. Overexpression of dominant-negative (DN) PKC-ε in lacrimal acini with replication-defective adenovirus (Ad) resulted in profound alterations in apical and basolateral actin filaments while significantly inhibiting carbachol-stimulated secretion of bulk protein and β-hexosaminidase. The chemical inhibitor GF-109203X (10 μM, 3 h), which inhibits PKC-α, -β, -δ, and -ε, also elicited more potent inhibition of carbachol-stimulated secretion relative to Gö-6976 (10 μM, 3 h), which inhibits only PKC-α and -β. Transduction of lacrimal acini with Ad encoding syncollin-green fluorescent protein (GFP) resulted in labeling of secretory vesicles that were discharged in response to carbachol stimulation, whereas cotransduction of acini with Ad-DN-PKC-ε significantly inhibited carbachol-stimulated release of syncollin-GFP. Carbachol also increased the recovery of secretory component in culture medium, whereas Ad-DN-PKC-ε transduction suppressed its carbachol-stimulated release. We propose that DN-PKC-ε alters lacrimal acinar apical actin remodeling, leading to inhibition of stimulated exocytosis and transcytosis.
Differential responses of frequency components of renal sympathetic nerve activity to arterial pressure changes in conscious rats
Authors: Bertram Delphine , Oréa Valérie , Chapuis Bruno , Barrès Christian , Julien Claude
Published: June 2005

The present study examined the effects of baroreceptor loading and unloading on the various rhythms present in the renal sympathetic nerve activity (RSNA) of 10 conscious rats. Short-lasting (4–5 min), steady-state decreases (from −10 to −40 mmHg) and increases (from 5 to 30 mmHg) in arterial pressure (AP) were induced by the intravenous infusion of sodium nitroprusside and phenylephrine, respectively. The relationship between changes in AP level and RSNA total power (fast Fourier transform analysis; 0–25 Hz) was characterized by an inverse sigmoid function. Basal AP was located 6.3 mmHg above AP at the midrange of the curve, that is, near the lower plateau. Sigmoid relationships were also observed for spectral powers in the low (LF, 0.030–0.244 Hz), respiratory (0.79–2.5 Hz) and high-frequency (HF, 2.5–25 Hz) bands. In contrast, in the MF band (0.27–0.76 Hz) containing oscillations associated with Mayer waves, the AP-RSNA power relationship showed a bell curve shape with a maximum at 21 mmHg below basal AP. Similarly, changes in RSNA power at the frequency of the heart beat were well characterized by a bell curve reaching a maximum at 22 mmHg below basal AP. Under baseline conditions, LF, MF, respiratory and HF powers contributed ∼3, 10, 18, and 69% of the total RSNA power, respectively. The pulse-synchronous oscillation of RSNA accounted for only 11 ± 1% of HF power. The contribution of HF power to total power did not change consistently with AP changes. Therefore, most of the baroreflex-induced changes in RSNA are mediated by changes in the amplitude of fast, irregular fluctuations.
Broadband frequency dependence of respiratory impedance in rats
Authors: Thamrin Cindy , Sly Peter D. , Hantos Zoltán
Published: June 2005

Past studies in humans and other species have revealed the presence of resonances and antiresonances, i.e., minima and maxima in respiratory system impedance (Zrs), at frequencies much higher than those commonly employed in clinical applications of the forced oscillation technique (FOT). To help understand the mechanisms behind the first occurrence of antiresonance in the Zrs spectrum, the frequency response of the rat was studied by using FOT at both low and high frequencies. We measured Zrs in both Wistar and PVG/c rats using the wave tube technique, with a FOT signal ranging from 2 to 900 Hz. We then compared the high-frequency parameters, i.e., the first antiresonant frequency (far,1) and the resistive part of Zrs at that frequency [Rrs(far,1)], with parameters obtained by fitting a modified constant-phase model to low-frequency Zrs spectra. The far,1 was 570 ± 43 (SD) Hz and 456 ± 16 Hz in Wistar and PVG/c rats, respectively, and it did not shift with respiratory gases of different densities (air, heliox, and a mixture of SF6). The far,1 and Rrs(far,1) were relatively independent of methacholine-induced bronchoconstriction but changed significantly with increasing transrespiratory pressures up to 20 cmH2O, in the same way as airway resistance but independently of changes to tissue parameters. These results suggest that, unlike the human situation, the first antiresonance in the rat is not primarily dependent on the acoustic dimensions of the respiratory system and can be explained by interactions between compliances and inertances localized to the airways, but this most likely does not include airway wall compliance.
Laryngeal muscle responses to mechanical displacement of the thyroid cartilage in humans
Authors: Loucks Torrey M. J. , Poletto Christopher J. , Saxon Keith G. , Ludlow Christy L.
Published: June 2005

Speakers may use laryngeal sensory feedback to adjust vocal fold tension and length before initiating voice. The mechanism for accurately initiating voice at an intended pitch is unknown, given the absence of laryngeal muscle spindles in animals and conflicting findings regarding their existence in humans. Previous reports of rapid changes in voice fundamental frequency following thyroid cartilage displacement suggest that changes in vocal fold length modulate laryngeal muscle contraction in humans. We tested the hypothesis that voice changes resulting from mechanical perturbation are due to rapid responses in the intrinsic laryngeal muscles. Hooked wire electrodes were used to record from the thyroarytenoid, cricothyroid, and sternothyroid muscles along with surface electrodes on the skin overlying the thyroid cartilage in 10 normal adults. Servomotor displacements produced consistent changes in the subjects’ vocal fundamental frequency at 70–80 ms, demonstrating changes in vocal fold length and tension. No simultaneous electromyographic responses occurred in the thyroarytenoid or cricothyroid muscles in any subjects. Instead, short-latency responses at 25–40 ms following stimulus onset occurred in the sternothyroid muscles, simultaneous with responses in the surface recordings. The sternothyroid responses may modulate long-latency changes in voice fundamental frequency (∼150 ms). The absence of intrinsic laryngeal muscle responses is consistent with a lack of spindles in these muscles. Our results suggest that other sensory receptors, such as mucosal mechanoreceptors, provide feedback for voice control.
Wave Response during Hydrostatic and Geostrophic Adjustment. Part I: Transient Dynamics
Authors: Chagnon Jeffrey M. , Bannon Peter R.
Published: June 2005

The adjustment of a compressible, stably stratified atmosphere to sources of hydrostatic and geostrophic imbalance is investigated using a linear model. Imbalance is produced by prescribed, time-dependent injections of mass, heat, or momentum that model those processes considered “external” to the scales of motion on which the linearization and other model assumptions are justifiable. Solutions are demonstrated in response to a localized warming characteristic of small isolated clouds, larger thunderstorms, and convective systems.

For a semi-infinite atmosphere, solutions consist of a set of vertical modes of continuously varying wavenumber, each of which contains time dependencies classified as steady, acoustic wave, and buoyancy wave contributions. Additionally, a rigid lower-boundary condition implies the existence of a discrete mode—the Lamb mode— containing only a steady and acoustic wave contribution. The forced solutions are generalized in terms of a temporal Green's function, which represents the response to an instantaneous injection.

The response to an instantaneous warming with geometry representative of a small, isolated cloud takes place in two stages. Within the first few minutes, acoustic and Lamb waves accomplish an expansion of the heated region. Within the first quarter-hour, nonhydrostatic buoyancy waves accomplish an upward displacement inside of the heated region with inflow below, outflow above, and weak subsidence on the periphery—all mainly accomplished by the lowest vertical wavenumber modes, which have the largest horizontal group speed. More complicated transient patterns of inflow aloft and outflow along the lower boundary are accomplished by higher vertical wavenumber modes. Among these is an outwardly propagating rotor along the lower boundary that effectively displaces the low-level inflow upward and outward.

A warming of 20 min duration with geometry representative of a large thunderstorm generates only a weak acoustic response in the horizontal by the Lamb waves. The amplitude of this signal increases during the onset of the heating and decreases as the heating is turned off. The lowest vertical wavenumber buoyancy waves still dominate the horizontal adjustment, and the horizontal scale of displacements is increased by an order of magnitude. Within a few hours the transient motions remove the perturbations and an approximately trivial balanced state is established.

A warming of 2 h duration with geometry representative of a large convective system generates a weak but discernible Lamb wave signal. The response to the conglomerate system is mainly hydrostatic. After several hours, the only signal in the vicinity of the heated region is that of inertia–gravity waves oscillating about a nontrivial hydrostatic and geostrophic state.

This paper is the first of two parts treating the transient dynamics of hydrostatic and geostrophic adjustment. Part II examines the potential vorticity conservation and the partitioning of total energy.
Seasonal Variability of Teleconnection Patterns
Authors: Frederiksen Jorgen S. , Branstator Grant
Published: June 2005

The seasonal variability of 300-hPa global streamfunction fields taken from a 40-yr period of reanalyzed observations starting on 1 January 1958 and from long 497- and 900-yr general circulation model (GCM) datasets forced by sea surface temperatures (SSTs) is examined and analyzed in terms of empirical orthogonal functions (EOFs), principal oscillation patterns (POPs), and particularly finite-time principal oscillation patterns (FTPOPs). The FTPOPs are the eigenvectors of the propagator, over a 1-yr period covering the annual cycle, that has been constructed by fitting a linear stochastic model with a time-dependent matrix operator to atmospheric fluctuations based on the daily or twice-daily 300-hPa streamfunction datasets.

The leading FTPOPs are large-scale teleconnection patterns and by construction they are the empirical analogs of finite-time normal modes (FTNMs) of linear instability theory. Hence, by comparing FTPOPs to FTNMs, the study provides insight into the ability of linear theory to explain seasonal and intraseasonal variability in the structure and growth rates of large-scale disturbances. The study finds that the leading FTPOP teleconnection patterns have similar seasonal cycles of relative growth rates and amplitudes to the leading FTNMs of the barotropic vorticity equation with 300-hPa basic states that change with the annual cycle; the largest amplitudes of both theoretical and empirical modes occur in late boreal winter or early spring, and minimum amplitudes in boreal autumn, with the GCM-based FTPOPs having additional secondary maxima in early boreal summer. In each month, there are leading POPs and EOFs that closely resemble the leading FTPOPs. Also, the growth rates of leading FTNMs and FTPOPs during each season are generally similar to those of respective leading normal modes and POPs calculated for that season. Thus the perturbations are reacting to the seasonally varying basic state faster than the state is changing and this appears to explain why linear planetary wave models with time-independent basic states can be useful. Nevertheless, intermodal interference effects, as well as intramodal interference effects, between the eastward and westward propagating components of single traveling modes, can play important roles in the evolution of FTPOPs and FTNMs, particularly in boreal spring.

This study has examined the roles of internal instability and interannual SST variability in the behavior of leading FTPOPs and has also used comparisons of FTPOPs and FTNMs for GCM simulations with and without interannually varying SSTs to assess the role of internal instability and SST variations in organizing interannual atmospheric variability. The comparison indicates that both factors are significant. The results found here also support a close relationship between the boreal spring predictability barrier of some models of climate prediction over the tropical Pacific Ocean and the amplitudes of large-scale instabilities and teleconnection patterns of the atmospheric circulation.
Multiplicative Noise and Non-Gaussianity: A Paradigm for Atmospheric Regimes?
Authors: Sura Philip , Newman Matthew , Penland Cécile , Sardeshmukh Prashant
Published: June 2005

Atmospheric circulation statistics are not strictly Gaussian. Small bumps and other deviations from Gaussian probability distributions are often interpreted as implying the existence of distinct and persistent nonlinear circulation regimes associated with higher-than-average levels of predictability. In this paper it is shown that such deviations from Gaussianity can, however, also result from linear stochastically perturbed dynamics with multiplicative noise statistics. Such systems can be associated with much lower levels of predictability. Multiplicative noise is often identified with state-dependent variations of stochastic feedbacks from unresolved system components, and may be treated as stochastic perturbations of system parameters. It is shown that including such perturbations in the damping of large-scale linear Rossby waves can lead to deviations from Gaussianity very similar to those observed in the joint probability distribution of the first two principal components (PCs) of weekly averaged 750-hPa streamfunction data for the past 52 winters. A closer examination of the Fokker–Planck probability budget in the plane spanned by these two PCs shows that the observed deviations from Gaussianity can be modeled with multiplicative noise, and are unlikely the results of slow nonlinear interactions of the two PCs. It is concluded that the observed non-Gaussian probability distributions do not necessarily imply the existence of persistent nonlinear circulation regimes, and are consistent with those expected for a linear system perturbed by multiplicative noise.
ITCZ Breakdown in Three-Dimensional Flows
Authors: Wang Chia-chi , Magnusdottir Gudrun
Published: June 2005

The intertropical convergence zone (ITCZ) is observed to undulate and at times break down into a series of tropical disturbances in several days. Some of these disturbances may develop into tropical cyclones and move to higher latitudes, while others dissipate, and the ITCZ may reform in the original region. It has been proposed that the ITCZ may break down because of its heating-induced potential vorticity (PV) anomalies. Here this process is examined in three-dimensional simulations using a primitive equation model. A simulation of the ITCZ in a background state of rest is compared to simulations in different background flows. The effect of different vertical structures of the prescribed heating is also examined.

Deep heating induces a positive PV anomaly in the lower troposphere, leading to a reversal of the PV gradient on the poleward side of the heating, while the induced PV anomaly at upper levels is negative, leading to a reversal of the PV gradient on the equatorward side of the heating. The response at upper levels leads to a weaker PV gradient change, but the response is greater in areal extent than the lower-tropospheric response. For shallow heating, the lower-tropospheric PV response is greater than that for deep heating, and there is no upper-tropospheric PV response. The ITCZ lasts longer before breaking in this case than in the deep heating case.

Effects of the background flow are mainly felt in the deep heating cases. When the background flow enforces the PV-induced wind field, ITCZ breakdown occurs more rapidly, whereas when the background flow is opposite to the PV-induced flow, ITCZ breakdown takes longer and the ITCZ may dissipate before breakdown.
The Stratiform and Convective Components of Surface Precipitation
Authors: Tremblay André
Published: June 2005

One year of precipitation records taken from a subset of the World Meteorological Organization (WMO) global rain gauge network has been analyzed. This analysis has shown that the distribution of accumulation of precipitation with the rainfall rate is characterized by an exponential law. This relationship seems to be universal and is present regardless of the averaging interval considered. The data structure suggests that this exponential distribution can be used as a basic state to partition surface precipitation into stratiform and convective components. The physical basis of this approach is investigated and discussed using Monte Carlo simulations based on a simple cloud model. The methodology is validated using a Fourier analysis in time, and average global monthly maps of convective and stratiform precipitation are presented to illustrate the feasibility of the technique.
Excitation Mechanism of Mixed Rossby–Gravity Waves in the Equatorial Atmosphere: Role of the Nonlinear Interactions among Equatorial Waves
Authors: Raupp Carlos F. M. , Silva Dias Pedro L.
Published: June 2005

One possible explanation for the relatively high signal of the mixed Rossby–gravity waves observed in the tropical atmosphere is explored in this paper. This explanation is based on the nonlinear interactions among equatorial waves, and is made by adopting the nonlinear shallow water equations on the equatorial β plane. These equations are solved by a spectral method that uses the eigensolutions of the linear problem as the expansion basis. Numerical simulations are performed with a specified stationary mass source representative of the tropospheric heating associated with the typical convective activity over the Amazon Basin during the austral summer period. The numerical results show that the mixed Rossby–gravity waves are excited by a nonlinear mechanism in which the slow modes excited by the thermal forcing generate a quasigeostrophic basic state that supplies energy especially to the mixed Rossby–gravity waves with zonal wavenumbers 4 and 5, which have periods of the order of 4 days. The phase propagation of these unstable mixed modes leads to a periodic energy exchange between the mixed Rossby–gravity waves and the quasigeostrophic modes (Rossby and ultralong Kelvin modes). This regular nonlinear energy exchange implies a 4-day-cycle vacillation in the solution, which might be linked to the 4–6-day local oscillations in the dynamical field data throughout the Amazon region found in observational studies. Besides the importance of quasigeostrophic modes in the excitation of mixed Rossby–gravity waves, the numerical results also suggest that the predominance of the slow modes is crucial for maintaining the high signal of the unstable mixed modes, since these waves are strongly suppressed by the inclusion of the fast modes in the integration.
Observations and Modeling of Banded Orographic Convection
Authors: Kirshbaum Daniel J. , Durran Dale R.
Published: June 2005

Radar images and numerical simulations of three shallow convective precipitation events over the Coastal Range in western Oregon are presented. In one of these events, unusually well-defined quasi-stationary banded formations produced large precipitation enhancements in favored locations, while varying degrees of band organization and lighter precipitation accumulations occurred in the other two cases. The difference between the more banded and cellular cases appeared to depend on the vertical shear within the orographic cap cloud and the susceptibility of the flow to convection upstream of the mountain. Numerical simulations showed that the rainbands, which appeared to be shear-parallel convective roll circulations that formed within the unstable orographic cap cloud, developed even over smooth mountains. However, these banded structures were better organized, more stationary, and produced greater precipitation enhancement over mountains with small-scale topographic obstacles. Low-amplitude random topographic roughness elements were found to be just as effective as more prominent subrange-scale peaks at organizing and fixing the location of the orographic rainbands.
Numerical Simulations of Interactions between Gravity Waves and Deep Moist Convection
Authors: Eitzen Zachary A. , Randall David A.
Published: June 2005

This study uses a numerical model to simulate deep convection both in the Tropics over the ocean and the midlatitudes over land. The vertical grid that was used extends into the stratosphere, allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates. A large number of trajectories are used to evaluate the behavior of tracers in the troposphere, and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement. Conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere. In addition, Fourier analysis is used to characterize the waves in the stratosphere; it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers. Finally, this study examines the wave energy flux as a means to provide a link between the tropospheric behavior of the convection and the strength of the waves in the stratosphere.
Wave Response during Hydrostatic and Geostrophic Adjustment. Part II: Potential Vorticity Conservation and Energy Partitioning
Authors: Chagnon Jeffrey M. , Bannon Peter R.
Published: June 2005

This second part of a two-part study of the hydrostatic and geostrophic adjustment examines the potential vorticity and energetics of the acoustic waves, buoyancy waves, Lamb waves, and steady state that are generated following the prescribed injection of heat into an isothermal atmosphere at rest. The potential vorticity is only nonzero for the steady class and depends only on the spatial and time-integrated properties of the injection. The waves contain zero net potential vorticity, but undergo a time-dependent vorticity exchange involving latent and relative vorticities.

The energy associated with a given injection may be partitioned distinctly among the various wave classes. The characteristics of this partitioning depend on the spatiotemporal detail of the injection, as well as whether the imbalance is generated by injection of heat, mass, or momentum. Spatially, waves of a scale similar to that of the injection are preferentially excited. Temporally, an extended duration injection preferentially filters high-frequency waves. An instantaneous injection, that is, the temporal Green’s function, contains the largest proportions of the high-frequency waves.

The proportions of kinetic, available elastic, and available potential energies that are carried by the various waves are functions of the homogeneous system. For example, deep buoyancy waves of small horizontal scale primarily contain equal portions of available potential and vertical kinetic energy. The steady state contains more available potential energy than kinetic energy at small horizontal scale, and vice versa. These qualities of the wave energetics illustrate the mechanisms that characterize the physics of each wave class.

The evolution and spectral partitioning of the energetics following localized warmings identical to those in Part I are presented in order to illustrate some of these basic properties of the energetics. For example, a heating lasting longer than a few minutes does not excite acoustic waves. However, Lamb waves of wide horizontal scale can be excited by a heating of several hours. The first buoyancy waves to be filtered by an extended duration heating are those of the deepest and narrowest structure that have a frequency approaching the buoyancy frequency. The energetics of the steady state depends only on the spatial and time-integrated properties of the warming. However, the energetics and transient evolution toward a given steady state depend on the temporal properties of the warming and may differ widely.
Moisture Tendency Equations in a Tropical Atmosphere
Authors: López Carrillo C. , Raymond D. J.
Published: June 2005

Direct diagnostic evaluation of the moisture tendency in the moisture equation is very difficult in practice because two poorly measured terms, moisture convergence and precipitation, dominate the equation. Using the near constancy in space and time of the tropical temperature profile, a variety of energy and entropy based equations have been employed to obtain indirect estimates of the moisture budget. In this paper rigorous versions of the energy and entropy equations are developed. The strengths and weakness of these two formulations are complementary, allowing the authors to estimate moistening and drying tendencies with high confidence when the two formulations are used together.

This study applies the theory to data from Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results demonstrate how convection regulates the tropospheric humidity, drying the atmosphere when it becomes too moist, and moistening it when it becomes too dry.