bluuebunny/crossref_metadata_2025 huggingface dataset:
Diversities in hepatic HIF-1, IGF-I/IGFBP-1, LDH/ICD, and their mRNA expressions induced by CoCl2 in Qinghai-Tibetan plateau mammals and sea level mice
Authors: Chen Xue-Qun , Wang Shi-Jun , Du Ji-Zeng , Chen Xiao-Cheng
Published: September 2006

Ochotona curzoniae and Microtus oeconomus are the native mammals living on the Qinghai-Tibetan-Plateau of China. The molecular mechanisms of their acclimatization to the Plateau-hypoxia remain unclear. Expressions of hepatic hypoxia-inducible factor (HIF)-1α, insulin-like growth factor-I (IGF-I)/IGF binding protein (BP)-1(IGFBP-1; including genes), and key metabolic enzymatic genes [lactate dehydrogenase (LDH)-A/isocitrate dehydrogenase (ICD)] are compared in Qinghai-Tibetan-Plateau mammals and sea-level mice after injection of CoCl2 (20, 40, or 60 mg/kg) and normobaric hypoxia (16.0% O2, 10.8% O2, and 8.0% O2) for 6 h, tested by histochemistry, Western blot analysis, ELISA, and RT-PCR. Major results are CoCl2 markedly increased 1) HIF-1α only in mice, 2) hepatic and circulatory IGF-I in M. oeconomus, 3) hepatic IGFBP-1 in mice and O. curzoniae, and 4) LDH-A but reduced ICD mRNA in mice (CoCl2 20 mg/kg) but were unchanged in the Tibetan mammals. Normobaric hypoxia markedly 1) increased HIF-1α and LDH-A mRNA in mice and M. oeconomus (8.0% O2) not in O. curzoniae, and 2) reduced ICD mRNA in mice and M. oeconomus (8.0% O2) not in O. curzoniae. Results suggest that 1) HIF-1α responsiveness to hypoxia is distinct in lowland mice and plateau mammals, reflecting a diverse tolerance of the three species to hypoxia; 2) CoCl2 induces diversities in HIF-1, IGF-I/IGFBP-1 protein or genes in mice, M. oeconomus, and O. curzoniae. In contrast, HIF-1 mediates IGFBP-1 transcription only in mice and in M. oeconomus (subjected to severe hypoxia); 3) differences in IGF-I/IGFBP-1 expressions induced by CoCl2 reflect significant diversities in hormone regulation and cell protection from damage; and 4) activation of anaerobic glycolysis and reduction of Krebs cycle represents strategies of lowland-animals vs. the stable metabolic homeostasis of plateau-acclimatized mammals.
Dynamic Synchronization of Purkinje Cell Simple Spikes
Authors: Shin Soon-Lim , De Schutter Erik
Published: September 2006

Purkinje cells (PCs) integrate all computations performed in the cerebellar cortex to inhibit neurons in the deep cerebellar nuclei (DCN). Simple spikes recorded in vivo from pairs of PCs separated by <100 μm are known to be synchronized with a sharp peak riding on a broad peak, but the significance of this finding is unclear. We show that the sharp peak consists exclusively of simple spikes associated with pauses in firing. The broader, less precise peak was caused by firing-rate co-modulation of faster firing spikes. About 13% of all pauses were synchronized, and these pauses had a median duration of 20 ms. As in vitro studies have reported that synchronous pauses can reliably trigger spikes in DCN neurons, we suggest that the subgroup of spikes causing the sharp peak is important for precise temporal coding in the cerebellum.
Spectral Receptive Field Properties Explain Shape Selectivity in Area V4
Authors: David Stephen V. , Hayden Benjamin Y. , Gallant Jack L.
Published: September 2006

Neurons in cortical area V4 respond selectively to complex visual patterns such as curved contours and non-Cartesian gratings. Most previous experiments in V4 have measured responses to small, idiosyncratic stimulus sets and no single functional model yet accounts for all of the disparate results. We propose that one model, the spectral receptive field (SRF), can explain many observations of selectivity in V4. The SRF describes tuning in terms of the orientation and spatial frequency spectrum and can, in principle, predict the response to any visual stimulus. We estimated SRFs for neurons in V4 of awake primates by linearized reverse correlation of responses to a large set of natural images. We find that V4 neurons have large orientation and spatial frequency bandwidth and often bimodal orientation tuning. For comparison, we estimated SRFs for neurons in primary visual cortex (V1). Consistent with previous observations, we find that V1 neurons have narrower bandwidth than that of V4. To determine whether estimated SRFs can account for previous observations of selectivity, we used them to predict responses to Cartesian gratings, non-Cartesian gratings, natural images, and curved contours. Based on these predictions, we find that the majority of neurons in V1 are selective for Cartesian gratings, whereas the majority of V4 neurons are selective for non-Cartesian gratings or natural images. The SRF describes visual tuning properties with a second-order nonlinear model. These results support the hypothesis that a second-order model is sufficient to describe the general mechanisms mediating shape selectivity in area V4.
Effects of Small Ischemic Lesions in the Primary Motor Cortex on Neurophysiological Organization in Ventral Premotor Cortex
Authors: Dancause Numa , Barbay Scott , Frost Shawn B. , Zoubina Elena V. , Plautz Erik J. , Mahnken Jonathan D. , Nudo Randolph J.
Published: September 2006

After a cortical lesion, cortical areas distant from the site of injury are known to undergo physiological and anatomical changes. However, the mechanisms through which reorganization of distant cortical areas is initiated are poorly understood. In a previous publication, we showed that the ventral premotor cortex (PMv) undergoes physiological reorganization after a lesion destroying the majority of the primary motor cortex (M1) distal forelimb representation (DFL). After large lesions destroying >50% of the M1 DFL, the PMv DFL invariably increased in size, and the amount of the increase was positively correlated with the size of lesion. To determine whether lesions destroying <50% of the M1 DFL followed a similar trajectory, we documented PMv reorganization using intracortical microstimulation techniques after small, ischemic lesions targeting subregions within the M1 DFL. In contrast to earlier results, lesions resulted in a reduction of the PMv DFL regardless of their location. Further, because recent anatomical findings suggest a segregation of PMv connectivity with M1, we examined two lesion characteristics that may drive alterations in PMv physiological reorganization: location of the lesion with respect to PMv connectivity and relative size of the lesion. The results suggest that after a lesion in the M1 DFL, the induction of representational plasticity in PMv, as evaluated using intracortical microstimulation, is related more to the size of the lesion than to the disruption of its intracortical connections.
WNK Protein Kinases Modulate Cellular Cl− Flux by Altering the Phosphorylation State of the Na-K-Cl and K-Cl Cotransporters
Authors: Kahle Kristopher T. , Rinehart Jesse , Ring Aaron , Gimenez Ignacio , Gamba Gerardo , Hebert Steven C. , Lifton Richard P.
Published: September 2006

Precise control of cellular Cl− transport is necessary for many fundamental physiological processes. For example, the intracellular concentration of Cl−, fine-tuned through the coordinated action of cellular Cl− influx and efflux mechanisms, determines whether a neuron’s response to GABA is excitatory or inhibitory. In epithelia, synchrony between apical and basolateral Cl− flux, and transcellular and paracellular Cl− transport, is necessary for efficient transepithelial Cl− reabsorption or secretion. In cells throughout the body, coordination of Cl− entry and exit mechanisms help defend against changes in cell volume. The Na-K-Cl and K-Cl cotransporters of the SLC12 gene family are important molecular determinants of Cl− entry and exit, respectively, in these systems. The WNK serine-threonine kinase family, members of which are mutated in an inherited form of human hypertension, are components of a signaling pathway that coordinates Cl− influx and efflux through SLC12 cotransporters to dynamically regulate intracellular Cl− activity.
Selenoproteins and Their Impact on Human Health Through Diverse Physiological Pathways
Authors: Moghadaszadeh Behzad , Beggs Alan H.
Published: September 2006

In the last few decades, the importance of selenium in human health has been the subject of numerous studies. It is believed that the physiological effects of selenium occur mainly through the function of selenoproteins, which incorporate selenium in the form of one or more selenocysteine residues. Recent advances in understanding the complex regulation of selenoprotein synthesis and functional characterization of several members of the selenoprotein family have contributed to an improved comprehension of the role(s) of selenium in human health and the great diversity of physiological pathways influenced by this trace element.
Molecular and Physiological Bases of the K+ Circulation in the Mammalian Inner Ear
Authors: Hibino Hiroshi , Kurachi Yoshihisa
Published: September 2006

Endolymph, the extracellular solution in cochlea, contains 150 mM K+ and exhibits a potential of approximately +80 mV relative to neighboring extracellular spaces. This unique situation, essential for hearing, is maintained by K+ circulation from perilymph to endolymph through the cochlear lateral wall. Recent studies have identified ion-transport molecules involved in the K+ circulation and their pathophysiological relevance.
Quick Minds Don't Blink: Electrophysiological Correlates of Individual Differences in Attentional Selection
Authors: Martens Sander , Munneke Jaap , Smid Hendrikus , Johnson Addie
Published: September 2006

A well-established phenomenon in the study of attention is the attentional blink—a deficit in reporting the second of two targets when it occurs 200–500 msec after the first. Although the effect has been shown to be robust in a variety of task conditions, not every individual participant shows the effect. We measured electroencephalographic activity for “nonblinkers” and “blinkers” during execution of a task in which two letters had to be detected in an sequential stream of digit distractors. Nonblinkers showed an earlier P3 peak, suggesting that they are quicker to consolidate information than are blinkers. Differences in frontal selection positivity were also found, such that nonblinkers showed a larger difference between target and distractor activation than did blinkers. Nonblinkers seem to extract target information better than blinkers do, allowing them to reject distractors more easily and leaving sufficient resources available to report both targets.
A Reevaluation of the Electrophysiological Correlates of Expert Object Processing
Authors: Scott Lisa S. , Tanaka James W. , Sheinberg David L. , Curran Tim
Published: September 2006

Subordinate-level object processing is regarded as a hallmark of perceptual expertise. However, the relative contribution of subordinate- and basic-level category experience in the acquisition of perceptual expertise has not been clearly delineated. In this study, participants learned to classify wading birds and owls at either the basic (e.g., wading bird, owl) or the subordinate (e.g., egret, snowy owl) level. After 6 days of training, behavioral results showed that subordinate-level but not basic-level training improved subordinate discrimination of trained exemplars, novel exemplars, and exemplars from novel species. Event-related potentials indicated that both basic- and subordinate-level training enhanced the early N170 component, but only subordinate-level training amplified the later N250 component. These results are consistent with models positing separate basic and subordinate learning mechanisms, and, contrary to perspectives attempting to explain visual expertise solely in terms of subordinate-level processing, suggest that expertise enhances neural responses of both basic and subordinate processing.
The Involvement of the Inferior Parietal Cortex in the Numerical Stroop Effect and the Distance Effect in a Two-digit Number Comparison Task
Authors: Liu Xun , Wang Hongbin , Corbly Christine R. , Zhang Jiajie , Joseph Jane E.
Published: September 2006

The neural mechanism of number representation and processing is currently under extensive investigation. In this functional magnetic resonance imaging study, we designed a number comparison task to examine how people represent and compare two-digit numbers in the brain, and whether they process the decade and unit digits in parallel. We manipulated the decade-unit-digit congruency and numerical distance between the pairs of numbers. We observed both Stroop-like interference and the distance effect in the participants' performance. People responded more slowly to incongruent pairs of numbers and pairs of a smaller distance. The inferior parietal cortex showed common and distinct patterns of activation for both attentional selection and number comparison processes, and its activity was modulated by the Stroop-like interference effect and the distance effect. Taken together, these results support both parallel and holistic comparison of two-digit numbers in the brain.
Electrophysiological Correlates of Retrieval Processing: Effects of Consistent versus Inconsistent Retrieval Demands
Authors: Johnson Jeffrey D. , Rugg Michael D.
Published: September 2006

Studies employing event-related potentials (ERPs) during tests of recognition memory have reported differences in neural activity elicited by new test items according to the specific demands of the retrieval task, such as retrieving studied words versus pictures. The present study investigated whether differential processing of new items is possible when retrieval demands vary unpredictably on a trial-by-trial basis. In separate study-test phases, subjects encoded lists of intermixed words and pictures, and undertook retrieval tests with words as test items. Each test item was preceded by a task cue that signaled whether subjects were to attempt to retrieve a word or a picture from the study list. In the “blocked”condition, the targeted study material remained constant throughout the test, whereas in the “mixed”condition, the targeted material varied unpredictably across trials. New-item ERPs were more positive-going when words rather than pictures were targeted in the “blocked” condition, replicating previous findings, but this effect was absent in the “mixed”condition. The findings are consistent with the hypothesis that differential processing of retrieval cues depends upon the adoption of different task sets (“retrieval orientations” that develop over multiple trials and cannot be adjusted merely in response to an instructional cue. Unlike the new-item ERPs, ERPs elicited by the task cues in the mixed condition differed according to targeted material, but only on trials when there was a switch between target material. The implications of these findings for understanding the different retrieval strategies engaged when retrieval demands are consistent versus inconsistent are discussed.
Coming Unbound: Disrupting Automatic Integration of Synesthetic Color and Graphemes by Transcranial Magnetic Stimulation of the Right Parietal Lobe
Authors: Esterman Michael , Verstynen Timothy , Ivry Richard B. , Robertson Lynn C.
Published: September 2006

In some individuals, a visually presented letter or number automatically evokes the perception of a specific color, an experience known as color-grapheme synesthesia. It has been suggested that parietal binding mechanisms play a role in the phenomenon. We used a noninvasive stimulation technique, transcranial magnetic stimulation (TMS), to determine whether the posterior parietal lobe is critical for the integration of color and shape in color-grapheme synesthesia, as it appears to be for normal color-shape binding. Using a color-naming task with colored letters that were either congruent or incongruent with the synesthetic photism, we demonstrate that inhibition of the right posterior parietal lobe with repetitive TMS transiently attenuates synesthetic binding. These findings suggest that synesthesia (the induction of color from shape) relies on similar mechanisms as found in normal perception (where the perception of color is induced by wavelength).
Facilitating Effect of 15-Hz Repetitive Transcranial Magnetic Stimulation on Tactile Perceptual Learning
Authors: Karim Ahmed A. , Schüler Anne , Hegner Yiwen Li , Friedel Eva , Godde Ben
Published: September 2006

Recent neuroimaging studies have revealed that tactile perceptual learning can lead to substantial reorganizational changes of the brain. We report here for the first time that combining high-frequency (15 Hz) repetitive transcranial magnetic stimulation (rTMS) over the primary somatosensory cortex (SI) with tactile discrimination training is capable of facilitating operant perceptual learning. Most notably, increasing the excitability of SI by 15-Hz rTMS improved perceptual learning in spatial, but not in temporal, discrimination tasks. These findings give causal support to recent correlative data obtained by functional magnetic resonance imaging studies indicating a differential role of SI in spatial and temporal discrimination learning. The introduced combination of rTMS and tactile discrimination training may provide new therapeutical potentials in facilitating neuropsychological rehabilitation of functional deficits after lesions of the somatosensory cortex.
Baghy in Islamic Law and the Thinking of Ibn Taymiyya
Authors: bin Mohd Sharif Mohd Farid
Published: September 2006

The paper focuses on the opinion of the jurists about the concept of baghy and its significance in Islamic law. The objective of this paper is to provide a comprehensive review of the issue of baghy, and the thinking of Ibn Taymiyya within the context of jihàd. The paper starts with a brief explanation of the lexical meaning of baghy and its position in classical texts. The paper continues with a discussion about the legal status of baghy in Ibn Taymiyya's view. Later, it attempts to shed some light on the issue of baghy and jihàd against unjust or corrupt imàms, and what is the relationship between them from the perspective of the two prime sources of Islam: the Qur'an and hadith, with special focus on Ibn Taymiyya's point of view. This topic is treated in detail in the present study, and most of this problem is as pertinent to the umma today as it was in the time of Ibn Taymiyya. It is hoped that the following exposition will have some valuable impact on the on-going debate about baghy and jihàd. It bears noticing, however, that this paper is only concerned with the views of the jurists of the four major Sunni schools. The views of other schools, including Shia, although interesting, will not be discussed.
The Influence of Quran and Islamic Financial Transactions and Banking
Authors: Halabi Abdel , Kazi Ashraf
Published: September 2006

The Quran is the holy book of the followers of Islam, where simple solutions to the day-to-day problems of life are discussed in detail. Whatever the nationality of a Muslim, the Quran and Islamic prayers remain in a single universal language called "Arabic". Thus, uniformity has been maintained throughout the world from the days of the Prophet Mohammed, in the seventh century to the twenty-first century. Financial transactions and banking based upon Shariah are growing rapidly today. Islamic banking has been widely accepted in many countries such as Pakistan, Malaysia, Brunei, and Saudi Arabia, and are an increasing presence in Canada and Australia. Islamic banking and financial transactions are different from conventional banks, and this has led to some criticisms. After tracing the history of Islamic Banking some of these criticisms are discussed. While Islamic Banking does face some challenges, it continues to grow, and this growth reflects the desire for social, political and economic systems based on Islamic principles.
The Decline of the Agrarian Economy in Palestine under Roman Rule
Authors: Gil Moshe
Published: September 2006

Five main problems constitute the background for the decline of Palestine's agrarian economy under the Romans. A considerable part of the land was held by the Roman state, a situation that became more extensive than can be documented under previous regimes. Taxation, as described in talmudic sources, pressed heavily on the cultivators. Usury, a matter contrary to sacrosanct ancient prescriptions, was burdening the agrarian population by stratagems and cover-ups. Expropriation became frequent and there were instances of flight of both owners and sharecroppers. Finally, marriage and inheritance laws and customs brought about a far-reaching parceling of estates. It is shown that the decline was caused not only by Roman oppression, but also by internal factors, which together caused urbanization on the one hand, and emigration on the other. Cinq problèmes principaux constituent l'arrière-plan pour le déclin de l'économie agraire de la Palestine sous les Romains. Une partie considérable de la terre a été tenue par l'état romain, une situation qui est devenue plus étendue que peut être documentée sous des régimes précédents. L'imposition, comme décrite dans des sources talmudiques, oppressait fortement sur les cultivateurs. L'usure, qui contredit les prescriptions antiques sacro-saintes, accablait la population agraire par des stratagèmes et dissimulations. L'expropriation est devenue fréquente et il y avait des exemples de fuite des propriétaires et des métayers. Finalement, le mariage et les lois et coutumes de l'héritage ont produit un morcellement excessif des domaines. Y est montré que le déclin a été produit non seulement par l'oppression romaine, mais également par des facteurs internes, qui ensemble ont causé l'urbanisation d'une part, et l'émigration de l'autre.
Orographic Enhancement of Precipitation over Low Mountain Ranges. Part II: Simulations of Heavy Precipitation Events over Southwest Germany
Authors: Kunz Michael , Kottmeier Christoph
Published: September 2006

A diagnostic precipitation model that combines linear theory of hydrostatic flow with parameterized microphysics is applied to several stratiform heavy precipitation events over the low mountain ranges of southwestern Germany. Model-simulated rainfall is in good agreement with observations in both magnitude and location, yielding correlation coefficients against observational data between 0.74 and 0.90. Two events that caused local flooding over and near the Black Forest mountains, on 11–13 December 1997 and on 28–29 October 1998, are discussed in detail. Results show that, in addition to orographic features, wind speed U, moist static stability Nm, and melting level are important parameters to describe the amount and spatial distribution of orographic precipitation. The effect of hydrometeor drifting significantly reduces the precipitation peaks near the crests, and the inclusion of evaporation decreases precipitation mainly in descent regions downstream of the mountains. Using the upslope approach instead of linear theory, the precipitation intensities increase substantially and primarily over and downstream of the mountain peaks, whereas the maxima are shifted slightly downstream. The best simulation results relative to the observations were obtained on a 2.5-km grid, whereas areal rainfall is underestimated by about 10% on a 5-km grid and by about 35% on a 10-km grid.
Virtual Towers Using Coherent Doppler Lidar during the Joint Urban 2003 Dispersion Experiment
Authors: Calhoun R. , Heap R. , Princevac M. , Newsom R. , Fernando H. , Ligon D.
Published: September 2006

During the Joint Urban 2003 (JU2003) atmospheric field experiment in Oklahoma City, Oklahoma, of July 2003, lidar teams from Arizona State University and the Army Research Laboratory collaborated to perform intersecting range–height indicator scans. Because a single lidar measures radial winds, that is, the dot product of the wind vector with a unit vector pointing along the lidar beam, the data from two lidars viewing from different directions can be combined to produce horizontal velocity vectors. Analysis programs were written to retrieve horizontal velocity vectors for a series of eight vertical profiles to the southwest (approximately upwind) of the downtown urban core. This technique has the following unique characteristics that make it well suited for urban meteorology studies: 1) continuous vertical profiles from far above the building heights to down into the street canyons can be measured and 2) the profiles can extend to very near the ground without a loss of accuracy (assuming clear lines of site). The period of time analyzed spans from 1400 to 1730 UTC (0900–1230 local time) on 9 July 2003. Both shear and convective heating are important during the development of the boundary layer over this period of time. Differences in 10- and 20-min mean profiles show the effect of the variation of position approaching the urban core; for example, several hundred meters above the ground, velocity magnitudes for profiles separated by less than a kilometer may differ by over 1 m s−1. The effect of the increased roughness associated with the central business district can be seen as a deceleration of the velocity and a turning of the wind direction as the flow approaches the core, up to approximately 10° for some profiles. This effect is evident below 400–500 m both in the wind directions and magnitudes. Recommendations are given for how this type of data can be used in a comparison with model data.
Bayesian Retrieval of Complete Posterior PDFs of Oceanic Rain Rate from Microwave Observations
Authors: Chiu J. Christine , Petty Grant W.
Published: September 2006

A new Bayesian algorithm for retrieving surface rain rate from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) over the ocean is presented, along with validations against estimates from the TRMM Precipitation Radar (PR). The Bayesian approach offers a rigorous basis for optimally combining multichannel observations with prior knowledge. While other rain-rate algorithms have been published that are based at least partly on Bayesian reasoning, this is believed to be the first self-contained algorithm that fully exploits Bayes’s theorem to yield not just a single rain rate, but rather a continuous posterior probability distribution of rain rate. To advance the understanding of theoretical benefits of the Bayesian approach, sensitivity analyses have been conducted based on two synthetic datasets for which the “true” conditional and prior distribution are known. Results demonstrate that even when the prior and conditional likelihoods are specified perfectly, biased retrievals may occur at high rain rates. This bias is not the result of a defect of the Bayesian formalism, but rather represents the expected outcome when the physical constraint imposed by the radiometric observations is weak owing to saturation effects. It is also suggested that both the choice of the estimators and the prior information are crucial to the retrieval. In addition, the performance of the Bayesian algorithm herein is found to be comparable to that of other benchmark algorithms in real-world applications, while having the additional advantage of providing a complete continuous posterior probability distribution of surface rain rate.
Temporal and Spatial Characteristics of Snowstorms in the Contiguous United States
Authors: Changnon Stanley A. , Changnon David , Karl Thomas R.
Published: September 2006

A climatological analysis of snowstorms across the contiguous United States, based on data from 1222 weather stations with data during 1901–2001, defined the spatial and temporal features. The average annual incidence of events creating 15.2 cm or more in 1 or 2 days, which are termed as snowstorms, exhibits great spatial variability. The pattern is latitudinal across most of the eastern half of the United States, averaging 0.1 storm (1 storm per 10 years) in the Deep South, increasing to 2 storms along the Canadian border. This pattern is interrupted by higher averages downwind of the Great Lakes and in the Appalachian Mountains. In the western third of the United States where snow falls, lower-elevation sites average 0.1–2 storms per year, but averages are much higher in the Cascade Range and Rocky Mountains, where 5–30 storms occur per year. Most areas of the United States have had years without snowstorms, but the annual minima are 1 or more storms in high-elevation areas of the West and Northeast. The pattern of annual maxima of storms is similar to the average pattern. The temporal distribution of snowstorms exhibited wide fluctuations during 1901–2000, with downward 100-yr trends in the lower Midwest, South, and West Coast. Upward trends occurred in the upper Midwest, East, and Northeast, and the national trend for 1901–2000 was upward, corresponding to trends in strong cyclonic activity. The peak periods of storm activity in the United States occurred during 1911–20 and 1971–80, and the lowest frequency was in 1931–40. Snowstorms first occur in September in the Rockies, in October in the high plains, in November across most of the United States, and in December in the Deep South. The month with the season’s last storms is December in the South and then shifts northward, with April the last month of snowstorms across most of the United States. Storms occur as late as May and June in the Rockies and Cascades. Snowstorms are most frequent in December downwind of the Great Lakes, with the peak of activity in January for most other areas of the United States.
Drought Analysis Based on a Marked Cluster Poisson Model
Authors: Cebrián Ana C. , Abaurrea Jesús
Published: September 2006

This paper presents an operational definition of drought events based on an “excess over threshold” approach applied on rainfall series and develops a stochastic model for describing droughts defined in that way. The model consists of a Poisson cluster process to represent drought occurrence and a marked process composed of three series of random variables (duration, deficit, and maximum intensity) to describe drought severity; it is theoretically justified, and adequate procedures to check its validity are suggested and applied on five Spanish rainfall series. Useful parameters for the design and planning of water resource systems, together with their confidence intervals, are estimated from the model.
A Comparison of Snow Telemetry and Snow Course Measurements in the Colorado River Basin
Authors: Dressler K. A. , Fassnacht S. R. , Bales R. C.
Published: September 2006

Temporal and spatial differences in snow-water equivalent (SWE) at 240 snow telemetry (SNOTEL) and at 500 snow course sites and a subset of 93 collocated sites were evaluated by examining the correlation of site values over the snow season, interpolating point measurements to basin volumes using hypsometry and a maximum snow extent mask, and variogram analysis. The lowest correlation at a point (r = 0.79) and largest interpolated volume differences (as much as 150 mm of SWE over the Gunnison basin) occurred during wet years (e.g., 1993). Interpolation SWE values based on SNOTEL versus snow course sites were not consistently higher or lower relative to each other. Interpolation rmse was comparable for both datasets, increasing later in the snow season. Snow courses correlate over larger distances and have less short-scale variability than SNOTEL sites, making them more regionally representative. Using both datasets in hydrologic models will provide a range of predicted streamflow, which is potentially useful for water resources management.
A Comparison of TRMM Microwave Techniques for Detecting the Diurnal Rainfall Cycle
Authors: Sanderson Victoria L. , Kidd Chris , McGregor Glenn R.
Published: September 2006

This paper uses rainfall estimates retrieved from active and passive microwave data to investigate how spatially and temporally dependent algorithm biases affect the monitoring of the diurnal rainfall cycle. Microwave estimates used in this study are from the Tropical Rainfall Measuring Mission (TRMM) and include the precipitation radar (PR) near-surface (2A25), Goddard Profiling (GPROF) (2A12), and PR–TRMM Microwave Imager (TMI) (2B31) rain rates from the version 5 (v5) 3G68 product. A rainfall maximum is observed early evening over land, while oceans generally show a minimum in rainfall during the morning. Comparisons of annual and seasonal mean hourly rain rates and harmonics at both global and regional scales show significant differences between the algorithms. Relative and absolute biases over land vary according to the time of day. Clearly, these retrieval biases need accounting for, either in the physics of the algorithm or through the provision of accurate error estimates, to avoid erroneous climatic signals and the discrediting of satellite rainfall estimations.
GLACE: The Global Land–Atmosphere Coupling Experiment. Part II: Analysis
Authors: Guo Zhichang , Dirmeyer Paul A. , Koster Randal D. , Sud Y. C. , Bonan Gordon , Oleson Keith W. , Chan Edmond , Verseghy Diana , Cox Peter , Gordon C. T. , McGregor J. L. , Kanae Shinjiro , Kowalczyk Eva , Lawrence David , Liu Ping , Mocko David , Lu Cheng-Hsuan , Mitchell Ken , Malyshev Sergey , McAvaney Bryant , Oki Taikan , Yamada Tomohito , Pitman Andrew , Taylor Christopher M. , Vasic Ratko , Xue Yongkang
Published: September 2006

The 12 weather and climate models participating in the Global Land–Atmosphere Coupling Experiment (GLACE) show both a wide variation in the strength of land–atmosphere coupling and some intriguing commonalities. In this paper, the causes of variations in coupling strength—both the geographic variations within a given model and the model-to-model differences—are addressed. The ability of soil moisture to affect precipitation is examined in two stages, namely, the ability of the soil moisture to affect evaporation, and the ability of evaporation to affect precipitation. Most of the differences between the models and within a given model are found to be associated with the first stage—an evaporation rate that varies strongly and consistently with soil moisture tends to lead to a higher coupling strength. The first-stage differences reflect identifiable differences in model parameterization and model climate. Intermodel differences in the evaporation–precipitation connection, however, also play a key role.
Improving Computation of Sensible Heat Flux over a Water Surface Using the Variational Method
Authors: Cao Zuohao , Ma Jianmin , Rouse Wayne R.
Published: September 2006

In this study, the authors have performed the variational computations for surface sensible heat fluxes over a large northern lake using observed wind, temperature gradient, and moisture gradient. In contrast with the conventional (Monin–Obukhov similarity theory) MOST-based flux-gradient method, the variational approach sufficiently utilizes observational meteorological conditions over the lake, where the conventional flux-gradient method performs poorly. Verifications using direct eddy-correlation measurements over Great Slave Lake, the fifth largest lake in North America in terms of surface area, during the open water period of 1999 demonstrate that the variational method yields good agreements between the computed and the measured sensible heat fluxes. It is also demonstrated that the variational method is more accurate than the flux-gradient method in computations of sensible heat flux across the air–water interface.
Relative Roles of Large-Scale Orography and Land Surface Processes in the Global Hydroclimate. Part I: Impacts on Monsoon Systems and the Tropics
Authors: Yasunari Tetsuzo , Saito Kazuyuki , Takata Kumiko
Published: September 2006

A series of numerical simulations by an atmospheric general circulation model (AGCM) was conducted to evaluate the relative roles of Tibetan Plateau (TP) and continental-scale land surface processes on the Asian monsoon and hydroclimates in other regions in the Tropics. Four boundary conditions were used to define experiments: a flat and bare-rock (nonvegetated) surface (NMR), a realistic TP with bare-rock surface (MR), MR conditions but with a water-holding soil layer (with 20 cm of field capacity) (MS), and TP with a vegetated surface with specified albedo and roughness of the current vegetation and the soil layer (MVS).

Systematic increases of precipitation (P) over the Asian monsoon region and other land areas in the Tropics were noticed from NMR, MR, MS, to MVS runs. Precipitation over the warm tropical western Pacific, in contrast, decreased from NMR to MVS runs although the same SST climatology was prescribed in all the experiments. The effect of TP orography produces wet (dry) climate regions to the west (east) of TP as shown in other GCM studies. In the Asian monsoon region both land surface effect (LSE) and TP effect (TE) contribute nearly equally to increase P, but in the West African monsoon region, TE contributes to decrease P while LSE plays a major role to increase P. LSE also enhances the subtropical anticyclone over the North Pacific through enhanced land–ocean thermal contrast.

In most of the monsoon regions and Tropics, the albedo (and roughness) effect of vegetation substantially increases available radiation, which in turn increases both evaporation (E) and atmospheric moisture convergence (C), and, as a result, significantly increases P. This positive feedback between E and C is likely to be a characteristic nature when and where vegetation albedo effect is significant under sufficient radiative energy, suggesting a prerequisite for Charney’s original hypothesis.
Relative Roles of Large-Scale Orography and Land Surface Processes in the Global Hydroclimate. Part II: Impacts on Hydroclimate over Eurasia
Authors: Saito Kazuyuki , Yasunari Tetsuzo , Takata Kumiko
Published: September 2006

A series of simplistic simulations from an AGCM coupled to a simple land surface scheme and water vapor tracers was performed to explore the relative roles of basic factors in land surface conditions, with regard to the seasonal evolution of the hydroclimate over Eurasia. Large-scale orography in Asia and vegetation (further decomposed to soil and vegetation skin) were evaluated, with orography represented in the model by surface altitude, soil represented by water-holding capacity, and vegetation skin represented by surface albedo and roughness.

The percentage of global annual precipitation over land (occupying 25.6% of the total surface) was 14.8%, 15.0%, and 21.7% for the mountainless “bare rock” (i.e., vegetationless) surface, and the bare-rock and vegetated surface, respectively. The result for evaporation was 8.9%, 9.0%, and 16.2%, respectively, showing higher sensitivity to the land surface changes than precipitation. The orography and vegetation (i.e., soil and vegetation skin) showed different impacts on Eurasian hydroclimate on the seasonal and regional scales. Thermodynamical forcings to the atmosphere increased over the continent with the inclusion of both. Large-scale orography in Asia exerted east–west contrast in the surface energy exchange in summer in eastern Eurasia. An increase in extratropical winter precipitation with mountains was also noticed because of the atmospheric vapor transport changes. Impact of soil and vegetation skin was clearly found in the warm season in the extratropics; soil impacts extratropical summer precipitation due to enhanced recycling of water and the resultant increased water supply.
RainFARM: Rainfall Downscaling by a Filtered Autoregressive Model
Authors: Rebora Nicola , Ferraris Luca , von Hardenberg Jost , Provenzale Antonello
Published: September 2006

A method is introduced for stochastic rainfall downscaling that can be easily applied to the precipitation forecasts provided by meteorological models. Our approach, called the Rainfall Filtered Autoregressive Model (RainFARM), is based on the nonlinear transformation of a Gaussian random field, and it conserves the information present in the rainfall fields at larger scales. The procedure is tested on two radar-measured intense rainfall events, one at midlatitude and the other in the Tropics, and it is shown that the synthetic fields generated by RainFARM have small-scale statistical properties that are consistent with those of the measured precipitation fields. The application of the disaggregation procedure to an example meteorological forecast illustrates how the method can be implemented in operational practice.
Intense Rainfall Events Affecting the La Plata Basin
Authors: Silva Viviane B. S. , Berbery Ernesto H.
Published: September 2006

The circulation features associated with intense precipitation events over the La Plata Basin (LPB) during the austral summers of 2001/02 and 2002/03 are investigated using the Eta Model runs generated at the University of Maryland. Based on the main mode of variability over LPB, two regions were selected: (i) the region of Brazil that is at the core of the South American summer monsoon system (SAMS) and (ii) the central region of LPB in southeastern South America (SESA). First, a comparison between the 24-h total precipitation in the Eta Model and the 24-h observed precipitation was made. Results show that the Eta Model captures well the temporal variability of precipitation events in both regions, although a positive bias is noticed over SAMS. Likewise, the model reproduces the distribution of precipitation rate over SESA, but not over SAMS. Nevertheless, the distribution of the moisture flux convergence intensity, which represents the dynamical forcing, is closer in shape to the observed precipitation distribution, suggesting that the model can be a useful tool in identifying the forcing for heavy precipitation events over both regions.

Composites of atmospheric and surface variables were constructed for intense precipitation events during austral summer over both regions. Intense rainfall over the central La Plata Basin (SESA) is linked to an amplified upper-tropospheric midlatitude wave pattern in which rainfall occurs just east of an enhanced cyclonic circulation. Accompanying this circulation pattern, an enhanced low-level jet (LLJ) transports warm, moist air from the Amazon toward the region, contributing to an increase in the thermal contrast over SESA. The combined patterns of thermal and dynamical variables suggest that large-scale systems, like frontal systems, are important in producing intense rainfall events. The SAMS region events have a similar upper-level structure as in SESA, but they are longer lived. In this case, the moisture fluxes are determined by an eastward shift of the LLJ, but also directly from the Amazon Basin to the north. As expected, precipitation events produce large increases of simulated runoff. The largest impact is on the SESA region, affecting the streamflow of the Paraná, Paraguay, and Uruguay, the three main rivers of the LPB.
An Automated Microlysimeter to Study Dew Formation and Evaporation in Arid and Semiarid Regions
Authors: Heusinkveld Bert G. , Berkowicz Simon M. , Jacobs Adrie F. G. , Holtslag Albert A. M. , Hillen Willy C. A. M.
Published: September 2006

The development of a simple and low-cost portable weighing microlysimeter that makes use of a load cell for automated recording and for studying daily dew formation, rate of accumulation, and subsequent evaporation in arid or semiarid regions during rainless seasons is presented. The sampling cup is 3.5 cm deep, with the load cell itself situated at 20-cm depth to minimize temperature effects. The device was tested in a sand dune experimental station situated near Nizzana, northwest Negev Desert, Israel, during which extensive micrometeorological measurements were collected. One microlysimeter was placed in a playa and a second was installed on the stabilized midslope of an adjacent linear sand dune. To assess the performance of the load cell microlysimeters (LCM), one pair of manual microlysimeters was installed next to each LCM. A third pair was installed at a point between the LCMs and a fourth pair above the midslope LCM. Sixteen overnight measurements were carried out within a 6-week period. The LCM could measure dew with an error of ±0.02 mm. The daily dew variation in the samples during the 16 overnight measurements ranged up to 0.2 mm on stable dune slopes but up to 0.4 mm on the playa. This difference is attributed to the playa’s high silt and clay content and salinity. Dew formation and accumulation were found to occur long before the soil-surface temperature reached the dewpoint temperature of the air. The cost of building this microlysimeter, excluding labor, is about $175 (U.S.).
An Automated 2D Multipass Doppler Radar Velocity Dealiasing Scheme
Authors: Zhang Jian , Wang Shunxin
Published: September 2006

An automated 2D multipass velocity dealiasing scheme has been developed to correct velocity fields when wind velocities are very large compared to the Nyquist velocity of the weather Doppler radars. The new velocity dealiasing algorithm is based on the horizontal continuity of velocity fields. The algorithm first determines a set of reference radials and gates by finding the weakest wind region. Then from these reference radials and gates, the scheme checks continuities among adjacent gates and corrects for the velocity values with large differences that are close to 2 × (Nyquist velocity). Multiple passes of unfolding are performed and velocities identified as “folded” with low confidence in an earlier pass are not unfolded until a discontinuity is detected with high confidence at a subsequent pass. The new velocity dealiasing scheme does not need external reference velocity data as do many existing algorithms, thus making it more easily applicable. Over 1000 radar volume scans that include tornadoes, hurricanes, and typhoons are selected to test and to evaluate the new algorithm. The results show that the new algorithm is very robust and very computationally efficient. In cases with many data voids, the new algorithm shows improvements over the current WSR-88D operational velocity dealiasing scheme. The new dealiasing algorithm is a simple and stand-alone program that can be a very useful tool to various Doppler radar data users.
Boundary Conditions for Limited-Area Ensemble Kalman Filters
Authors: Torn Ryan D. , Hakim Gregory J. , Snyder Chris
Published: September 2006

One aspect of implementing a limited-area ensemble Kalman filter (EnKF) involves the specification of a suitable ensemble of lateral boundary conditions. Two classes of methods to populate a boundary condition ensemble are proposed. In the first class, the ensemble of boundary conditions is provided by an EnKF on a larger domain and is approximately a random draw from the probability distribution function for the forecast (or analysis) on the limited-area domain boundary. The second class perturbs around a deterministic estimate of the state using assumed spatial and temporal covariance relationships. Methods in the second class are relatively flexible and easy to implement. Experiments that test the utility of these methods are performed for both an idealized low-dimensional model and limited-area simulations using the Weather Research and Forecasting (WRF) model; all experiments employ simulated observations under the perfect model assumption. The performance of the ensemble boundary condition methods is assessed by comparing the results of each experiment against a control “global” EnKF that extends beyond the limited-area domain. For all methods tested, results show that errors for the limited-area EnKF are larger near the lateral boundaries than those from a control EnKF, but decay inside the limited-area domain so that errors there are comparable to the control case. The relatively larger errors near the boundaries in the limited-area EnKF originate from not assimilating observations outside the limited-area domain and, in the second class of methods, from deficiencies in boundary spatial and temporal covariances. Overall, these experiments suggest that for observation densities typical in numerical weather prediction models, ensemble boundary conditions can be specified in the absence of a global ensemble without significant penalty in the domain interior by perturbing around an ensemble mean.