bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations of climate, albedo, and surface radiation over cleared and undisturbed amazonian forest
Authors: Bastable H. G. , Shuttleworth W. J. , Dallarosa R. L. G. , Fisch G. , Nobre C. A. 
Published: February 2007

AbstractMeasurements from the first comparative study of climate over Amazonian tropical forest and an embedded deforested clearing are presented. Observations comprise a continuous 60‐day run of data from mid‐October to mid‐December 1990, covering the end of the dry season and the beginning of the wet season. Mean hourly observations are calculated for the whole period; and for two 10‐day periods, one in the dry season and one at the start of the wet season. Much greater variation in weather variables was observed at the clearing compared with over the forest. While the mean values of temperature and specific humidity deficit differed by less than 1°C and 1 g kg−1 respectively, their daily ranges at the clearing were twice those at the forest. Mean daily albedo of the forest was 13.1 per cent, agreeing well with other tropical forest measurements, and of the clearing was 16.3 per cent, somewhat lower than the values currently being used in GCMs. The surface energy balance was investigated and mean available energy calculated for each site. The significant difference in the daily pattern of net radiation between the sites was found to be at least as much due to differences in the longwave radiation balance as to differences in albedo. The diurnal pattern of net radiation therefore changed between dry and wet periods as the higher plant water stress experienced by clearing vegetation altered the daily temperature cycle.
Assessing climate model sensitivity to prescribed deforested landscapes
Authors: Pitman A. J. , Durbidge T. B. , Henderson‐Sellers A. , McGuffie K. 
Published: February 2007

AbstractThe results from a series of 3‐ to 6‐year simulations of the climatic impacts of tropical deforestation using a version of the NCAR Community Climate Model (CCM1–Oz) indicate considerable sensitivity to the specification of the vegetation and soil that replaces the tropical forest. The simulations, which encompass landscapes from forest, through grass with some trees, grass‐only, no vegetation with forest soils, to a devastated terrain, suggest that the predicted climate change depends about equally on at least three factors: (i) the global model and its large‐scale circulation sensitivity, (ii) the length of the model simulation, and (iii) the nature of the prescribed land‐use change, particularly the relative magnitudes of the changes (forested to deforested) in albedo and vegetation roughness length.
Effects of changing exposure of thermometers at land stations
Authors: Parker D. E. 
Published: February 2007

AbstractIn view of the implications for the assessment of climatic changes since the mid‐nineteenth century, systematic changes of exposure of thermometers at land stations are reviewed. Particular emphasis is laid on changes of exposure during the late nineteenth and early twentieth century when shelters often differed considerably from the Stevenson screens, and variants thereof, which have been prevalent during the past few decades. It is concluded that little overall bias in land surface air temperature has accumulated since the late nineteenth century: however, the earliest extratropical data may have been biased typically 0.2°C warm in summer and by day, and similarly cold in winter and by night, relative to modern observations. Furthermore, there is likely to have been a warm bias in the tropics in the early twentieth century: this bias, implied by comparisons between Stevenson screens and the tropical sheds then in use, is confirmed by comparisons between coastal land surface air temperatures and nearby marine surface temperatures, and was probably of the order of 0.2°C.
Optimizing a network of rain‐gauges over india to monitor summer monsoon rainfall variations
Authors: Singh Nityanand 
Published: February 2007

AbstractA network of rain‐gauges has been optimized to reconstruct the spatially representative summer monsoon rainfall series (1871–1984) of India prepared by averaging the normalized rainfall (actual divided by mean) of 306 rain‐gauges. Three approaches have been attempted: (i) random selection, (ii) fitting a multiple linear regression and (iii) selecting objectively a subset of a few gauges, the mean of which shows the highest correlation coefficient (CC) with the all‐India series. By averaging a randomly selected 45 rain‐gauges, an average CC with the all‐India rainfall series of ca. 0.94 was achieved, and by averaging 100 gauges the average CC was ca. 0.97. By fitting a multiple linear regression between the all‐India series and the normalized rainfall series of 306 gauges, a maximum of 34 independent gauges (parameters) were identified and the estimated rainfall series showed a highest CC of 0.9969 with the full series. In the third approach, a subset of 34 rain‐gauges was identified following an objective criterion; the mean rainfall of this subset showed a CC of 0.9931 with the all‐India series. For routine updating of the all‐India summer monsoon rainfall series, however, 35 rain‐gauges were selected by applying the third approach to 64 randomly chosen India Meteorological Department (IMD) rain‐gauges better known for their timely availability of data. The reconstructed (CC = 0.9866) all‐India summer monsoon rainfall series for the period 1871–1992 is presented.
An analysis of the circulation characteristics and energy budget of a dry, asymmetric, east‐west urban canyon. I. Circulation characteristics
Authors: Arnfield A. John , Mills Gerald M. 
Published: February 2007

AbstractWind characteristics within urban canyons are of considerable significance for pollution diffusion, for assessing the nature of the atmospheric environment at street level, and in determining the energy budget of the canyon. This study presents an analysis of the circulation characteristics for a deep, east‐west, asymmetric urban canyon (located in Columbus, Ohio, USA), based on measurements of ambient wind at roof level, vertical velocities at the canyon‐top, and within‐canyon horizontal winds. Canyon‐top vertical velocity was normally directed upward, even with cross‐canyon winds, indicating along‐canyon horizontal convergence. Its speed was approximately related to the magnitude of the southerly, easterly, and westerly components of the roof‐level wind. Three‐fifths of the data sets showed evidence of a vortex circulation superimposed upon the mean vertical motion, although its speed and direction were not clearly related to the direction of the cross‐canyon wind. Some of the perplexing aspects of the results may be attributable to the asymmetric structure of the canyon. Overall, these results suggest that wind fields within and above urban canyons may not be as simply as empirical studies hitherto have suggested and that attempts at modelling these characteristics of the urban climate must recognize this.
Regionalization of daily mesoscale rainfall in the tropical wet/dry climate of the townsville area of north‐east queensland during the 1988–1989 wet season
Authors: Lyons W. F. , Bonell M. 
Published: February 2007

AbstractThis paper describes the use of unrotated principal component analysis (PCA), various oblique rotated principal component (PC) solutions, and the VARIMAX orthogonal rotation scheme. One of the objectives is to determine which PC solution achieves the most satisfactory degree of “simple structure” in the distribution of PC loadings, based on rainfall data collected during the 1988–1989 wet season from a comparatively dense rain‐gauge network (in excess of one gauge per 25 km2) in the Townsville area of tropical north‐east Queensland, Australia. The Harris‐Kaiser Case II BTB rotation was subsequently judged to be the most appropriate PC solution for the total wet season record, and for subsets based on the three most frequently occurring synoptic circulations.Daily isohyetal maps and radar imagery are used to show that the rotated PCs could be physically interpreted. The PC loadings derived from the Harris‐Kaiser II BTB rotation were then used as input to the Ward clustering strategy for regionalization of the total wet season record. The interactions between different synoptic circulations and changes in the spatial patterns of mesoscale rainfall are discussed as a basis for understanding the regionalization of the 1988–1989 wet season. The analysis demonstrates the need for a longer period of record before precipitation affinity areas, or regions of relatively coherent rainfall, can be used for forecasting purposes. None the less, the work shows the inadequacy of using the official gauge site at the local meteorological office as representative of the region, and further highlights the importance of local topographical controls on the synoptic‐scale circulation for producing distinct spatial rainfall patterns. It is believed that this is one of the first studies attempting a regionalization of rainfall at a mesoscale within the tropics.
Spatial and temporal sea‐surface temperature, covariances in the mediterranean
Authors: Bartzokas A. , Metaxas D. A. , Ganas I. S. 
Published: February 2007

AbstractUsing sea‐surface temperature data for the post‐war period, the Mediterranean Sea is divided objectively (principal components factor analysis) into subareas with similar covariances. This division is not the same in every season of the year. In summer, two subareas are found, the west and the east. In spring and autumn three, and in winter four significant subareas denote physical oceanographic and meteorological processes. The scores of the analyses show clearly the minimum of the late 1970s and then the warming of recent years somewhat delayed in the eastern Mediterranean.
Guinean and sahelian rainfall anomaly indices at annual and monthly scales (1933–1990)
Authors: Moron Vincent 
Published: February 2007

AbstractThe annual and monthly rainfall variability in north tropical Africa are analysed by principal component analysis in order to detect the main coherent modes. The Sahel constitutes the first mode, although it is divided close to 10°W into an Atlantic section and a Continental section. The Guinean zone is less coherent, and is divided into distinct modes. The subequatorial area never formed a distinct mode. Rainfall variability for the coherent areas is constructed from rainfall anomaly indices (RAI), based on the coherent areas, and a rainfall typology taking into account the spatial pattern of the rainfall anomaly fields and the intensity of the anomaly. Their evolution (mainly since 1950) is synchronous on the Sahelian and the Guinean zones with the opposition between the 1950s and 1960s (wetter than normal) and the 1970s and the 1980s (drier than normal). In particular, the area of drought, which has plagued the Sahel since 1968, extends to Guinean Africa, mainly after the mid‐70s. The typology allows us to investigate the relationships at both the annual and the monthly scale.
Satellite recorded vegetation response to drought in brazil
Authors: Liu William T. H. , Massambani Oswaldo , Nobre Carlos A. 
Published: February 2007

AbstractA normalized difference vegetation index (NDVI) derived from satellite data is used to study drought evolution in the South American continent. National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) Global Area Coverage (GAC) data are used to produce NDVI maps for the South American continent during the period from 1 August 1981 to 30 June 1987. A 15‐day maximum‐value composite procedure is used to partially eliminate cloud contamination and atmospheric attenuation. Vegetation response to drought is studied by inspection of the temporal and spatial evolutions of monthly drought area maps, which are delineated by NDVI values lower than 0.22. Drought area evolution patterns over the continent during the period of 1981–1987 for the months of May and September are discussed. The results show a well‐defined regional dependence of the drought area variability. Drought dynamics analyses are performed for the dry year of 1982–1983 and for the wet year of 1984–1985. This information is used to discuss the relationship of the drought pattern with the El Niño‐Southern Oscillation (ENSO). Emphasis is given to the north‐eastern region of Brazil, for which the relative drought area coverage was computed to demonstrate its high interannual drought variability. An intensification of this behaviour during the 1982–1983 ENSO event was identified in this area. The results indicate the potential use of satellite NDVI imagery to monitor drought occurrences as well as to study climatic variability on regional and continental scales.
Recent climate variability in the vicinity of the antarctic peninsula
Authors: King J. C. 
Published: February 2007

AbstractSurface air temperature records from stations on the west coast of the Antarctic Peninsula show a higher degree of interannual variability and stronger long‐term warming trends than recorded elsewhere in Antarctica. Possible mechanisms for driving these fluctuations are investigated. The extreme climatic sensitivity of this region may be linked to a stronger coupling between temperatures and regional sea‐ice extent than is seen elsewhere in Antarctica. Significant interannual persistence of air temperature anomalies suggests a link with ocean temperatures or circulation.
Changes in the rate of evaporation from the dead sea
Authors: Stanhill G. 
Published: February 2007

AbstractHeat balance calculations indicate that during the last 40 years a marked decrease in the evaporation rate from the Dead Sea has accompanied its increased salinity. Two‐thirds of the estimated 17 per cent decrease is attributed to the reduced vapour pressure of its now salt‐saturated waters, the remaining one‐third to the reduction in radiation balance caused by the greater longwave loss from its warmer sea surface. The rate of evaporation from a hypothetical Dead Sea with a surface level restored to previous levels by an influx of Mediterranean waters was estimated to be 158 per cent of its current rate, which is 1.05 m per year. Two‐thirds of this increase was attributed to the greater vapour pressure gradient between the less saline surface water and the atmosphere, one‐third to the increased radiation balance at its cooler sea surface. Although the mechanism for these changes are well understood and easily calculated, a number of complex interactions exist between the various effects that do not allow a quantitative relationship to be established analytically between the Dead Sea's surface level or salinity and rate of evaporation. However, empirically, the linear relationship between annual evaporation, E (m year−1), and surface density, D (g cm−3), E = 4.701 ‐ 2.926 D. accounts for 98 per cent of the variation between evaporation from a salt‐free and from a salt‐saturated Dead Sea.
Summer moisture variability across Europe, 1892–1991: An analysis based on the palmer drought severity index
Authors: Briffa K. R. , Jones P. D. , Hulme M. 
Published: February 2007

AbstractMonthly Palmer Drought Severity Indices (PDSI) have been calculated for the period 1892–1991 over a 5° latitude by 5° longitude grid covering Europe and south‐west Asia from 35 °N to 70 °N and 10 °W to 60 °E. These indices are used to describe the spatial and temporal details of relative moisture variability during summer (June‐August). The full series of mean summer PDSI maps are presented. Over Europe as a whole, there has been a consistent (but statistically insignificant) increase in moisture supply throughout the period of record. The 1930s and 40s were exceptionally dry. The summer of 1947 was the driest, both in terms of average PDSI but also in terms of the spatial extent of moderate drought. However, the summer of 1921 was by far the most extreme when considering the spatial extent of severe drought conditions. Widespread drought conditions also prevailed over many regions of Europe during the 1890s. The wettest summers occurred in 1987 and 1916. The total area of Europe experiencing either severe dry or severe wet conditions has increased noteably during recent years.Nine regions of coherent summer moisture variability are objectively defined by orthogonal rotation of the principal components of the summer PDSI. The nine rotated components, which explain 60 per cent of total variability of this data set, represent moisture variability in north‐western Europe (NWEUR), the north‐west Mediterranean (NWMED), the lower Volga (LVOLG), central European Russia (CERUS), the north‐east Mediterranean (NEMED), the southern Caspian Sea (SCASP), the Pechora Basin (PECHB), the Danube Basin (DANUB), and northern Fennoscandia (NFENN). The last 3 years have been very dry in NWEUR and NWMED. The most recent summer in our analysis, 1991, was the wettest on record in both CERUS and NEMED. Preliminary spectral analyses provide little evidence for a solar‐moisture relationship in these European data over this period.
Temporal discontinuities in precipitation in the central north american prairie
Authors: Kemp P. R. , Cornelius J. M. , Reynolds J. F. 
Published: February 2007

AbstractUnderstanding the potential for future climate change to affect ecosystems or agriculture in a region will depend, in part, on understanding how variable the present climate is and what its present effects are. Because the central prairie region of North America undergoes short‐term climate shifts (particularly drought), and appears sensitive to these changes, we were interested in characterizing the duration and nature of precipitation fluctuations. We used split, moving‐window dissimilarity analysis to locate transition points between periods of relatively homogeneous rainfall over the Kansas region. We identified statistically significant discontinuities in precipitation that appear to represent shifts in the regional climate during the last 115 years. All of the transitions were associated with changes in May, June, and July rainfall. Drought and drought cycles were the dominant fluctuations over decade‐long periods. Over somewhat longer periods (20–30 years) there were transitions, varying in abruptness, that may also be related to drought or perhaps larger scale climatic fluctuations. The relatively strong periodicity shown by the decadal discontinuities supports the contention that drought climates are triggered, or ended, by a cyclic phenomenon. The use of dissimilarity analysis allowed us to identify fluctuations in climate of the central North American prairie that were not previously described, and that may have been significant enough to influence natural and agricultural ecosystems.
Lidar‐observed long‐term variations in urban aerosol characteristics and their connection with meteorological parameters
Authors: Devara P. C. S. , Raj P. E. , Sharma S. , Pandithurai G. 
Published: February 2007

AbstractMore than 200, weekly spaced, lidar‐derived vertical profiles of aerosol concentration in the lower atmosphere (up to 1380 m above ground level) obtained during night‐time between October 1986 and August 1990 at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32'N, 73°51'E, 559 m above mean sea‐level), India, have been used to study the long‐term variations in aerosol concentration in different air layers. Selected meteorological parameters for the above period at Pune have also been examined to investigate their association with the aerosol concentration. The spectral analysis of the data revealed significant periodicities in four different characteristic ranges, namely 2.5–13.5, ca. 27, ca. 33 and 40–48 weeks in both lidar‐derived aerosol content and meteorological parameters; the fourth range being more predominant in all the parameters. These results, together with those of cross‐correlation analysis of the data, indicate an association between the long‐term trends present in both aerosol and meteorological parameters at the station.
Recent and future climate change in east asia
Authors: Hulme Mike , Zhao Zong‐Ci , Jiang Tao 
Published: February 2007

AbstractThe signing of the UN Framework Convention on Climate Change in Rio de Janeiro in June 1992 by 160 nations has firmly identified global climate change due to human pollution as a pressing global environmental concern. Among the responsibilities that the nations which ratify the Convention will have are the drawing up of inventories of greenhouse gas sources and sinks and the formulation of national strategies to respond to climate change through adaptive and or preventive measures. One requirement for identifying appropriate response strategies will be the undertaking of regional assessments of climate change and its associated impacts.This paper is concerned with climate change in the East Asian region, both over the last 100 years (using instrumental data) and also for the next 100 years (using results from climate model experiments). The juxtaposing of these two analyses, historical and future, enables a better interpretation of the significance of regional climate change to be made. Instrumental temperature and precipitation data for the East Asian region are analysed and compared with the observed global‐scale trends in these two variables. Although the region has undoubtedly warmed over the last century, understanding the exact causes of the complex seasonal, diurnal, and spatial dimensions of this warming is difficult. We examine the role of increasing urbanization in inducing rising temperatures and suggest that, although substantial, urban warming cannot account for all of the observed temperature change. The paper also illustrates a flexible composite‐model approach to regional climate change scenario construction that avoids the need for multiple transient GCM experiments, which can explicitly incorporate the effects of intermodel uncertainty, and is flexible enough to incorporate new scientific findings and results from new GCM experiments. The scenario presented here suggests that by 2050,meanconditions are expected to be warmer than the extremely warm seasonal anomalies that occurred during the most recent decade in East Asia. Precipitation is estimated to rise over most of the region in all seasons, although the uncertainty range attached to this estimate is much wider than for temperature.
Classification system of precipitation gauge site exposure: Evaluation and application
Authors: Sevruk B. , Zahlavova L. 
Published: February 2007

AbstractThe precipitation gauge site exposure is assessed from the station history records. Four classes and three interim classes ranging from open to protected gauge sites are used. They are characterized by the average vertical angle of obstacles around the gauge, as measured in eight directions of the wind rose. The accuracy of class estimates was checked in the field, and the error for an experienced person was found to be approximately ±0.5 of a class. Applications of the classification system for estimation of wind‐induced error of precipitation measurement and for detection of inhomogeneities of precipitation time‐series are discussed.