bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interannual variability of surface climate in the Amazon basin
Authors: Marengo José A. 
Published: February 2007

AbstractThis empirical study examines the circulation mechanisms of anomalously wet and dry years in the Amazon basin. Data sources include surface ship observations in the tropical Atlantic, eastern Pacific, and Indian Oceans, as well as various hydrometeorological indices in Amazonia during 1951–1983. Rainfall and river water level anomalies in northern Amazonia are associated with distinct circulation patterns in the tropical Atlantic, particularly at the March–April peak of the rainy season. Thus, abundant rainfall in northern Amazonia and high Rio Negro water levels are accompanied by a strong North Atlantic high, steep meridional pressure gradient on its equatorward side, accelerated North‐east trades, and cool surface waters in the tropical North Atlantic. The intensified North‐east trades may entail enhanced boundary‐layer moisture transport from the tropical North Atlantic into the Amazon basin. This ensemble of atmospheric and oceanic anomalies is characteristic of, but not limited to, the high phase of the Southern Oscillation (defined by anomalously high/low pressure at Tahiti/Darwin).
A model‐based approach to the calculation of global warming potentials (GWP)
Authors: Rotmans J. , Den Elzen M. G. J. 
Published: February 2007

AbstractThe Global Warming Potential (GWP) of greenhouse gas emissions can be defined as a greenhouse pendant to the Ozone Depleting Potential (ODP). Global Warming Potentials are calculated for the most important greenhouse gases (CO2, CH4, CO, N2O, CFC‐11, CFC‐12, CFC‐13, CFC‐14, CFC‐113, CFC‐114, CFC‐115, CFC‐116, CF3Br, CCl4, CH3CCl3, and HCFC‐22) and eight potential CFC substitutes using the integrated climate assessment model IMAGE. Two different methods are presented for the calculation of GWP values using IMAGE: one that generates equivalent pulses for all greenhouse gases, and an iterative trace‐back method which calculates the different pulses required to achieve an identical global temperature increase for all greenhouse gases. In addition the influence of the emission scenario used is tested when determining GWPs; it is demonstrated that GWPs are indeed scenario‐dependent, so the choice of the underlying emission scenario is important. Finally, the GWPs calculated using these methods are compared with GWPs that have been published previously. It appears that our GWP estimates are substantially higher than the IPCC estimates, which can be explained by the fact that our carbon cycle model has a balanced global carbon budget. This results in lower projections of future atmospheric carbon dioxide compared with the IPCC projections.
The spatial organization of daily rainfall over Mallorca, Spain
Authors: Sumner Graham , Ramis Clemente , Guijarro José A. 
Published: February 2007

AbstractDaily rainfall affinity areas are derived for the island of Mallorca using four years of data, and a 96 × 96 intersite correlation matrix. An initial visual impression of the nature of rainfall organization is afforded by the mapping of correlation links between sites. The Serra de Tramontana form a climatological as well as topographic barrier, producing a marked alignment in spatial rainfall occurrence in that part of the island. Elsewhere ‘core’ sites are identified, about which rainfall correlation is high for distances of up to 15 km. These centre on higher elevation locations in the Serra de Llevant and in the central area, and also the Palma and Campos coastal embayments. Use of rotated principal components and cluster analyses applied to the correlation matrices permits the division of the island into seven major rainfall areas. The uplands of the north‐west and east of the island provide clear units in terms of both exposure and altitude, and their general exposure to prevailing rain‐bearing winds appears important, whilst an urban effect due to Palma and clear sea‐breeze convergence effects near the centre of the island are also implied.
An analysis of Australian seasonal rainfall anomalies: 1950–1987. II: Temporal variability and teleconnection patterns
Authors: Drosdowsky Wasyl 
Published: February 2007

AbstractA detailed examination of the variability of Australian district rainfall of seasonal time‐scales over the period 1950–1987 is described. In Part I, S‐ and T‐mode rotated principal component analysis (RPCA) was used to obtain a compressed representation of Australian district rainfall anomalies on seasonal time‐scales.In this paper, the temporal variability of these spatial patterns is examined, and their relationship to some large‐scale circulation indices, such as the Southern Oscillation (SO) and Pittock's L index. The S‐mode components show large intercomponent correlations as a result of the rotation of the principal components, although much of this is due to a common relationship to the SO. The T‐mode components are less strongly interrelated and only the first two show large correlations with the SO. The relationship with the SO and the L index are consistent with previous studies. Spectral analysis shows that most components do not have any dominant periodicity. Two distinct biennial tendencies are identified; in the north‐east associated with the SO, and in the south‐east associated with the L index.The large‐scale circulation anomalies associated with both the S‐ and T‐mode patterns are examined using the Comprehensive Ocean Atmosphere Data Set (COADS) and a network of rawindsonde stations over Australia and the South‐west Pacific. Three dominant teleconnection patterns are identified; the well‐known Southern Oscillation anomalies associated with the dominant T1 pattern of continental‐scale rainfall anomalies, a predominantly winter season Indonesian‐Indian Ocean pattern previously documented by Nicholls, and a spring/summer south Tasman Sea pattern. The evolution of these patterns is examined through composites, and the physical mechanisms for the initiation and maintenance of the anomaly patterns are discussed. In the latter two cases both the rainfall and SST anomalies appear to be driven by anomalies in the large‐scale mid‐latitude circulation.
Luni‐solar 18.6‐ and 10–11‐year solar cycle signals in South African rainfall
Authors: Currie Robert G. 
Published: February 2007

AbstractSpectrum analysis of 59 South African rain‐gauge records yields evidence for two peaks with periods 18.2·1.4 years (57 out of 59 series covering virtually the entire country) and 10.3·0.5 years (in 37 series covering almost all except easternmost South Africa). They are identified as the luni‐solar 18.6‐year Mn and 10–11‐year solar cycle Sc signals in climate; their phases and amplitudes are non‐stationary with respect to both time and geography and, in particular, 180° phase changes in wave polarity are observed. These phase changes occurred in the early part of the century and by mid‐epochs 1964.0 and 1982.6 (mid‐epochs are dates of minimum in Mn tidal forcing) a unipolar cell of drought encompassed virtually the entire nation. Constructive interference by the Sc wave, which reached a minimum near 1981, exacerbated the droughts of mid‐epoch 1982.6 which were more severe than even those of the 1960s. The results confirm and extend in many respects those found by P. D. Tyson and his co‐workers in the 1970s.
The effect of coastline curvature on the weakening of atlantic tropical cyclones
Authors: Rogers Robert E. , Davis Robert E. 
Published: February 2007

AbstractThis study attempts to determine the relationship between the curvature of the coastline and the filling (increase in central pressure) of hurricanes and tropical storms by comparing both the rate of filling and the total filling for storms striking convex, concave, and linear coastlines. The USA and Mexican coastline was approximated by a subjective smoothing procedure, and the coastal curvature corresponding to each landfalling Atlantic tropical cyclone from 1900 to 1979 was measured and grouped into one of the three curvature categories. Storm‐filling rates and total amounts of filling were determined before and after landfall by computing the change in wind speed for various Saffir‐Simpson hurricane intensity categories. The averages of these variables within each strength and curvature grouping were compared in order to determine if they were statistically different. Storms were also compared in order to determine if stronger storms fill a greater total amount than weaker storms, regardless of the coastline's curvature.Concave coasts were found to be associated with storms filling both more rapidly and by a greater amount than convex coasts for weak hurricanes and strong tropical storms, and they were associated with storms that filled by a greater amount for hurricanes of moderate strength. This most likely results from the lower water‐to‐land ratios associated with storms striking concave coasts and the reduction in latent and sensible heat fluxes from the surface. Also, stronger storms were found to fill more rapidly and by a greater total amount than weaker storms, and storms striking the East Coast generally filled more rapidly and by a greater total amount than storms striking the Gulf Coast or Florida.
Interannual variability of rainfall in the eastern horn of Africa and indicators of atmospheric circulation
Authors: Beltrando Gérard , Camberlin Pierre 
Published: February 2007

AbstractRelationships between rainfall variations in the Eastern Horn of Africa, the Southern Oscillation, and the Indian Ocean temperature and pressure surface fields are studied for the period 1932–83. Rainfall data consist of stations and regional indices calculated for three selected areas experiencing quite different rainfall patterns. The results indicate significant negative correlations between northern autumn rains in Somalia and the Southern Oscillation during the same season. These rains are also negatively correlated with pressure in the Western Indian Ocean, and positively correlated in the Eastern Indian Ocean. The reverse pattern is shown with sea‐surface temperature. This agrees very well with the observations made in Kenya as far as the short rains of October‐November are concerned.Central Ethiopia summer rains, in contrast, indicate significant positive correlations with the Southern Oscillation, at zero and 3 months lag. El Niño years often correspond to drought years in this region. Evidence of an inverse relationship between the amount of rainfall in Ethiopia during summer (especially during September) and both the pressure and sea temperature over the Indian Ocean is also given. Correlations with the Arabian Sea are particularly strong.However, teleconnections between summer rains in Northern Ethiopia (Eritrea) and the ENSO or the Indian Ocean fields are much weaker.These results suggest that, although summer rains over Ethiopia are said to be related to the monsoon air flow from the Congo Basin and the Atlantic Ocean, there also exist quite strong connections with the surface conditions prevailing in the Indian and Pacific Oceans.
Detection of trend or change in annual flow of Australian rivers
Authors: Chiew F. H. S. , McMahon T. A. 
Published: February 2007

AbstractChanges in streamflow volumes resulting from climatic change can affect the management of water resources. However, the detection of a statistically significant trend can be difficult because of the large interannual variability and the relatively short period of instrumental record. In this paper, five statistical tests are applied to the historical annual streamflow series of 30 unregulated Australian rivers, located in protected natural catchments, in order to detect trends or changes in the means. The Student t‐statistic is also used to describe the relationship between interannual variability and the magnitude of change and length of data required to identify a statistically significant trend. The analysis indicates that, with the current data set, there is no clear evidence to suggest that the greenhouse effect is impacting on Australian streamflow volumes. The change required to identify a statistically significant change in the mean is directly proportional to the interannual variability, and less dependent on the length of data available. The interannual variability of Australian streams is twice that of Northern Hemisphere streams, therefore, a greater change is required in Australian flow volumes before a statistically significant change can be identified. The analysis of available historical records, however, indicates that statistically significant trends can be detected in the future flow volumes if the scenarios predicted by the G'CMs are realized.
Weather categorization based on the average linkage clustering technique: An application to European mid‐latitudes
Authors: Huth Radan , Nemesova Ivana , Klimperová Nina 
Published: February 2007

AbstractThe computer‐assisted classification of weather at Prague‐Clementinum used the average linkage clustering technique. Since the results of the clustering exhibit the snowballing effect, the usual methods of determining the threshold aggregation level (i.e. the level at which the clustering procedure is to be terminated) appeared to be inapplicable. A new method based on Monte Carlo simulations of the means was developed. Its key idea is the termination of the clustering procedure at different aggregation levels in different parts of the data set. This ensures that the number of resultant clusters is reasonable, while minimizing the numbers of very small clusters and unclustered days.The weather categorization resulted in 44 clusters for 14 winters in the period 1965–1978. Thirty‐one of the clusters had sizes of 5 or more days. The Monte Carlo scores, comparing the means and variances of the clusters with those of a large number of subsets chosen randomly, indicate that all the resulting clusters represent meaningful weather types.This study may provide a basis for nucleated clustering, which will enable us to deal with longer data series and to study the long‐term trends of the properties of weather types.
Variations of hemispheric zonal index since 1899 and its relationships with air temperature
Authors: Koźuchowski K. M. 
Published: February 2007

AbstractMean monthly values of the zonal index of surface pressure for the zone 35°–65°N during the period 1899–1990 are studied. The extreme values – 11·5 hPa in February 1947 and 16·5 hPa in January 1978 define the range of zonal index variability. The highest annual value occurred in 1990. On average, the maximum of zonal index occurs in October (mean value 7·5 hPa), the minimum in May (2·5 hPa). Spectral variance analysis shows 2‐month, 3‐month, 6‐month, annual, quasi‐biennial, and 13·2‐year cyclicity in time series of monthly values. The quasi‐biennial and 13‐year cyclicity appear also in seasonal values of the zonal index.Instability of the zonal index spectra and autocorrelation for monthly values has been noted.The period under study is divided into three subperiods characterized by high (1899–1938 and 1972–1990) and low (1939–1971) zonal indexes.The correlation and correspondence between zonal index and air temperature changes of the Northern Hemisphere and over Europe has been also examined.
Monthly anticyclonicity and cyclonicity in the southern hemisphere; Averages for january, april, july, and october
Authors: Leighton R. M. 
Published: February 2007

AbstractGeographical distribution across the Southern Hemisphere of 15‐year averages (23‐year averages in the Australian Region) of monthly anticyclonicity and cyclonicity as well as monthly anticyclone and cyclone immobility times, for the months of January, April, July and October for the years 1973–1987 (1965–1987 in the Australian Region) are presented in the form of maps.Comparisons are made with an existing atmospheric climatology of the Southern Hemisphere by the National Climate Centre of the Bureau of Meteorology, Melbourne covering the period 1976–1990 calculated from numerical analyses and with relevant climatologies contained in the World Survey of Climatology. References are made to past works relating to the climatology of the Southern Hemisphere and synoptic features of the climatology are discussed.
Mapping temperature using kriging with external drift: Theory and an example from scotland
Authors: Hudson Gordon , Wackernagel Hans 
Published: February 2007

AbstractLand suitability mapping requires information about climate, topography, and soils in relation to crop performance. Climatic data are available from recording stations which present point samples and so interpolation is needed to generate estimates for non‐sampled points. The annual temperature cycle must be interpolated differently for different land suitability projects. A common theme, however, is spatial interpolation and here we investigate the application of kriging with external drift to mapping January mean temperatures in Scotland. The spatial structure of the mean temperature is analysed using variograms computed in different directions. From these we see that January temperature is second‐order stationary in the north‐south direction. Hence the variogram exists in that direction and is taken to represent the underlying variogram. This variogram is modelled and used in universal kriging to produce point‐kriged estimates on a 5‐km square grid. These estimates do not adequately show the variation in temperature between stations and so the correlation with elevation was exploited in universal kriging with elevation as external drift. This method gives a kriged estimate for temperature that reproduces the correlation with elevation at the climate stations.
Spatial and temporal variations of the january circumpolar vortex over the northern hemisphere
Authors: Davis Robert E. , Benkovic Stephanie R. 
Published: February 2007

AbstractTemporal and spatial variations of the Northern Hemisphere's circumpolar vortex are analysed for each January from 1947 to 1990. Our data set is developed by digitizing the 546‐dam isoheight from 50‐kPa charts and recording the latitude of this contour at each 10° meridian. Principal components analysis is applied to the resulting 699‐day by 36‐variable matrix to examine the temporal and spatial evolution of the circumpolar vortex.The first principal component is comparable to the Pacific‐North America (PNA) teleconnection pattern. Over the 44 Januarys analysed, the frequency of the positive phase of the PNA pattern has increased. Principal component 2 is similar to the Eurasian pattern and varies between axially asymmetric zonal flow and a three‐wave pattern centred over the pole. The asymmetric pattern, which is characterized by higher heights over western Europe and Scandinavia, has increased in frequency over the study period. With the third principal component, which is similar to the East Atlantic teleconnection pattern, the strength of the Icelandic Low varies markedly. Time series of scores on the third component indicate that 50‐kPa heights over the North Atlantic are lower over the past 20 years. The fourth principal component is related to vortex area. The northern vortex has occupied a more expanded position since the mid‐1960s. These first four principal components explain half of the total variance in the data.In toto, these results indicate that the January circumpolar vortex has expanded over the past two decades. Most of the expansion has occurred in the vicinity of the Aleutian Low and has produced increased meridional flow throughout much of the Western Hemisphere. This circulation change could account for the observed increased occurrence of warm air masses in winter over eastern Alaska and western Canada, increased cyclone occurrence in the north‐western Atlantic, and both the increased frequency of Arctic outbreaks and declining temperatures in the south‐eastern USA. The overall vortex expansion is contrary to general circulation model forecasts that predict a decrease in the meridional temperature gradient of the Northern Hemisphere as trace‐gas concentrations increase.
Creation of homogeneous composite climatological reference series
Authors: Peterson Thomas C. , Easterling David R. 
Published: February 2007

AbstractMost techniques used to adjust climatological time series for inhomogeneities require a homogeneous reference series for comparison with each time series being evaluated. However, creating homogeneous reference series from data with unknown inhomogeneities presents many obstacles. Although a truly homogeneous reference series may, in fact, not be obtainable, in this article we present a method that has proven successful at minimizing inhomogeneities in the creation of reference climatological time series. The method utilizes a multistep process based on non‐parametric statistics and an alternative way of relating two time series through correlation analysis. This alternative uses the year‐to‐year change in the variable under consideration (e.g. temperature) as the basis for correlation.
An automated procedure for the identification of synoptic types applied to the new zealand region
Authors: Kidson John W. 
Published: February 2007

AbstractCluster analysis has been applied to 9 years of daily 1000 hPa analyses for 1980–1988 over the New Zealand region. The resulting 13 synoptic groupings are characterized mainly by high‐pressure cells and pressure gradients reflecting the predominant wind directions. Low‐pressure centres are not well represented, presumably because of their smaller horizontal scale and lower frequency of occurrence.Seasonal variations in cluster frequency over this period typically differ by a factor of two. The most persistent patterns are associated with highs to the south of New Zealand, whereas the transitions between clusters show the familiar sequence of eastward‐propagating high‐pressure cells interspersed with troughs.It is anticipated that these synoptic classifications will prove helpful in interpreting inter‐annual climate fluctuations, in validating the performance of climate models for the New Zealand region and in providing improved guidance to forecasters. Their application to the analysis of daily and monthly variations in climatic elements is described in a companion paper.
Climate change, potential evapotranspiration and moisture availability in the mediterranean basin
Authors: Palutikof J. P. , Goodess C. M. , Guo X. 
Published: February 2007

AbstractSimple methods for estimating potential evapotranspiration, requiring only temperature and day length data, are compared by reference to the results from the Penman method. A modification of the Blaney and Criddle method, in which the c parameter is calculated from seasonal regression equations with the mean monthly temperature as the independent variable, is proposed and tested. It is found to work sufficiently well in the area of interest, the Mediterranean Basin. For a network of 248 Mediterranean temperature stations, present‐day seasonal mean potential evapotranspiration is estimated by this method. Using the results from four equilibrium‐mode general circulation models, seasonal mean scenarios of potential evapotranspiration per 1°C rise in global mean temperature caused by the enhanced greenhouse effect are presented. Comparison of scenarios of the change in potential evapotranspiration and scenarios of the change in precipitation indicates an unfavourable shift in moisture availability due to the enhanced greenhouse effect, throughout the Mediterranean region.