bluuebunny/crossref_metadata_2025_split huggingface dataset:
A re‐evaluation of rainfall variability in the sahel. Part I. Characteristics of rainfall fluctuations
Authors: Nicholson Sharon E. , Palao Ian M. 
Published: February 2007

AbstractThis article deals with the characteristics of rainfall variability in West Africa. Time series of June—July, August—September and annual rainfall anomalies are derived for 19 regions, most of which are in the Sahel—Soudan zones of West Africa. The temporal characteristics of the series, such as trend, persistence, and low frequency variance are evaluated using regression, lag‐1 autocorrelation, and spectral analysis. High‐frequency‐filtered series are also derived. The spatial teleconnections among the regions are examined using linear correlations and principal component analysis. The study shows that there are primarily three spatial modes of rainfall variability in the region and these differ with respect to the part of the rainy season in which they are most important and to what extent they describe high and low‐frequency components of the variability. The study also defines three broad homogeneous sectors and demonstrates that the characteristics of rainfall variability in these sectors differ markedly. A strong contrast between the bulk of the Sahel—Soudan and its West Coast sector is apparent.
Seasonal and annual rainfall variations over Nigeria
Authors: Anyadike R. N. C. 
Published: February 2007

AbstractVariations of monthly and annual rainfall over the southern, middle belt and northern regions of Nigeria as well as the country as a whole are examined for a 72–year period (1916–1987). In this way the zonal distribution of the country's rainfall is taken into account. The extent and nature of non‐random changes, such as fluctuations, trend, and persistence, are investigated. The fluctuations were filtered by a Gaussian low‐pass filter and the resulting curves are discussed. Trend analysis showed a tendency towards decreasing annual rainfall totals in all the regions, with rates of decrease being greatest after 1961 in the southern region. All regions experienced the reverse of the trend during the 1931–1960 period. Overall, no significant persistence was evident in all the series. Power spectrum analysis revealed the existence of significant oscillations in the rainfall totals. These have time periods of 2·00–2·82 years in the middle belt and northern regions. 3·00–4·80 years in the middle belt, and 8·009·60 years in all the regions. The implications of these fluctuations, and continued application of the 1931–1960 normal for planning purposes, are pointed out, as well as suggestions for further lines of inquiry.
The climatology and characteristics of drought in the eastern Cape of South Africa
Authors: Jury Mark R. , Levey Kevin 
Published: February 2007

AbstractAlong the south‐eastern seaboard of Africa, a drought‐prone area is found between the humid subtropics and a deser. Convective mid‐summer precipitation in the north‐east is contrasted with stratiform winter rains in the west. Mean annual precipitation is <500 mm while potential evaporation is >2000 mm. According to time series analysis of rainfall records, dry spells recur at intervals of 3·5 and 18·2 years, most notably in the period 1940–1970. By contrast, excessive rainfall characterized the mid‐1970s. Extreme dry and wet years are analysed for circulation, convection and sea‐temperature differences. Below‐normal sea temperatures to the south‐west and east of the study area are associated with drought in the eastern Cape. Circulation differences indicate that low‐level westerly winds sweep across the region, in association with a stationary subtropical westerly wave of wavelength 3000 im and amplitude 1500 km. A positive outgoing longwave radiation anomaly indicative of reduced cloudiness and water vapour is noted in a north‐west—southeast band extending from Namibia across the eastern Cape watershed. Anticyclonic vorticity anomalies of the order of 10−5s−1 across the subtropics of southern Africa are common in dry years. Lower divergence to upper convergence anomalies of the order of 2 × 10−6s−1 are the driving forces of subsidence over the eastern Cape. The analysis of climatic patterns associated with dry spells will assist in forcasting seasonal rainfall, planning agricultural production, and optimizing water resources.
An assessment of air quality variations in the south‐western USA using an upper air synoptic climatology
Authors: Davis Robert E. , Gay David A. 
Published: February 2007

AbstractDaily particulate concentrations in the Desert South‐west from 1984 to 1988 are analysed using a synoptic climatology based upon tropospheric thermal, moisture, and flow conditions. Using a combination of principal components analysis and cluster analysis, 13 distinct synoptic types (clusters) are identified that correspond to seasonal variations in the atmosphere's general circulation. These include summer clusters, which reflect monsoonal and non‐monsoonal conditions, winter clusters defined by the positions of the polar and subtropical jets and shortwave ridges and troughs, and clusters that predominate in the transition seasons.Particulate concentrations vary significantly by synoptic type. Three clusters have poor air quality. ‘Summer monsoon’ days have high humidity and cloud cover, conditions that encourage aerosol growth. ‘Continental high’ days have a slow‐moving anticyclone centred over the Great Basin that traps particulates within the boundary layer. ‘Rockies ridge’ days are associated with strong south‐westerly flow and the advection of regional haze from southern California into the Desert South‐west. In all of these clusters, high humidity or cloud cover enhance particulate growth. Good air quality in the summer occurs on monsoonal ‘break’ days when relative humidity and cloud cover decrease. In the winter, good air quality occurs when Arctic or continental polar air masses are present, or when either the polar or subtropical jets are strong and positioned over the South‐west. In some of these latter situations, widespread precipitation removes particulates through wet deposition.These results suggest that the Navajo Generating Station (NGS), a large coal‐fired power plant on the Arizona‐Utah border, does not contribute significantly to air quality degradation in the Grand Canyon National Park, Arizona. Most of the days with high particulate levels are associated with transport from southern California or unstable summer days with high humidity and contributions from many point and regional sources. There may be some contribution from the NGS on ‘continental high’ days, but when this cluster occurs on consecutive days, air quality improves rather than declines. This research provides a useful framework for future mesoscale modelling studies of air quality in south‐western USA.
Adjustment of temperature and rainfall records for site changes
Authors: Rhoades D. A. , Salinger M. J. 
Published: February 2007

AbstractMethods are presented for estimating the effect of known site changes on temperature and rainfall measurements. Parallel cumulative sums of seasonally adjusted series from neighbouring stations are a useful exploratory tool for recognizing site‐change effects at a station that has a number of near neighbours. For temperature data, a site‐change effect can be estimated by a difference between the target station and weighted mean of neighbouring stations, comparing equal periods before and after the site change. For rainfall the method is similar, except for a logarithmic transformation. Examples are given. In the case of isolated stations, the estimation is necessarily more subjective, but a variety of graphical and analytical techniques are useful aids for deciding how to adjust for a site change.
Early detection of the start of the wet season in tropical climates
Authors: Jolliffe Ian T. , Sarria‐dodd Doris E. 
Published: February 2007

AbstractIn many tropical and sub‐tropical climates the year is divided into well‐defined wet and dry seasons. To maximize agricultural production it is important that crops are planted as early as possible in a wet season, but deciding exactly when the wet season has started may be a problem. A decision can be made on the basis of previous years' data, or we may try to incorporate information from the current season. The latter approach is discussed in the present paper, and shown to be potentially of greater value than relying solely on historical data.
Albedo of tropical grass: A case study of pre‐ and post‐burning
Authors: Fisch G. , Wright I. R. , Bastable H. G. 
Published: February 2007

AbstractMeasurements of reflected shortwave radiation were made at an Amazonian ranchland site for a period in which the grass was completely burnt and then subsequently regrew. For the 35 days prior to the fire the mean albedo was 0.19. After the fire the albedo was reduced by a factor two and thereafter took about 80 days to recover to its previous value. The influence on the energy balance is described and it is suggested that such seasonal albedo changes during the dry season may need to be described in climate models for the prediction of the seasonal impact of deforestation.
Luni‐solar 18.6‐ and 10—11‐year solar cycle signals in H. H. lamb's dust veil index
Authors: Currie Robert G. 
Published: February 2007

AbstractMaximum entropy and Yule‐Walker methods of spectrum analysis applied to Lamb's dust veil indices (dvi) for the Northern Hemisphere (1500–1968) show two strong peaks, with periods of 18.6±0.5 and 10.8±0.3 years. They are identified as the 18.6‐year luni‐solar Mn and 10–11‐year solar cycle Sc signals, which have recently been reported in a wide variety of climate and economic time series. The signals were transformed into the time domain by band‐pass filters, their wavetrains summed, and the sum superimposed on trend‐like components of the dvi; it is found that they account for 48 per cent of variance in the index.
Indian ocean sea‐surface temperature patterns and australian winter rainfall
Authors: Smith Ian 
Published: February 2007

AbstractIndian Ocean sea‐surface temperatures (SSTs) for the period 1950–1988 are analysed using principal component analysis, and their relationships with Australian winter rainfall totals for the period 1950–1979 are studied using regression analysis. As has been demonstrated by others, significant simultaneous correlations exist between the dominant patterns in the Indian Ocean and the wintertime rainfall over a large part of Australia. There is also evidence of significant correlations between autumn SST patterns and winter rainfall.These relationships are tested using multiple linear‐regression‐based predictions of winter rainfall categories for the period 1980–1988. Skill is quantified in terms of categorical predictions. Predictions based on the autumn SSTs exhibit more skill than those based on the autumn SOI, but much less than predictions based on the concurrent winter indices.
Linking air mass analysis to daily and monthly mid‐tropospheric flow patterns
Authors: Schwartz Mark D. , Skeeter Brent R. 
Published: February 2007

AbstractAir mass analysis, though widely used in early atmospheric studies, has seldom been employed in recent decades. In part, this may be due to the lack of agreement on a quantitative air mass classification technique. Synoptic analyses (of which air mass analysis is one example) have much potential for examining the relationships among a variety of surface processes and climate. Schwartz (1991) proposed an integrated air mass classification system that was able to overcome some of the limitations of previous methods. This study further validates that approach by quantitatively linking these air masses to 500‐hPa height and surface pressure patterns. Cluster analysis was used with daily and average monthly air mass distributions in the north‐central USA to identify similar groups. For the daily analyses, average 500‐hPa height, surface pressure, and air mass percentage coverage patterns were determined for the groups in each season. In the monthly analyses, transects of 500‐hPa height difference were examined with the multiple analysis of variance (MANOVA) technique in order to detect significant changes relative to the clusters. Our results show that: (i) integrated‐method air mass percentage coverage distributions can be related quantitatively to a small number of meaningful 500‐hPa height and surface pressure patterns in all seasons; (ii) key transects can be used to describe changes in average monthly air mass dominance and 500‐hPa flow patterns from one year to another; and (iii) for the period 1958–1981, cool air masses decreased in frequency over the study area during spring and summer.
Experimental predictions of climatic variability for lead times of twelve months
Authors: Hunt B. G. , Zebiak S. E. , Cane M. A. 
Published: February 2007

AbstractInterannual variability of present‐day climate has been clearly linked to the occurrence of large‐scale sea‐surface temperature anomalies, particularly in the Pacific Ocean. Prediction of such anomalies many seasons in advance by using relatively simple, coupled oceanic‐atmospheric models provides a basis for predicting the atmospheric climate over the same period. This is achieved by inserting the sea‐surface temperature anomalies predicted by the coupled model at appropriate time intervals into a global climatic model and integrating forward in time. Prediction experiments for 1991 and 1992 have been conducted on this basis using sea‐surface temperature anomalies predicted for the Pacific Ocean. Global and regional rainfall outcomes are presented here, although the predictions are not expected to be valid for the whole globe. Detailed results are given for Australia and southern Africa, which experienced severe drought conditions in 1991 and 1992. Useful skill, with statistical significance for predictions when substantial rainfall anomalies occurred, was obtained for these regions, indicating the potential utility of the method. Considerable scope exists for improvements in the technique presented here, particularly in the global climatic model used, so that increasing accuracy should result as the technique is developed. Operational implementation of this method is essentially straightforward.
Box‐jenkins univariate modelling for climatological time series analysis: An application to the monthly activity of temperature inversions
Authors: Davies T. D. , Milionis A. E. 
Published: February 2007

AbstractBox‐Jenkins modelling has some advantages over other techniques for the analysis of time series of climatological variables. Not only does it provide more information than other methods of anlysis, in a more elegant way, but it is also perfectly acceptable from the mathematical point of view. Other methods may not be immediately applicable because of the problem of autocorrelation in time series. The method of Box‐Jenkins univariate modelling is briefly discussed. As an example of its application to climatological time series analysis, and as an illustration of its usefulness, we examined the monthly activity of temperature inversions over Hemsby (eastern England) over a 14‐year period. The results showed that the monthly activity series, for both surface and elevated inversions, are stationary. However. the series for surface midnight inversions has a seasonal non‐stationarity of lag 12. There is a 1Zmonth seasonality for surface inversions and a weaker 6‐month seasonality for elevated inversions. The monthly activity of surface inversions exhibits less variation than the monthly activity of elevated inversions. This simply reflects the fact that the physical processes responsible for the formation of surface midnight inversions have a more regular evolution overtime than those responsible for the formation of elevated inversions. These results are in accordance with those obtained by using standard statistical techniques.
Interannual variability of some trace elements and surface aerosol
Authors: Kane R. P. 
Published: February 2007

AbstractAfter correcting for seasonal variations and long‐term (linear or quadratic) trends, the residual interannual anomalies (variations) of the trace elements and surface aerosol show periodicities in the Quasi‐biennial Oscillation (2–3 years) and 3–5 years range. Quasi‐biennial Oscillations (QBO) of some elements match with the QBO of equatorial 50‐hPa wind, but for some others, matching is not good. For some elements, matching with Southern Oscillation index is good. The relationship is probably through the sea‐surface temperature changes, which affect the role of the ocean as a source/sink for these trace elements. Interaction between equatorial wind QBO and extratropical phenomena should also be involved.
Intensity and form of the urban heat island in barcelona
Authors: Moreno‐garcia M. Carmen 
Published: February 2007

AbstractA statistical analysis of the differences between the daily minima in the centre of Barcelona and those of the airport, supplemented by temperature readings taken along a number of transects through the urban area, have revealed the intensity of the heat island effect, which reaches a maximum intensity of 8°C. It was also possible to plot the spatial configuration of the latter.
Relationship of new zealand daily and monthly weather patterns to synoptic weather types
Authors: Kidson John W. 
Published: February 2007

AbstractThe effectiveness of the classification of daily mean sea‐level pressure patterns over New Zealand into 13 synoptic types by Kidson (1994) has been tested through their relationship with daily and monthly variations in temperature, precipitation, sunshine, and daily wind run over the period 1980–1990.The mean anomalies of these weather elements for each synoptic class often showed spatially consistent patterns, with departures falling in the second and fourth (below normal and above normal) quintiles. These were readily interpretable in terms of the effects of advection, differences in static stability, and the influence of mountain ranges on the low‐level circulation.On a monthly basis, 60 per cent of the variance in the frequencies of occurrence of the 13 synoptic types was found to be due to three significant EOFs. These formed the basis of an iterative clustering process to group the flow patterns for the 11‐year period into eight sets of monthly analogues or “regimes”, for which the composite patterns of the weather element were obtained.Overall, the results suggest that the synoptic classifications are likely to be helpful in specifying daily values of weather elements, and in interpreting the monthly departures of the New Zealand climate. They should also prove useful in validating climate model performance for the New Zealand region and in providing better detail of the regional climate changes likely to result from the greenhouse effect.
Correlation of solar radiation with climatological data for port harcourt, nigeria
Authors: Kuye Ayoade , Jagtap S. S. 
Published: February 2007

AbstractA total of 42 different empirical model equations for estimating global insolation from other meteorological parameters is discussed and their predictions compared with measured values for Port Harcourt. The parameters are sunshine hours, relative humidity, temperature as well as geographical declination, latitude and altitude. It is found that a number of the models give significantly the same level of prediction. The average error in the calculated insolation being between 1.7 and 2.6 per cent (maximum deviation less than 7 per cent) when 8‐year monthly average data are used. Utilizing the individual monthly average or daily average data resulted in higher errors in the range 6–7 per cent (maximum deviation less than 33 per cent).
Modelling and forecasting seasonal precipitation in Florida: A vector time‐domain approach
Authors: Chu Pao‐Shin , Katz Richard W. , Ding Ping 
Published: February 2007

AbstractSome major stages of vector autoregressive (AR) modelling consisting of specification, order determination, estimation, diagnostic checking, and forecasting are described. To illustrate the utility of multivariate AR models for climate teleconnection research, the seasonal Southern Oscillation Index (SOI) and a precipitation index in Florida are modelled jointly. Two bivariate AR processes, order one and order four, are selected as candidate models to represent the joint series.To make a comparison of model performance, one‐season‐ahead forecasts of Florida precipitation are generated from the bivariate AR models, as well as from a simple regression model, for recent years that are independent from the period on which the model is constructed. Results show that seasonal forecasts from the two‐dimensional, order‐one model are somewhat better than the other two models. One new and important finding of this study is that, in addition to winter precipitation forecast skill, there is also a forecast skill for autumn precipitation. The physical mechanisms by which these teleconnections might arise are briefly discussed. Other applications of vector models are suggested.
Modelling evaporation from a high subarctic willow‐birch forest
Authors: Blanken Peter D. , Rouse Wayne R. 
Published: February 2007

AbstractContinuous measurements of the energy balance were made during the 1991 growing season over a dwarf willow‐birch forest located near Churchill, Manitoba. Intensive measurements of stomatal conductance for several species were taken on three fair‐weather days. These represented a wide range of air temperatures and leaf‐to‐air vapour pressure deficits and allowed the quantification of the surface‐atmosphere interaction. Modelling evaporation on a 0‐5 h basis can be performed accurately using a modified version of the Penman‐Monteith combination model coupled to a submodel of stomatal conductance. With a vegetated surface cover of about 90 per cent at full leafing, vegetation plays an important role in the overall moisture flux because 80 per cent is a result of transpiration. Simulating various vegetation‐change scenarios shows that species composition, through differences in stomatal behaviour, has a marked effect on evaporation.
The estimation of thermal atmospheric radiation under cloudy conditions
Authors: Alados‐Arboledas L. , Vida J. , Olmo F. J. 
Published: February 2007

AbstractAmong the surface radiation budget components that are needed to understand the climate of the Earth, the thermal atmospheric radiation component is the only one that is not measured routinely, so it must be estimated indirectly. The presence of clouds substantially hampers this task, supplementing the emission of water vapour and carbon dioxide in the lower atmosphere. The methods proposed to estimate thermal atmospheric radiation often rely on a cloudless sky model and a corrective term that takes into account the cloud contribution. Several models for estimating the thermal atmospheric radiation under cloudy conditions have been tested using measurements recorded in Granada (Spain) during a period of 2 years. The cloudless sky model provides estimation with an error of about 5 per cent, whereas the cloudy skies models, after some modifications, estimate thermal atmospheric radiation with an error of about 6 per cent. Our results show the convenience of a quadratic dependence on cloud amount for cloudy skies models. In addition to this, it seems convenient to use available information about the radiative properties of clouds to assign different cloud emittances for different types of clouds within each level, especially for middle level clouds.