bluuebunny/crossref_metadata_2025 huggingface dataset:
GCM simulation of the Sahel 1984 drought with alternative specifications of observed SST
Authors: Druyan Leonard M. , Hastenrath Stefan
Published: February 2007

Two climate simulations using the NASA/Goddard Institute for Space Studies coarse‐resolution GCM are compared in order to investigate the sensitivity of modelled summer precipitation over West Africa to the specification of observed sea‐surface temperatures (SST). Both experiments used analyses of observed SST for the boreal spring and summer of 1984, but one was derived from NOAA publications while the second came from COADS archives. Values of the NOAA SST for the tropical Atlantic were somewhat higher during June–August, leading to larger modelled evaporation rates and a model hindcast of heavy precipitation over West Africa in August, contrary to observational evidence. By comparison, dry conditions were simulated using COADS SST. The results highlight the importance of quality observations of SST and they demonstrate how sensitive the GCM is to these data.
The exceptional hot spell of early August 1990 in the United Kindgom
Authors: Burt Stephen
Published: February 2007

An intense heatwave affected the British Isles in August 1990. The climatological aspects as well as the spread and extent of the high temperatures are considered. Comparisons are made with other notable heat waves over the last 175 years.
El Nino/southern oscillation modification to the structure of the monsoon and tropical cyclone activity in the Australasian region
Authors: Evans Jenni L. , Allan Robert J.
Published: February 2007

Streamfunction and velocity potential fields, calculated from monthly averaged station data sets, are composited for ENSO and anti‐ENSO extremes in the Australasian region. Four January and four February data sets are used for each of the composites. Gridded sea‐surface temperature (SST) and highly reflective cloud (HRC) data are composited in a similar manner. These data are used to investigate the effect of the phase of ENSO on the Australasian summer monsoon and tropical cyclone activity in the region.

Changes in the structure of the monsoon are found to be consistent with composited tropical cyclogenesis and cyclone track data. These effects extend to the north and west of Australia, in addition to the signal previously identified in the Queensland region. During ENSO phases, the summer monsoon trough is weak and displaced equatorward, vertical wind shear is reduced and warmer SSTs are found to the north‐west of Australia and in the central equatorial Pacific. Tropical cyclone activity is reduced to the north‐east of Australia, but increases to the north and north‐west of the continent. Owing to the associated changes in the steering flow, coastal crossings are enhanced in Western Australia and the Northern Territory, but suppressed in Queensland. In the anti‐ENSO composite, the reverse generally is observed. Features specific to the anti‐ENSO are that far fewer storms occur to the north of Australia and storms off the west coast tend to track off‐shore, persisting further south. This southward persistence also is evident on the east coast, but here the likelihood of coastal crossing is enhanced compared with the ENSO composite.
SOI phase relationships with rainfall in eastern Australia
Authors: Stone Roger , Auliciems Andris
Published: February 2007

Phases of the Southern Oscillation Index (SOI) have been identified using cluster analysis. The monthly phases are associated with amounts of rainfall expressed in terms of probability distributions for various locations in eastern Australia. The phase representing rapid rise in SOI indicates above median rainfall during Southern Hemisphere autumn and spring at the locations analysed. The phase representing consistently positive SOI generally corresponds with above median rainfall amounts while the phase representing consistently negative SOI corresponds with below median rainfall amounts. As SOI phases relate to actual rainfall amounts, expressed in terms of probability distributions, the phases have, for instance, direct application to agricultural decision support programmes.
The horizontal and vertical extension of the Persian Gulf pressure trough
Authors: Bitan Arieh , Sa'Aroni Hadas
Published: February 2007

The Persian Gulf Barometric Trough is an extension of the south‐west Asian Monsoon. It starts in the middle of June, stabilizing by the end of the month, remaining dominant during July and August and disappears very quickly in mid‐September. Because of its thermal origin its height is limited to about 1500 m. Above it dominates, during the summer months, the subtropical high‐pressure system with its Azores extension covering the Mediterranean region. The transitional zone between these two pressure systems is an inversion zone, whose lower base sometimes reaches the mountain tops of Israel and even lower. On such occasions the daily maximum temperatures are higher at the stations in the mountains than in the coastal plain.

Because of its thermal origin, it was expected that diurnal changes of temperature must affect the horizontal and vertical extension of the Persian Gulf Trough. However, the diurnal fluctuations of the pressure are mainly remarkable at stations at the margin of the trough, while at those stations affected directly by it, the daily fluctuations are minimized by irregular periodic changes in the intensity of the Persian Trough occurring every few days. These changes are due mainly to fluctuations of the upper level high‐pressure system. Changes in the position of the Persian Trough influence greatly the daily weather in the Levant.
General circulation model simulations of winter and summer sea‐level pressures over north America
Authors: McCare Gregory J. , Legates David R.
Published: February 2007

Temporal variability of synoptic‐scale circulation is a dominant factor in regional temporal climate variations. In the midlatitudes, temporal variability of synoptic‐scale circulation has been found to be related to temporal variations in regional air temperature and precipitation. General circulation model (GCM) simulations of long‐term changes in synoptic‐scale circulation may be useful in assessing the effects of climate change on regional air temperature and precipitation.

Atmospheric pressure is an important component of synoptic‐scale circulation. In this paper, observed sea‐level pressures were used to evaluate winter and summer sea‐level pressures over North America simulated by the Goddard Institute for Space Studies (GISS) and the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation models. The objective of the study is to determine how similar the spatial and temporal distributions of GCM‐simulated daily sea‐level pressures over North America are to observed distributions.

Overall, both models are better at reproducing observed within‐season variance of winter and summer sea‐level pressures than they are at simulating the magnitude of mean winter and summer sea‐level pressures. Results indicate that winter sea‐level pressures are better simulated by the GISS model than by the GFDL model. The GFDL model simulates anomalously high winter sea‐level pressures over north‐eastern North America. In summer, the GISS model underestimates sea‐level pressures, whereas the GFDL model overestimates sea‐level pressures over most of North America. Kolmogorov‐Smirnov tests indicate that much of the error in model simulations can be attributed to differences between simulated and observed means. Comparisons of spatial correlation matrices of observed and simulated sea‐level pressures indicate that GCMs simulate spatial variability of sea‐level pressures that is similar to observed. These results suggest that GCMs are able to simulate major components of synoptic‐scale circulation over North America, especially for winter.
An analysis of Australian seasonal rainfall anomalies: 1950–1987. I: Spatial patterns
Authors: Drosdowsky Wasyl
Published: February 2007

A detailed analysis of the variability of Australian district rainfall on seasonal time‐scales over the period 1950–1987 is described. This paper, Part I, describes the dominant spatial modes or patterns of variability. The major analysis tool is rotated principal component analysis (RPCA), used in both the S and T modes. Various criteria are examined to determine the number of components to rotate, including conducting trial rotations and comparison of the resulting patterns with the corresponding one‐point correlation maps. The stability of the chosen solutions is examined by repeating the analysis on various subsets of the data.

The S‐mode analysis, which groups districts with similar temporal variation, provides a regionalization of the continent into eight coherent and approximately equally sized regions. The results of this analysis closely resemble those obtained from cluster analysis.

The T‐mode analysis clusters seasons with similar large‐scale spatial variations (anomaly patterns). The similarity measure used in the T‐mode analysis is the congruence coefficient, rather than the correlation or covariance. The patterns produced by this analysis consist of continental‐scale anomalies, similar in some respects to the unrotated S‐mode patterns, but more amenable to meteorological interpretation. In particular the first pattern, which accounts for approximately 25 per cent of the total variance consists of anomalies of the same sign over the entire continent centred on south‐east Australia.

The relationship between the two modes of representation is also explored. Regression equations are developed to express the spatially complex T‐mode patterns in terms of the localized S‐mode patterns, and alternatively, to partition the variance of each of the S‐mode patterns between the T‐mode components. In Part II the temporal variability and the relationship of these patterns to the Southern Oscillation and other large‐scale circulation anomalies are examined.
Luni‐solar 18.6‐ and solar cycle 10–11‐year signals in USA air temperature records
Authors: Currie Robert G.
Published: February 2007

Spectrum analysis of 1197 USA air temperature records yields evidence for two peaks with periods 18.8 ± 1.7 and 10.4 ± 0.5 years. Tests by the t‐statistic show that both are significant at confidence levels of 99.9 per cent, and both account for 23 per cent of total variance in the raw data. They are identified as the luni‐solar 18.6‐year Mn and solar cycle Sc 10–11‐year signals in climate, induced by the twelfth largest constituent tide acting on the Earth and a variation of 10 to 11 years in the Sun's luminosity of the order of 0.1 per cent. Amplitude and phase of Mn wavetrains are highly non‐stationary with respect to both time and geography; in particular, abrupt 180° phase changes in wave polarity are often observed. Amplitude and phase of the Sc waves are also highly non‐stationary, with those east of the Rocky Mountains out of phase with waves to the west. These results consolidate and greatly extend and clarify earlier studies of Currie based on far less American data.
Synoptic climatology of atlantic coast North‐Easters
Authors: Davis Robert E. , Demme Gregory , Dolan Robert
Published: February 2007

A classification of extratropical storms in the north‐western Atlantic Ocean is developed based upon the storm's origin, track, and intensification. All storms producing at least 1.6‐m deep‐water waves at Cape Hatteras, North Carolina from 1943 to 1984 are included. Eight distinct storm types are identified, and their seasonality, interannual variation, and relationship to a previously devised storm‐intensity scale are discussed. The most dangerous storms are cyclones which originate either over Florida or north of Cuba from October through to April, travel northward, and are blocked by a stagnating anticyclone over New England or the North Atlantic. Coastal storm frequencies declined from the mid‐1960s through to the mid‐1970s and increased through to 1984, but the frequency of potentially damaging storms has increased since 1965.
Decreasing precipitation trend in the Marathon area, Greece
Authors: Amanatidis G. T. , Paliatsos A. G. , Repapis C. C. , Bartzis J. G.
Published: February 2007

The long‐term precipitation series (1926–1990) from a 10 rain gauge station network in the Marathon area, Greece, have been statistically examined for trends. Application of the Mann—Kendall rank statistic test to the annual time series revealed a significant decreasing trend in the precipitation over the area. Similar decreasing trends are observed in neighbouring regions to the Marathon area (Athens basin and Beotia). The differences in precipitation trends during the transitional seasons among the three areas seem to be caused by the urbanization process. The seasonal variations and the periodicities of precipitation in the study areas also are examined. Finally, the spatial distribution of precipitation and the relation of precipitation amounts to the station height in the Marathon area are discussed.
The effect of domain shape on principal components analyses: A reply
Authors: Legates David R.
Published: February 2007

In a previous paper, I reevaluated the domain shape dependence arguments of Buell and concluded that ‘unrotated’ principal components do represent, to a very large degree, the underlying structure represented in the dispersion matrix. Richman's comments are largely based as a defence of component rotation—a subject that was not addressed in my original paper. It is my thesis that much of the alleged uninterpretability of ‘unrotated’ components stems from an attempt to retrieve characteristic scenarios or ‘modes of the variation’ (which PCA does not purport to do) and not from an overdependence on the shape of the domain. This misapplication often results from a confusion of the goals of principal components analysis and common factor analysis as is evidenced in Richman's comments.
Monthly‐mean temperature anomalies in relation to spatial scale in Japan
Authors: Murata Akihiko M.
Published: February 2007

Using monthly‐mean temperature data over Japan, the monthly‐mean temperature anomaly (MMTA) is investigated with special reference to its spatial scale. Relationship between occurrence probability of the MMTA and distance indicates that the occurrence probability is almost constant up to around 800 km and then rapidly decreases in magnitude. However, re‐examination of the relationship reveals that the MMTA has a spatial scale of around 1600 km as a minimum, which corresponds to the macro β or α scale. In addition to this principal investigation, seasonal dependence and temporal changes of the MMTA are also investigated.
Class—A Canadian land surface scheme for GCMS, II. Vegetation model and coupled runs
Authors: Verseghy D. L. , McFarlane N. A. , Lazare M.
Published: February 2007

In the companion to the present paper, the soil model associated with CLASS (Canadian Land Surface Scheme) was outlined. In this paper, the accompanying vegetation model is described. This model includes physically based treatment of energy and moisture fluxes from the canopy as well as radiation and precipitation cascades through it, and incorporates explicit thermal separation of the vegetation from the underlying ground. Seasonal variations of canopy parameters are accounted for. The morphological characteristics of the ‘composite canopy’ associated with each grid square are calculated as weighted averages over the vegetation types present. Each grid square is divided into a maximum of four separate subareas: bare soil, snow‐covered, vegetation‐covered, and snow‐and‐vegetation covered.

Test runs were done in coupled mode with the Canadian Climate Centre GCM, to evaluate the performance of CLASS compared with that of the simpler land surface scheme previously used. Two versions of CLASS were run: one with ponded surface water saved between time steps, and one with it discarded. For the seasons of June—July—August and December—January—February, diagnostic calculations showed that the old scheme underestimated the globally averaged land surface screen temperature by as much as 3.0°C, and overestimated the globally averaged precipitation rate over land by up to 1.0 mm day−1. CLASS, on the other hand, produced screen temperature anomalies, varying in sign, of 0.2–0.3°C, and positive precipitation anomalies of 0.6–0.7 mm day−1. The relatively poor performance of the old model was attributed to its neglect of vegetation stomatal resistance, its assumption that the contents of the soil moisture ‘bucket’ had to be completely frozen before the surface temperature could fall below 0°C, and its use of the force‐restore method for soil temperatures, which systematically neglects long‐term thermal forcing from the soil substrate. The assumption made in most GCMs that excess surface water immediately becomes overland runoff is shown to result in substantial overestimates of surface screen temperatures in continental interiors.
Variations of some seasonal rainfall characteristics in Queensland, Australia: 1921–1987
Authors: Lough J. M.
Published: February 2007

Summer and winter indices of rainfall total, intensity, and contributions of rain‐days of different intensities were developed from 70 stations in Queensland over the period 1921–1987. In both summer and winter, only a few days of relatively high intensity rainfall contribute most to the seasonal rainfall total. In wetter summers, although the numbers of rain‐days of different magnitude rainfall all increase, it is days with rainfall in excess of 50 mm day−1 that contribute most to the increased seasonal total. Year‐to‐year and longer time‐scale variations in seasonal rainfall totals are matched by similar variations in secondary rainfall characteristics, i.e. wetter years or periods are likely to have more rain‐days and rainfall of greater intensity than drier years or periods. Variations of the secondary rainfall characteristics show similar relationships with the Southern Oscillation as total rainfall. The correlations with the SOI are, with one exception, insignificant for the period, 1921–1950, of ‘weak’ SOI teleconnections. Only the date by which 15 per cent of the summer seasonal rainfall is accumulated (representing pre‐monsoon rainfall) has maintained a significant and stable relationship with the SOI over time. Rainfall in Queensland is more closely linked with the number of tropical cyclones actually making landfall than the total number of cyclones in the region. Even in years when the large‐scale circulation is not conducive to tropical cyclone activity, a single tropical cyclone crossing the coast can lead to substantial rainfall amounts.
The random nature of drought: Mathematical and physical causes
Authors: Gordon A. H.
Published: February 2007

Annual and monthly rainfall records for three regions of the United Kingdom and five locations in Australia have been examined with specific regard to the frequencies of droughts and dry spells. It is shown that plots of cumulative totals of precipitation tend to obey are sine law behaviour and the excursions above and below the × axis fall within the limits of patterns to be expected by chance.

Runs of successive values of negative anomalies from the monthly median were counted and their mean and theoretical recurrence times computed. Chi‐square tests suggested that the frequencies of runs were no more nor less than might be expected from chance expectation in the United Kingdom. In Australia the frequencies in the Perth, W. A., Adelaide, S. A., and Hobart, Tasmania records showed similar characteristics to those in the United Kingdom. However in Melbourne and Sydney the frequencies of runs of negative anomalies from the monthly median showed high significance > 1% that they were more frequent than would be expected. This higher than expected frequency of droughts and dry spells is attributed to the ENSO factor. It is suggested that overall the occurrence of precipitation events is a chance mechanism although some regions, notably southeast Australia, northeast Brazil and the Sahel are affected by climatically forced mechanisms such as sea surface temperature anomalies, blocking, over grazing etc. A discussion is offered of the meaning of “naturally” occurring drought in terms of physical interactions described by nonlinear mathematical equations and alternatively in terms of casino probability.
A comparison of Lamb circulation types with an objective classification scheme
Authors: Jones P. D. , Hulme M. , Briffa K. R.
Published: February 2007

An objective scheme, initially developed by Jenkinson and Collison, is used to classify daily circulation types over the British Isles, along the lines of the subjective method devised by Lamb. The scheme uses daily grid‐point mean sea‐level pressure data for the region. The results of the analysis over the period 1881–1989 are compared with ‘true’ Lamb weather types. The frequencies of objectively developed types are highly correlated with traditional Lamb types, especially so for synoptic (cyclonic and anticyclonic) types, although still good for wind directional types. Comparison of the two classification schemes reveals negligible differences between the correlations of the counts of circulation types and regional temperature and rainfall. The major difference between the two classification schemes is that the decline of the westerlies since 1940 is less evident with the objective scheme.
Deterministic signals in European fish catches, wine harvests, and sea‐level, and further experiments
Authors: Currie Robert G. , Wyatt T. , O'Brien Douglas P.
Published: February 2007

Maximum entropy spectrum analysis of six fish catch series, seven series giving dates of wine harvest, and forty four height of sea‐level records from Europe yields evidence for two peaks with periods 18–19 and 10–11 years, the same terms recently reported in European tree‐ring chronologies. For each series the two wavetrains are obtained by bandpass filters, summed, superimposed on the trend‐like components of the raw data, and plotted against the raw data. The contribution, on average, of the waves to total variance in the raw data varies from a high of 50 per cent for fish catches to a low of 14 per cent for dates of wine harvest (the mean contribution for height of sea‐level is 18 per cent). The peaks are identified as the 18·6‐year luni‐solar, Mn, and 10–11‐year solar cycle, Sc, signals, which also have been reported recently in other climate variables, such as air temperature, air pressure, in rain‐gauge and tree‐ring data from North and South America, South Africa, Tasmania, and New Zealand; and in sea‐surface temperature as well as in American crop yield and other economic data. Further experiments show that with 110 years, or more, of data the Yule‐Walker method of spectrum analysis has sufficient resolution to resolve both signals. It is also shown that failure to apply a properly designed digital high‐pass filter to climate records prior to spectrum analysis usually leads to failure in detecting the terms.
Spectral band resolution of solar radiation in Athens, Greece
Authors: Jacovides C. P. , Kallos G. B. , Steven M. D.
Published: February 2007

A 14‐year (1977–1990) record of global solar radiation measurements performed in Athens, Greece, has been utilized to determine the distribution of radiant energy in the various wavelength bands. The monthly mean values of the irradiation ratios in the spectral intervals, blue (0·380–0·525 μm), green‐orange (0·525–0·630 μm), red (0·630–0·710 μm), and photosynthetically active radiation (PAR) (0·380–0·710 μm) and the global irradiation (0·3–2·8 μm) compare favourably with values reported in the literature for different locations over a wide geographical area.

The irradiation ratios exhibit seasonal variations attributable to changes in local air‐mass climatology. It is observed that the proportion of the radiant energy in the various spectral bands relative to the global solar irradiation increases as sky conditions change from ‘clear’ to ‘partly cloudy’. Finally, the observed seasonal dependence of the broad‐band spectral energy distribution is essentially caused by changes in the composition of the air masses (turbidity, airborne pollutants, clouds) in residence at the measurement site in the course of the year.
A preliminary assessment of the spatial and temporal characteristics of human comfort in China
Authors: McGregor Glenn R.
Published: February 2007

A simple empirical index of human thermal comfort is applied to the problem of assessing China's human climate resource. Considerable spatial and temporal variation of the human climate resource occurs in China. The human climate resource is discussed in terms of its synoptic‐scale climatic controls and the implications the spatial and temporal variations of the resource holds for the rapidly developing tourist industry in China.
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

Measurements 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

The 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

In 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

A 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

Wind 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

This 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

Using 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

The 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

A 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

Surface 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

Heat 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

Monthly 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

Understanding 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

More 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

The 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

The 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.