bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regionalization of Indian monsoon rainfall and long‐term variability signals
Authors: Iyengar R. N. , Basak P. 
Published: February 2007

AbstractLarge regions in India with homogeneous variability of monsoon rainfall are identified with the help of principal component analysis. Four major regions, called principal regions, are first demarcated. Even though the variance explained by the first PC is only 21 per cent, it can be used to organize 45 per cent of the surface area into a coherent region. A novel sequential methodology wherein at every step the grouped stations are sieved out is also proposed. This helps in identifying 10 sequentially homogeneous regions accounting for 91 per cent of the total area under consideration. The four principal regional rainfall series reflect the interannual variability originally present in the data set. These are mutually uncorrelated and hence represent four independent monsoon anomaly patterns also. The first and the fourth principal regions contain temporal signals well discriminated from white noise.
Reconstruction of New Zealand climate indices back to AD 1731 using dendroclimatic techniques: Some preliminary results
Authors: Salinger M. J. , Palmer J. G. , Jones P. D. , Briffa K. R. 
Published: February 2007

AbstractReconstructions of temperature and zonal and meridional flow over New Zealand are presented for the period back to AD 1731. The reconstructions have made use of ring‐width chronologies from five endemic species (three different genera); the first time multispecies reconstructions have been attempted in New Zealand. The chronologies were standardized using techniques that attempted to maintain as much of the low‐frequency variance in the tree‐ring series as possible, so that long‐term climatic trends could be detected. In independent periods verification, the reconstructions of temperature explain between 30 and 33 per cent of the variance, whereas zonal and meridional flow reconstructions explain 31–43 per cent and 18–39 per cent of the variance, respectively.
Climate of two locations on the Southwestern corner of Hudson Bay: AD 1720–1729
Authors: Ball Timothy 
Published: February 2007

AbstractLack of historic climate data is a severe limit to advancing understanding of climate and improving general circulation models. Diaries maintained by the Hudson's Bay Company at Churchill and York Factory on Hudson Bay are analysed to determine a synoptic climate for the decade 1720–1729, a critical decade within the Little Ice Age. Subjective data are converted by a coding system to objective numerical data for computer analysis. Instrumental temperatures were not available this early, however, wind direction, number of days with precipitation events including rain, snow, freezing rain, and hail were recorded. In addition, first day of rain in spring, snow in autumn and number of days with thunder are analysed. Weather conditions during the decade are presented for other parts of the world. Results show similarities with these climate records. Overall the conditions reflect Little Ice Age conditions. The first pentad is markedly different than the second, which has greater variation in all variables. This pattern parallels sunspot activity. The decade has a meridional pattern, however, this is more pronounced in the second pentad.
Impact of the greenhouse effect on sea‐ice characteristics and snow accumulation in the polar regions
Authors: Hunt B. G. , Gordon H. B. , Davies H. L. 
Published: February 2007

AbstractAn extensive analysis has been made of the simulated sea‐ice behaviour for current and doubled carbon dioxide levels for both polar regions. The sea‐ice variations were computed as a component of the overall performance of a global climatic model. This model simulated the major climatic processes, but used an elementary oceanic representation known as theQ‐flux parameterization. For simplicity, dynamical processes were omitted from the sea‐ice formulation. For current conditions the sea‐ice extent, thickness, seasonal and interannual variability were reasonably simulated, particularly for the Northern Hemisphere. The major deficiency was the lack of regions with very thick sea‐ice, which is known to be generated in the real world by dynamical interactions. Very substantial reductions occurred in the sea‐ice thickness, and to a lesser extent in sea‐ice area, under greenhouse conditions, with the major impact being in summer. Water mass accumulation over the great ice‐sheets agreed moderately well with limited observations for control conditions. An increase in accumulation rate was simulated for both polar regions in the greenhouse experiment. The results indicate that, overall, a first‐order representation of sea‐ice behaviour is obtainable with a thermodynamics‐only sea‐ice parameterization.
Variability of the African convection centre as viewed by outgoing longwave radiation records and relationships with sea‐surface temperature patterns
Authors: Moron Vincent 
Published: February 2007

AbstractThe main African convection centre (ACC) is delimited by the 5°‐square areas with outgoing longwave radiation less than 235 W m−2 in the domain 17·5°N‐17·5°S and 18°W–46°E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 1974 to December 1991. The relationships between the variability of the ACC and the main sea‐surface temperature (SST) patterns were then studied. Correlation and composite analyses demonstrate that the first principal component of SST, representing mainly the variability of the eastern and the central tropical Pacific, is associated strongly with the extension and the mean intensity of the ACC. Both are strongest when cold conditions prevail in the eastern and central Pacific (= La Niña event) and smallest when warm conditions occur in the eastern and central Pacific (= El Niño event). This relationship is strongest during the boreal summer, when ACC is elongated from the Atlantic Ocean to the Ethiopian highlands. The second principal component, representative of the south‐eastern and equatorial Atlantic, is also linked with the extension and the longitudinal position of the ACC (greatest extension/westernmost position when the equatorial and South Atlantic is anomously warm, and inversely). The intermonthly variability of the latitude seems more noisy and less related to the large‐scale SST patterns than the other parameters.
Recent frost date trends in the north‐eastern USA
Authors: Cooter Ellen J. , Leduc Sharon K. 
Published: February 2007

AbstractUncertainty in projections of future climate, along with a need for policy makers and management to respond to change in climate, highlight the importance of the detection of trends in climatological time series. Selected indicators of regional climate status and change may well be related to indicators of ecological condition. Climate factors are known to stress ecosystems. With the identification and description of trends in biologically important climate descriptors this knowledge could be used to provide scenarios of biological changes. One aspect of climate which stresses forest ecosystems is described by the annual date of the last hard spring‐freeze (minimum temperature ⩽ −2·2°C). Averaged for New England, there was a significant linear trend indicating an earlier initiation of frost‐free conditions (negative slope) for the period 1961–1990.Significant time trends were detected locally at stations throughout much of the New England regions as well. Temporal discontinuities in trend, spatial relationships, and urban influence were considered. The presence of trends in time does not appear to be related to geographical location. The direction of trend (positive or negative) exhibits some geographical coherency, which may be related to climatological variables such as percentage of possible sunshine and cloud cover.
Sea‐surface temperature — South African rainfall associations, 1910–1989
Authors: Mason S. J. 
Published: February 2007

AbstractThe main features of sea‐surface temperature variability in the South Atlantic and the south‐west Indian Oceans are identified and their interaction with the Southern Oscillation discussed. Most of the variance is explained by coherent features of variability in the South Atlantic Ocean. Tropical and subtropical features dominate the variance, but this may be partly a reflection of data availability. Many of the principal components are associated with rainfall over southern Africa and the strongest associations occur with sea‐surface temperatures in the western equatorial Indian Ocean, the Agulhas system, and the central South Atlantic Ocean.
Complex demodulation and the estimation of the changing continentality of Europe's climate
Authors: Thompson R. 
Published: February 2007

AbstractSix long records of European mean monthly temperature have been analysed for changes in continentality of climate using the time series technique of complex demodulation. Variations in amplitude and phase of the annual temperature cycle as estimated by the complex demodulation, in combination with low‐pass filtering, are found to be coherent across much of Europe, from distinctly maritime to distinctly continental locations. The most significant departure of continentality found during the last 460 years is the maritime period of the 1920s when cool summers accompanied mild winters along with a retardation of the seasons throughout Europe.
The effect of station drift on the estimation of shifts in meteorological records due to site changes
Authors: Rhoades D. A. , Neill W. A. 
Published: February 2007

AbstractThe presence of station drift can seriously affect tests of significance of the shift due to a site change when neighbouring stations are used to adjust a meteorological series. The series of differences between a station and its neighbours (on which such tests are based) are often moderately autocorrelated; this is evidence that station drift effects commonly exist. Two types of station drift, both of which appear to be present in real meteorological series, are considered here: transient drift, modelled as a first‐order autoregressive process, and enduring drift, modelled as a random walk. A method is given to estimate the size of each of these effects in real data sets, using data from the periods between site changes, and hence to correct the variance of the estimated shift for station drift. The optimal length of the adjustment period can also be determined; it depends mainly on the size of the enduring station drift.
Global and terrestrial precipitation: A comparative assessment of existing climatologies
Authors: Legates David R. 
Published: February 2007

AbstractOver the past 20 years, several global and terrestrial precipitation climatologies have been developed. These climatologies have been used extensively, for example, to evaluate general circulation model simulations of the present‐day climate, as input fields in global hydrological studies, and to validate satellite precipitation algorithms. If these climatologies differ significantly, the results of these applications may be affected adversely.In this paper, three global precipitation climatologies—developed by Schutz and Gates, Jaeger, and Legates and Willmott—are examined comparatively. Additionally, three terrestrial precipitation archives—compiled by Eischeidet al., Leemans and Cramer, and Hulme—are compared with the Jaeger and the Legates and Willmott climatologies to assess precipitation over land areas and the importance of the time period of record on long‐term averages.Results indicate that seasonal precipitation estimates from the Schutz and Gates climatology are considerably smaller than either of the other two climatologies and its annual average estimate is much smaller than most estimates of global precipitation made since 1960. Zonally, however, the smaller estimates are predominantly located in lower latitudes although the general spatial pattern is similar to that of the other two global climatologies. Spatial gradients and areas of precipitation maxima are much smaller in the Schutz and Gates climatology, which accounts for its lower estimates. Qualitatively, the Jaeger climatology agrees well with that of Legates and Willmott although Legates and Willmott's estimates are much greater along the Inter Tropical Convergence Zone. Oceanic estimates vary considerably which underscores the uncertainties in estimating oceanic precipitation. Over land, the Legates and Willmott climatology compares favourably with the observation‐based estimates from the terrestrial archives, leading to the conclusion that observation‐based climatologies are consistent regardless of the time period of record and are preferable to climatologies compiled subjectively.
Seasonal and regional variations of tropospheric temperatures in the Northern Hemisphere 1976–1990
Authors: Weber Gerd Rainer 
Published: February 2007

AbstractThe 300–1000 hPa monthly average thickness data for the Northern Hemisphere (NH) published by the synoptic climatology group of the Free University of Berlin are analysed on a seasonally aggregated basis and with respect to regional variations. It is shown that the rise in tropospheric temperatures between 1976 and 1990 began over the tropical oceans—when temperatures in the mid‐latitudes were still falling—continued over continental areas of the mid‐latitudes in the late 1970s, fell in the of the first half of the 1980s and continued again in the second half of the 1980s. Temperatures over the mid‐latitude oceans rose slowly in the late 1970s, fell in the early 1980s and rose strongly in the late 1980s. High‐latitude tropospheric temperatures showed no significant change throughout the period.In terms of seasonal variations, the largest warming relative to the late 1970s occurred over mid‐latitude continents in winter. However, compared with the base period used here, 1951–1960, the largest warming in absolute terms occurred over the low‐latitude oceans in summer and autumn and over mid‐latitude continents in spring. Low‐latitude warming was particularly strong over the Pacific Ocean. There was some significant warming over mid‐latitude continents in summer in the 1980s, which was of the same magnitude as the cooling in previous decades. The high latitudes are generally still colder than during the 1950s even though there has been some warming there as well since the 1970s. Around latitude 35°N, a ring of minimum warming appears in all seasons except winter.In the tropics, tropospheric warming is larger than surface warming; in the mid‐latitudes it is of comparable magnitude and in the higher latitudes it is smaller than surface warming.
Characteristic surface energy balances for different climate types
Authors: Kraus Helmut , Alkhalaf Adnan 
Published: February 2007

AbstractAn attempt is made to answer the question of whether the different climate types of the Köppen‐Geiger classification are also characterized by distinct annual courses of the surface energy balance terms. For this purpose the KöppenGeiger climate map was linked with Budyko's atlas of the heat balance of the Earth. For every climate area shown on the Köppen‐Geiger map (and classified by a certain combination of up to three letters) the annual course of the energy balance terms was extracted from Budyko's atlas and plotted as an energy balance diagram. Then the annual courses of the energy balance terms of all areas classified as equable by Köppen‐Geiger (i.e. being characterized by the same combination of up to three letters) and independent of where in the world they occur could be compared. It became evident from this that each climate type (characterized by a certain letter combination) shows a distinct structure for its energy balance diagram. Thus there is an unambiguous relationship between the Köppen‐Geiger classification and the distinctive structure of the annual course of the components of the surface energy balance. There is only one exception: the BSh climate, with its transitional character throughout the world.
Variations in heating and cooling degree‐days in the south‐eastern USA, 1960–1989
Authors: Soulé Peter T. , Suckling Philip W. 
Published: February 2007

AbstractTemporal trends and spatial variability of heating and cooling degree‐days are examined for a portion of the south‐eastern USA for the period 1960–1989. Temporal variability is examined through simple time‐series analyses, regression analyses, and a climate departure index (CDI). Maps of 30‐, 15‐, 10‐, and 5‐year climatic normals for degree‐days are presented.The CDI indicates that heating degree‐day (HDD) variability was high during the 1970s with a sudden drop to low variability during the 1980s. Simple regressions show weak downward trends for actual HDD values across the region during the study period. However, the HDD decline was more pronounced through the 1980s, coinciding with the period of low year‐to‐year variability. Isoline maps show that most sites recorded distinctly fewer HDD in the most recent 5‐year period compared with longer term averages.Although the long‐term trend for cooling degree‐days (CDD) is slightly positive, there is considerable interyearly and interdecadal variability. Unlike HDD, there were no sustained periods with consistently high or low variability for CDD. Mapped patterns of climatic normals show that CDD values peaked across the study area during the most recent 5‐year period.Mapped patterns for both HDD and CDD can be influenced by data for large urban sites. Repeating the analyses without the seven largest urban centres resulted in less anomalous spatial patterns but almost no shift in study area mean‐degree‐day or CDI values and their temporal patterns. Atlanta emerged as the most distinct anomaly for the mapped patterns.From an applied viewpoint, the most significant finding occurred for the heating season with the combination of a sustained downward trend in HDD and comparatively low variability around the long mean (low CDI values) during the last 13 years of the study period. This period represents a span where the climate‐driven demand for space heating was decreasing and the heating‐season generating capacities for power generation utilities were not challenged.
A new method for detecting undocumented discontinuities in climatological time series
Authors: Easterling David R. , Peterson Thomas C. 
Published: February 2007

AbstractThe development of homogeneous climatological time series is a crucial step in examining climate fluctuations and change. We review and test methods that have been proposed previously for detecting inhomogeneities, and introduce a new method we have developed. This method is based on a combination of regression analysis and non‐parametric statistics. After evaluation against other techniques, using both simulated and observed data, our technique appears to have the best overall performance.
Temporal variability of the 40–50‐day oscillation in tropical convection
Authors: Anyamba Ebby Kamila , Weare Bryan C. 
Published: February 2007

AbstractThe temporal variability of the structure and two‐dimensional phase propagation of the 40–50‐day oscillation in tropical convection are diagnosed using complex empirical orthogonal function (CEOF) analysis of the 1974–1988 outgoing longwave radiation (OLR) data.Results from autoregressive spectrum analysis of the OLR time series indicate that apart from the well‐known 40–50‐day peak, there are other significant spectral peaks near 20–30 and 17 days. In much of the tropics, excluding the equatorial Indian and western Pacific Oceans, these higher frequency peaks appear to be distinct from the 40–50 day spectral peak.The dominant spatial mode of the 40–50‐day oscillation consists of the well‐known equatorial dipole and associated eastward propagation. Interactions between this mode and the extratropical 40–50‐day oscillation are manifested through the propagation of convection anomalies to and from the tropics via the North Pacific, north‐east Atlantic and north‐east African subtropics. The sense of this propagation varies from season to season and year to year.Analysis of the oscillation during individual summers and winters and each of the 1976–1977, 1982–1983 and 1986–1987 El Niño‐Southern Oscillation (ENSO) events revealed marked variability in the oscillation's characteristics. The characteristic dipole and associated eastward propagation were suppressed during the winter of 1980–1981 and the entire 1982–1983 ENSO episode. In 1975–1976 and 1983–1984, convection anomalies were confined to the Indian Ocean and Australia sector and the spatial pattern differed from the characteristic equatorial dipole. The equatorial dipole was most pronounced in February‐May 1981, December 1984 to May 1985 and during the 1976–1977 ENSO. During certain occasions, such as the 1981–1982 and 1983–1984 winters, there was westward as well as eastward propagation from an apparent heating source in the east Indian Ocean.
Associations between Antarctic katabatic flow and the upper level winter vortex
Authors: Simmonds Ian , Law Rachel 
Published: February 2007

AbstractWe address the extent to which modifications to the surface wind field over Antarctica impact on the upper level winter vortex. This is approached by performing two sensitivity studies with a general circulation model. In the first experiment we have eliminated the katabatic outflow from the continent by removing the slope (i.e. we removed the topography of Antarctica). In the second experiment we weaken the surface flow by increasing the surface momentum drag coefficient over Antarctica.The results show a weakened upper level circulation in the no‐topography experiment but a strengthened vortex in the increased drag experiment. The different response is related to the effect of the boundary forcings on the thermal structure of the atmosphere. In the no‐topography simulation, significant warming occurs throughout the Antarctic troposphere and this is apparently associated with changes in cyclone behaviour. This appears to be the dominant effect on the upper level vortex. In the drag case the impact on temperature is much smaller but is still an important influence on the upper level circulation.We find that there is no simple, unambiguous relationship between the strength of the katabatic flow and the depth of the upper level vortex; it is clear that thermodynamic processes are important in determining the latter.
Comparison of observed and modelled radiation budget over the Tibetan Plateau using satellite data
Authors: Sun Zhian 
Published: February 2007

AbstractThe radiation budget over the Tibetan Plateau is investigated using radiation models together with the data from the International Satellite Cloud Climatology Project (ISCCP) and the Earth Radiation Budget Experiment (ERBE). A method of using the ISCCP spectral surface albedo in determining the radiation budget is proposed and tested against observations. Three cloud levels (low, middle, and high) with different phase states are considered in the radiative simulations. The effect of dust aerosols on the radiation budget is also taken into account in the study. The simulations are performed using climatology monthly mean radiosonde profiles observed at 35 stations on the Tibetan Plateau and compared with the ERBE observations.The results indicate that the radiation budget in clear sky conditions can be well modelled using the monthly mean radiosonde data. The monthly mean total scene radiation budget is also simulated satisfactorily using the radiation models in conjunction with the ISCCP data, although significant discrepancies can be found in certain regions owing to uncertainties in the calculations. The cloud properties over this high plateau are found to be different from elsewhere. The most significant differences in the cloud properties are their altitude, which is much higher, and water content, which is less than at lower altitudes. As a result, cloud over the Tibetan Plateau has positive forcing in the winter and less negative radiative forcing in the summer compared with low altitudes.