bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atmospheric synoptic conditions associated with the initiation of north‐west African depressions
Authors: Prezerakos N. G. , Michaelides S. C. , Vlassi A. S. 
Published: February 2007

AbstractThis study presents a discussion of the main characteristics, and at the same time gives a detailed classification, of the north‐west African depressions within the framework of the close relationship between the 500‐hPa flow and the origin, development, and movement of surface depressions.The classification relies mainly on the similarities and differences present in the 500‐hPa flow patterns when each north‐west African depression first appears on the surface synoptic chart. For a detailed discussion and, especially for a record of the synoptic conditions that are favourable for the formation of north‐west African depressions, mean 500‐hPa hight and anomaly charts and mean temperature charts, for the years 1970–1974, have been drawn for each subcategory into which the 79 cases fall.For each of these subcategories, mean charts have also been drawn for 850‐hPa hight and temperature, mean sea‐level (MSL) pressure, and MSL pressure anomalies. The classification resulted in the north‐west African depression being divided in five main categories A, B, C, D, and ST. Category A is divided into four subcategories, the depressions of which appear only during spring. Categories B and C are divided into two subcategories, B1, B2 and C1, C2, and these too occur only in spring, except for subcategory C2, which also appears in autumn. Category D is also divided into two subcategories, which appear only during winter. Category ST (stationary depressions) includes only four cases out of 79 north‐west African depressions. These are shallow, warm‐cored atmospheric circulation systems having no correspondence with the 500‐hPa flow and which appear in late spring and early autumn.The study showed that the north‐west African depressions do not exhibit significant differences from other extratropical depressions. Their origin, development, and movement largely follow (except for category ST) Sutcliffe's and Petterssen's traditional theories of development.
Development of an automated spatial synoptic climatological classification
Authors: Davis Robert E. , Kalkstein Laurence S. 
Published: February 2007

AbstractA spatial synoptic climatological index is developed that both characterizes the dynamic and thermodynamic surface weather regime and is capable of assessing and analysing the impact of synoptic‐scale variations on numerous environmental parameters. Based upon surface weather data for the contiguous USA for 1984, daily maps are produced that show those areas under the influence of similar weather conditions. The index is developed by applying principal components analysis to a daily matrix of 141 stations by 24 weather elements (chosen to represent the thermal‐moisture and surface flow characteristics). The resulting component scores are grouped using a two‐stage clustering technique. This yields a map showing lobes of air having relatively homogeneous weather characteristics. These lobes (clusters) are spatially coherent and correspond closely to surface weather map features.To allow for daily tracking of the clusters and identification days or weeks after disappearance, the means of each of the daily clusters are grouped across days. The resulting 90‐cluster categorization describes all of the major synoptic situations that occurred in 1984. Some of the common categories include maritime and continental polar air masses, frontal passages, and continental high dominance. These groups demonstrate seasonality, regionality, and high within‐category similarity. The resulting maps are useful since they are surface weather maps yet add clarity for environmental interpretation.
USA corn yields, the El Niñmo and agricultural drought: 1867–1988
Authors: Handler Aul 
Published: February 2007

AbstractThe magnitude of spatial and lagged correlation between the sea‐surface temperature anomalies of the eastern tropical Pacific Ocean (El NiñMo) and corn yield in the USA is presented. The record is not homogeneous in that the correlation level varies quite strongly over time. The period between 1910 and 1950 shows completely uncorrelated behaviour. In the most recent 40 years the correlation is found to be strongest in the region just south of the Great Lakes in the states of Illinois, Iowa, and Indiana. Correlation maps are presented that show the degree of association for the corn yield in those 41 states for which records are available. For the entire record the highest correlations occur with the sea‐surface temperature anomalies appearing after the corn is harvested in September to February of the following year. Since corn yields are a proxy for summer agricultural drought in the central part of the USA, the droughts during the period 1910 to 1950 must have had some other cause.
Onset of thunderstorms and precipitation over Northern Nigeria
Authors: Omotosho J. Bayo 
Published: February 2007

AbstractAn empirical prediction scheme for the start of thunderstorms, and the onset and expected amount of rainfall for any year at Kano, Nigeria, is presented, using 8 years' upper air data. The years investigated include two drought years (1973 and 1974) and 3 years of above average rainfall (1978, 1980, and 1988).Agriculturally sufficient and reliable rainfall begins 5–6 weeks after the vertical wind shear below the African Easterly Jet, ΔUL(surface, 700 hPa), and the mid‐tropospheric shear ΔUM (700–400 hPa), simultaneously satisfy the condition −20≤UL≤−5 ms−1 and 0≤UM ≤10 ms−1, as previously put forward by Omotosho. The total precipitation for any year is found to be well correlated with the total moisture anomaly (specific humidity) from the week of the above‐critical wind shear to the week of rainfall onset. This makes it possible to estimate the expected rainfall total at the very onset of the rains.
Interhemispheric contrasts of mean global temperature anomalies
Authors: Gordon A. H. 
Published: February 2007

AbstractNorthern and Southern Hemisphere series of surface temperature anomalies are compared. The series studied are the University of East Anglia Climatic Research Unit (CRU) monthly series (1854–1986) and the UK Meteorological Office (MO) quarterly series (1856–1989). A major difference is the marked seasonal variation of the warming trend in the Northern Hemisphere, with maximum in winter and minimum in summer. Analysis of the annual cycle of the CRU set suggests a shift in phase of the warm peak in the annual cycle of temperature anomalies from July to January for the period. This shift is a characteristic of the annual cycle itself and does not have to be associated with a greater warming trend in winter than in summer, although it may be.The series were converted into interannual differences from one month or quarter to the corresponding month or quarter in the following year. Globally, the sequential values of the positive and negative modes of the interannual differences suggest a slow relaxation towards zero with the absolute values of the interannual coolings decreasing faster than those of the interannual warmings. Spectral analyses of the first‐order interannual differences of the monthly CRU and of the quarterly MO series suggest that the temperature field reacts to a Quasi‐Biennial Oscillation pulse in the Northern Hemisphere and to a stronger ENSO pulse in the Southern Hemisphere.
Climate anomalies in Europe associated with ENSO extremes
Authors: Fraedrich Klaus , Müller Klaus 
Published: February 2007

AbstractSurface pressure, temperature and precipitation anomalies in Europe are composed for the El Niño‐Southern Oscillation (ENSO) warm and cold extremes. During warm event winters, negative pressure departures at western and central European stations are associated with positive temperature and precipitation anomalies; the reverse signals are observed in northern Europe. During cold episodes the field of negative pressure deviations is shifted northward with positive temperature and precipitation anomalies, whereas higher pressure is observed over central Europe. This shift of the anomalies corresponds to a shift in the dominating cyclone track (deduced from weather maps), which may be interpreted as the response of the (sensitive tail end of the) cross‐Atlantic storm track on the high‐pressure anomalies occurring at times in the northern or central part of the North Atlantic/European sector during warm or cold ENSO winters, respectively.
The influence of pre‐existing soil moisture content on Australian winter climate
Authors: Simmonds Ian , Lynch Amanda H. 
Published: February 2007

AbstractWe have performed some experiments with the University of Melbourne General Circulation Model to determine the transient response of the climate system to the imposition of soil moisture anomalies over the Australian continent. Two sets of cases have been performed in which the soil over the entire continent was saturated and was completely dried on the first day of winter and then allowed to evolve normally for 4 months.The evaporation over most of the Australian continent in the ‘saturated’ case initially was significantly greater than that in the mean and this situation persisted for the 4 month's duration of the experiments, into the spring. A similar statement is true for the reduction of evaporation in the ‘dry’ experiments, although the magnitude was not as great. As dictated by surface energy considerations, the sensible heat fluxes over most of Australia assumed signs opposite to those of the evaporation and magnitudes somewhat smaller, but the residual differences were still significant in September. Other atmospheric parameters, such as precipitation, surface temperature and mean sea‐level pressure tend to show much less persistence when averaged over Australia as a whole. However, many regions do show longer influence of the perturbed initial conditions.Of considerable interest to the value of Australian winter and spring crops is the finding that the soil moisture content still showed significant anomalies persisting into the fourth month, with an areal mean of 2.7 cm more than the control in the ‘wet’ case and 1.5 cm less in the ‘dry’. This persistence of, albeit exaggerated, initial anomalies of winter soil moisture suggests that early winter soil moisture conditions may hold some potential for forecasting Australian winter crop productivity. We have found the ‘halving time’ of these large‐scale soil moisture anomalies to be about 2 months and somewhat longer at higher latitudes. These findings are consistent with many other studies and are encouraging in that most of Australia's wheat is grown in that part of the continent.
Climatological criteria for estimation of runoff by linear regression
Authors: Schwarzmaier Gertrud , Mayer Helmut , Beyer Ulrich 
Published: February 2007

AbstractMonthly runoff data of the southeast of North America were analysed by a linear regression model. The model is to be validated for the prognosis of runoff and the description of runoff and its influencing meteorological and geoecological variables. The area studied was a region in the southeast of North America chosen on the basis of the climatological criteria of the Köppen‐Geiger climate classification. A further differentiation was also made between the four seasons and the two predominant types of land cover. Every single examination of the individual influencing variables revealed reasonable results according to the physical context between runoff and its influencing variables. The comparison between measured runoff values and estimated runoff values also showed an excellent coincidence in 35 out of 39 cases examined.
Energy balance differences and hydrologic impacts across the northern treeline
Authors: Lafleur Peter M. , Rouse Wayne R. , Carlson Derek W. 
Published: February 2007

AbstractEnergy balance measurements were made over wet tundra and a nearby open conifer forest near Churchill, Manitoba during the summer periods of 1989 and 1990. Little difference was found between net radiation, Q*, and ground heat fluxes, QG, for the two sites: Q* at the forest exceeded Q* at the tundra by only 2–5 per cent; QG averaged 9 and 12 per cent of Q* for the forest and tundra, respectively.The sensible, QH, and latent, QE, heat fluxes showed the greatest differences between the sites. When surface moisture was not limiting, QE was largest for the tundra and QH was largest at the forest. During a drying cycle in 1989 the energy balances for the two sites were similar. An analysis of wind direction on energy partitioning suggests that the tundra was more responsive to meteorological changes than the forest. The implications of this study for surface water balances in the subarctic are discussed.
Classification of summer monsoon rainfall patterns over India
Authors: Kulkarni Ashwini , Kripalani R. H. , Singh S. V. 
Published: February 2007

AbstractSeasonal (June through September) percentage departure from normal rainfall patterns over India have been classified by objective methods utilizing data for a 120‐year period (1871–1990). The methods used are the map‐to‐map correlation method and the k‐means clustering method. Empirical orthogonal functions (EOFs) are also presented.It is seen that 75 per cent of the charts can be classified into six distinct types by the map‐to‐map method. Six distinct types also are obtained by the k‐means method. The first four dominant EOFs explain 52 per cent of the variance.Intercorrelations and contingency tables among the types obtained by these methods and visual examination suggests that the dominant patterns are similar, irrespective of the method used. It is also seen that the monsoon rainfall for the country as a whole and the spatial patterns may have no relationship. Even during normal monsoon years, the spatial patterns may be different.The advantages and disadvantages of the methods used are discussed.
Deterministic signals in USA precipitation records: Part II
Authors: Currie Robert G. , O'Brien Douglas P. 
Published: February 2007

AbstractPower spectra of 1203 American rainfall records show evidence for two peaks with mean periods of 18.5 ± 1.8 and 10.6 ± 0.6 years, and statistical tests show that both are significant at confidence levels of 99.9 per cent. These are identified as induced by the luni‐solar 18.6‐year constituent tide and a 10–11‐year solar cycle variation in the sun's luminosity of the order of 0.1 per cent. Amplitude and phase of the 18.6 year wavetrains are highly non‐stationary, and abrupt 180° phase changes in wave polarity are often observed. Wave maxima/minima are generally in phase or out of phase with epochs (epochs are dates of maximum in tidal forcing which occurred at 1898.9, 1917.5, etc.). Polarity maps show that for epochs 1898.9, 1917.5, 1936.1 and 1954.7 the major part of the nation's landmass experienced droughty conditions, which reached a maximum in both amplitude and areal extent at 1936.1, the Dust Bowl era. At mid‐epoch 1964.0 and epoch 1973.3 so many waves changed phase by 180° that the major part of the landmass was wet at the epoch. Analogous phenomena have been found in tree‐ring data from several continents, and implications for economic science are briefly discussed.
Cold windchill spells in the south Balkans: A study of the synoptic situations
Authors: Giles B. D. , Balafoutis C. J. 
Published: February 2007

AbstractUsing hourly data of temperature and wind speed for Thessaloniki over the period October 1959 to April 1978, values of windchill in excess of 1000 Kcal m−2 h−1 were abstracted. Windchill days and windchill spells are defined and 67 of the latter noted, all occurring in winter between November and March. Within these spells, windchill episodes were identified from an hour by hour analysis of the data and 22 discontinuous episodes were excluded from further consideration. The surface and 500‐hPa charts for the remaining 45 episodes were used to note the main synoptic features over Europe and the Mediterranean. None of the standard synoptic classifications were found to be suitable for this purpose but a basic patterns did emerge. We identified six surface and seven 500‐hPa patterns and these are discussed in association with the windchill episodes.
Connections between air temperature and precipitation and the geopotential height of the 500 hPa level in A meridional cross‐section in Europe
Authors: Kożuchowski K. , Wibig J. , Maheras P. 
Published: February 2007

AbstractThe correlation coefficients between air temperature, precipitation, and geopotential heights of the 500 hPa level for six stations in Europe, located along the 20°E meridian from Scandinavia to Greece, for the period of 1951–1985 are calculated. The fields of correlation coefficients for each station and season are described. It is observed that the correlation coefficients of temperatures are, as a rule, significantly greater than for precipitation. How meridional and zonal circulation determine temperatures and precipitation has been examined.
Long‐range prediction of the onset and end of the rainy season in the West African Sahel
Authors: Omotosho J. 'Bayo 
Published: February 2007

AbstractUsing upper‐wind data for three stations across the West African Sahel, simple empirical schemes for predicting the onset and cessation of the rainy season for more than 2 months ahead are presented. Agriculturally reliable rainfall commences about 70 days after the first sudden changes in wind direction from westerly to easterly at the 400 hPa level and above. These sudden changes signal the withdrawal of the subtropical (westerly) jet, thus leading to the establishment of the African easterly jet at the 700 hPa level. Cessation of rainfall occurs about 80 days after the destruction, at the peak of the rainy season, of the mid‐tropospheric (700–400 hPa) vertical wind shear. A method for estimating the length of the rainy or growing season also is proposed.
Heat balance characteristics during fine periods on the lower parts of the Franz Josef Glacier, South Westland, New Zealand
Authors: Ishikawa N. , Owens I. F. , Sturman A. P. 
Published: February 2007

AbstractHeat balance observations were carried out during fine conditions at a site on the lower Franz Josef Glacier in June 1988 and February 1990 and compared with results obtained in August, October, and December 1981. Surface ice melt occurred during all seasons, with the mean melt rate in summer about eight times larger than in winter. The seasonal variation of the various contributions to ice melt was also identified. Sensible heat flux was the dominant heat source, contributing 80 per cent and 55 per cent of the total energy gain in winter and summer, respectively. Latent heat transfer contributed similar amounts in winter (20 per cent) and summer (25 per cent). Net radiation was a heat sink in winter (—13 per cent) and was similar to latent heat transfer in summer at 21 per cent. A newly developed simple method for estimating ice melt using only air temperature is presented and helps to explain the seasonal variations of ice melt.
Consequences of winter tropical pressure anomalies in the Australian region
Authors: Simmonds Ian , Rocha Alfredo , Walland David 
Published: February 2007

AbstractWe have performed three general circulation model (GCM) experiments with a view to isolating the direct thermal effects of imposed sea‐surface temperature (SST) anomaly patterns to the north of Australia from the dynamic effects associated with the circulation changes they induce. We have done this by a novel technique of adding bias terms to the pressure‐tendency equation but leaving all other aspects of the model unchanged. The nature of the three pressure ‘nudging’ terms were designed so that in long model runs the simulated sea‐level reductions would be similar to those induced in the SST anomaly experiments performed previously. Hence, we have forced low‐level circulation anomalies without imposing any direct surface thermal forcing. The results are compared with standard runs performed with SST forcing.The changes in evaporation in the Australian region were rather different in the comparable pressure‐forcing and SST‐forced experiments. However, most of the parameters considered here responded to the surface‐pressure forcing in a very similar way to that due to ocean‐temperature forcing considered in our earlier study. This was true, in particular, for winter precipitation over Australia. The results suggest that, at least in the Australian tropics, the apparently large impacts of SST anomalies are associated fundamentally with the anomalous circulations they set up rather than the direct impact of the heated ocean waters themselves. We find, as have others, that precipitation anomalies are associated closely with changes of the low‐level convergence of moisture. Indeed, an intriguing finding from our present study is that anomalies of evaporation and precipitation assume opposite signs over most of the domain.Analyses with the comprehensive ocean‐atmosphere data set (COADS) imply that there is some persistence of winter tropical sea‐level pressure in the Australian region, independent of the local endurance of SST. Such persistence may provide some independent skill for Australian winter climate outlooks.
Temporal and spatial characteristics of coastal rainfall anomalies in Papua New Guinea and their relationship to the Southern Oscillation
Authors: McGregor Glenn R. 
Published: February 2007

AbstractThirty‐year rainfall records for seven coastal locations in Papua New Guinea were analysed to assess the spatial and temporal characteristics of rainfall anomalies and the general response of coastal rainfall to the Southern Oscillation (SO). Spatial and temporal variability of rainfall anomalies are a distinct feature of the coastal locations analysed. Despite the spatial variability of rainfall anomaly behaviour, an all Papua New Guinea rainfall anomaly index shows significant concurrent and lag inverse associations with the Southern Oscillation Index of Wright. Anomalously high (low) pressure in the Papua New Guinea region leads to low (high) rainfall in the concurrent and ensuing season. Rainfall anomaly periodicities of 7–8 years lie within the time‐scale of 2–10 years for ENSO events, but individual locations demonstrate a variable response to ENSO events. Study results fill an important geographical gap in the understanding of the spatial and temporal characteristics of rainfall variability in the western tropical Pacific.
Summertime along‐valley wind variations in the wright valley Antarctica
Authors: McKendry Ian G. , Lewthwaite Errol W. D. 
Published: February 2007

AbstractObservations from several sites are utilized to investigate spatial and temporal variations in the local wind regime. The average condition consists of a tongue of easterly up‐valley winds extending the length of the valley. About 23 per cent of the time this tongue is pushed down‐valley beyond the western edge of Lake Vanda by westerly downslope winds. These winds seldom penetrate to the mouth of the valley and instead, a ‘front’ is formed between the up‐valley and down‐valley flows. Migration of the front appears to be related to synoptic controls rather than local thermal forcing. Support is provided for the view that the westerlies are episodic downslope winds associated with the deflection of strong upper level flow into the valley system. Superimposed on this broad pattern are diurnal variations in the strength of valley winds associated with changing stability.