摘要:

ABSTRACTIn this study, 24 climatic variables which measure various aspects of the physical controls and features of climate were subjected to factor analysis for the purpose of identifying the underlying structure of the regional climatology of Nigeria. The result of the analysis showed that 3 factors can be used to characterize the regional climatology of the country namely; the airmass residential time, the wind regime and precipitation characteristics (mainly in terms of total amount, mean intensity and length of the rainy season). These 3 factors altogether explain 91.9% of the total variation. By means of group analysis programme the country was then divided into 7 and 14 climatic regions, the first for a broad climatological study and the latter for use if detailed local work in regional climatology of Nigeria is desired.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880178

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTThis study begins with a short review of the climato-logical evidence which has been presented of a warming of the Northern Hemisphere climate during the period 1880 to 1950. It is shown that winter temperatures in general increased continously from 1880 to 1940 over most of the hemisphere and particularly in high latitudes. There was however a period of slow or no increase in temperatures from 1910 to 1920. Summer temperatures showed a slight increase from 1880 to 1910, a decrease from 1910 to 1920 and then a continous increase until 1950. Key areas of strong temperature increase in winter have proved to be the Arctic, northern Scandinavia and USSR, southern Canada and most of the USA. Similar areas of strong warming in summer have proved to exist in Scandinavia, USSR, northern USA and southern Canada. Hence in many areas there was considerable warming both in winter and summer.For the whole Northern Hemisphere, the annual mean temperature increase from 1880 to 1950 was about 0.6°C while mean temperature in January rose from the coldest to the warmest decade by as much as 6°C in the Arctic and in parts of southern Canada and northern USA. July temperatures similarly rose 3°C in northern Scandinavia and in the Great Plains of the USA and Canada.In the subsequent part, it is demonstrated that after 1950 temperatures have shown much less of consistent trends. The 1950's were still reasonably warm both in summer and winter but the 1960's showed a definite cooling in both seasons. The 1970's again were in general warmer than the 1960's but the temperature level of the first half of the century was not reached.The general circulation conditions which lead to the warming of the Northern Hemisphere in the period 1880–1950 are also summarized. It is shown that from 1880 to 1920 the main cause was an increase in the temperature latitude zonal westerlies while from 1920 to 1940 the general circulation was more meridional with dominating southwesterly to south-easterly wind components, whereby the carrying of warm air into high latitudes was further enhanced.In the second main part of the study the impact of the Northern Hemisphere warming is discussed with particular reference to three key areas, the Arctic, northern Scandinavia and the Great Plains in northern America. It is shown that the warming had considerable consequences for sea temperatures in the northern Atlantic and Arctic waters which in turn led to impact on deep-sea fishing and sea transport in northern latitude areas. Cod catching and industry spred from Iceland waters all the way to Spitsbergen, along the east coast of Greenland and to Jakobs- havn on the Greenland west coast. Sea transport, north of Siberia, was normal throughout the winter in the late 1930's.The warming had a considerable impact on agriculture in northern Finland and in Canada due to the lengthening of the vegetation season. In the 1930's and 1940's settlers in both countries moved northwards into areas not hitherto used for agriculture. In Finland, these settlers experienced a catastrophic setback in the cold 1960's and had to abandon their homes. In Canada, the gains from the move towards the north in the 1930's were more than counterbalanced by the droughts that hit agricultural production in the more central parts of the Great Plains in the same period. Various socio-economic efforts to mitigate such adverse consequences of climate impact on agriculture have been undertaken in many areas situated on the climatic margin in the Northern Hemisphere during the last decades. It is concluded that many areas in the developing countries, where such efforts are not yet undertaken are still suffering from impact of climate fluctuations in a similar way that areas on the margin in the Northern Hemisphere suffered earlier in this century.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880179

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTThe water balance of Storglaciären was measured during the 1984 melt season. Water input to the glacier exceeded discharge from it in late May and early June, resulting in storage of∼0.5×106m3of water (∼0.16 m3/m2). From mid June until early August input and discharge were approximately inbalance, in contrast to results reported in the literature from two other glaciers. Then from mid August until the end of the melt season water was released from storage.Other measurements made on Storglaciären and reported elsewhere suggest that subglacial cavities begin to open in mid July and reach a maximum total volume of∼0.5×106m3in mid August. If this is the case, the initial water storage that occurs in June must be in englacial reservoirs such as porous firn and crevasses. The water may then move into subglacial storage locations later in the season.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880180

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTRecent mapping of the surface and the bed of Mikkaglaciären by aerial photography and radio-echo techniques, respectively, provide a basis for calculations of flow mechanics and for further understanding of its sensitivity to climate change.Along a transverse profile on the tongue of the glacier the velocity decreased to about 50 % between 1900 and 1960. This decrease was caused by a general thinning of the glacier and is in remarkably good agreement with a simple laminar-flow theory.Study of ice flow and climatic records suggests that the glacier was in an unstable condition at its last maximum, which is surprising since its extension at that time was very close to its Holocene maximum. Studies of the annual net ablation gradient from recent years and also from the turn of the century suggest values around 0.012 m/m. Given these values, the profile could not have been in a steady state. A gradient of ca 0.002 m/m would have been required to produce the shape of the 1900-glacier.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880181

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTThe size of Austerdalsisen, northern Scandinavia's largest glacier, has decreased considerably since the beginning of the twentieth century, a feature common to other glaciers of the Svartisen area. Changes since 1870 are well-documented. In the early 1960s, strain-rate investigations on the lower part of the glacier tongue indicated that vertical strain was negligible, although rates of surface ablation were high. This was a period of particularly rapid change of surface elevation. The most recent changes of the glacier are illustrated by comparisons of photo- grammetric maps from 1945, 1954, 1968, 1970, 1979 and 1983. Whilst climatically-induced mass balance variations must have had a major influence on the general behaviour of the Svartisen glaciers, much of the decrease of Austerdalsisen has resulted from calving into lakes at its margins. During the 1970s, the calving rate increased as the western margin retreated into deeper water. Between 1975 and 1981, much of the calving was associated with the development of embayments at the margin. In July 1982, a large part of the tongue broke up and the glacier retreated very rapidly across the lake Austerdalsvatnet. Subsequently, the stability of the tongue appears to have been low: substantial calving now occurs along 2.5 km of the glacier's border. As proposals have been made for further developments of hydroelectric power in the area, monitoring of Austerdalsisen's behaviour should be continued.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880182

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTThe fluctuations of the Rio del Plomo glaciers have been studied during the period 1909 to 1983 through the use of topographic maps, published data, aerial photographs taken in 1955, 1963 and 1974, and topographic measurements taken in April 1983, of the tongue of Glaciar Oriental del Juncal. There has been a general and important glacial recession between 1909 and 1974; two glacial tongues have repeatedly experienced sudden advances and are therefore considered to be surging glaciers.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880183

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTOn Prins Oscars Land, situated in the northern part of Nordaustlandet, Svalbard, the diatom flora and chemical conditions in lake sediments have been studied. The aim of the investigation was to achieve information about the Late Weichselian history of the peninsula and the Holocene shore displacement.In the majority of the investigated lakes the thickness of the Holocene deposits is less than 100 cm. In the obtained cores there is evidence of an ice cover on Prins Oscars Land in the Late Weichselian. However, only in the southern part of the peninsula the sediments are resting on a bed of till. Regarding the other lakes, the influence of the last glaciation is restricted to a compaction of Weichselian sediments. Prior to 11 000 years B.P. there were ice-free coastal fringes, and about 10 000 years B.P. the ice had escaped from the inland areas in the northern part of the peninsula. The deglaciation of the southern section is not dated.In the northern part of Prins Oscars Land, a lake at 32 m a.s.l. was isolated from the sea slightly prior to 10 000 years B.P. In this area the probably more than 11 000 years old Holocene marine limit is at an altitude of 48m. The relative small rate ofthe emergence indicates a rather thin ice cover over the peninsula in the Late Weichselian.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880184

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTA turf-banked gelifluction lobe in south-central Norway is described together with detailed14C dating of buried soil material, measurements of current activity, and sedimento-logical, geotechnical and micromorphological analyses. Three stratigraphic units are recognised; a silty sand upper unit (Unit 1) overlying heterogeneous sandy sediments containing organic bands up to 2 cm thick (Unit 2), which in turn overlies a buried soil of thickness 75 cm (Unit 3, the Main Buried Soil) developed on the underlying till. Analyses indicate that the gelifluction and frost creep responsible for the formation of this lobe affected not only till but also colluvial (slope wash) deposits. Particularly in Unit 2, well-sorted layers of fine sand and coarse silt alternating with organic bands, indicate episodic accumulation of colhivium separated by intervals of pedogenesis.Nineteen14C dates were obtained from eight points along the length of the Main Buried Soil and from a vertical section through the lobe, including organic bands. A complex interpretation is outlined, taking into account such factors as Apparent Mean Residence Time, age-depth relationships, and the possible effects of erosion, contamination and natural variability. Environmental reconstruction indicates the following sequence of events. After about 300014C years B.P., an initial colluvial phase covered the Main Buried Soil, interrupted by at least two pedogenic intervals, which began by about 1730 and14C years B.P., Gelifluction is inferred to have been initiated after about 100014C years B.P., the lobe front possibly advancing at an average rate of about 8.4 mm y-1. The Main Buried Soil is considered to have formed during the period between regional deglaciation, approximately 900014C years B.P., and the initiation of colluviation. Palaeoclimatic implications are discussed.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880185

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTSpatial and temporal variations in channel morphology, velocity and shear stress, bedload transport rate, and bedload and bed material size distribution were measured over five summer weeks in the braided Lyngsdalselva in Arctic Norway. Velocities and shear stresses reflected streamwise convergence and divergence of flow, and in turn influenced bedload transport rates although these depended also on the availability at the surface of appropriate-sized sediment. Large and small particles had almost equal mobility, so transport rate increased rapidly with shear stress as coarse sediment began to move and in so doing exposed finer particles. Size-selective transport is nevertheless indicated by down-reach and down-bar fining. The spatial patterns of shear stress and bedload transport rate within one divided-single-divided channel cycle changed with discharge, as did the resulting channel changes. In high meltwater flows, with a peak transport rate of 0.3 kg m-1s-1, erosion was localised at two zones of flow convergence and tended to maintain the non-uniform channel geometry. During a higher rain-flood, with transport rates up to 3 kg m-1s-1a downstream fall in shear stress in the main distributary led to medial deposition and consequent lateral erosion, creating a wider, shallower, more uniform channel. Grain size distributions of bedload at high and low shear stresses match fairly well those of floodplain gravels and falling stage flood deposits respectively.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880186

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

ABSTRACTAs an integral part of the drainage basin study of the Burhi Dihing river, an attempt has been made here to analyse the form and process of the river channel, with emphasis on hydraulic geometry and form-process response. The longitudinal profile of the river is concave upward with three knick points representing four segments of different erosional phases. The meander radius and the meander wavelength show a more linear relationship. The cross section of the river varies from trapezoidal to asymmetric in shape; the width decreases but depth and velocity increase towards downstream. The variation of hydraulic parameters during passage of a flood reveals that stage, mean velocity and suspended sediment content have higher values in the rising of discharge as compared to the recession period. The scouring of bed is assosiated with flood and silting with recession. Maximum fluctuation of the bed profile occurs during the flood season, during low flow period the bed profile remains almost constant. The change of bed profile in consecutive years is found to depend on the magnitude of the peak flow and the volume of water discharge.

ISSN:0435-3676    

DOI:10.1080/04353676.1986.11880187

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor