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1.
PETER FREDERIKSEN M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):16-24
Frcdcriksen, Peter: Climatic influence on morphology and chemistry of nine loess profiles, Argentine. Geografisk Tiddskrift 81:16–24. Copenhagen, October, 1981. Nine profiles developed in loess under a subtropical, continental climate with a pronounced climatic gradient (udic to aridicj were investigated morphologically and chemically in order to elucidate the influence of climate on soil genesis. Four morphological types developed: a) A1A2BtC-soils, b) ABC-soils, c) A(B)C-soils and d) AC-soils. Some variations could be related to the climatic variation, others were better related to texture or to palaeoclimatic (periglacial) conditions. 相似文献
2.
利用青藏高原气象台站逐日最大风速数据和JRA-55再分析资料,通过引入集中期和集中度的概念,分析了1971—2012年高原大风在风季的分布形态及其环流背景。结果表明:青藏高原的大风天气在春季(3—5月)最多,在夏末秋初(8—10月)最少。1971—2012年,大风日数以14 d/10a的速度减少,同时大风日数的年较差也在缩小。大风集中期随纬度增大而延后,并且在近42年大体呈提前的趋势,从3月底4月初提前至2月底3月初。大风集中度则有增大的趋势,并取决于大风日数,大风日数越多,集中度越低。高原大风集中期受到急流系统经向位移的制约,2月和3月北非和西亚地区的副热带急流以及4月中层西风带偏南时,伴随着副热带气压偏低,青藏高原春季大风天气偏多,大风集中期偏晚。反之,大风天气偏少,集中期偏早。大风集中度的大小则与中亚和高原地区2—4月副热带急流强度有关,2月和4月副热带急流偏弱、3月急流偏强时,大风日数集中在3月,集中度较高。反之,集中度较低。春季(3月)高原大风天气是冷、暖空气系统共同作用的结果,高原东部的大风天气多受北方冷空气系统影响,高原西部的大风天气多受南方暖空气系统影响、以西南风为主。 相似文献
3.
积雪是影响气候变化的重要因子,准确、及时的获取积雪覆盖范围,进行动态变化监测意义重大。利用MODIS数据进行土库曼斯坦积雪监测,提取积雪信息的研究较少。利用MODIS L1B 500 m分辨率数据,通过几何校正、去云预处理,应用归一化差分积雪指数（NDSI）算法和综合阈值判别法,获取了土库曼斯坦2011年11月～2012年4月山区积雪覆盖范围和面积等数据信息,揭示了土库曼斯坦山区积雪发生的时空特征。土库曼斯坦南部的科佩特山区是该国降雪的核心地区,积雪面积均在1月达到最大值,随后积雪面积随温度的升高而减少。山区积雪面积、月均气温、月降雨量之间存在着显著的相关性,其相关系数分别为0.742 9和0.568 4。结果表明,在监测时段积雪面积随气温的降低、降雨量的减少而增加。 相似文献
4.
Alejandra L. Cameselle César R. Ranero Dieter Franke Udo Barckhausen 《Basin Research》2017,29(Z1):73-95
Rifted margins are created as a result of stretching and breakup of continental lithosphere that eventually leads to oceanic spreading and formation of a new oceanic basin. A cornerstone for understanding what processes control the final transition to seafloor spreading is the nature of the continent‐ocean transition (COT). We reprocessed multichannel seismic profiles and use available gravity data to study the structure and variability of the COT along the Northwest subbasin (NWSB) of the South China Sea. We have interpreted the seismic images to discern continental from oceanic domains. The continental‐crust domain is characterized by tilted fault blocks generally overlain by thick syn‐rift sedimentary units, and underlain by fairly continuous Moho reflections typically at 8–10 s twtt. The thickness of the continental crust changes greatly across the basin, from ~20 to 25 km under the shelf and uppermost slope, to ~9–6 km under the lower slope. The oceanic‐crust domain is characterized by a highly reflective top of basement, little faulting, no syntectonic strata and fairly constant thickness (over tens to hundreds of km) of typically 6 km, but ranging from 4 to 8 km. The COT is imaged as a ~5–10 km wide zone where oceanic‐type features directly abut or lap on continental‐type structures. The South China margin continental crust is cut by abundant normal faults. Seismic profiles show an along‐strike variation in the tectonic structure of the continental margin. The NE‐most lines display ~20–40 km wide segments of intense faulting under the slope and associated continental‐crust thinning, giving way to a narrow COT and oceanic crust. Towards the SW, faulting and thinning of the continental crust occurs across a ~100–110 km wide segment with a narrow COT and abutting oceanic crust. We interpret this 3D structural variability and the narrow COT as a consequence of the abrupt termination of continental rifting tectonics by the NE to SW propagation of a spreading centre. We suggest that breakup occurred abruptly by spreading centre propagation rather than by thinning during continental rifting. We propose a kinematic evolution for the oceanic domain of the NWSB consisting of a southward spreading centre propagation followed by a first narrow ridge jump to the north, and then a younger larger jump to the SE, to abandon the NWSB and create the East subbasin of the South China Sea. 相似文献
5.
南极半岛及附近地区经常出现大风天气,它是影响该地区的主要天气现象.造成大风的主要天气系统是极地气旋.极地气旋的强弱、移速和路径的不同,对南极半岛及附近地区的影响也不同.而周围的环境流场也是形成大风的重要因素.所以,分析天气形势背景,对做好该地区大风天气现象的预报是十分重要的.本文利用1985年1月到1987年10月中国南极长城站接收的智利南极弗雷气象中心播发的南半球地面传真天气图,北京气象中心绘制的南半球地面和500hPa高空天气图资料,结合长城站的地面气象观测资料,对影响南极半岛及附近地区的大风天气过程进行了分析和研究.主要根据地面天气图上的天气形势归纳为四种类型:(1)强极地高压型;(2).强副热带高压型;(3)南美大陆高压型;(4)副热带高压脊线南伸型.同时,结合分析结果提出了预报南极半岛及附近地区大风天气的思路. 相似文献
6.
7.
L. Knopoff R. G. Mitchel E. G. Kausel † F. Schwab ‡ 《Geophysical Journal International》1979,56(1):211-218
Summary. The Lg phase has been shown previously to be a collection of higher-mode surface waves guided by the continental crust (Knopoff, Schwab & Kausel). A simple scaling between continental and oceanic crustal thicknesses suggests that a search for an oceanic Lg phase should be made in the period range from 1 to 2s. In a search for SH polarized Lg arrivals over oceanic paths, we found that in addition to the fundamental mode, seismo-grams at relatively short ranges in the Pacific showed the presence of only the first higher mode with group velocities on the steep portion of the dispersion curve rather than at the group velocity minimum as expected. Numerical model analysis indicates that, contrary to the continental case, there is no strong confluence of stationary phases of higher-mode crustal waves in the appropriate period range to produce Lg wave packets; this is due to small but significant differences in scaled crustal structures. Further, lateral variations in the thickness of oceanic sediments are sufficient to scatter most of the crustal surface-wave energy within a relatively short distance. Even were this thickness uniform, attenuation in the sediments would be strong enough to absorb the Lg stationary phases in a short distance. 相似文献
8.
Recent advances on reconstruction of climate and extreme events in China for the past 2000 years 总被引：6，自引：1，他引：5
China is distinguished by a prominent monsoonal climate in the east of the country, a continental arid climate in the northwest and a highland cold climate on the Qinghai-Tibet Plateau. Because of the long history of Chinese civilization, there are abundant and well-dated documentary records for climate variation over the whole of the country as well as many natural archives (e.g., tree-rings, ice cores, stalagmites, varved lake sediments and corals) that enable high-resolution paleoclimatic reconstruction. In this paper, we review recent advances in the reconstruction of climate and extreme events over the last 2000 years in China. In the last 10 years, many new reconstructions, based on multi-proxies with wide spatial coverage, have been published in China. These reconstructions enable us to understand the characteristics of climate change across the country as well as the uncertainties of regional reconstructions. Synthesized reconstructed temperature results show that warm intervals over the last 2000 years occurred in AD 1–200, AD 551–760, AD 951–1320, and after AD 1921, and also show that cold intervals were in AD 201–350, AD 441–530, AD 781–950, and AD 1321–1920. Extreme cold winters, seen between 1500 and 1900, were more frequent than those after 1950. The intensity of regional heat waves, in the context of recent global warming, may not in fact exceed natural climate variability seen over the last 2000 years. In the eastern monsoonal region of China, decadal, multi-decadal and centennial oscillations are seen in rainfall variability. While the ensemble mean for drought/flood spatial patterns across all cold periods shows a meridional distribution, there is a tri-pole pattern with respect to droughts south of 25°N, floods between 25° and 30°N, and droughts north of 30°N for all warm periods. Data show that extreme drought events were most frequent in the periods AD 301–400, AD 751–800, AD 1051–1150, AD 1501–1550, and AD 1601–1650, while extreme flood events were frequent in the periods AD 101–150, AD 251–300, AD 951–1000, AD 1701–1750, AD 1801–1850, and AD 1901–1950. Between AD 1551–1600, extreme droughts and flood events occurred frequently. In arid northwest China, climate was characterized by dry conditions in AD 1000–1350, wet conditions in AD 1500–1850, and has tended to be wet over recent decades. On the northeastern Qinghai-Tibet Plateau, centennial-scale oscillations in precipitation have occurred over the last 1000 years, interrupted by several multi-decadal-scale severe drought events. Of these, the most severe were in the 1480s and 1710s. In southwest China, extreme droughts as severe as those seen in Sichuan and Chongqing in 2006 are known to have occurred during historical times. 相似文献
9.
In this study, we used 30 years of an operational sea surface temperature (SST) product, the NOAA Optimum Interpolation (OI) SST Version 2 dataset, to examine variations in Arctic SSTs during the period December 1981–October 2011. We computed annual SST anomalies and interannual trends in SST variations for the period 1982–2010; during this period, marginal (though statistically significant) increases in SSTs were observed in oceanic regions poleward of 60°N. A warming trend is evident over most of the Arctic region, the Beaufort Sea, the Chuckchi Sea, Hudson Bay, the Labrador Sea, the Iceland Sea, the Norwegian Sea, Bering Strait, etc.; Labrador Sea experienced higher temperature anomalies than those observed in other regions. However, cooling trends were observed in the central Arctic, some parts of Baffin Bay, the Kara Sea (south of Novaya Zemlya), the Laptev Sea, the Siberian Sea, and Fram Strait. The central Arctic region experienced a cooling trend only during 1992–2001; warming trends were observed during 1982–1991 and 2002–2010. We also examined a 30-yr (1982–2011) record of summer season (June–July–August) SST variations and a 29-yr (1982–2010) record of September SST variations, the results of which are discussed. 相似文献
10.
While speculation exists on global and regional climate change for temperature and precipitation, relatively little research is available on snowfall and its changes. Twenty-six sites were selected to describe and analyze various characteristics of snowfall in Pennsylvania from 1950–1951 through 1989–1990. Overall, the state experienced a significant stepwise change in seasonal snowfall total during this period. Abnormally high seasonal totals prevailed from 1957–1958 through 1971–1972. This rise in snowfall was accompanied by colder-than-normal temperatures and a dramatic increase in large daily snow events. Principal components analysis (PCA) revealed that the seasonal temporal patterns were not uniform across the state. The PCA revealed four distinct seasonal regions. These regions exhibited everything from nearly linear increases and decreases over time to cyclical formations. PCA performed on the months of November through April each unveiled between three and five separate temporal regions. PCA analyses generally identified an eastern region, a north-central region, and a western region across Pennsylvania. [Key words: regionalization, principal components, variability, snowfall, climate change, Pennsylvania.] 相似文献
11.
Climate anomalies in the southern high latitudes associated with the Subtropical Dipole Mode 
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下载免费PDF全文 Climate anomalies in the southern high latitude associated with the Subtropical Dipole Mode (SDM) are investigated using a 23-year database consisting of SLP (sea level pressure), surface air temperature (SAT) and sea surface temperature (SST). The analysis depicts, for the first time, the spatial variability in the relationship of the above variables with the Subtropical Dipole Mode Index (SDI). It suggests that the SDM signal exists in the southern high latitudes and the correlation fields exhibit a wavenumber-3 pattern around the circumpolar Southern Ocean. Lead-lag correlation analysis used to the SLP, SAT, and SST anomalies with the SDI time series at the positive and negative correlation extremes shows that the southern-high-latitude climate responses to SDM almost instantaneously proposing the connection is by atmospheric and not by oceanic propagation. 相似文献
12.
Kathleen R. Stoof-Leichsenring Annett Junginger Lydia A. Olaka Ralph Tiedemann Martin H. Trauth 《Journal of Paleolimnology》2011,45(3):353-367
Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth
century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea,
flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years
was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment
core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon
concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic
zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later
a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century.
The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified
two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by
natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted
those of natural climate variation. 相似文献
13.
Bohumil M. Svoma Daniel S. Krahenbuhl Chad E. Bush Jonny W. Malloy Joshua R. White Melissa A. Wagner 《自然地理学》2013,34(3):174-187
A critical issue in research concerning long-term climate change is the relationship between circulation features and global temperature variations. We establish that the annual areal size of the northern hemisphere subtropical high pressure belt (SHPB), as defined by seven 500-hPa height isohypses, shares over 70% of the variability with global annual near-surface air temperature since 1948. The area enclosed by the 5850-m isohypse of the 500-hPa surface in the northern hemisphere has more than doubled since the 1950s, with greatest increases over northern Africa, the Middle East and India. A long-term historical run of a coupled global climate model shows rapidly increasing SHPB annual sizes, since the mid-1970s. Since the SHPB’s descending air produces increased aridity, SHPB expansion may transition humid regions to more arid lands. To examine this aspect, first, variations in recorded precipitation using a gridded database for the region experiencing expansion of the SHPB show a decrease in precipitation (though significant only at the 88% confidence level) over the last 60?years. Second, variations in a 0.5° spatial resolution monthly drought index, the Standardized Precipitation Evapotranspiration Index, are highly correlated (+0.78) with annual variations in the area enclosed by the 500-hPa height isohypses. These results support those of previous investigations that suggest further northward expansion of the northern hemisphere subtropical dry zones with continued global climate change. 相似文献
14.
Monthly mean temperatures and monthly precipitation totals at six stations from theCappadocian sub‐region in the continental Central Anatolia region of Turkey were analysed in order to detect the response of the variability in the Cappadocian climate to the variability of the North Sea ‐ Caspian Pattern Index (NCPI). Most of this region is classified as semi‐arid according to various climate classifications. Time series of the NCPI for the period 1958–1998, enabled each month from October toApril to be classified as belonging to the negative phase NCP(?), positive phase NCP(+) or neutral conditions. Monthly temperature and precipitation series for each station were analysed separately for both phases. Temperatures during NCP(?) were found to be considerably higher than during NCP(+). These results confirm previous results regarding the role of the NCP in controlling the temperature regime in that region. No significant differences were found in precipitation totals between the two phases, but major differences were identified in their spatial structure. 相似文献
15.
《Polar Science》2007,1(1):1-15
Statistical characteristics of the surface meteorology are examined at Syowa Station (69°00′S, 39°35′E), which is located on an island near the coastal region of the Antarctic continent, based on operational observations made over the 50-year period from February 1957 through January 2007, which includes missing periods equivalent to 5 years. Statistics are obtained for the surface temperature, sea level pressure (SLP), and horizontal winds in terms of frequency distribution, frequency power spectra, seasonal variation, diurnal variation, inter-annual variation, and trends, using hourly observation data, and several interesting characteristics are elucidated. The mean temperature, SLP, and wind speed over the 50-year period are −10.5 °C, 986 hPa, and 6.6 m s−1, respectively. The frequency distribution of temperature is far from the normal one, because less variation exists in summer at higher temperatures. The predominant wind direction is northeasterly (southwestward), and a weak secondary peak is observed in the southerly (northward) direction in the frequency distribution. The directional constancy of winds is 0.78. The frequency spectra over a wide range of 2 h to 20 years exhibit clearly isolated peaks corresponding to annual and diurnal frequencies and their higher harmonics. An important finding is that the spectral shape is proportional to a power of the frequency with a transition frequency for all physical parameters. The transition frequencies correspond to about 5 days for temperature and winds and 3 days for SLP, most likely due to cyclonic activity. A peak in the 11-year solar cycle is not identified in any spectrum. Another interesting feature is the dominance of semi-annual and semi-diurnal variations in SLP, while annual and diurnal variations are dominant for temperature and winds. Statistically significant trends are not detected for annual mean surface temperature and SLP over the 50-year period, while a positive trend is significant for wind speed. These trends are also examined as a function of the months. The inter-annual variation of SLP is well correlated with that of the Antarctic Oscillation index, indicating that Syowa Station can be regarded as a typical Antarctic station. Furthermore, statistical analysis was conducted for blizzards (severe snow storms), in terms of duration, and seasonal and inter-annual variation in frequency of occurrence. It is shown that the blizzards are dominant in the period from late March to late October. No systematic variation in blizzard frequency was observed during the 50-year period. Instead, the frequency depends largely on the year with a minimum of nine in 1988 and a maximum of 42 in 1982. As a typical example, a synoptic chart is used to show the cause of a strong snow storm on 27 May 1996, when the absolute maximum gust was observed. 相似文献
16.
F. Guillocheau D. Rouby C. Robin C. Helm C. Le Carlier de Veslud J. Braun 《Basin Research》2012,24(1):3-30
The terrigeneous sediment budget of passive margin basins records variations in continental relief triggered by either deformation or climate. Consequently, it becomes a major challenge to determine sediment accumulation histories in a large number of basins found in various geodynamic contexts. In this study, we developed a GIS‐based method to determine the sediment budget at the scale of a whole basin (from the upstream continental onlap to the most distal deepest marine deposits) and the associated uncertainties. The volume of sediments preserved in the basin for each time interval was estimated by interpolation between cross‐sections and then corrected from in situ production and porosity to obtain terrigeneous solid volumes. This approach was validated by applying it to Namibia–South African passive margin basins for which independent data are available. We determined by a statistical approach the variances associated with each parameter of the method: the geometrical extrapolation of the section (8–43%), the uncertainties on seismic velocities for the depth conversion (2–10%), on the absolute ages of stratigraphic horizons (0.2–12%), on the carbonate content (0.2–46%) and on remaining porosities estimation (3–5%). Our estimates of the accumulated volumes were validated by comparison with previous estimates at a lower temporal resolution in the same area. We discussed variations in accumulation rates observed in terms of relief variations triggered by climate and/or deformation. The high accumulation rates determined for the Lower Cretaceous, progressively decreasing to a minimum in the Mid‐Cretaceous, are consistent with the progressive relaxation of a rift‐related relief. The following increase to an Upper Cretaceous maximum is consistent with a major relief reorganization driven either by an uplift and/or a change to more humid climate conditions. The lower accumulation rate in the Cenozoic suggests a relief reorganization of lesser amplitude over that period. 相似文献
17.
横断山区典型海洋型冰川物质平衡研究 总被引：2，自引：1，他引：1
玉龙雪山发育着对气候变化响应极为敏感的典型海洋型冰川。基于2008-2013年共5个物质平衡年观测数据,对玉龙雪山规模最大的白水1号冰川物质平衡特征进行分析,为评估横断山区气候和冰川变化之间的关系奠定基础。结果表明：2008-2013年白水1号冰川物质平衡最大值仅为-907 mm w.e.,最小值则达到-1872 mm w.e.。2008年冰川平衡线高度为4972 m,2009-2013年白水1号冰川积累区近乎消失。白水1号冰川积累期主要集中于10月至次年5月,6-9月为强消融期,积累量几乎为零,消融量占全年80%,属冬春季积累型冰川。2008-2009、2011-2012和2012-2013年平均物质平衡梯度为1230 mm w.e. （100 m）-1,消融期物质平衡梯度小于年物质平衡梯度,消融期初与消融期末物质平衡梯度小于100 mm w.e.（100 m）-1。 相似文献
18.
近40ka来海南岛海岸沙地气候与环境演变 总被引：1，自引：0，他引：1
选择海南岛东、西海岸具有代表性和高分辨率特征的木堆、棋子湾等地层剖面,在建立年代序列的基础上,对风成沙粒度组成与参数、SC/D值及磁化率等代用指标的研究表明,末次冰期间冰阶时气候相对温暖,滨海平原上河流三角洲前移,湿地、沙丘与交错分布;末次盛冰期时气候干凉,海岸沙地上形成了多道平行延伸的古沙垄(丘),并与大陆架古沙丘形成连续性沉积;末次冰消期时气候快速变化,古沙垄(丘)或加积发育或固定成壤;全新世以来气候回暖并波动变化,次生沙丘经历多次半固定、固定－沙丘加积、活化的演变。 相似文献
19.
云南2009～2010年秋冬春连旱成因分析 总被引：2，自引：0，他引：2
2009年秋季至2010年春季,云南降水量比常年同期偏少50%～78%,创有记录以来最少,气温比常年同期偏高0.9～2.5℃,发生了百年不遇的秋、冬、春连旱。分析其发生的原因主要是：2009年秋季开始,西太平洋副热带高压偏强,阻断了从孟湾和南海到云南的水汽输送,加之东亚大槽偏弱偏北、亚洲极涡偏弱,导致冷暖空气不能在云南上空＂相遇＂,造成降水偏少。2009年6月开始El Nino事件开始显现,冬季达到旺盛期,在其影响下,南海、中南半岛到西印度洋的对流活动受到抑制,造成输送至云南的水汽偏弱。全球气候变暖使各种气象要素的变化偏离了平均值,容易引发极端气候事件,导致近年来干旱发生的频率增多增强。 相似文献
20.
黄渤海海岸季节性风沙气候环境 总被引：6，自引：0，他引：6
分析了黄渤海海岸气候形成因素和影响风沙活动的各种气候要素的季节性变化特征，指出冬、春季研究区受东亚大陆气团的影响，形成了干旱、多风的风沙气候环境，尤其是渤海海岸地区冬、春季气候条件与我国内陆沙漠区和严重沙漠化地区相似，也存在风沙灾害的威胁。 相似文献