Effect of solar heliospheric parameters on different components of daily variation in cosmic rays     

Rekha Agarwal Mishra  Rajesh K. Mishra 《Earth, Moon, and Planets》2007,100(3-4):181-194

In the present work the data of three different neutron monitoring stations, Deep River, Tokyo and Inuvik located at different geomagnetic cutoff rigidities and altitudes has been harmonically analysed for the period 1980–1993, 1980–1990 and 1981–1993 respectively to investigate for a comparative study of diurnal, semi-diurnal and tri-diurnal anisotropies in cosmic ray (CR) intensity in connection with the change in IMF Bz component and solar wind velocity on 60 quietest days. It is observed that the amplitude of first harmonic is highly anti-correlated to the solar wind velocity during the period of high-speed solar wind stream (HSSWS) epoch on quiet days for three neutron monitor stations at different geomagnetic rigidity thresholds. During quiet days the amplitude of all the three harmonics significantly deviates on the onset of HSSWS epoch, whereas the direction of the anisotropy of all the three harmonics remains time invariant at three different cut off rigidity stations. The amplitude as well as the direction of anisotropy of all the three harmonics does not have time variation characteristics associated with Bz component of IMF on geo-magnetically most quiet days.  相似文献   

A comparison of simulated monsoon circulations and snow accumulation in Asia during the mid-Holocene and at the Last Glacial Maximum     

Andrew B. G. Bush 《Global and Planetary Change》2002,32(4)

Tropical climatology through the last glacial cycle is believed to have ranged from colder, windier conditions at the Last Glacial Maximum (LGM) to relatively warm, stable conditions during the Holocene. Changes in strength of the South Asian monsoon have previously been determined from a variety of proxy data and have been attributed primarily to changes in radiative forcing, although tropical sea surface temperature (SST) is known to play a fundamental role in regulating monsoon strength and is also believed to have changed throughout the late Quaternary.In this study, the monsoons simulated in a coupled atmosphere–ocean general circulation model (GCM) configured for the mid-Holocene (6000 years B.P.) and for the LGM (21,000 years B.P.) are compared. The colder and windier conditions simulated for the LGM produced a summer monsoon whose westerly winds are stronger and whose precipitation and snowfall into the eastern Himalaya are increased, with drier conditions over the rest of the Indian subcontinent and over most of southwest Asia.The mid-Holocene monsoon circulation is stronger than today, and annual mean snow accumulation is increased over the northwestern Himalaya. These changes in precipitation and snow accumulation are analyzed in terms of the altered atmospheric circulations, which are in turn driven by changes in radiative forcing, sea surface temperatures, and sea surface height. All of these factors are therefore demonstrated to be important in governing the spatial distribution of snow and ice deposition in the Himalaya during the late Quaternary, and are likely to have contributed to the observed asynchroneity of Himalayan glaciation and Northern Hemisphere ice sheet volume.  相似文献   

末次冰消期以来民勤盆地沉积地层记录及年代学研究     

赵强  李秀梅  王乃昂 《地层学杂志》2008,32(1):27-32

石羊河流域位于西北干旱区河西走廊东段,是西北干旱区与东部季风区的交汇过渡地带。流域下游的民勤盆地分布有大量保存完整的湖相沉积地层和湖岸地貌,这些沉积地层和地貌景观在整个西北干旱、半干旱地区极具代表性,是进行古气候环境研究的理想场所。鉴于此,选取民勤盆地的青土湖剖面、西渠剖面、沙坑井剖面、九坨墚剖面作为研究对象,通过剖面地层对比及可靠14C测年,探讨了区域末次冰消期以来的气候变化的几个大的阶段。主要结论和认识如下:13000aBP前和9500—6700aBP两个阶段,区域沉积地层以风成砂、河流砂沉积为主,气候环境表现为干旱;13000—9500aBP和6700—1100aBP两个阶段,区域沉积地层表现为湖相沉积的粉砂沉积为主,气候环境表现为湿润;1100—0aBP风成砂等的沉积阶段,气候环境表现为干旱。  相似文献   

A late Pleistocene long pollen record from Lake Urmia, NW Iran   总被引：4，自引：0，他引：4  

Morteza Djamali  Jacques-Louis de Beaulieu  Madjid Shah-hosseini  Valrie Andrieu-Ponel  Philippe Ponel  Abdolhossein Amini  Hossein Akhani  Suzanne A.G. Leroy  Lora Stevens  Hamid Lahijani  Simon Brewer 《Quaternary Research》2008,69(3):413-420

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.  相似文献   

Exposure age chronology of the last glaciation in the eastern Pyrenees   总被引：2，自引：0，他引：2  

Magali Delmas  Yanni Gunnell  Régis Braucher  Didier Bourlès 《Quaternary Research》2008,69(2):231-241

We present a chronology of ice recession in the eastern Pyrenees based on in situ-produced ¹⁰Be data obtained from the Têt paleoglacier complex. The sampling strategy is based on the relative chronology provided by a detailed geomorphological map of glacial landforms. Results indicate that the last maximum ice advance occurred late (i.e., during Marine Isotope Stage 2) compared to the chronology currently established for the rest of the Pyrenees. Despite debatable evidence for a glacial readvance during the Oldest Dryas stade, ice-cap melt-out was rapid, residual cirque glaciers having disappeared by the Allerød interstade. This is consistent both with North Atlantic excursions established by the Greenland ice cores and paleoenvironmental data for the region. The rapid response of the east-Pyrenean ice cap to temperature variations is primarily linked to its small size compared to larger Pyrenean ice fields, to the dry Mediterranean climate, and to topography-related nonlinearities in which a small vertical rise in equilibrium line altitude generates a large change in ice mass. Possible sources of age uncertainty are discussed in the context of sampling design for single-nuclide (¹⁰Be) dating of landform sequences in formerly glaciated landscapes.  相似文献   

1981-2010年青藏高原降雪日数时空变化特征   总被引：2，自引：2，他引：0       下载免费PDF全文

除多  洛桑曲珍  杨志刚  杨勇 《应用气象学报》2017,28(3):292-305

利用青藏高原气象站降雪日数观测资料,分析1981-2010年青藏高原降雪日数的时空变化特点和主要影响因素。结果表明:降雪日数总体上呈青藏高原中东部高寒地区、喜马拉雅山脉南麓和祁连山脉流域降雪日数多,南部河谷和北部湖盆区降雪日数少的空间分布格局;春季降雪日数占全年的45%,其次是冬季（28%）和秋季（22%）,夏季最少（5%）;30年内青藏高原平均年降雪日数呈明显减少趋势,降幅达10.5 d/（10 a）,其中,春季降幅最大（4.8 d/（10 a））,夏季最小（1.2 d/（10 a））;年降雪日数在1997年发生了由多到少的气候突变;降雪日数年内分布呈双峰型,峰值出现在冬夏大气环流的转换季节,青藏高原大气环流的转换期与上升运动相联系的低值天气系统和高空温湿条件均有利于降雪出现;青藏高原降雪日数的明显减少与气温的显著上升呈线性关系。  相似文献   

THE SPATIOTEMPORAL CHARACTERISTICS OF LIGHT RAIN DAYS AND LOW CLOUD COVER UNDER HEAVY POLLUTION OVER SOUTH CHINA     

符传博  丹利  陈红  何鑫 《热带气象学报(英文版)》2017,23(2):229-236

By using the data set of light rain days and low cloud cover at 51 stations in South China (SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows: (1) The trends of light rain days and low cloud cover over SC are opposite (light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area. (2) The regression coefficients of light rain days and low cloud cover during 1960–2005 are 4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level. (3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter. (4) There are two regions with large values of aerosol optical depth (AOD), which distribute in central and southern Guangxi and Pearl River Delta (PRD) of Guangdong, and the value of AOD in PRD is up to 0.7. The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.  相似文献   

青海湖东岸末次冰期冰盛期和早全新世沙漠范围重建   总被引：1，自引：1，他引：0       下载免费PDF全文

王中  刘向军  丛禄 《盐湖研究》2017,25(2):67-75

基于野外沉积物调查、已报道的风成沉积物年代和重建的湖泊水位波动曲线,初步绘制了末次冰期冰盛期和全新世早期青海湖东岸的沙漠范围。初步认为,末次冰期冰盛期时青海湖大幅度萎缩,湖底沉积物暴露并遭受风蚀,在偏西风的搬运下,近岸粗颗粒砂堆积在日月山西侧和倒淌河河谷,形成流动沙丘,细颗粒沉积物被向东搬运沉积至河湟谷地和黄土高原。倒淌河源头的沙丘最晚是在末次冰期盛冰期(23~16ka BP)沙漠扩张时形成并残留至今的;青海湖东部日月山西侧山麓地带和倒淌河河谷中、晚全新世黄土、古土壤下部普遍沉积的风成砂是末次冰期冰盛期和全新世早期(11~9 ka BP)青海湖东岸地区大范围沙化的证据。  相似文献   

Morphological and sedimentary responses to ice mass interaction during the last deglaciation          下载免费PDF全文

Richard C. Chiverrell  Matthew J. Burke  Geoffrey S.P. Thomas 《第四纪科学杂志》2016,31(3):265-280

During decline of the last British–Irish Ice Sheet (BIIS) down‐wasting of ice meant that local sources played a larger role in regulating ice flow dynamics and driving the sediment and landform record. At the Last Glacial Maximum, glaciers in north‐western England interacted with an Irish Sea Ice Stream (ISIS) occupying the eastern Irish Sea basin (ISB) and advanced as a unified ice‐mass. During a retreat constrained to 21–17.3 ka, the sediment landform assemblages lain down reflect the progressive unzipping of the ice masses, oscillations of the ice margin during retreat, and then rapid wastage and disintegration. Evacuation of ice from the Ribble valley and Lancashire occurred first while the ISIS occupied the ISB to the west, creating ice‐dammed lakes. Deglaciation, complete after 18.6–17.3 ka, was rapid (50–25 m a^?1), but slower than rates identified for the western ISIS (550–100 m a^?1). The slower pace is interpreted as reflecting the lack of a calving margin and the decline of a terrestrial, grounded glacier. Ice marginal oscillations during retreat were probably forced by ice‐sheet dynamics rather than climatic variation. These data demonstrate that large grounded glaciers can display complex uncoupling and realignment during deglaciation, with asynchronous behaviour between adjacent ice lobes generating complex landform records.

  相似文献   

基于DFA的雷暴日时间序列分形特征分析     

杨天琦  邱洋  江珂 《气象与环境科学》2016,39(4):115-120

运用最小二乘法、非趋势波动分析(DFA)与小波变换三种方法对比分析许昌市1961—2012年52 a雷暴日时间序列的变化特性,揭示雷暴日的长程相关性及其内在规律。研究结果表明:许昌市52 a月雷暴日时间序列属于分形时间序列,存在内在的长程相关性,其雷暴日数每10 a减少1.6689天,雷暴日时间序列长程幂律相关的标度指数为0.8940,该幂律关系至少可持续17个月,并将2011年和2012年观测数据作为验证数据加以验证,结果与DFA分析结果一致;雷暴日时间序列具有2个显著的标度不变区域,存在一个突变点,反映了雷暴日系统具有复杂的物理作用机制;三种分析方法均得出许昌市雷暴日呈减少趋势的结论,最小二乘法虽然能定量计算出雷暴日每10 a的减少量,但年度尺度较大,精确度变低,而DFA和小波分析法的分析结果更加细致;但在定量描述雷暴日变化趋势上DFA法优于小波分析结果,而在分析雷暴日时序的细节分量和周期特性时小波分析更加清晰;DFA法可作为预测未来雷暴日发展趋势时长的有效方法之一。  相似文献