Late Quaternary fluvial aggradation and incision in the monsoon‐dominated Alaknanda valley,Central Himalaya,Uttrakhand, India

The present study aims to explain the spatial and temporal variability in phases of aggradation/incision in response to changes in climate and seismicity during the late Quaternary in the Alaknanda River valley (a major tributary of the river Ganges or Ganga). Geomorphology, stratigraphy and optical dating of the fluvial sediment reveal that the oldest fluvial landforms preserved in the south of the Main Central Thrust are debris flow terraces developed during the early part of pluvial Marine Isotopic Stage 3. Following this, a period of accelerated incision/erosion owing to an increase in uplift rate and more intense rainfall occurred. In the Lesser Himalaya, three phases of valley fill aggradation around 26 ± 3 ka, 18 ± 2 ka and 15 ± 1 ka and 8 ± 1 ka occurred in response to changes in monsoon intensity and sediment flux. The last phase was regionally extensive and corresponds to a strengthening of the early Holocene Indian Summer Monsoon. A gradual decline in the monsoon strength after 8 ± 1 ka resulted in reduced fluvial discharge and lower sediment transport capacity of the Alaknanda River, leading to valley fill incision and the development of terraces. The study suggests that fluvial dynamics in the Alaknanda valley were modulated by monsoon variability and the role of tectonics was subordinate, limited to providing accommodation space and post‐deposition modification of the fluvial landforms. Copyright © 2010 John Wiley & Sons, Ltd.     

1960-2009年西南地区极端干旱气候变化(英文)

Based on the daily data of temperature and precipitation of 108 meteorological stations in Southwest China from 1960 to 2009, we calculate the monthly and yearly surface humid indexes, as well as the extreme drought frequency. According to the data, the temporal and spatial characteristics of the extreme drought frequency in inter-annual, inter-decadal, summer monsoon period and winter monsoon period are analyzed. The results are indicated as follows. (1) In general, the southwestern Sichuan Basin, southern Hengduan Mountains, southern coast of Guangxi and northern Guizhou are the areas where the extreme drought frequency has significantly increased in the past 50 years. As for the decadal change, from the 1960s to the 1980s the extreme drought frequency has presented a decreasing trend, while the 1990s is the wettest decade and the whole area is turning wet. In the 2000s, the extreme drought frequency rises quickly, but the regional differences reduce. (2) During summer monsoon period, the extreme drought frequency is growing, which generally occurs in the high mountains around the Sichuan Basin, most parts of Guangxi and "the broom-shaped mountains" in Yunnan. It is distinct that the altitude has impacts on the ex-treme drought frequency; during winter monsoon period, the area is relatively wet and the extreme drought frequency is decreasing. (3) During summer monsoon period, the abrupt change is observed in 2003, whereas the abrupt change during winter monsoon period is in 1989. The annual extreme drought frequency variation is a superposition of abrupt changes during summer monsoon and winter monsoon periods. The departure sequence vibration of annual extreme drought frequency is quasi-5 years and quasi-12 years.     

Hydrography and circulation in the northwestern Bay of Bengal during the retreat of southwest monsoon

The distribution of temperature and salinity in the upper 500 m of the northwestern Bay of Bengal, adjoining the east coast of India, during the retreat of southwest monsoon (September) of 1983 is presented. This study reveals coastal upwelling (limited to the upper 40 m) induced by the local winds. Waters of higher surface salinity near the coast characterize the upwelling. The freshwater influx near the head of the Bay diluted the surface salinity to as low as 26.0 × 10⁻³. The surface circulation was weak and led to a net transport of 2.0 × 10⁶m³.s⁻¹ directed towards northeast.     

双涡互旋的数值模拟试验

本文应用准地转正压无辐散模式对双涡的相互作用进行了数值模拟试验。试验结果表明：（1）只考虑相对涡度平流的情况下双涡以互旋为主，而且随着初始间距的缩小，互旋越来越明显。双涡的相互作用与它们的初始间距以及它们的强度和结构有密切的关系。（2）双涡的移动加速和减速都是出现在它们移动方向改变的时刻，当移动方向向逆时针方向变化时移速减慢，否则加快。     

强弱南海夏季风年广西的天气及预测概念模型

利用南海季风试验研究(1997～2000)的成果资料,对强弱南海夏季风年广西的天气作了对比研究,主要分析了雨季开始、年雨量分配及丰欠、热带气旋活动特点等方面的差异并归纳出一个简单的预测概念模型,可供业务工作者在制作年景预测上参考。     

Driving forces of tropical deforestation: The role of remote sensing and spatial models

Remote sensing technologies are increasingly used to monitor landscape change in many parts of the world. While the availability of extensive and timely imagery from various satellite sensors can aid in identifying the rates and patterns of deforestation, modelling techniques can evaluate the socioeconomic and biophysical forces driving deforestation processes. This paper briefly reviews some emerging spatial methodologies aimed at identifying driving forces of land use change and applies one such methodology to understand deforestation in Mexico. Satellite image classification, change analysis and econometric modelling are used to identify the rates, hotspots and drivers of deforestation in a case study of the southern Yucatán peninsular region, an enumerated global hotspot of biodiversity and tropical deforestation. In particular, the relative roles of biophysical and socioeconomic factors in driving regional deforestation rates are evaluated. Such methodological approaches can be applied to other regions of the forested tropics and contribute insights to conservation planning and policy.     

南海夏季风爆发与热带太平洋两类海温型关系的年代际差异

南海夏季风爆发日期在1993/1994年出现年代际偏早的转变,利用海温和再分析资料的研究证实西北太平洋增暖和两类海温型的年代际差异可能是导致此种变化的重要成因。进一步的研究揭示出在南海夏季风爆发出现年代际变化的背景下,南海夏季风爆发日期与太平洋海温的关系也出现明显的变化:1993/1994年之前的第一年代东太平洋(EP)型海温异常起主导作用,而1993/1994年之后的第二年代两类海温型均影响了季风爆发,但以中太平洋(CP)型海温异常为主。第一年代,东太平洋型增温(EPW)通过抑制西北太平洋-孟加拉湾的对流活动,在菲律宾海、孟加拉湾西部激发出两个距平反气旋,使越赤道气流建立偏晚、孟加拉湾低槽填塞、西北太平洋副热带高压增强,进而导致南海夏季风爆发偏晚,且其影响可从4月维持到5月;而中太平洋型增温(CPW)对季风爆发前期的流场无显著影响。第二年代,CPW通过抑制菲律宾-孟加拉湾东部的对流活动,在菲律宾-孟加拉湾激发出一个距平反气旋,使孟加拉湾低槽填塞、南海地区副高增强,进而阻碍季风爆发,且显著影响仅出现在4月;EPW对4月大气环流场的影响与第一年代较为接近,在菲律宾-孟加拉湾一带产生的风场、对流场异常稍弱于CPW,但其影响无法持续到5月。     

海南岛表土花粉和热带植被模拟研究

调查分析了海南岛各种热带植被下的表土花粉,并根据花粉数据进行植被类型的模拟。结果表明,表土花粉类型复杂,优势种不明显,反映了热带植被下的植物种类繁多复杂的特性。分模拟能够较好地反映热带气候下的雨林,季雨林和干草原植被,其地理位置与地区植被的地理分布基本一致,海南岛山地的花粉模拟还恢复了热带山地植被,而海岸红树林植被能够被海岸带的花粉证据所模拟。该研究能够为我国大范围表土花粉调查和热带植被类型提供花     

热带气旋暴雨增幅造成北方特大暴雨的预报

利用人工神经元网络的非线性决策特性，采用前向多层的误差反向传输网络，研制了一个登陆北上热带气旋暴雨增幅造成北方特大暴雨的预报方法－－能自动判虽有无暴雨增幅及其出现地区的人工神经元分类预报网络。该方法简便客观，试用效果较好，即可投入业务使用。