Evolution of Asian Summer Monsoon and the Slowly Varying Disturbances

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不同人为干扰方式对桂西北喀斯特草丛群落土壤种子库组成与分布的影响

采用野外调查和室内萌发相结合的方法,对桂西北典型喀斯特峰丛洼地刈割、开垦和火烧3种不同人为干扰方式下草丛群落的土壤种子库进行了比较研究。结果表明: ① 3种不同干扰方式草丛群落土壤种子库密度存在显著差异,其种子密度大小为: 刈割群落> 开垦群落> 火烧群落;②刈割、开垦、火烧干扰草丛种子主要分布在0～ 2cm ( 67% )、2～ 5cm ( 55% )、5～ 10cm ( 37% )的土层中;③刈割群落土壤种子库中乔、灌、草生活型的物种比例大于开垦和火烧干扰群落;④ 3种不同干扰方式草丛群落土壤种子库的丰富度指数、Sha nno n-Wie ner 指数和Simpson指数的大小顺序均为: 刈割群落> 开垦群落> 火烧群落,同群落物种数变化趋势一致,与生态优势度呈相反趋势;均匀度指数大小顺序为: 刈割群落> 火烧群落> 开垦群落。⑤从土壤种子库与地面植被物种组成相似性系数来看,刈割群落和开垦群落相似性系数较大,而火烧群落地上与地下物种组成有较大区别,相似性系数为0.296。研究结果表明,刈割干扰相对开垦和火烧更有利于喀斯特地区草丛群落土壤种子库的维持与保护。      

基于MODIS时序数据的中国西南地区主要植被生态系统干扰动态监测及分析

在自然或人为活动的干扰下,生态系统的正常功能或多或少受到影响.生态系统干扰信息可为跟踪气候变化响应、探寻全球碳循环路径和维系生态系统功能提供重要参考.飞速发展的遥感技术为生态系统干扰信息的获取提供了新的思路,高时空分辨率的遥感影像能及时有效地监测干扰事件发生的时间和位置.本文以中国西南地区为例,选用2005-2016年...     

基于多尺度分割算法的湿地干扰格局研究

以三江平原具有典型湿地特征的建三江区为例,首先采用不同时间段归一化植被指数（NDVI）差值的变化监测人类活动改变的土地利用变化程度,然后结合遥感图像多尺度分割法,分析湿地系统的8种类型空间干扰格局,计算干扰度（PD）、干扰邻近度（PDD）及二者的相关性。结果表明：研究区土地利用类型变化对多尺度干扰格局的分布有明显影响,耕地、草地和沼泽地总干扰率较高,变化频繁;水域、林地和沼泽在干扰类型C1、C2中分布较广,但干扰值低,面积小;耕地分别占干扰类型C7、C8的74.38%和61.76%,干扰值高且面积大,说明耕地是建三江区湿地系统的主要干扰源。干扰邻近度说明干扰在一定尺度上发生,当干扰度PD＆lt;0.4或PD＆gt;0.7,且干扰邻近度PDD＆gt;PD时,干扰对周边土地类型必定产生影响。本研究为湿地生态系统脆弱性和恢复力的评价提供有效的生态特征指标。     

2000/2001年冬季北欧异常流型形成机理及其对我国北方天气的影响

从Rossby波能量的频散和瞬变斜压扰动的正压反馈角度,探讨了2000/2001年冬季盛行的斯堪的纳维亚环流型(正位相)的维持机理,并讨论了其对我国北方地区天气气候的影响。该环流型上游部分,即北大西洋和斯堪的纳维亚半岛的两个活动中心主要由瞬变斜压扰动的正压反馈所形成,部分由Rossby波能量频散所维持。而下游部分,即贝加尔湖附近的气旋式环流异常主要由Rossby波能量从上游频散所形成和维持。与该环流型对应,冷空气在西、中西伯利亚堆积,并在其南侧的西风气流区中平流,使得我国华北部分地区和东北地区比常年冷。该环流型导致新疆北部地区、内蒙古东部及东北地区降雪量显著增强。大西洋急流的东伸及对应斜压扰动的显著加强是预报北疆和内蒙古东部及东北地区多雪的一个重要前兆因子。     

Characterization of organic matter in sediment cores of the Todos os Santos Bay, Bahia, Brazil, by elemental analysis and 13C NMR

The impact of human activity on the sediments of Todos os Santos Bay in Brazil was evaluated by elemental analysis and ¹³C Nuclear Magnetic Resonance (¹³C NMR). This article reports a study of six sediment cores collected at different depths and regions of Todos os Santos Bay. The elemental profiles of cores collected on the eastern side of Frades Island suggest an abrupt change in the sedimentation regime. Autoregressive Integrated Moving Average (ARIMA) analysis corroborates this result. The range of depths of the cores corresponds to about 50 years ago, coinciding with the implantation of major onshore industrial projects in the region. Principal Component Analysis of the ¹³C NMR spectra clearly differentiates sediment samples closer to the Subaé estuary, which have high contents of terrestrial organic matter, from those closer to a local oil refinery. The results presented in this article illustrate several important aspects of environmental impact of human activity on this bay.     

Average anisotropy characteristics of high energy cosmic ray particles and geomagnetic disturbance index Ap

The average characteristics of the diurnal and semi-diurnal anisotropy of cosmic ray intensity at relativistic energies have been obtained by using data from the worldwide grid of neutron monitor for the period 1989 to 1996. The complex behaviour of the diurnal amplitudes and time of maxima (phase) and its association with the Ap index on a long-term and day-to-day basis have been studied. Even though the general characteristics, on a yearly average basis, have not changed significantly during this period, both the diurnal and semi-diurnal amplitudes and phases vary significantly, besides significant changes being observed for different interplanetary conditions on a short-term basis. It is found that the relationship between the Ap index and the diurnal vector is out of phase during the period 1991 to 1995. On a long-term basis, the correlation of diurnal variation with Ap index has been found to vary during the solar cycle. On a short-term basis, it has been observed that the high Ap days are usually associated with higher amplitudes with phase shifted to earlier hours.     

旅游干扰对纳帕海湖滨草甸湿地土壤水文调蓄功能的影响

在野外调查和室内分析的基础上,研究了旅游干扰对纳帕海湖滨草甸湿地土壤蓄水功能和水文调节能力的影响。结果表明,旅游干扰对草甸湿地表层土壤环境的破坏作用显著。随着旅游干扰强度增加,草甸湿地0～20cm表层土壤容重显著增加,孔隙度减小,土壤持水能力急剧下降,以未受旅游干扰作为参照,在轻度、中度和重度干扰下草甸表层土壤饱和持水能力分别下降了10%、48%和75%,表明土壤蓄水功能在高强度旅游干扰作用下退化显著。未受旅游干扰区草甸湿地土壤有效调蓄水空间、非毛管孔隙度、初渗速率和稳渗速率分别为1897g/kg、44%、3.14mm/min和1.92mm/min,在重度干扰作用下分别下降了77%、43%、94%和96%,高强度旅游干扰作用下草甸湿地土壤水文调蓄功能显著退化。     

Western disturbances seen with AMSU-B and infrared sensors

Western disturbances (WD) of winter and pre-monsoon seasons are the important sources of rainfall in the Indo-Gangetic plains. WDs are troughs or circulations in the westerly winds modified by the Himalayas. Operationally, WDs are monitored using infrared (IR) and water vapour (WV) images. Advanced Microwave Sounding Unit-B (AMSU-B), flying onboard the NOAA satellites, also allows WDs to be monitored in five microwave frequencies. Two are in water vapour window (89, 150 GHz) and three are absorption channels (centred at 183.31 GHz). Unlike the top of cloud view in IR or WV, AMSU-B radiances show the effect of moisture and hydrometeors in different layers. Two cases of WD (17 April 2001 and 18–19 February 2003) are discussed using the microwave data from AMSU-B and the IR and WV data from Meteosat-5. The aim here is to demonstrate the skill of AMSU-B in delineating structure of WDs. In particular, the cold intrusion and the moist conveyor belts are examined. It was found that the multi-channel view of the AMSU-B permits a better understanding of the moist structures seen in the conveyor belts. The à trous wavelet transform is used to clearly bring out mesoscale features in WDs. AMSU-B brings out intense convection as a large depression of BTs (>50K) at 150/176 GHz, cirrus and moist bands at 180/182 GHz. Mesoscale convection lines within WDs that last short time are shown here for the first time only in the AMSU-B images. Large-scale cirrus features are separated using the à trous wavelet transform. Lastly, it is shown that there is a good likeness in the rain contours in the 3-h rain 3B42 (computed from TRMM and other data) to AMSU-B depressions in BT. Overall, AMSU-B shows better skill in delineating the structure of clouds and rain in WDs.