Stable carbon isotope ratios in lake and swamp sediments as a proxy for prehistoric forest clearance and crop cultivation in the Neotropics

Close correspondence between stable carbon isotope ratios ( ¹³ C), pollen, and charcoal profiles in sediment cores from Laguna Zoncho and Machita swamp, Costa Rica, shows that prehistoric forest clearance and crop cultivation can be detected in the stable carbon isotope ratios of total organic carbon ( ¹3C _TOC ). Analyses of δ 13C _TOC complement evidence from pollen, charcoal, and phytoliths and provide a proxy that is sensitive to the intensity and/or proximity to core sites of prehistoric forest clearance and agriculture in watersheds. Stable carbon isotope analyses are particularly useful in situations in which other evidence of forest clearance and agriculture is limited.     

Effects of the number of stations and time resolution on derivation

For at least 30 years now it has been well known that the Dst index can be modelled using the solar wind as input. Since then, many attempts have been made to improve the predictability of Dst using different approaches. These attempts are useful, for instance, to understand which features of the solar wind–magnetosphere interactions are most important in producing magnetospheric activity and how the Dst index would improve the space weather forecast. The Dst index is by far the most reliable and simple indication that a magnetic storm is in progress. In this work, the effect of using more than four magnetic stations and shorter time intervals than the hourly averages used in Sugiura's procedures is evaluated. The discussion is based on the results presented by Burton in 1975 and Feldstein in 1984 considering 4 or 12 magnetic stations and time averages of 2.5 min for a magnetic disturbed period that occurred from February 7–28, 1967, including two geomagnetic storms. The analysis has shown that the global representation of a magnetic storm by the standard Dst (Sugiura) is well preserved either using 4, 6, 12 magnetic stations or using 1 h, 2.5 min 1 min averages. A brief review of the current understanding of Dst has been included to support the discussions. The analysis performed has shown that a more refined Dst index (time and number of stations>4) would be useful to investigate the intrinsic processes and the different current systems involved in the ring current development during magnetic storms; the standard Dst, as it is conceived, is quite adequate to monitor geomagnetic storms and identify their overall features; concerning the magnetic stations normally considered, the inclusion of higher magnetic latitude stations (>35) may underestimate the observed Dst.     

Unstable kinetic Alfvén wave in partially ionized plasma

The stability of kinetic Alfven waves is discussed for a partially ionized plasma with a flux of ionizing electrons which balance the plasma particle losses. Accidental electromagnetic perturbations are shown to be unstable due to the energy change of ionizing electrons.     

4D一体化多媒体电子地图集理论方法和技术研究与开发--以《云南省生态环境多媒体电子地图集》为例

本文首先研究了4D数据一体化多媒体电子地图集的理论和信息机理,包括4D数据在电子地图集中的集成、融合和应用的信息机理,多源多类信息交互认知和传输机理,4D信息的查询、分析、模拟、调控和表达的信息机理,以及4D数据一体化电子地图集的理论框架。其次,文章深入研究和解决了建立4D一体化多媒体电子地图集过程中的诸多技术方法问题,例如多源多类数据的集成和融合、基于主导数据库的多重表达、多媒体地图动画、基于4D数据的信息分析和量算、生态环境信息动态仿真和虚拟表达等。在论文第三部分,文章介绍了作者研发的《云南省生态环境多媒体电子地图集》成果,包括其结构、功能、内容、超媒体链接等方面的设计,查询功能和分析量算功能的开发,以及本电子地图集的分析应用成果。     

POS辅助航空摄影测量精度分析

通过陕西勉县测区的POS辅助航空摄影测量试验,本文对SWDC-4搭载POS/AV 510 V5系统获取的航测数据使用直接定向法和POS辅助空中三角测量2种方法进行1∶10 000成图精度验证。结果证明:国产SWDC-4航摄仪与POS/AV系统集成进行POS辅助空三的加密成果能满足该测区1∶10 000地形图测图的平面和高程精度要求,直接定向也是可行的。     

利用遥感技术建立墨西哥热带地上生物量模型(英文)

Spatially-explicit estimation of aboveground biomass(AGB) plays an important role to generate action policies focused in climate change mitigation,since carbon(C) retained in the biomass is vital for regulating Earth’s temperature.This work estimates AGB using both chlorophyll(red,near infrared) and moisture(middle infrared) based normalized vegetation indices constructed with MCD43A4 MODerate-resolution Imaging Spectroradiometer(MODIS) and MOD44B vegetation continuous fields(VCF) data.The study area is located in San Luis Potosí,Mexico,a region that comprises a part of the upper limit of the intertropical zone.AGB estimations were made using both individual tree data from the National Forest Inventory of Mexico and allometric equations reported in scientific literature.Linear and nonlinear(expo-nential) models were fitted to find their predictive potential when using satellite spectral data as explanatory variables.Highly-significant correlations(p = 0.01) were found between all the explaining variables tested.NDVI62,linked to chlorophyll content and moisture stress,showed the highest correlation.The best model(nonlinear) showed an index of fit(Pseudo-r2) equal to 0.77 and a root mean square error equal to 26.00 Mg/ha using NDVI62 and VCF as explanatory variables.Validation correlation coefficients were similar for both models:lin-ear(r = 0.87**) and nonlinear(r = 0.86**).     

Monsoon Change in East Asia in the 21st Century: Results of RegCM3

The authors investigate monsoon change in East Asia in the 21st century under the Special Report on Emissions Scenarios (SRES) A1B scenario using the results of a regional climate model, RegCM3, with a high horizontal resolution. First, the authors evaluate the model’s performance compared with NCEP-NCAR reanalysis data, showing that the model can reliably reproduce the basic climatology of both winter and summer monsoons over East Asia. Next, it is found that the winter monsoon in East Asia would slightly weaken in the 21st century with spatial differences. Over northern East China, anomalous southerly winds would dominate in the mid-and late-21st century because the zonal land-sea thermal contrast is expected to become smaller, due to a stronger warming trend over land than over ocean. However, the intensity of the summer monsoon in East Asia shows a statistically significant upward trend over this century because the zonal land-sea thermal contrast between East Asia and the western North Pacific would become larger, which, in turn, would lead to larger sea level pressure gradients throughout East Asia and extending to the adjacent ocean.     

一种平面四参数法坐标转换方法的实现

简述了GPS坐标转换技术,详细介绍了一种平面四参数坐标转换的方法,然后采用VB6.0编写程序实现此坐标转换方法,并对这种坐标转换方法进行了验证。程序界面简捷,直观,实用,程序精度较高,在平时的工作中的到较好的应用。     

Optimization of mooring observations in Northern Bering Sea

The problem of the optimal sampling strategy for moored current velocity observations in the Northern Bering Sea is addressed. We analyze dynamically induced correlations in the North Bering Sea currents and conduct their sensitivity analysis to optimize positions of a limited number of moorings. Optimization of the sampling strategy is performed with respect to robustness of the reconstruction of the North Bering Sea circulation with a particular emphasis on the accurate monitoring of the mean Bering Strait transport. Computations reveal four major regions in the North Bering Sea basin that are highly correlated with the Bering Strait transport. Apart from the regions within the Bering Strait itself, they include the Anadyr Strait and a region 100 km south of the Cape of Prince of Wales. Results of the sensitivity analysis are tested in the framework of twin data experiments with the quasi-stationary and oscillatory background circulations.     

Present-day climatology and projected changes of warm and cold days in the CNRM-CM3 global climate model

The impact of global warming on the warmest and coldest days of the annual cycle is explored according to an A2 scenario simulated by the CNRM-CM3 climate model in the framework of the IPCC AR4 intercomparison. Given the multi-model spread in IPCC projections, a validation strategy is proposed using the NCEP/NCAR reanalysis. Validation of the late twentieth century model climatology shows that warm and cold model events are slightly too long and infrequent. Although interannual trends in the warm (cold) day occurrence were positive (negative) only for six (three) of the nine considered sub-continental regions, simulated model trends are always positive (negative). This different behaviour suggests that simulated non-anthropogenic decadal variability is small relative to anthropogenic trends. Large-scale synoptic processes associated with European regional warm and cold peaks are also described and validated. Regional cold peaks are better reproduced than warm peaks, whose intensity accuracy is limited by other physical variables. Positive (negative) winter anomalies of sea and land surface temperature lead to summers with severe (weak) temperatures. These inter-annual anomalies are generated by a persistent pressure dipole over Europe. Regarding climate change, warm (cold) events will become more (less) frequent and longer (shorter). The number of warm days will largely rise and the number of cold days will dramatically decrease. The intensity of warm days will be particularly pronounced over Europe, given the projected summer drying in this region. However, according to the limited skill of the CNRM model, these results must be considered with caution.