On the evolution of finite-amplitude disturbance to the barotropic and baroclinic quasigeostrophic flows     

Mu Mu  Xiang Jie 《大气科学进展》1998,15(1):113-123

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C3植物光合作用日变化的模拟   总被引：28，自引：1，他引：27  

于强  任保华  王天铎  孙菽芬 《大气科学》1998,22(6):867-880

对前人光合作用-气孔导度耦合模型进行了修正,建立了光合作用-蒸腾作用-气孔导度的耦合模型,它概括了叶片上各主要物理过程和生理过程之间的相互联系和制约关系。 用数值方法研究了不同环境因子（太阳辐射、温度、湿度和风速等）对光合作用、蒸腾作用和气孔导度的日变化及中午降低（midday depression）的影响。 主要结果是:（1）当边界层导度减小时,光合“午睡”加剧,蒸腾作用减弱,但作为反馈调节,气孔导度增加。 （2）气孔导度的最适温度最低,光合作用次之,蒸腾作用最适温度最高。当光合作用中午受到高温的胁迫时,气孔导度下降的幅度最大,光合作用次之,蒸腾作用的降幅最小。一天中,气孔导度降低的持续时间最长,蒸腾作用降低的持续时间最短。（3）空气绝对湿度越低,气孔导度越低,光合午睡越明显。蒸腾作用则决定于饱和水汽压差(Vpd)和气孔导度两个因素的相反的作用。蒸腾作用随Vpd增加而增大,但Vpd超过一定值后,反而使蒸腾作用下降。 （4）当温度在光合最适温度以上时,太阳辐射的增加使叶温增加,引起光合“午睡”的加剧和气孔导度的降低。（5）ci/cs在中午的降低表明气孔的关闭是光合作用“午睡”现象的原因。  相似文献   

科尔沁地区本世纪温度变化     

任国玉 《气象科学》1998,18(4):373-380

根据5个代表性台站的温度等级资料,得到了东北科尔沁地区1911－1988年区域平均的温度等级时间变化序列。这个地区冬季温度在年际、年代际和长期趋势上的变化与辽东半岛地区十分相似,但夏季温度的变化在各种时间尺度上同辽东半岛均存在较显著差异。本世纪科尔沁地区冬季温度和辽东半岛一样出现了明显增暖趋势,而夏季温度的变凉趋势却不如后者显著。  相似文献   

The Precambrian of the Anti-Atlas (Morocco): A geochronological synthesis     

René Charlot 《Precambrian Research》1976,3(3):273-299

Twenty total rock Rb/Sr isochrons ($\text{λ}{}^{87}\text{Rb}\text{= 1.47 · 10}{}^{\mathrm{?11}}\text{yr}{}^{\mathrm{?1}}$) and many individual data, mainly obtained by the K/Ar and Rb/Sr methods, on total rocks and minerals show that the orogenic story of the Precambrian of the Anti-Atlas, which was studied in its western and central parts, began with the Eburnean orogeny (1900-1650 m.y.). Up to now there is no good evidence of an older basement, even if the rather high initial ratio (0.707–0.709) of some Eburnean granites might suggest that such a basement exists at depth. There is also no geochronological evidence of plutonism until in early Panafrican time (680 m.y.) there started a period of intense magmatic and thermal activity which was ended by the emplacement of late post-tectonic granites at 530-520 m.y.The late Panafrican acid volcanism does not generally give suitable material for Rb/Sr dating, because of the great mobility of the radiogenic strontium in such a material even under very weak thermal conditions.  相似文献   

层次分析法在彩票抽奖方案选择中的应用   总被引：1，自引：0，他引：1  

杨韧  张志让  武英涛  廖磊  刘韶凤 《成都信息工程学院学报》2004,19(3):451-457

采用层次分析法对29种彩票抽奖方案进行排序,较为科学地解决了比较多种方案优劣程度的问题,得到了彩票抽奖方案选择问题的优化解.  相似文献   

A comparative study of extensive machine learning models for predicting long-term monthly rainfall with an ensemble of climatic and meteorological predictors     

Zhengzheng Zhou  Jie Ren  Xiaogang He  Shuguang Liu 《水文研究》2021,35(11):e14424

Rainfall prediction is of vital importance in water resources management. Accurate long-term rainfall prediction remains an open and challenging problem. Machine learning techniques, as an increasingly popular approach, provide an attractive alternative to traditional methods. The main objective of this study was to improve the prediction accuracy of machine learning-based methods for monthly rainfall, and to improve the understanding of the role of large-scale climatic variables and local meteorological variables in rainfall prediction. One regression model autoregressive integrated moving average model (ARIMA) and five state-of-the-art machine learning algorithms, including artificial neural networks, support vector machine, random forest (RF), gradient boosting regression, and dual-stage attention-based recurrent neural network, were implemented for monthly rainfall prediction over 25 stations in the East China region. The results showed that the ML models outperformed ARIMA model, and RF relatively outperformed other models. Local meteorological variables, humidity, and sunshine duration, were the most important predictors in improving prediction accuracy. 4-month lagged Western North Pacific Monsoon had higher importance than other large-scale climatic variables. The overall output of rainfall prediction was scalable and could be readily generalized to other regions.  相似文献   

美国中东部温带稳定≥10℃积温     

任国玉 《地理研究》1987,6(4):70-76

应用修订的康拉德公式计算美国中东部温带地区日均温稳定≥10℃积温,并同我国相应纬度地区作了对比。这一对比揭示出我国东部温带并非世界同纬度地带夏半年热量资源最丰富。  相似文献   

GROUNDWATER QUALITY AND CONTAMINATION INDEX MAPPING IN CHANGCHUN CITY, CHINA   总被引：13，自引：0，他引：13  

Hamadoun BOKAR 《中国地理科学(英文版)》2004,14(1):63-70

1INTRODUCTIONGroundwater in Changchun City assures about 45% of total water supply. Drinking water supply of Chang-chun City was mostly served by surface water from Shitoukoumen and Xinlicheng reservoirs located in the east and south of the city (ZHANG, 1993). However, with the development of urban construction the ground-water especially from deep boreholes is also used for drinking purpose in suburban areas. The urbanization process in Changchun City threatens the groundwater quali…  相似文献   

Shift-share Analysis on International Tourism Competitiveness - A Case of Jiangsu Province   总被引：5，自引：0，他引：5  

SHI Chunyun ZHANG Jie YANG Yang ZHOU Zhang 《中国地理科学(英文版)》2007,17(2):173-178

Shift-share analysis has been confirmed a useful approach in the study of regional economics and many kinds of extended shift-share models have been advanced and put into practice in economic studies, but few have hitherto been introduced and applied to the tourism research in China. Moreover understanding the spatially competitive relationship is of paramount importance for marketers, developers, and planners involved in tourism strategy development. Based on international tourism receipts from 1995 to 2004, this study aims at probing into the spatial competitiveness of interna- tional tourism in Jiangsu Province in comparison with its neighbors by applying a spatially extended shift-share model and a modified dynamic shift-share model. The empirical results illustrate that exceptional years may exist in the ap- plication of dynamic shift-share models. To solve this issue, modifications to dynamic shift-share model are put forward. The analytical results are not only presented but also explained by the comparison of background conditions of tourism development between Jiangsu and its key competitors. The conclusions can be drawn that the growth of international tourism receipts in Jiangsu mainly attributes to the national component and the competitive component and Zhejiang is the most important rival to Jiangsu during the period of 1995-2004. In order to upgrade the tourism competitiveness, it is indispensable for Jiangsu to take proper positioning, promoting and marketing strategies and to cooperate and integrate with its main rivals.  相似文献   

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孟国杰  申旭辉  伍吉仓  任金卫 《大地测量与地球动力学》2007,27(1):19-23

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