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1.
近40年西南地区的气候变化事实   总被引:37,自引:10,他引:27  
马振锋  彭骏  高文良  田宏 《高原气象》2006,25(4):633-642
利用西南地区(云南、贵州、重庆、四川、西藏)1961—2000年139个气象观测站常规地面观测资料年平均值,对西南地区近40年来气候的年际和年代际变化特征进行了分析。揭示了青藏高原、川西高原、云贵高原在20世纪后40年气温上升、降水增加、湿度增大趋势显著,而在四川盆地东北部和西南部的气温则存在明显的下降趋势,表明西南地区气候变化与全球变暖存在非同步性。通过对各气候要素年际和年代际变化序列的分离,得出了西南地区不同气候要素基本都存在明显的年际和年代际变化振荡周期,对这些气候要素存在的突变现象进行了检验,发现气温首先在青藏高原地区开始突变,然后是云贵高原区,最后是四川盆地、贵州东部丘陵区。其他气候要素的突变时间多数也是先从青藏高原开始。由此可见,西南地区气候要素在高海拔地区比低海拔地区突变时间为早,全球气温突变要比西南地区的气温突变要早。  相似文献   
2.
2004年7月冷空气活动及其对西南地区强降水的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
陈艳  丁一汇 《气象学报》2006,64(6):743-759
利用中国逐日站点降水资料和NCEP/NCAR再分析资料,分析了2004年盛夏(7月)中国西南地区的强降水过程及冷空气活动在降水过程中的作用。结果显示:西南地区强降水与冷空气的活动关系密切,强降水的发生是中高纬环流变化和低纬系统共同作用的结果。首先,中纬度的低槽冷涡与登陆北上台风和东移西南涡合并,以及东亚地区横槽向竖槽的迅速转变,造成了7月上旬和中旬中高纬环流的3次大调整,东亚地区长波迅速增幅,从而导致了盛夏罕见的大范围冷空气向低纬地区的侵袭。与此同时,暖湿的西南夏季风十分活跃,二者在中国南方地区产生强烈相互作用,结果在冷空气南侧形成大范围的对流性降水。其中,冷空气活动对降水的影响主要表现在3个方面:其一,中高层冷空气的迅速南下常伴有偏南高空急流,位于急流中心左前方的次级环流上升支为降水的形成提供了有利的动力抬升条件。其二,冷空气向南推进极大地增强了大气的斜压性,有利于斜压扰动的发展。冷空气迅速南下造成对流有效位能释放,从而形成大范围的对流活动。另外,中高层干冷空气的平流也是暴雨区位势不稳定得以重建并产生持续性强降水的重要原因。  相似文献   
3.
湿位涡守恒条件下西南涡的发展   总被引:6,自引:0,他引:6       下载免费PDF全文
朱禾  邓北胜  吴洪 《气象学报》2002,60(3):343-351
运用高分辨率数值预报模式 (HIRLAM)模拟了一次中国西南地区在多种活跃天气系统影响下 ,西南涡的发展过程。分析了东亚季风、青藏高压、地形等多种尺度与不同高低空环流形势配合以及在湿位涡守恒条件下对流发展时 ,潜热及不稳定能量的释放 ,对中尺度涡旋和强对流发生发展的作用 ,探讨了西南涡和局地降水增强与消亡的成因与理论 ,并具有实用意义  相似文献   
4.
This study analyzes the relationships of stable isotopes in precipitation with temperature, air pressure and humidity at different altitudes, and the potential influencing mechanisms of control factors on the stable isotopes in precipitation in Southwest China. There appear marked negative correlations of the δ18O in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water (PW)at the Mengzi, Simao and Tengchong stations on the synoptic timescale; the marked negative correlations between the δ18O in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850hPa are different from the temperature effect in middle-high-latitude inland areas. In addition, the notable positive correlation between the δ18O in precipitation and the dew-point deficit △Td at different altitudes is found at the three stations. Precipitation is not the only factor generating an amount effect. Probably,the amount effect is related to the variations of atmospheric circulation and vapor origins. On the annual timescale, the annual precipitation amount weighted-mean δ18O displays negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with an abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in Southwest China and generates abnormally strong rainfall on the way. Meanwhile, the abnormally strong condensation process will release more condensed latent heat in the atmosphere, and this will lead to a rise of atmospheric temperature during rainfall but a decline of δ18O in the precipitation. On the other hand, in the years with an abnormally weak summer monsoon, the precipitation and the atmospheric temperature during rainfalls decrease abnormally but the δ18O in precipitation increases.  相似文献   
5.
A new circulation index (ISW) that can realistically describe winter temperature variations over Southwest China is defined based on analysis of the NCEP/NCAR reanalysis data (version 1) and the observations at 585 stations in China. The study period is from January 1961 to February 2011. The relationship between ISW and general circulation patterns in East Asia is also analyzed. Results show that ISW successfully captures the variations in winter temperature over Southwest China. High ISW values correspond to the intensified Mongolian high, the weakened Aleutian low, increases in the strength of the Middle East westerly jet stream over the south of the Tibetan Plateau (TP), and decreases in the strength of the subtropical westerly jet over the north of the TP. Meanwhile, the East Asian trough deepens and extends southwestward, making it easier for the cold air mass from the north to intrude Southwest China along the trough. These circulation patterns lead to a decrease in winter temperature over Southwest China (and vice versa). In addition to the East Asian winter monsoon, the two westerly jets that dominate the upper level circulation over East Asia also exert important influences on winter temperature in Southwest China, especially the Middle East westerly jet to the south of the TP.  相似文献   
6.
The spatial-temporal features of the extremely severe drought and the anomalous atmospheric circulation in summer 2006 are analyzed based on the NCEP/NCAR reanalysis data, the characteristic circulation indices given by the National Climate Center of China, and the daily precipitation data of 20 stations in the east of Southwest China (ESC) from 1959 to 2006. The results show that the rainless period started from early June and ended in early September 2006 with a total of more than 80 days, and the rainfall was especially scarce from around 25 July to 5 September 2006. Precipitation for each month was less than normal, and analysis of the precipitation indices shows that the summer precipitation in 2006 was the least since 1959. The extremely severe drought in the ESC in summer 2006 was closely related to the persistent anomalies of the atmospheric circulation in the same period, i.e., anomalies of mid-high latitude atmospheric circulation, western Pacific subtropical high (WPSH), westerlies, South Asian high, lower-level flow, water vapor transport, vertical motion, and so on. Droughts usually occur when the WPSH lies anomalously northward and westward, or anomalously weak and eastward. The extreme drought in summer 2006 was caused by the former. When the WPSH turned stronger and shifted to the north and west of its normal position, and the South Asian high was also strong and lay eastward, downdrafts prevailed over the ESC and suppressed the water vapor transfer toward this area. At the same time, the disposition of the westerlies and the mid-high latitude circulation disfavored the southward invasion of cold air, which jointly resulted in the extremely severe drought in the ESC in summer 2006. The weak heating over the Tibetan Plateau and vigorous convective activities over the Philippine area were likely responsible for the strong WPSH and its northwestward shift in summer 2006.  相似文献   
7.
青藏高原冬季风演变的新特征及其与中国西南气温的关系   总被引:1,自引:0,他引:1  
王颖  李栋梁  王慧  郑然 《高原气象》2015,34(1):11-20
利用1951 2011年NCEP/NCAR再分析资料和1960 2010年西南地区77站月平均气温数据,定义了冬季代表月(1月)青藏高原(下称高原)季风强度和位置的新指数,并分析了该指数与中国西南地区地面气温的关系,结果表明:(1)代表高原冬季风的冷高压强度和位置具有明显的年际、年代际变化,20世纪70年代末发生了由弱到强的突变,80年代中期则是由偏北到偏南的突变。在全球变暖的大背景下,高原冬季风强度的振荡频率加快,由较长的7年周期向4年周期转化;位置指数的4年与10年周期存在明显的反相变化,自2005年以来位置振荡周期由10年向4年转化,南北摆动更为频繁。(2)当高原冬季风偏强时,北方冷空气与西南暖湿空气在西南地区交汇减弱,云量减少,辐射增温作用使西南地区温度一致偏高,西南地区东部低层出现异常下沉运动中心,下沉增温作用使该地区温度偏高更明显;当偏弱时,则相反。(3)当高原冬季风偏北时,北方较强冷空气南下,南支槽加深,西南暖湿空气与北方冷空气交汇于川滇地区,产生异常上升运动,云量增多,接收的太阳辐射减少,且冷空气活动频繁,西南地区温度一致偏低,上升冷却作用使西部气温偏低更明显;当偏南时,则相反。  相似文献   
8.
何俊琦  余锦华  高歌  王静 《气象科学》2015,35(4):454-461
利用西南地区60站1961—2011年的日平均气温、降水量资料求得半年尺度的气象干旱指数值,包括帕尔默干旱指数、标准化降水干旱指数、Z指数、降水距平百分率指数。采用超前相关、相似和技巧评分两种计算方法检测与西南地区农业灾情最适宜的气象干旱指数。基于最适宜的干旱指数,给出西南地区农业干旱灾害可能发生的风险分布。结果表明:Z指数定义的冬半年气象干旱对西南地区农业旱情的指示性较其他3种气象干旱指标更优。冬半年Z指数小于等于-0.84时引发的西南地区农业干旱灾害成灾率大于8%的风险平均达0.53,农业干旱绝收率大于5%的风险平均达0.37,风险最大地区位于贵州西北部。结论有助于深入认识气象干旱指数与农业干旱灾情的联系,对于西南地区农业干旱的检测预测有一定的应用价值。  相似文献   
9.
In the last decade, a series of severe and extensive droughts have swept across Southwest China, resulting in tremendous economic losses, deaths, and disruption to society. Consequently, this study is motivated by the paramount importance of as- sessing future changes in drought in Southwest China. Precipitation is likely to decrease over most parts of Southwest China around the beginning of the century, followed by widespread precipitation increases; the increase in potential evapotran- spiration (PET), due to the joint effects of increased temperature and surface net radiation and decreased relative humidity, will overwhelm the whole region throughout the entire 21st century. In comparative terms, the enhancement of PET will outweigh that of precipitation, particularly under Representative Concentration Pathway (RCP) 8.5, resulting in intensified drought. Generally, the drying tendency will be in the southeast portion, whereas the mountainous region in the northwest will become increasingly wetter owing to abundant precipitation increases. Droughts classified as moderate/severe according to historical standards will become the norm in the 2080s under RCP4.5/RCP8.5. Future drought changes will manifest different characteristics depending on the time scale: the magnitude of change at a time scale of 48 months is nearly twice as great as that at 3 months. Furthermore, we will see that not only will incidences of severe and extreme drought increase dramatically in the future, but extremely wet events will also become more probable.  相似文献   
10.
An objective identification technique for regional extreme events(OITREE) and the daily compositedrought index(CI) at 101 stations in Southwest China(including Sichuan, Yunnan, Guizhou, and Chongqing)are used to detect regional meteorological drought events between 1960 and 2010. Values of the parameters of the OITREE method are determined. A total of 87 drought events are identified, including 9 extreme events. The 2009–2010 drought is the most serious in Southwest China during the past 50 years. The regional meteorological drought events during 1960–2010 generally last for 10–80 days, with the longest being 231days. Droughts are more common from November to next April, and less common in the remaining months.Droughts occur more often and with greater intensity in Yunnan and southern Sichuan than in other parts of Southwest China. Strong(extreme and severe) regional meteorological drought events can be divided into five types. The southern type has occurred most frequently, and Yunnan is the area most frequently stricken by extreme and severe drought events. The regional meteorological drought events in Southwest China have increased in both frequency and intensity over the study period, and the main reason appears to be a significant decrease in precipitation over this region, but a simultaneous increase in temperature also contributes.  相似文献   
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