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1.
Climate change has the potential ability to alter the occurrence and severity of extreme events. Though predicting changes
of such extreme events is difficult, understanding them is important to determine the impacts of climate change in various
sectors. This paper presents the change in rainfall extremes in the monsoon season in south-west Indian peninsula. Daily rainfall
data were analysed for the entire Kerala state in India to determine if the extreme rainfall had changed over the 50-year
period. Several indices were derived from the data to identify the extreme rainfalls. The trends of all the extreme indices
were assessed by parametric ordinary least square regression technique, which were tested for significance at 95% level. Results
showed significant decrease in monsoon rainfall extremes in Kerala that would affect the tendency of change in seasonal total
rainfall. This study provides a comprehensive knowledge on extreme monsoon precipitation in Kerala, which could also be employed
to study changing climate at local scale in other regions. 相似文献
2.
In July, heating of the continents in the Northern Hemisphere results in strengthened monsoon systems which bring rains to West Africa. In Nigeria, the annual rainfall total decreases from over 3,800 mm at Forcados on the coast to under 650 mm at Maiduguri in the north-east of the country. June, July, August and September are the rainiest months throughout the country. In many parts of the south, however, there is “supposed to be” a slight break in the rains for some 2 to 3 weeks in late July and early August or the so called “August break”. In this study, we are underscoring the obvious that climate is changing. The daily series of rainfall data for 1983–2003 analyzed between the months of July–August for some sites in the Eastern humid zone of Southern Nigeria shows that the “August break” may indeed “be breaking”. We have discussed some practical approaches to climate change research in this monsoon region. 相似文献
3.
During the last 30 years, the climate of the West African Sahel has undergone various changes, especially in terms of rainfall. This has large consequences for the poor-resource farmers depending mainly on rainfed agriculture. This paper investigates the impacts of current climate variability and future climate change on groundnut and cowpea production in Niger for three major agricultural regions, including the groundnut basin.Niger was one of the largest West African groundnut producing and exporting countries. Groundnut production – as a cash crop – dropped fromabout 312,000 tons in the mid 1960s (about 68% exported) to as low as 13,000tons in 1988 and increased again to 110,000 tons in 2000. Cowpea, a food crop, showsa different tendency, going from 4,000 tons in the mid fifties to a maximum of 775,000 tons in 1997, and its cultivated area is still increasing. It is also a cash crop in local economies (especially for women).To highlight the impact of climate change on groundnut and cowpea production (significantly determined by rainfall in July, August and September), the following components of the rainfall regime were calculated for the period 1951–1998: mean annual and monthly rainfall, beginning, end and lengthof the rainy season, number of rainy days per month, amount of rainfall per rainy day and the maximum length of dry spell per month. Three sub-periods whose duration varied per region were defined: for Dosso 1951–1968,1969–1984 and 1985–1998; for Maradi 1951–1970, 1971–1987 and1988–1998; and for Zinder 1951–1966, 1967–1984 and 1985–1998. A change in rainfallregime components was observed between the three sub-periods, which were characterized in chronological order by wet, dry and intermediate conditions. To assess the impact of climate variability and change on groundnut and cowpea production, a statistical modeling approach has been followed, based on thirteen predictors as described and discussed in the preceding paper. Climate change is mimicked in terms of reduced total amount of rainfall for the three main rainfall months and an increased temperature, while maintaining other significant predictors at a constant level. In 2025,production of groundnut is estimated to be between 11 and 25% lower, while cowpeayield will fall maximally 30%. Various strategies to compensate thispotential loss are presented for the two crops. 相似文献
4.
Dependence of Indian monsoon rainfall on moisture fluxes across the Arabian Sea and the impact of coupled model sea surface temperature biases 总被引：2，自引：2，他引：0
The Arabian Sea is an important moisture source for Indian monsoon rainfall. The skill of climate models in simulating the monsoon and its variability varies widely, while Arabian Sea cold sea surface temperature (SST) biases are common in coupled models and may therefore influence the monsoon and its sensitivity to climate change. We examine the relationship between monsoon rainfall, moisture fluxes and Arabian Sea SST in observations and climate model simulations. Observational analysis shows strong monsoons depend on moisture fluxes across the Arabian Sea, however detecting consistent signals with contemporaneous summer SST anomalies is complicated in the observed system by air/sea coupling and large-scale induced variability such as the El Ni?o-Southern Oscillation feeding back onto the monsoon through development of the Somali Jet. Comparison of HadGEM3 coupled and atmosphere-only configurations suggests coupled model cold SST biases significantly reduce monsoon rainfall. Idealised atmosphere-only experiments show that the weakened monsoon can be mainly attributed to systematic Arabian Sea cold SST biases during summer and their impact on the monsoon-moisture relationship. The impact of large cold SST biases on atmospheric moisture content over the Arabian Sea, and also the subsequent reduced latent heat release over India, dominates over any enhancement in the land-sea temperature gradient and results in changes to the mean state. We hypothesize that a cold base state will result in underestimation of the impact of larger projected Arabian Sea SST changes in future climate, suggesting that Arabian Sea biases should be a clear target for model development. 相似文献
5.
Climate change has affected the temperature and rainfall characteristics worldwide. However, the changes are not equal for all regions and have localized intensity and must be quantified locally to manage the natural resources. Orissa is an eastern state in India where agricultural activities mainly depends on the rainfall and thus face problems due to changing patterns of rainfall due to changing climate. In the present study, attempts were made to study temporal variation in monthly, seasonal and annual rainfall over the state during the period from 1871 to 2006. Long term changes in rainfall characteristics were determined by both parametric and non-parametric tests. The analysis revealed a long term insignificant decline trend of annual as well as monsoon rainfall, where as increasing trend in post-monsoon season over the state of Orissa. Rainfall during winter and summer seasons showed an increasing trend. Statistically monsoon rainfall can be considered as very dependable as the coefficient of variation is 14.2%. However, there is decreasing monthly rainfall trend in June, July and September, where as increasing trend in August. This trend is more predominant in last 10?year. Based on departure from mean, rainfall analysis also showed an increased number of dry years compared to wet years after 1950. This changing rainfall trend during monsoon months is major concern for the rain-fed agriculture. More over, this will affect hydro power generation and reservoir operation in the region. 相似文献
6.
The wheatbelt of Western Australia shows a distinct Mediterranean climate with most of the rainfall occurring in the winter months. The main factor limiting plant production in this region is rainfall. Due to clearing of native vegetation, dryland salinity is a major problem in south-west Australia. Since the mid 1970s the region has experienced a significant decrease in winter rainfall. Across nine sites, growing season rainfall (May to October) decreased by an average of 11% and the sum of rainfall in June and July (June + July) decreased by 20%. We used the ASPIM-Nwheat model in combination with historic climate data to study the impact of recent climate change on the hydrology and production of wheat based farming systems by comparing results for before and after 1975. Despite the large decline in rainfall, simulated yields based on the actual weather data did not fall. At the same time, simulated drainage decreased by up to 95% which will significantly reduce the spread of dryland salinity. These results were due to the rainfall changes mainly occurring in June and July, a period when rainfall often exceeds crop demand and large amounts of water are usually lost by deep drainage. The findings will have significant implications for estimates of future climate change impacts in this region with changes in rainfall causing non-proportional impacts on production and hydrological aspects, such as deep drainage and waterlogging, where proportionality is often presumed. 相似文献
7.
The Indian landmass has been divided into homogeneous clusters by applying the cluster analysis to the probability density function of a century-long time series of daily summer monsoon (June through September) rainfall at 357 grids over India, each of approximately 100 km × 100 km. The analysis gives five clusters over Indian landmass; only cluster 5 happened to be the contiguous region and all other clusters are dispersed away which confirms the erratic behavior of daily rainfall over India. The area averaged seasonal rainfall over cluster 5 has a very strong relationship with Indian summer monsoon rainfall; also, the rainfall variability over this region is modulated by the most important mode of climate system, i.e., El Nino Southern Oscillation (ENSO). This cluster could be considered as the representative of the entire Indian landmass to examine monsoon variability. The two-sample Kolmogorov-Smirnov test supports that the cumulative distribution functions of daily rainfall over cluster 5 and India as a whole do not differ significantly. The clustering algorithm is also applied to two time epochs 1901–1975 and 1976–2010 to examine the possible changes in clusters in a recent warming period. The clusters are drastically different in two time periods. They are more dispersed in recent period implying the more erroneous distribution of daily rainfall in recent period.
相似文献8.
The authors investigate possible changes of monsoon rainfall and associated seasonal (June-JulyAugust) anomaly patterns over eastern China in the late 21st century under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 emission scenario as simulated by a high-resolution regional climate model (RegCM3) nested in a general circulation model (FvGCM/CCM3).Two sets of multi-decadal simulations are performed at 20-km grid spacing for present day and future climate conditions.Results show that the RegCM3 reproduces the mean rainfall distribution;however the evolution of the monsoon rain belt from South China to North China is not well simulated.Concerning the rain pattern classifications,RegCM3 overestimates the occurrence of Pattern 1 (excessive rainfall in northern China) and underestimates that of Pattern 2 (increased rainfall over the Huai River basin).Under future climate conditions,RegCM3 projects less occurrence of Pattern 1,more of Pattern 2,and little change of Pattern 3 (rainfall increase along the Yangtze River).These results indicate that there might be increased rainfall over the Huai-Yellow River area and reduced rainfall over North China in the future,while rainfall over the lower reaches of the Yangtze River basin is not modified significantly.Uncertainties exist in the present study are also discussed. 相似文献
9.
Zulfaqar Sa’adi Shamsuddin Shahid Tarmizi Ismail Eun-Sung Chung Xiao-Jun Wang 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):489-500
Climate change may not change the rainfall mean, but the variability and extremes. Therefore, it is required to explore the possible distributional changes of rainfall characteristics over time. The objective of present study is to assess the distributional changes in annual and northeast monsoon rainfall (November-January) and river flow in Sarawak where small changes in rainfall or river flow variability/distribution may have severe implications on ecology and agriculture. A quantile regression-based approach was used to assess the changes of scale and location of empirical probability density function over the period 1980-2014 at 31 observational stations. The results indicate that diverse variation patterns exist at all stations for annual rainfall but mainly increasing quantile trend at the lowers, and higher quantiles for the month of January and December. The significant increase in annual rainfall is found mostly in the north and central-coastal region and monsoon month rainfalls in the interior and north of Sarawak. Trends in river flow data show that changes in rainfall distribution have affected higher quantiles of river flow in monsoon months at some of the basins and therefore more flooding. The study reveals that quantile trend can provide more information of rainfall change which may be useful for climate change mitigation and adaptation planning. 相似文献
10.
Some evidence of climate change in twentieth-century India 总被引：1，自引：0，他引：1
The study of climate changes in India and search for robust evidences are issues of concern specially when it is known that
poor people are very vulnerable to climate changes. Due to the vast size of India and its complex geography, climate in this
part of the globe has large spatial and temporal variations. Important weather events affecting India are floods and droughts,
monsoon depressions and cyclones, heat waves, cold waves, prolonged fog and snowfall. Results of this comprehensive study
based on observed data and model reanalyzed fields indicate that in the last century, the atmospheric surface temperature
in India has enhanced by about 1 and 1.1°C during winter and post-monsoon months respectively. Also decrease in the minimum
temperature during summer monsoon and its increase during post-monsoon months have created a large difference of about 0.8°C
in the seasonal temperature anomalies which may bring about seasonal asymmetry and hence changes in atmospheric circulation.
Opposite phases of increase and decrease in the minimum temperatures in the southern and northern regions of India respectively
have been noticed in the interannual variability. In north India, the minimum temperature shows sharp decrease of its magnitude
between 1955 and 1972 and then sharp increase till date. But in south India, the minimum temperature has a steady increase.
The sea surface temperatures (SST) of Arabian Sea and Bay of Bengal also show increasing trend. Observations indicate occurrence
of more extreme temperature events in the east coast of India in the recent past. During summer monsoon months, there is a
decreasing (increasing) trend in the frequency of depressions (low pressure areas). In the last century the frequency of occurrence
of cyclonic storms shows increasing trend in the month of November. In addition there is increase in the number of severe
cyclonic storms crossing Indian Coast. Analysis of rainfall amount during different seasons indicate decreasing tendency in
the summer monsoon rainfall over Indian landmass and increasing trend in the rainfall during pre-monsoon and post-monsoon
months. 相似文献
11.
Muthusamy Murugan Paddu Krishnappa Shetty Raju Ravi Aavudai Anandhi Arulappan Joseph Rajkumar 《Climatic change》2012,110(3-4):737-753
In this study we analyzed climate and crop yields data from Indian cardamom hills for the period 1978–2007 to investigate whether there were significant changes in weather elements, and if such changes have had significant impact on the production of spices and plantation crops. Spatial and temporal variations in air temperatures (maximum and minimum), rainfall and relative humidity are evident across stations. The mean air temperature increased significantly during the last 30?years; the greatest increase and the largest significant upward trend was observed in the daily temperature. The highest increase in minimum temperature was registered for June (0.37°C/18?years) at the Myladumpara station. December and January showed greater warming across the stations. Rainfall during the main monsoon months (June–September) showed a downward trend. Relative humidity showed increasing and decreasing trends, respectively, at the cardamom and tea growing tracts. The warming trend coupled with frequent wet and dry spells during the summer is likely to have a favorable effect on insect pests and disease causing organisms thereby pesticide consumption can go up both during excess rainfall and drought years. The incidence of many minor pest insects and disease pathogens has increased in the recent years of our study along with warming. Significant and slight increases in the yield of small cardamom (Elettaria cardamomum M.) and coffee (Coffea arabica), respectively, were noticed in the recent years.; however the improvement of yield in tea (Thea sinensis) and black pepper (Piper nigrum L.) has not been seen in our analysis. 相似文献
12.
利用西沙永兴岛、珊瑚岛的日降水量资料、欧洲中期数值预报中心再分析资料,以及热带气旋最佳路径资料,统计分析了西沙地区降水的气候特征,并用REOF和K-means聚类相结合的合成分析方法,对9-10月该地区非台强降水过程的环流形势进行分类。结果表明:(1)西沙地区在12月到次年4月降水少而在5-11月降水多,降水量最多为9和10月;(2)9-10月西沙地区非台强降水过程的环流形势可分为西南季风槽型、季风槽与冷空气结合型和强冷空气型等三类,其中西南季风槽型主要出现在20世纪90年代的9月,强冷空气型主要出现在10月并在90年代以后明显增多,这主要与南海季风槽在90年代偏活跃,冷空气活动在90年代以后偏强有关。 相似文献
13.
Projected changes in South Asian summer monsoon by multi-model global warming experiments 总被引：1，自引：0，他引：1
S. S. Sabade Ashwini Kulkarni R. H. Kripalani 《Theoretical and Applied Climatology》2011,103(3-4):543-565
South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) dataset. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices, middle (2031–2050) and end of the twenty-first century (2081–2100), in the non-mitigated Special Report on Emission Scenarios B1, A1B and A2 .There is large inter-model variability in the simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of the 25 models are able to simulate space–time characteristics of the South Asian monsoon precipitation reasonably well. The response of these selected ten models has been examined for projected changes in seasonal monsoon rainfall. The multi-model ensemble of these ten models projects a significant increase in monsoon precipitation with global warming. The substantial increase in precipitation is observed over western equatorial Indian Ocean and southern parts of India. However, the monsoon circulation weakens significantly under all the three climate change experiments. Possible mechanisms for the projected increase in precipitation and for precipitation–wind paradox have been discussed. The surface temperature over Asian landmass increases in pre-monsoon months due to global warming and heat low over northwest India intensifies. The dipole snow configuration over Eurasian continent strengthens in warmer atmosphere, which is conducive for the enhancement in precipitation over Indian landmass. No notable changes have been projected in the El Niño–Monsoon relationship, which is useful for predicting interannual variations of the monsoon. 相似文献
14.
P. P. Sreekala S. V. Bhaskara Rao M. S. Arunachalam C. Harikiran 《Theoretical and Applied Climatology》2014,118(1-2):107-114
Using the NCEP/NCAR reanalysis wind and temperature data (1948–2011) and India Meteorological Department (IMD) rainfall data, a long-term trend in the tropical easterly jet stream and its effect on Indian summer monsoon rainfall has been explained in the present study. A decreasing trend in zonal wind speed at 100 mb (maximum decrease), 150 mb, and 200 mb (minimum) is observed. The upper-level (100, 150, and 200 mb) zonal wind speed has been correlated with the surface air temperature anomaly index (ATAI) in the month of May, which is taken as the difference in temperature anomaly over land (22.5°N–27.5°N, 80°E–90°E) and Ocean (5°S–0°S, 75°E–85°E). Significant high correlation is observed between May ATAI and tropical easterly jet stream (TEJ) which suggests that the decreasing land–sea temperature contrast could be one major reason behind the decreasing trend in TEJ. The analysis of spatial distribution of rainfall over India shows a decreasing trend in rainfall over Jammu and Kashmir, Arunachal Pradesh, central Indian region, and western coast of India. Increasing trend in rainfall is observed over south peninsular and northeastern part of India. From the spatial correlation analysis of zonal wind with gridded rainfall, it is observed that the correlation of rainfall is found to be high with the TEJ speed over the regions where the decreasing trend in rainfall is observed. Similarly, from the analysis of spatial correlation between rainfall and May ATAI, positive spatial correlation is observed between May ATAI and summer monsoon rainfall over the regions such as south peninsular India where the rainfall trend is positive, and negative correlation is observed over the places such as Jammu and Kashmir where negative rainfall trend is observed. The decreased land–sea temperature contrast in the pre-monsoon month could be one major reason behind the decreased trend in TEJ as well as the observed spatial variation in the summer monsoon rainfall trend. Thus, the study explained the long-term trend in TEJ and its relation with May month temperature over the Indian Ocean and land region and its effect on the trend and spatial distribution of Indian summer monsoon rainfall. 相似文献
15.
ENSO 与中国东部夏季降水的关联 总被引：8，自引：1，他引：7
计算1 月减6 月El Niño 3.4 指数与6—8 月平均200、850 hPa 风场的相关矢量,分析中等或强ElNiño/La Niña 事件后的夏季(6—8 月)中国东部降水异常分布、西太平洋副热带高压异常特征。结果表明,对ENSO 的响应,无论高、底层大气环流还是西太平洋副热带高压,1970 年代中期气候突变后变为更敏感。主要表现在:对衰减的El Niño 的响应,夏季南亚高压偏东,西太平洋副热带高压偏强、偏西、偏南,印度季风、南海季风减弱,黄河下游以南副热带季风增强。黄河中下游及以南形成异常环流辐合带,由El Niño 导致的降水正异常最有可能出现在这一西南-东北的带状区域。对衰减的La Niña 响应大致相反。 相似文献
16.
Xingwen Jiang Yueqing Li Song Yang Guangbi He 《Theoretical and Applied Climatology》2014,117(3-4):565-577
The variability of climate in the lee side of the Tibetan Plateau (TP) often exhibits unique features. In this study, the authors investigate the variations of early autumn rainfall in the lee side of the TP (LSTP). The rainfall amount and number of rain days in LSTP increase from August to September. The center of heavy and torrential rains during September is located in LSTP as well. These unique features are attributed to later withdrawal of the East Asian summer monsoon in the middle and higher troposphere compared to the lower troposphere and stronger South Asian summer monsoon and thermal forcing of the TP. The September rainfall in LSTP experienced strong interdecadal fluctuation, with overall below normal rainfall from mid-1980s to late 2000s, while there was no apparent long-term trend in the August and October rainfall amount. The above normal September rainfall is associated with an anomalous anticyclone over the western North Pacific, a weaker-than-normal ridge around the Lake Baikal, a stronger-than-normal East Asian jet stream, and warmer air over the southeastern TP. The interdecadal decrease in rainfall in September may be caused by the central equatorial Pacific warming, which induces an anomalous cyclone over the western North Pacific. The September anomalous cyclone is stronger and more westward compared to that in August and October, and thus favors the below normal rainfall in LSTP. 相似文献
17.
This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations. 相似文献
18.
长江中下游气候的长期变化及基本态特征 总被引：21，自引：9，他引：21
研究了1885年以来，我国长江中下游四季及年降水量，四季及年平均气温的长期变化，指出长江中下游四个季及年的总降水量（平均气温）都是正的趋势，但有季节的差异，春季是升温同时增雨最显著的季节，还研究了我国长江中下游降水与气温的气候基本态及气候变率的特征及时间演变规律，指出，60年代以后夏季气温变化的异常程度几乎比以前大了一倍，在冬季，近期在暖背景下的冬季气温变率变小的特征表明长江中下游可能出现持续发暖冬特征，还指出，80年代后我国的长江中下游存季降水处于高基本态与高气候变率时段，应注意频繁发生的夏季洪涝灾害，研究还指出，长江中下游夏季降水与印度季风的气候基本态反相关密切，印度季风及东亚夏季风与长江中下游夏季气温变化在各种尺度上有明显的正相关。 相似文献
19.
利用四子王旗气象站1959—2010年月平均气象资料,在较长时间尺度上分析了植物生长季节(5—9月)月平均气温、降水量和日照百分率的变异度,以及降水与温度、降水与日照百分率之间的关系,评估了降水是否是影响温度和日照的主要因素。结果表明:①5月和9月降水量较少,日照百分率大,气温低;月降水量和平均气温的变异度较大,日照百分率的变异度相对较小;而7、8月降水较多、气温较高,气温和降水变异度都较小。②5月和9月温度受降水以外因子影响较大,其与降水的相关性较差;6—8月,温度与降水呈显著的负相关关系,降水量多则气温低,影响效果明显。③除6月外,各月降水量与日照百分率负相关关系显著,线性拟合效果优于气温,日照百分率随降水量的增加明显降低。盛夏,受夏季风影响,该地水汽条件好,云层厚且不易消散,导致光照少,是日照百分率较低的主要原因。 相似文献
20.
O. P. Singh 《Meteorology and Atmospheric Physics》2001,78(1-2):1-9
Summary
El Ni?o/Southern Oscillation (ENSO) is known to cause world-wide weather anomalies. It influences the Indian Monsoon Rainfall
(IMR) also. But due to large spatial and temporal variability of monsoon rains, it becomes difficult to state any single uniform
relationship between the ENSO and IMR that holds good over different subdivisions of India, though the general type of relationship
between all India monsoon rainfall and ENSO is known since long. The selection of the most suitable ENSO index to correlate
with the IMR is another problem. The purpose of the present study is twofold, namely, to examine the relationship between
the ENSO and IMR for entire monsoon season by using an ENSO index which represents the ENSO phenomenon in a comprehensive
way, namely, the Multivariate ENSO Index (MEI) and to establish the relationships between MEI and IMR for every meteorological
subdivision of India for each monsoon month; i.e. June, July, August and September. A comparison of MEI/IMR correlations has
been made with Southern Oscillation Index (SOI)/IMR correlations. The result may find applications in the long range forecasting
of IMR on monthly and subdivisional scales, especially over the high monsoon rainfall variability regions of Northwestern
and the Peninsular India.
Received October 27, 2000 相似文献