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1.
Summary Monthly rainfall data for 135 stations for periods varying from 25 to 125 years are utilised to investigate the rainfall
climatology over the southeast Asian monsoon regime. Monthly rainfall patterns for the regions north of equator show that
maximum rainfall along the west coasts occurs during the summer monsoon period, while the maximum along the east coasts is
observed during the northeast monsoon period. Over the Indonesian region (south of the equator) maximum rainfall is observed
west of 125 °E during northern winter and east of 125 °E during northern summer.
The spatial relationships of the seasonal rainfall (June to September) with the large scale parameters – the Subtropical Ridge
(STR) position over the Indian and the west Pacific regions, the Darwin Pressure Tendency (DPT) and the Northern Hemisphere
Surface Temperature (NHST) – reveal that within the Asian monsoon regime, not only are there any regions which are in-phase
with Indian monsoon rainfall, but there are also regions which are out-of-phase. The spatial patterns of correlation coefficients
with all the parameters are similar, with in-phase relationships occurring over the Indian region, some inland regions of
Thailand, central parts of Brunei and the Indonesian region lying between 120° to 140 °E. However, northwest Philippines and
some southern parts of Kampuchea and Vietnam show an out-of-phase relationship. Even the first Empirical Orthogonal Function
of seasonal rainfall shows similar spatial configuration, suggesting that the spatial correlation patterns depict the most
dominant mode of interannual rainfall variability. The influence of STR and DPT (NHST) penetrates (does not penetrate) upto
the equatorial regions. Possible dynamic causes leading to the observed correlation structure are also discussed.
Received October 10, 1996 Revised February 25, 1997 相似文献
2.
C. V. Singh 《Meteorology and Atmospheric Physics》2004,85(4):227-234
Summary The present study involves the use of Empirical Orthogonal Function (EOF) analysis/Principal Component Analysis (PCA) to compare the dominant rainfall patterns from normal rainfall records over India, coupled with the major modes of the Outgoing Long-wave Radiation (OLR) data for the period (1979–1988) during the monsoon period (June–September). To understand the intraseasonal and interannual variability of the monsoon rainfall, daily and seasonal anomalies have been obtained by using the (EOF) analysis. Importantly, pattern characteristics of seasonal monsoon rainfall covering 68 stations in India are highlighted.The purpose is to ascertain the nature of rainfall distribution over the Indian continent. Based on this, the percentage of variance for both the rainfall and OLR data is examined. OLR has a higher spatial coherence than rainfall. The first principal component of rainfall data shows high positive values, which are concentrated over northeast as well as southeast, whereas for the OLR, the area of large positive values is concentrated over northwest and lower value over south India apart from the Indian ocean. The first five principal components explain 92.20% of the total variance for the rainfall and 99.50% of the total variance for the outgoing long-wave radiation. The relationship between monsoon rainfall and Southern Oscillations has also been examined and for the Southern Oscillations, it is 0.69 for the monsoon season. The El-Niño events mostly occurred during Southern Oscillations, i.e. Walker circulation. It has been found that the average number of low pressure system/low pressure system days play an important role during active (flood) or inactive (drought) monsoon year, but low pressure system days play more important role in comparison to low pressure systems and their ratio are (16:51) and (13:25) respectively. Significantly, the analysis identifies the spatial and temporal pattern characteristics of possible physical significance. 相似文献
3.
Stratospheric zonal wind and temperature in relation to summer monsoon rainfall over India 总被引：1，自引：0，他引：1
Summary The interannual variability of the Indian summer monsoon (June–September) rainfall is examined in relation to the stratospheric
zonal wind and temperature fluctuations at three stations, widely spaced apart. The data analyzed are for Balboa, Ascension
and Singapore, equatorial stations using recent period (1964–1994) data, at each of the 10, 30 and 50 hPa levels. The 10 hPa
zonal wind for Balboa and Ascension during January and the 30 hPa zonal wind for Balboa during April are found to be positively
correlated with the subsequent Indian summer monsoon rainfall, whereas the temperature at 10 hPa for Ascension during May
is negatively correlated with Indian summer monsoon rainfall. The relationship with stratospheric temperatures appears to
be the best, and is found to be stable over the period of analysis.
Stratospheric temperature is also significantly correlated with the summer monsoon rainfall over a large and coherent region,
in the north-west of India. Thus, the 10 hPa temperature for Ascension in May appears to be useful for forecasting summer
monsoon rainfall for not only the whole of India, but also for a smaller region lying to the north-west of India.
Received July 30, 1999 Revised March 17, 2000 相似文献
4.
5.
东亚季风区夏季陆地生态系统碳循环对东亚夏季风的响应 总被引：3，自引：1，他引：2
东亚地区陆地生态系统的时空变率表现出明显的对季风气候的响应特征。使用EOF（经验正交分解）方法分析了AVIM2动态植被陆面模式离线模拟试验模拟的1953～2004年东亚季风区夏季陆地生态系统总初级生产力（GPP）、生态系统净初级生产力（NPP）、净生态系统初级生产力（NEP）、植被呼吸以及土壤呼吸的时空分布特点,探讨了东亚夏季风对陆地生态系统碳循环影响机制。研究发现,在强季风年,江淮地区高温少雨的特点限制了光合作用,造成GPP偏低;而华南地区在强季风年气候温暖湿润,利于植被生长,GPP偏高。季风对于植被呼吸和土壤呼吸影响不明显,使得GPP和植被呼吸之差NPP的变化及NPP和土壤呼吸之差NEP的变化与GPP的变化保持一致。在强季风年江淮流域地区干热的气候条件使得NPP和NEP降低;但是在华南地区温度升高的同时降水增多使得在NPP偏高的基础上NEP也偏高。 相似文献
6.
Nachiketa Acharya Sarat C. Kar U. C. Mohanty Makarand A. Kulkarni S. K. Dash 《Theoretical and Applied Climatology》2011,105(3-4):505-520
The 2009 drought in India was one of the major droughts that the country faced in the last 100?years. This study describes the anomalous features of 2009 summer monsoon and examines real-time seasonal predictions made using six general circulation models (GCMs). El Ni?o conditions evolved in the Pacific Ocean, and sea surface temperatures (SSTs) over the Indian Ocean were warmer than normal during monsoon 2009. The observed circulation patterns indicate a weaker monsoon in that year over India with weaker than normal convection over the Bay of Bengal and Indian landmass. Skill of the GCMs during hindcast period shows that neither these models simulate the observed interannual variability nor their multi-model ensemble (MME) significantly improves the skill of monsoon rainfall predictions. Except for one model used in this study, the real-time predictions with longer lead (2- and 1-month lead) made for the 2009 monsoon season did not provide any indication of a highly anomalous monsoon. However, with less lead time (zero lead), most of the models as well as the MME had provided predictions of below normal rainfall for that monsoon season. This study indicates that the models could not predict the 2009 drought over India due to the use of less warm SST anomalies over the Pacific in the longer lead runs. Hence, it is proposed that the uncertainties in SST predictions (the lower boundary condition) have to be represented in the model predictions of summer monsoon rainfall over India. 相似文献
7.
华南初夏干旱及多雨年份的季风环流特征 总被引：2，自引：0，他引：2
本文根据1961—1980年我国华南5月降水量资料,划分5月的旱或涝。并挑选1963、1966(干旱)1973、1975(涝)四年作为典型年,从天气气候角度分析了初夏季风环流结构与华南5月旱涝关系。华南地区旱5月和涝5月在夏季风来临早迟、持续期长短、强度强弱等方面都有明显差异。华南5月出现旱或涝,不仅在同期全球环流,而且在前期环流,特别是北半球中高纬度几个活动中心也有明显的差异。1月以阿留申低压及冰岛低压,4月以太平洋高压及大西洋高压差别比较明显。华南5月降水量的多少与前期3月低纬气压指标值有较好关系,涝 相似文献
8.
The summer monsoon rainfall totals for 31 meteorological subdivisions of India for the years 1901-1980 are analysed. The analysis reveals that four leading eigenvectors (EVs) are significant and account for 65 % of the total variance.The spatial pattern of the first EV exhibits in phase fluctuations over almost the whole India. The large coefficients of this vector can be considered as representative of the conditions of large-scale flood and drought over the country. The second pattern reveals the fluctuations mostly over the North Indian region (north of 20o latitude) probably in association with the Western Disturbances. The third pattern indicates fluctuations over the North-West and the North-East India in opposite phase and the fourth pattern exhibits the characteristic features of fluctuations associated with ‘break’. The spectral analysis of the coefficients of these EVs revealed quasi-periodicities of 2-5 years.On the basis of examination of the elements of these EVs the country has been divided into seven homogeneous regions. Rainfall indices of these regions and of the four EVs have been examined for seek-ing for association with some oceanic and atmospheric variables. The association is significant for the coefficients of the first EV and for the rainfall indices of central and South India. Among all the variables examined, Darwin pressure tendencies have the highest association and appear to be of special significance in prediction of the monsoon rainfall. 相似文献
9.
Summary In 2002, India had experienced one of the most severe droughts. The severe drought conditions were caused by the unprecedented
deficient rainfall in July 2002, in which only 49% of the normal rainfall was received. One of the major circulation anomalies
observed during July 2002, was the active monsoon trough over Northwest (NW) Pacific and enhanced typhoon activity over this
region. The present study was designed to examine the long-term relationships between Tropical Cyclone (TC) activity over
NW Pacific and monsoon rainfall over India in July.
A statistically significant negative correlation between TC days over NW Pacific and July rainfall over India was observed.
Spatial dependence of the relationship revealed that TCs forming over NW Pacific east of 150° E and moving northwards have
an adverse effect on Indian monsoon rainfall. It was observed that TCs forming over the South China Sea and moving westwards
may have a positive impact on monsoon rainfall over India. Enhanced TC activity over NW Pacific during July 2002 induced weaker
monsoon circulation over the Indian region due to large-scale subsidence. 相似文献
10.
O. S. R. U. Bhanu Kumar S. Ramalingeswara Rao S. Ranganathan S. S. Raju 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(1):21-28
Aim of this diagnostic study is to investigate the impact of intra-seasonal oscillations in terms of number, duration and intensity on rainfall during June through September, 1979–2006. Analysis of wavelet spectra for winds at 850 hPa field for monsoon period reveals number and duration of oscillations, which exercise profound influence on monsoon rainfall. Results indicate that four to six oscillations appear in normal rainfall or flood cases, while two or three oscillations are identified in the years of drought episodes. Though total duration of above oscillations is varied from 25 to 85 days, the duration is short (20 to 35 days) obviously in the years of less number of oscillations and also the number of oscillations are directly related to the monsoon rainfall. The coefficient of correlation between them is 0.56, which is significant at 1% level. To examine the strength of intra-seasonal oscillations in terms of different indices on seasonal rainfall is investigated. The Madden and Julian Oscillation Index shows an inverse relationship with rainfall, where as a direct relationship is noticed between Monsoon Shear Index and rainfall for the study period. Both results are significant at 5% level. To consolidate the above statistical relationships, seasonal circulation changes in the contrasting years of monsoon rainfall have been examined; present study reveals that anomaly negative outgoing longwave radiation is noticed over most of Arabian Sea, Indian sub-continent and the Bay of Bengal during June through September in flood year (1988). But opposite convective activity is true in drought year (2002). Similarly the spatial U-850 hPa field distribution showed much stronger monsoon winds in 1988, while zonal circulation was very weak in 2002. Such differences are observed in the anomaly zonal wind field at 200 hPa also. Over the monsoon region U-850 hPa field is almost a mirror image of U-200 hPa distribution of wind field. Finally annual cycles of U-850 and U-200 hPa fields reflect striking difference at 200 hPa level during the summer monsoon period in flood and drought years. 相似文献
11.
Variability and associated mechanisms of summer rainfall over east China are identified and described using both observations and a general circulation model (GCM) simulation. The observations include two data sets: the 90-station, 1470–1988 annual drought/flood index and the 60-station, 1889–1988 monthly mean precipitation measurements. The GCM data set is a 100-year equilibrium simulation of the present climate. Spectra of the drought/flood index indicate decadal cycles which decrease from north (47 y) to south (21 y). Correlation coefficients show decadal variability in the relationship between index values along the Yangtse River valley and those over northeast and southeast China. Analysis of the measured data confirms this result; for example, the correlation was small during 1889–1918, but significantly negative during 1930–1959. When compared with precipitation measurements, the GCM better simulates monthly means and variances along the Yangtse River valley. Three distinct 30-year periods of interannual variability in summer rainfall are found over this area. During each period, rainfall is negatively correlated with spring surface temperature over a remote region and is identified with variations in a specific component of the east Asian monsoon circulation: (1) when Eurasian temperatures decrease, the thermal contrast across the Mei-Yu front increases and frontal rainfall intensities; (2) lower temperatures over the Sea of Japan/northwest Pacific Ocean are identified with enhanced easterly flow, moisture transport and rainfall; (3) when tropical east Pacific Ocean temperatures decrease, rainfall associated with the low latitude monsoon trough increases. Given that the GCM generates decadal changes in the relationship between the physical mechanisms, the east Asian monsoon and planetary general circulations and east China rainfall, future studies should focus on the predictability of these changes with the use of improved and much longer GCM simulations. 相似文献
12.
华北汛期降水与亚洲季风异常关系的研究 总被引：15，自引：1，他引：15
文中诊断分析了华北汛期降水与亚洲季风区环流异常以及低纬地区热源异常的关系,结果表明:在华北汛期干旱年,亚洲季风偏弱,而在华北汛期降水偏多年,亚洲季风较强,并巳存在两个明显的变化中心,一个位于印度半岛中北部地区,另一个位于菲律宾群岛附近。华北汛期干旱年上述两个地区的热源偏弱,而降水偏多年则偏强。 华北地区干旱年和降水偏多年的前期亚洲季风区热源就已存在明显的不同:华北汛期干旱年前期,亚洲季风区的热源偏弱且位置偏南,表现出季节变化推迟的趋势;华北汛期降水偏多年前期,亚洲季风区的热源偏强且位置偏北,表现出季节变化提早的趋势。 利用IAP L9R15 AGCM气候数值模式,进一步研究了亚洲季风区凝结潜热加热异常对大气环流和华北地区降水的影响,结果表明,印度半岛中北部地区和菲律宾附近地区的凝结潜热加热异常将引起青藏高压和西太平洋副高的异常变化,进而影响到华北地区的降水。 相似文献
13.
亚洲夏季风环流的低频振荡与江淮梅雨 总被引：4，自引：2，他引：4
根据欧洲中心1980～1983年4～9月的200hpa和850hpa格点资料，利用滤波技术和经验正交函数（EOF）分析方法，研究了亚洲地区夏季风环流低频振荡的特征及其对江淮地区梅雨的影响。结果表明：季风环流的低频变化存在三种主要的空间分布型，其中，第一特征向量与江淮地区梅雨期的大尺度环流形势相似，它们的位相转换与季风系统各主要成员的活动密切相关；江淮地区低频气旋性切变线的活动对梅雨期的长短乃至该区的干旱和洪涝有重要的影响。 相似文献
14.
基于经验正交函数和奇异值分解对东亚季风区跨季度夏季降水距平的订正方法 总被引：6，自引：2，他引：4
基于经验正交函数(EOF)和奇异值分解(SVD)方法,作者对IAP9L-AGCM后报的东亚季风区1984～2003年共20年的跨季度夏季降水距平场进行回归订正,并对订正前后降水距平场与实测场间的空间相似性、强度、以及年际变化相关性进行分析.结果表明这两种订正方案均能明显提高夏季降水距平预报场与实测场间的空间相似性和年际变化相关性;而基于EOF的订正方案对强度的订正效果要优于基于SVD的订正方案.此外,在此基础上,我们进一步提出多种订正方法集合的思想. 相似文献
15.
16.
本文通过对比几种不同的东亚夏季风强度指数,发现东亚及附近地区海陆表面温度的变化与东亚夏季风强度有密切联系。在此基础上,根据强、弱夏季风年东亚表面温度差值的逐候数据做EOF分析,结果发现:第一模态可以揭示从春到夏的季节转换,中国东部陆地增温相对较快,而西太平洋及孟加拉湾海温增温较慢,季节转换提前,有利于夏季风偏强;第二模态则反映了春季中高纬度地区增温快、中低纬增温慢的情形,有利于夏季风增强。在5月份两种模态的综合作用显示:陆地较冷、海洋较暖,夏季陆地的快速增温、海洋增温慢,有利于夏季风增强。将上述影响因素引入到改进的东亚夏季风强度指数中,修正后的指数可以反映东亚地区5月到夏季的海陆增温特点以及季节转换的早晚,并更好地描述了季风区中、高纬度的热力差异,合理地解释夏季风强度与西北太平洋副高及低空急流的关系,因此新指数能够更好地反映全国范围内夏季降水的特点。 相似文献
17.
Summary Teleconnections between the seasonal rainfall anomalies of March through May (“long-rains”) over eastern Africa (Uganda,
Kenya and Tanzania) and the lower equatorial stratospheric (30-mb) zonal winds for the 32-year period 1964–1995 are examined
using statistical methods. The analysis is based on the application of the simple correlation method and QBO/rainfall composite
analysis. A statistical study of spatial correlation patterns is made in an effort to understand the climatic associations
between the equatorial stratospheric zonal wind and regional rainfall at the interannual scale. The aim of this analysis is
to establish whether this global signal can be employed as predictor variable in the long-range forecasts. The study is part
of an ongoing investigation, which aims at designing a comprehensive and objective, multi-variate-forecast system of seasonal
rainfall over eastern Africa. The correlation parameters include simultaneous (zero lag), and the non-zero lag correlations.
The statistical significance of the correlation coefficient [r] is tested based on the Monte Carlo t-statistical method, and
the standard correlation tables.
Our results indicate significant positive simultaneous and non-zero lag correlations between rainfall over parts of East Africa
and lower equatorial stratospheric zonal wind during the months of March–May and June–August. Significantly high correlations
are concentrated over the western regions of eastern Africa with peak values of (+ 0.8) observed over these areas. These associations
have been observed to be more prominent during lag than in the simultaneous correlations. Strong month to month lag coherence
is observed after June prior to the onset of the March to May seasonal rainfall and persists for more than 4 months. Correlation
indices for the eight homogeneous rainfall regions over eastern Africa which are derived from our Empirical Orthogonal Function/Cluster
analysis shows a clear annual cycle with significant relationships between QBO and seasonal rainfall occurring during boreal
summer (June–August). The season with the weakest relationship is December–February. It is however, noted that although the
coherence between QBO-Index and rainfall during the long-rains is significantly high, there are some wet/dry years for which
the relationship between the long rains and the lower equatorial zonal wind are not significant (for example in 1966, 1973
and 1983). These years have been associated with strong and prolonged ENSO events. Preliminary comparison of the QBO-Index
and the newly found Indian Ocean dipole mode index (DMI) indicates that the two climate variables may be significantly related.
Of the six high dipole mode events in the Indian Ocean that were observed in 1961, 1967, 1972, 1982, 1994 and 1997, all except
1967 coincided with the easterly phase of the QBO-Index and below normal rainfall over western highlands of eastern Africa.
Contingency analyses indicate 60 percent likelihood for the occurrence of above normal rainfall during the westerly phase
of the QBO and 63 percent likelihood of below normal rainfall during the east phase of the QBO. Our correlation analysis results
indicate that about 36 percent of the variability of the long-rains season over eastern Africa are associated with the QBO-Index.
Our results further show that the tendency of the lower equatorial stratosphe ric zonal wind prior to the season is a good
indicator of the performance of the long rains of eastern Africa. A positive OND minus JJA QBO trend is a good indicator for
the non-occurrence of drought over eastern Africa. Similarly, a negative trend is a good indicator for the non-occurrence
of high rainfall over the region. The identified characteristics and domain of influence of the QBO signal in different regions
of East Africa suggests that this global oscillator may offer useful input to objective multi-variate rainfall prediction
models for eastern Africa.
Received June 4, 1999 Revised November 25, 1999 相似文献
18.
历史时期(1765-1980年)西藏水旱雪灾规律的探讨 总被引：7，自引：0，他引：7
本文利用近千份藏文灾情历史档案和清政府驻西藏办事大臣有泰的日记和联豫的奏稿,以及西藏气象观测记录(1951—1980年),对西藏高原历史时期的水、旱、雪灾作了初步探讨,主要结论如下: 1.近百年来藏南的水旱灾是交替出现的,有三个多水期(1883—1906,1916—1934,1947—1962)和三个干旱期(1907—1915,1935—1946,1963—1980)。干旱期有逐渐加长的趋势。 2.西藏除了有变干的总趋势外,水旱灾还有明显的3.8—2.6年的周期。这与普遍存在的“准两年脉动”周期大体上一致。 3.藏南农区的降水量即使高于常年的一倍也不易形成洪水泛滥和大面积的内涝,但年降水量比常年少100mm以上就可造成严重干旱,农业生产大幅度减产。 4.造成西藏干旱的原因很多也很复杂,除高原气候近期有变干暖的总趋势外,近20年来水浇地和有效灌溉面积的扩大,以及农作物的种植比例不适当,象过份扩大冬小麦种植面积等亦会造成农业干旱。 5.19世纪以来,藏北高原共发生15次严重大雪灾,其中尤以1828—1829年,1927—1928年,1887—1888年三次雪灾最为严重。但近50年,发生的雪灾较过去有所减轻。不过,1967—1968年雪灾也较为严重。 相似文献
19.
C. Svensson 《Theoretical and Applied Climatology》1999,62(3-4):147-161
Summary The design and operation of hydro-structures for flood control and water conservation bring a need for improved characterization
of precipitation patterns. A 73 000 km2 study area in East Central China is situated in the East Asian monsoon region and experiences a strong seasonality in the
rainfall regime. The characteristics of daily rainfall from 230 gauges during 1967–1986 were investigated for four periods
in the summer monsoon season using empirical orthogonal function analysis (EOF) and extended empirical orthogonal function
analysis (EEOF). The EOF analysis showed that for all four periods most of the variance was explained by an elongated spatial
rainfall pattern. The pattern varied in direction, from roughly west-east to southwest-northeast, in the different periods.
The zonally oriented patterns were interpreted as being caused by the stationary Mei-Yu front and the southwest-northeast
patterns interpreted as cold fronts in cyclones that were developing over the study area. The latitude of the rain belt described
by the first mode moved slightly northward with the advance of the East Asian monsoon from the first period, 9–22 June, to
the third period, 23 July–5 August, and then withdrew southward again in accordance with the known seasonal movement of the
Mei-Yu front. The EEOF analysis was used to show the development of the rainfall area over sequences of three days. During
all four periods rainfall intensified on the second day, compared to the first and third days. During the first and last periods,
9–22 June and 5 August–30 September, respectively, there appeared to be little movement in the rainfall. During the second
and third periods, the patterns were interpreted as a cold front in a developing cyclone. The results show the connection
between the temporal variation in rainfall intensity and the temporal succession of spatial patterns over three day periods
and should be used in the construction of design rainfalls for the study area.
Received February 10, 1998 Revised June 23, 1998 相似文献
20.
Summary The Regional Climate Model RegCM3 has been used to examine its suitability in simulating the Indian summer monsoon circulation
features and associated rainfall. The model is integrated at 55 km horizontal resolution over a South Asia domain for the
period April–September of the years 1993 to 1996. The characteristics of wind at 850 hPa and 200 hPa, temperature at 500 hPa,
surface pressure and rainfall simulated by the model over the Indian region are examined for two convective schemes (a Kuo-type
and a mass flux scheme). The monsoon circulation features simulated by RegCM3 are compared with those of the NCEP/NCAR reanalysis
and the simulated rainfall is validated against observations from the Global Precipitation Climatology Centre (GPCC) and the
India Meteorological Department (IMD). Validation of the wind and temperature fields shows that the use of the Grell convection
scheme yields results close to the NCEP/NCAR reanalysis. Similarly, the Indian Summer Monsoon Rainfall (ISMR) simulated by
the model with the Grell convection scheme is close to the corresponding observed values. In order to test the model response
to land surface changes such as the Tibetan snow depth, a sensitivity study has also been conducted. For such sensitivity
experiment, NIMBUS-7 SMMR snow depth data in spring are used as initial conditions in the RegCM3. Preliminary results indicate
that RegCM3 is very much sensitive to Tibetan snow. The model simulated Indian summer monsoon circulation becomes weaker and
the associated rainfall is reduced by about 30% with the introduction of 10 cm of snow over the Tibetan region in the month
of April. 相似文献