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1.
Summary The relationship between the all-India summer monsoon rainfall and surface/upper air (850, 700, 500 and 200 mb levels) temperatures over the Indian region and its spatial and temporal characteristics have been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India and subdivisional summer monsoon rainfall and various seasonal air temperatures at 73 surface observatories and 9 radiosonde stations (1951–1980) have been used in the analysis. The Correlation Coefficients (CCs) between all-India monsoon rainfall and seasonal surface air temperatures with different lags relative to the monsoon season indicate a systematic relationship.The CCs between the monsoon rainfall and surface-air temperature of the preceding MAM (pre-monsoon spring) season are positive over many parts of India and highly significant over central and northwestern regions. The average surface air temperature of six stations i.e., Jodhpur, Ahmedabad, Bombay, Indore, Sagar and Akola in this region (Western Central India, WCI) showed a highly significant CC of 0.60 during the period 1951–1980. This relationship is also found to be consistently significant for the period from 1950 to present, though decreasing in magnitude after 1975. WCI MAM surface air temperature has shown significant CCs with the monsoon rainfall over eleven sub-divisions mainly in northwestern India, i.e., north of 15 °N and west of 80 °E.Upper air temperatures of the MAM season at almost all the stations and all levels considered show positive CCs with the subsequent monsoon rainfall. These correlations are significant at some central and north Indian stations for the lower and middle tropospheric temperatures.The simple regression equation developed for the period 1951–1980 isy = – 183.20 + 8.83x, wherey is the all-India monsoon rainfall in cm andx is the WCI average surface air temperature of MAM season in °C. This equation is significant at 0.1% level. The suitability of this parameter for inclusion in a predictive regression model along with five other global and regional parameters has been discussed. Multiple regression analysis for the long-range prediction of monsoon rainfall, using several combinations of these parameters indicates that the improvement of predictive skill considerably depends upon the selection of the predictors.With 9 Figures  相似文献   

2.
Monsoon precipitation in the AMIP runs   总被引：5，自引：1，他引：4  
 We present an analysis of the seasonal precipitation associated with the African, Indian and the Australian-Indonesian monsoon and the interannual variation of the Indian monsoon simulated by 30 atmospheric general circulation models undertaken as a special diagnostic subproject of the Atmospheric Model Intercomparison Project (AMIP). The seasonal migration of the major rainbelt observed over the African region, is reasonably well simulated by almost all the models. The Asia West Pacific region is more complex because of the presence of warm oceans equatorward of heated continents. Whereas some models simulate the observed seasonal migration of the primary rainbelt, in several others this rainbelt remains over the equatorial oceans in all seasons. Thus, the models fall into two distinct classes on the basis of the seasonal variation of the major rainbelt over the Asia West Pacific sector, the first (class I) are models with a realistic simulation of the seasonal migration and the major rainbelt over the continent in the boreal summer; and the second (class II) are models with a smaller amplitude of seasonal migration than observed. The mean rainfall pattern over the Indian region for July-August (the peak monsoon months) is even more complex because, in addition to the primary rainbelt over the Indian monsoon zone (the monsoon rainbelt) and the secondary one over the equatorial Indian ocean, another zone with significant rainfall occurs over the foothills of Himalayas just north of the monsoon zone. Eleven models simulate the monsoon rainbelt reasonably realistically. Of these, in the simulations of five belonging to class I, the monsoon rainbelt over India in the summer is a manifestation of the seasonal migration of the planetary scale system. However in those belonging to class II it is associated with a more localised system. In several models, the oceanic rainbelt dominates the continental one. On the whole, the skill in simulation of excess/deficit summer monsoon rainfall over the Indian region is found to be much larger for models of class I than II, particularly for the ENSO associated seasons. Thus, the classification based on seasonal mean patterns is found to be useful for interpreting the simulation of interannual variation. The mean rainfall pattern of models of class I is closer to the observed and has a higher pattern correlation coefficient than that of class II. This supports Sperber and Palmer’s (1996) result of the association of better simulation of interannual variability with better simulation of the mean rainfall pattern. The hypothesis, that the skill of simulation of the interannual variation of the all-India monsoon rainfall in association with ENSO depends upon the skill of simulation of the seasonal variation over the Asia West Pacific sector, is supported by a case in which we have two versions of the model where NCEP1 is in class II and NCEP2 is in class I. The simulation of the interannual variation of the local response over the central Pacific as well as the all-India monsoon rainfall are good for NCEP2 and poor for NCEP1. Our results suggest that when the model climatology is reasonably close to observations, to achieve a realistic simulation of the interannual variation of all-India monsoon rainfall associated with ENSO, the focus should be on improvement of the simulation of the seasonal variation over the Asia West Pacific sector rather than further improvement of the simulation of the mean rainfall pattern over the Indian region. Received: 2 June 1997 / Accepted: 8 January 1998  相似文献   

3.
Weakening of Indian summer monsoon rainfall in warming environment   总被引：1，自引：1，他引：0  
Though over a century long period (1871–2010) the Indian summer monsoon rainfall (ISMR) series is stable, it does depict the decreasing tendency during the last three decades of the 20th century. Around mid-1970s, there was a major climate shift over the globe. The average all-India surface air temperature also shows consistent rise after 1975. This unequivocal warming may have some impact on the weakening of ISMR. The reduction in seasonal rainfall is mainly contributed by the deficit rainfall over core monsoon zone which happens to be the major contributor to seasonal rainfall amount. During the period 1976–2004, the deficit (excess) monsoons have become more (less) frequent. The monsoon circulation is observed to be weakened. The mid-tropospheric gradient responsible for the maintenance of monsoon circulation has been observed to be weakened significantly as compared to 1901–1975. The warming over western equatorial Indian Ocean as well as equatorial Pacific is more pronounced after mid-70s and the co-occurrence of positive Indian Ocean Dipole Mode events and El Nino events might have reinforced the large deficit anomalies of Indian summer monsoon rainfall during 1976–2004. All these factors may contribute to the weakening of ISMR.  相似文献   

4.
Summary Relationships of Indian monsoon rainfall with Sea Surface Temperature (SST) and Southern Oscillation Index (SOI) tendencies from DJF to MAM and those between concurrent SST and SOI tendencies are important in view of their large-scale character. Some of these have application in the field of forecasting. Bias on these or any other relationships can possibly arise from a few years of extreme data. Whether the bias results in suppression of an existing relationship, in creating a relationship when none exists, or strenghthening or weakening an existing relationship, over any period, needs to be examined, and if found so, the bias should be removed and bias-free relationships should be discussed and considered for applications. This problem has been examined in respect of the forementioned relationships by following an objective procedure for removing the bias. Removal of the bias has made a notable difference in respect of the strength as well as significance of the relationship over some periods, for some relationships. The main features of the relationships free from such bias are: (a) Indian monsoon rainfall and SST tendency from DJF to MAM before as well as after monsoon are significantly related except within 1904–1940 in respect of relationship with tendency before monsoon, (b) Indian monsoon rainfall and SOI tendency before and after monsoon are significantly related over some non-overlapping component periods only, (c) though the best SST-SOI tendency coupling is for DJF to MAM tendency, no coupling is observed between these tendencies within 1904–1940, (d) linkage of SST tendency from DJF to MAM with the preceding Indian monsoon rainfall appears to be stronger than that with the concurrent SOI tendency and continues even during the period of no coupling between the tendencies, thus bringing out the dominating active role played by the Indian monsoon.With 3 Figures  相似文献   

5.
Urbanisation has burdened cities with many problems associated with growth and the physical environment. Some of the urban locations in India are becoming increasingly vulnerable to natural hazards related to precipitation and flooding. Thus it becomes increasingly important to study the characteristics of these events and their physical explanation. This work studies rainfall trends in Delhi and Mumbai, the two biggest Metropolitan cities of Republic of India, during the period from 1951 to 2004. Precipitation data was studied on basis of months, seasons and years, and the total period divided in the two different time periods of 1951–1980 and 1981–2004 for detailed analysis. Long-term trends in rainfall were determined by Man-Kendall rank statistics and linear regression. Further this study seeks for an explanation for precipitation trends during monsoon period by different global climate phenomena. Principal component analysis and Singular value decomposition were used to find relation between southwest monsoon precipitation and global climatic phenomena using climatic indices. Most of the rainfall at both the stations was found out to be taking place in Southwest monsoon season. The analysis revealed great degree of variability in precipitation at both stations. There is insignificant decrease in long term southwest monsoon rainfall over Delhi and slight significant decreasing trends for long term southwest monsoon rainfall in Mumbai. Decrease in average maximum rainfall in a day was also indicated by statistical analysis for both stations. Southwest monsoon precipitation in Delhi was found directly related to Scandinavian Pattern and East Atlantic/West Russia and inversely related to Pacific Decadal Oscillation, whereas precipitation in Mumbai was found inversely related to Indian ocean dipole, El Ni?o- Southern Oscillation and East Atlantic Pattern.  相似文献   

6.
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   

7.
ＲｅｌａｔｉｏｎｓｈｉｐｓｂｅｔｗｅｅｎＲｅｇｉｏｎａｌＩｎｄｉａｎＳｕｍｍｅｒＭｏｎｓｏｏｎＲａｉｎｆａｌｌａｎｄＥｕｒａｓｉａｎＳｎｏｗＣｏｖｅｒＢ．Ｐａｒｔｈａｓａｒａｔｈｙ（ＩｎｄｉａｎｉｎｓｔｉｔｕｔｅｏｆＴｒｏｐｉｃａｌＭｅｔｅｏｒｏｌｏ...  相似文献   

8.
The day-to-day behavior of Indian summer monsoon rainfall (IMR) is associated with a hierarchy of quasi-periods, namely 3?C7, 10?C20 and the 30?C60?days. These two periods, the 10?C20?days and the 30?C60?days have been related with the active and break cycles of the monsoon rainfall over the Indian sub-continent. The seasonal strength of Indian summer monsoon rainfall may depend on the frequency and duration of spells of break and active periods associated with the fluctuations of the above intra-seasonal oscillations (ISOs). Thus the predictability of the seasonal (June through September) mean Indian monsoon depends on the extent to which the intra-seasonal oscillations could be predicted. The primary objective of this study is to bring out the dynamic circulation features during the pre-monsoon/monsoon season associated with the extreme phases of these oscillations The intense (weak) phase of the 10?C20 (30?C60) days oscillation is associated with anti-cyclonic circulation over the Indian Ocean, easterly flow over the equatorial Pacific Ocean resembling the normal or cold phase (La Nina) of El Nino Southern Oscillation (ENSO) phenomenon, and weakening of the north Pacific Sub-tropical High. On the other hand the weak phase of 10?C20?days mode and the intense phase of 30?C60?days mode shows remarkable opposite flow patterns. The circulation features during pre-monsoon months show that there is a tendency for the flow patterns observed in pre-monsoon months to persist during the monsoon months. Hence some indications of the behavior of these modes during the monsoon season could be foreshadowed from the spring season patterns. The relationship between the intensity of these modes and some of the long-range forecasting parameters used operationally by the India Meteorological Department has also been examined.  相似文献   

9.
Summary Zonally averaged surface air temperatures have been analysed to form time series of surface air temperature anomalies over the tropics (TTA), extratropics (ETA), the poles (PTA) and the whole northern hemisphere (NHTA) for the period 1901–1990. The temporal statistical relationships between these temperature time series and Indian monsoon rainfall over all India (AIR), northwest India (NWR) and peninsular India (PIR) have been examined for the above period.The northern hemispheric January–February (JF) temperature correlates significantly and positively with all the three monsoon rainfall series, the regional peninsular rainfall series (PIR) displaying the best correlation. The Strongest correlation is observed during 1951–1980 for both AIR and NWR but weakened in 1961–1990. For PIR, the highest correlation is observed during 1961–1990, remaining almost stable since 1951–1980. The JF series AIR monsoon relationship showed the highest correlation over the tropics during 1901–1940, over the polar region during 1941–1980 and over the northern hemisphere during 1951–1980. AIR and NWR moreover show a significant negative relationship with simultaneous, succeeding autumn and following year TTA series, while AIR and PIR monsoon rainfall series show significant positive association with the following year PTA series.The results also suggest that cooler January–February NHTA not only lead to a poor monsoon, but a poor monsoon also leads to warmer temperatures over the tropics and cooler temperatures over the polar region in the following year.With 1 Figure  相似文献   

10.
Summary The relationship between the surface air pressure field during the pre-monsoon months and the Indian summer monsoon rainfall is analysed using climate data from 105 stations situated in Eurasia between 0°–60° N and 20°–100° E. Moreover, grid-point data for the whole northern hemisphere are used. Pressure during April over an area around 50° N and 35° E is found to show a significant negative correlation with the subsequent monsoon rainfall. During May the pressure over a large part of the study area south of 40° N shows a significant correlation with its highest value in the heat low region over Pakistan. It is assumed that monitoring of pressure variations over this region may be useful in predicting monsoon rainfall, particularly the rainfall during the first half of the season. Certain limitations of the climate data in this region are also discussed.With 5 Figures  相似文献   

11.
影响华北汛期降水的水汽输送过程   总被引：9，自引：3，他引：6  
利用1951～2005年NCEP再分析资料和中国160站月降水资料,分析了华北汛期水汽输送的时空特征及其与降水的关系,发现不同水汽通道对华北降水的影响区域不同。华北的水汽输送也具有明显的年际变化,华北多雨年和少雨年的水汽通量分布有明显差异。EOF分析表明,在华北汛期多雨年,上述水汽通道有向华北地区的正异常水汽输送。华北汛期水汽主要来自亚洲季风水汽输送,其次是西风带的水汽输送,它们与降水具有相似的年代际变化。1970年代中期以后,季风的水汽输送显著减弱,西风带水汽输送的重要性相对增大,华北降水在1980年代初的突变与季风水汽输送1970年代中期的突变密切相关。  相似文献   

12.
我国夏季雨型的前期异常特征及预报方法的初步研究   总被引：5，自引：2，他引：3  
用１９５１～１９９５年资料研究了我国东部夏季降水各雨型的前期大气环流及我国地面气象要素场的异常特征．结果表明,在冬季１月份北太平洋地区、秋季中国南海地区的海平面气压场有预报我国夏季雨型的信号．夏季不同雨型的前期冬季特征不同,我国的降水、气温场也有差异,４月份我国大范围的温度异常也是值得注意的预测信号．这些特征可以作为我国夏季雨型的预报信号及预报工具．  相似文献   

13.
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   

14.
Summary Monthly mean surface fields of different meteorological parameters and evaporation are studied for the 1979 (poor monsoon) and 1983 (good monsoon) monsoon seasons over the Arabian Sea, in order to understand the role of evaporation on the Indian monsoon rainfall. It is noticed that in general, the sea surface temperatures are higher in 1983 throughout the monsoon season than in 1979 in the Arabian Sea excepting western region. The mean rates of evaporation on a seasonal scale are found to be equal in both years (3.66×1010 and 3.59×1010 tons/day in 1979 and 1983, respectively). No coherence is observed between the evaporation and the west coast rainfall within a season. It is also noted that the pressure distribution over the Arabian Sea is even important to advect the moisture towards the west coast of India, through winds.With 10 Figures  相似文献   

15.
通过对１９５１ ～１９９４ 年我国夏季１６０ 个站降水资料的分析,指出Ｅｌ Ｎｉ珘ｎｏ 盛期在我国华北地区具有显著的降水负异常。为了解释这种降水负异常产生的原因,利用ＮＣＥＰ／ＮＣＡＲ１９４９ ～１９９６ 年再分析资料,分析了夏季印度季风区的水汽输送在东亚季风区水汽输送中的作用。结果表明,印度季风区的水汽输送与我国华北地区的水汽输送有显著的正相关。Ｅｌ Ｎｉ珘ｎｏ期间往往对应着弱印度季风,即Ｅｌ Ｎｉ珘ｎｏ 盛期与弱印度夏季风相联系的弱水汽输送造成了我国华北地区水汽输送的减弱,使得华北地区上空大气中可降水量产生显著负异常,由此导致了负的降水异常。  相似文献   

16.
The year 2019 experienced an excess monsoon season over the Indian region, with the seasonal rainfall being 110 % of the long period average (LPA). Several zones across the country suffered multiple extreme rainfall events and flood situations resulting in a massive loss of life and property. The first half of 2019 experienced a moderate El Niño Modoki event that lasted till mid-summer. Another important feature of 2019 was the strongest recorded positive Indian Ocean Dipole (IOD) that lasted approximately seven months from May to November. This study has examined the reasons for the intra-seasonal variability of rainfall over India during the 2019 monsoon using available remote sensing and reanalysis data. Our analysis has shown that the presence of El Niño and the formation of a very severe cyclonic storm (VSCS) in the Arabian Sea were unfavorable for the monsoon onset and its northward advancement during June. However, the Walker circulation associated with El Niño helped strengthen the IOD developed early in the Indian Ocean, much before the monsoon onset. The anomalously strong IOD strengthened the monsoon circulation during July-September and resulted in excess rainfall over India.  相似文献   

17.
Summary The main objective of this study was to develop empirical models with different seasonal lead time periods for the long range prediction of seasonal (June to September) Indian summer monsoon rainfall (ISMR). For this purpose, 13 predictors having significant and stable relationships with ISMR were derived by the correlation analysis of global grid point seasonal Sea-Surface Temperature (SST) anomalies and the tendency in the SST anomalies. The time lags of the seasonal SST anomalies were varied from 1 season to 4 years behind the reference monsoon season. The basic SST data set used was the monthly NOAA Extended Reconstructed Global SST (ERSST) data at 2° × 2° spatial grid for the period 1951–2003. The time lags of the 13 predictors derived from various areas of all three tropical ocean basins (Indian, Pacific and Atlantic Oceans) varied from 1 season to 3 years. Based on these inter-correlated predictors, 3 predictor sub sets A, B and C were formed with prediction lead time periods of 0, 1 and 2 seasons, respectively, from the beginning of the monsoon season. The selected principal components (PCs) of these predictor sets were used as the input parameters for the models A, B and C, respectively. The model development period was 1955–1984. The correct model size was derived using all-possible regressions procedure and Mallow’s “Cp” statistics. Various model statistics computed for the independent period (1985–2003) showed that model B had the best prediction skill among the three models. The root mean square error (RMSE) of model B during the independent test period (6.03% of Long Period Average (LPA)) was much less than that during the development period (7.49% of LPA). The performance of model B was reasonably good during both ENSO and non-ENSO years particularly when the magnitudes of actual ISMR were large. In general, the predicted ISMR during years following the El Ni?o (La Ni?a) years were above (below) LPA as were the actual ISMR. By including an NAO related predictor (WEPR) derived from the surface pressure anomalies over West Europe as an additional input parameter into model B, the skill of the predictions were found to be substantially improved (RMSE of 4.86% of LPA).  相似文献   

18.
利用华北地区20站夏季降水资料和NCEP/NCAR再分析资料,采用趋势分析、合成分析等方法,对华北夏季降水减少与北半球大气环流异常进行对比分析。结果表明,华北夏季降水量1951—2008年呈显著减少趋势,平均每10 a减少13.4 mm,1965年发生了气候突变,之后降水量减少更加明显。北半球大气环流在1965年前后有明显不同：1）1951—1965年夏季500 hPa高度场欧洲大槽、贝加尔湖槽较深,乌拉尔山高压脊较强,经向环流表现突出;而1966—2008年夏季欧洲大槽、贝加尔湖槽较浅,乌拉尔山高压脊较弱,纬向环流表现突出。2）1951—1965年夏季500 hPa蒙古冷槽位置偏北偏西,冷空气活动经常影响华北地区;而1966—2008年夏季蒙古冷槽位置东移南压到河套附近,冷空气经常影响华北以南以东地区。3）1951—1965年夏季海平面气压场蒙古低压异常强大,而1966—2008年蒙古低压明显减弱。4）1951—1965年夏季850 hPa东亚夏季风一直伸展到华北、东北地区,蒙古地区存在明显的气旋性环流,在河套附近产生风向辐合;而1966—2008年东亚夏季风在到达30°N附近风速显著减小,很少越过长江到达华北地区,在长江流域形成了风速辐合,同时蒙古地区的气旋性环流消失,河套附近的风向辐合变的很弱。1951—1965年华北多雨是由于东亚夏季风水汽的有效输送和河套附近的风向辐合造成的,而1966—2008年长江流域多雨是由于东亚夏季风在这里产生了风速辐合造成的。华北夏季降水减少与北半球大气环流异常有很好的联系。  相似文献   

19.
中国与印度夏季风降水的比较研究   总被引：37，自引：0，他引：37  
本文用1951—1980年中国和印度的降水资料研究了两个地区在西南季风时期(6—9月)总雨量变化的关系。发现印度的雨量变化与中国各地雨量的相关关系有正、有负,最明显的是印度中西部与我国华北地区有较高的正相关。进一步对两个地区降水存在遥相关的原因进行了分析,发现南亚次大陆低压是联系两个季风区雨量变化的重要环节。中国季风雨量与印度季风雨量的相关趋势,主要决定于中国各地雨量与东亚夏季风强度的关系。   相似文献   

20.
The characteristics of moisture transport over the Asian summer monsoon region and its relationship with summer precipitation in China are examined by a variety of statistical methods using the NCEP/NC AR reanalysis data for 1948-2005.The results show that:1) The zonal-mean moisture transport in the Asian monsoon region is unique because of monsoon activities.The Asian summer monsoon region is a dominant moisture sink during summer.Both the Indian and East Asian monsoon areas have their convergence cente...  相似文献   

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