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1.
D. R. Pattanaik 《Pure and Applied Geophysics》2007,164(8-9):1527-1545
The present study is an attempt to examine the variability of convective activity over the north Indian Ocean (Bay of Bengal
and Arabian Sea) on interannual and longer time scale and its association with the rainfall activity over the four different
homogeneous regions of India (viz., northeast India, northwest India, central India and south peninsular India) during the
monsoon season from June to September (JJAS) for the 26 year period (1979 to 2004). The monthly mean Outgoing Long-wave Radiation
(OLR) data obtained from National Oceanic and Atmospheric Administration (NOAA) polar orbiting spacecraft are used in this
study and the 26-year period has been divided into two periods of 13 years each with period-i from 1979 to 1991 and period
-ii from 1992 to 2004. It is ascertained that the convective activity increases over the Arabian Sea and the Bay of Bengal
in the recent period (period -ii; 1992 to 2004) compared to that of the former period (period -i; 1979 to 1991) during JJAS
and is associated with a significantly increasing trend (at 95% level) of convective activity over the north Bay of Bengal
(NBAY). On a monthly scale, July and August also show increase in convective activity over the Arabian Sea and the Bay of
Bengal during the recent period and this is associated with slight changes in the monsoon activity cycle over India. The increase
in convective activity particularly over the Arabian Sea during the recent period of June is basically associated with about
three days early onset of the monsoon over Delhi and relatively faster progress of the monsoon northward from the southern
tip of India. Over the homogeneous regions of India the correlation coefficient (CC) of OLR anomalies over the south Arabian
Sea (SARA) is highly significant with the rainfall over central India, south peninsular India and northwest India, and for
the north Arabian Sea (NARA), it is significant with northwest India rainfall and south peninsular rainfall. Similarly, the
OLR anomalies over the south Bay of Bengal (SBAY) have significant CC with northwest India and south peninsular rainfall,
whereas the most active convective region of the NBAY is not significantly correlated with rainfall over India. It is also
found that the region over northeastern parts of India and its surroundings has a negative correlation with the OLR anomalies
over the NARA and is associated with an anomalous sinking (rising) motion over the northeastern parts of India during the
years of increase (decrease) of convective activity over the NARA. 相似文献
2.
3.
Two different equatorial quasi-biennial oscillation (QBO) indices, two reanalyses and radiosonde observations are used to analyze the Arctic stratospheric temperature and height. This analysis was used to assess the uncertainties in the connection of solar forcing, QBO and the Arctic variability. The results show that (1) the frequency of the westerly/easterly phases of the QBO over the stratospheric equator has a significant multiple peak seasonal variation. The primary seasonal peaks occur in February, March and April for the westerly phase of the QBO and the easterly phase peaks in June, July and August. (2) The correlation of stratospheric Arctic temperature and height with the solar radio flux shows statistical significance in February or July/August even if there is no stratified phase of QBO (easterly and westerly phases) involved. However, when the correlation was computed according to the stratified phase of QBO, the solar signals in both temperature and height fields are remarkably amplified in February and November under the westerly phase, but the signal in the height field is most significant only in August under the easterly phase. (3) The impact of the QBO and solar forcing on the stratospheric temperature and heights in the Arctic varies depending on the season. The impacts are also sensitive to the specific height of the QBO-defined level that is used, the specific period of the analysis and the dataset used. 相似文献
4.
O. S. R. U. BHANU KUMAR 《水文科学杂志》2013,58(5):515-525
Abstract This paper presents the relationship between Indian summer monsoon total rainfall and two parameters from Eurasian snow cover, one being the winter snow cover extent and the other the area of spring snowmelt. Satellite-derived Eurasian snow cover extent and Indian monsoon rainfall data were obtained from the NOAA/NESDIS and the India Meteorological Department (IMD) for the period 1966–1985. Seasonal cyclic variations of snow cover showed a higher swing in both the winter and the spring seasons of the cycle as compared to the remaining seasons of the year in the lower region of the cycle. The established inverse relation between winter snow cover and monsoon rainfall during June to September is further extended. Winter snow cover is very strongly correlated with spring snowmelt over Eurasia. Spring snowmelt area is obtained by subtracting the May snow cover extent from that of the previous February. The variations of spring snowmelt were also compared with Indian total monsoon rainfall. The detected correlation is stronger between snowmelt and monsoon rainfall than between the winter snow cover and the monsoon rainfall. There is also a significant multiple correlation among winter snow cover, spring snowmelt and monsoon rainfall. Lastly, a significant multiple correlation suggested a multiple regression equation which might improve the climatic prediction of monsoon rainfall over India. 相似文献
5.
The monsoon seasons of 2010 and 2011, with almost identical seasonal total rainfall over India from June to September, are associated with slightly different patterns of intraseasonal rainfall fluctuations. Similarly, the year 2012, with relatively less rainfall compared to 2010 and 2011, also witnessed different intraseasonal rainfall fluctuations, leading to drought-like situations over some parts of the country. The present article discusses the forecasting aspect of monsoon activity over India during these 3 years on an extended range time scale (up to 3 weeks) by using the multimodel ensemble (MME), based on operational coupled model outputs from the ECMWF monthly forecasting system and the NCEP’s Climate Forecast System (CFS). The average correlation coefficient (CC) of weekly observed all-India rainfall (AIR) and the corresponding MME forecast AIR is found to be significant, above the 98 % level up to 2 weeks (up to 18 days) with a slight positive CC for the week 3 (days 19–25) forecast. However, like the variation of observed intraseasonal rainfall fluctuations during 2010, 2011 and 2012 monsoon seasons, the MME forecast skills of weekly AIR are also found to be different from one another, with the 2012 monsoon season indicating significant CC (above 99 % level) up to week 2 (12–18 days), and also a comparatively higher CC (0.45) during the week 3 forecast (days 19–25). The average CC between observed and forecasted weekly AIR rainfall over four homogeneous regions of India is found to be the lowest over the southern peninsula of India (SPI), and northeast India (NEI) is found to be significant only for the week 1 (days 5–11) forecast. However, the CC is found to be significant over northwest India (NWI) and central India (CEI), at least above the 90 % level up to 18 days, with NWI having slightly better skill compared to the CEI. For the individual monsoon seasons of 2010, 2011 and 2012, there is some variation in CC and other skill scores over the four homogeneous regions. Thus the slight variations in the characteristics of intraseasonal monsoon rainfall over India is associated with variations in predictive skill of the coupled models and the MME-based predictions of intraseasonal monsoon fluctuations for 2–3 weeks, providing encouraging results. The MME forecast in 2010 is also able to provide useful guidance, well in advance, about an active September associated with a delayed withdrawal of the monsoon and also the heavy rainfall over north Pakistan. 相似文献
6.
基于1961-2016年国家气象信息中心整编的气象台站逐日降水以及NCAR/NCEP再分析等资料,对我国典型夏季风影响过渡区夏季降水的异常时空特征及成因进行分析,结果表明：典型夏季风影响过渡区夏季降水EOF展开第一模态呈全区一致性特征,而且该模态时间系数没有明显的长期变化趋势,第二模态呈西北和东南反位相变化特征.相关分析表明夏季中纬度西风带是影响典型夏季风影响过渡区夏季降水异常的最主要因子,高原夏季风为次要因子,东亚夏季风的影响较弱,而且东亚夏季风主要通过其子系统——西太平洋副热带高压的东西摆动来影响.此外在夏季中纬度西风偏弱年,高空急流位置偏南,急流轴在典型夏季风影响过渡区向东南方向发生了"倾斜",对应500 hPa呈异常的西北气流控制,同时由于高空急流在过渡区减弱,使得高层发生异常的气流辐合,低层辐散,通过高低层环流之间的质量和动量调整,垂直场表现为异常下沉运动,低层的辐散也减弱了西南暖湿气流的北上,水汽来源少,最终使得典型夏季风影响过渡区夏季降水偏少,反之亦然.这是夏季中纬度西风带影响典型夏季风影响过渡区夏季降水的可能机理. 相似文献
7.
Identification of best predictors for forecasting seasonal rainfall and runoff in Australia 总被引：2，自引：0，他引：2
The first step towards developing a reliable seasonal runoff forecast is identifying the key predictors that drive rainfall and runoff. This paper investigates the lag relationships between rainfall across Australia and runoff across southeast Australia versus 12 atmospheric‐oceanic predictors, and how the relationships change over time. The analysis of rainfall data indicates that the relationship is greatest in spring and summer in northeast Australia and in spring in southeast Australia. The best predictors for spring rainfall in eastern Australia are NINO4 [sea surface temperature (SST) in western Pacific] and thermocline (20 °C isotherm of the Pacific) and those for summer rainfall in northeast Australia are NINO4 and Southern Oscillation Index (SOI) (pressure difference between Tahiti and Darwin). The relationship in northern Australia is greatest in spring and autumn with NINO4 being the best predictor. In western Australia, the relationship is significant in summer, where SST2 (SST over the Indian Ocean) and II (SST over the Indonesian region) is the best predictor in the southwest and northwest, respectively. The analysis of runoff across southeast Australia indicates that the runoff predictability in the southern parts is greatest in winter and spring, with antecedent runoff being the best predictor. The relationship between spring runoff and NINO4, thermocline and SOI is also relatively high and can be used together with antecedent runoff to forecast spring runoff. In the northern parts of southeast Australia, the atmospheric‐oceanic variables are better predictors of runoff than antecedent runoff, and have significant correlation with winter, spring and summer runoff. For longer lead times, the runoff serial correlation is reduced, especially over the northern parts, and the atmospheric‐oceanic variables are likely to be better predictors for forecasting runoff. The correlations between runoff versus the predictors vary with time, and this has implications for the development of forecast relationship that assumes stationarity in the historical data. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
Dynamical mechanism of the stratospheric quasibiennial oscillation impact on the South China Sea Summer Monsoon 总被引：1，自引：0，他引：1
The National Center for the Atmospheric Research (NCAR) middle atmospheric model is used to study the effects of the quasi-biennial oscillation in the stratosphere (QBO) on the tropopause and uppe troposphere, and the relationship between the QBO and South China Sea Summer Monsoon (SCSSM is explored through NCEP (the National Centers for Environmental Prediction)/NCAR, ECMWF (Euro pean Centre for Medium-Range Weather Forecasts) monthly mean wind data and in situ sounding data The simulations show that the QBO-induced residual circulations propagate downwards, and affect the tropopause and upper troposphere during the periods of mid-late QBO phase and phase transition Meanwhile, diagnostic analyses indicate that anomalous circulation similar to SCSSM circulation is generated to strengthen the SCSSM during the easterly phase and anomalous Hadley-like circulation weakens the SCSSM during the westerly. Though the QBO has effects on the SCSSM by meridiona circulation, it is not a sole mechanism on the SCSSM TBO mode. 相似文献
9.
M. Janga Reddy S. Adarsh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(4):1063-1085
Time–frequency characterization is useful in understanding the nonlinear and non-stationary signals of the hydro-climatic time series. The traditional Fourier transform, and wavelet transform approaches have certain limitations in analyzing non-linear and non-stationary hydro-climatic series. This paper presents an effective approach based on the Hilbert–Huang transform to investigate time–frequency characteristics, and the changing patterns of sub-divisional rainfall series in India, and explored the possible association of monsoon seasonal rainfall with different global climate oscillations. The proposed approach integrates the complete ensemble empirical mode decomposition with adaptive noise algorithm and normalized Hilbert transform method for analyzing the spectral characteristics of two principal seasonal rainfall series over four meteorological subdivisions namely Assam-Meghalaya, Kerala, Orissa and Telangana subdivisions in India. The Hilbert spectral analysis revealed the dynamic nature of dominant time scales for two principal seasonal rainfall time series. From the trend analysis of instantaneous amplitudes of multiscale components called intrinsic mode functions (IMFs), it is found that both intra and inter decadal modes are responsible for the changes in seasonal rainfall series of different subdivisions and significant changes are noticed in the amplitudes of inter decadal modes of two seasonal rainfalls in the four subdivisions since 1970s. Further, the study investigated the links between monsoon rainfall with the global climate oscillations such as Quasi Bienniel Oscillation (QBO), El Nino Southern Oscillation (ENSO), Sunspot Number (SN), Atlantic Multidecadal Oscillation (AMO) etc. The study noticed that the multiscale components of rainfall series IMF1, IMF2, IMF3, IMF4 and IMF5 have similar periodic structure of QBO, ENSO, SN, tidal forcing and AMO respectively. As per the seasonal rainfall patterns is concerned, the results of the study indicated that for Assam-Meghalaya subdivision, there is a likelihood of extreme rare events at ~0.2 cycles per year, and both monsoon and pre-monsoon rainfall series have decreasing trends; for Kerala subdivision, extreme events can be expected during monsoon season with shorter periodicity (~2.5 years), and monsoon rainfall has statistically significant decreasing trend and post-monsoon rainfall has a statistically significant increasing trend; and for Orissa subdivision, there are chances of extremes rainfall events in monsoon season and a relatively stable rainfall pattern during post-monsoon period, but both monsoon and post-monsoon rainfall series showed an overall decreasing trend; for Telangana subdivision, there is a likelihood of extreme events during monsoon season with a periodicity of ~4 years, but both monsoon and post-monsoon rainfall series showed increasing trends. The results of correlation analysis of IMF components of monsoon rainfall and five climate indices indicated that the association is expressed well only for low frequency modes with similar evolution of trend components. 相似文献
10.
The 2010 boreal summer marked a worldwide abnormal climate. An unprecedented heat wave struck East Asia in July and August 2010. In addition to this, the tropical Indian Ocean was abnormally warm during the summer of 2010. Several heavy rainfall events and associated floods were also reported in the Indian monsoon region. During the season, the monsoon trough (an east–west elongated area of low pressure) was mostly located south of its normal position and monsoon low pressure systems moved south of their normal tracks. This resulted in an uneven spatial distribution with above-normal rainfall over peninsular and Northwest India, and deficient rainfall over central and northeastern parts of India, thus prediction (and simulation) of such anomalous climatic summer season is important. In this context, evolution of vertical moist thermodynamic structure associated with Indian summer monsoon 2010 is studied using regional climate model, reanalysis and satellite observations. This synergised approach is the first of its kind to the best of our knowledge. The model-simulated fields (pressure, temperature, winds and precipitation) are comparable with the respective in situ and reanalysis fields, both in intensity and geographical distribution. The correlation coefficient between model and observed precipitation is 0.5 and the root-mean-square error (RMSE) is 4.8 mm day?1. Inter-comparison of model-simulated fields with satellite observations reveals that the midtropospheric temperature [Water vapour mixing ratio (WVMR)] has RMSE of 0.5 K (1.6 g kg?1), whereas the surface temperature (WVMR) has RMSE of 3.4 K (2.2 g kg?1). Similarly, temporal evolution of vertical structure of temperature with rainfall over central Indian region reveals that the baroclinic nature of monsoon is simulated by the model. The midtropospheric warming associated with rainfall is captured by the model, whereas the model failed to capture the surface response to high and low rainfall events. The model has strong water vapour loading in the whole troposphere, but weaker coherent response with rainfall compared to observations. Thus, strong water vapour loading and overestimation of rainfall are reported in the model. This study put forward that the discrepancy in the model-simulated structure may be reduced by assimilation of satellite observations. 相似文献
11.
Archana Nair Nachiketa Acharya Ankita Singh U. C. Mohanty T. C. Panda 《Pure and Applied Geophysics》2013,170(11):1945-1967
In this study the predictability of northeast monsoon (Oct–Nov–Dec) rainfall over peninsular India by eight general circulation model (GCM) outputs was analyzed. These GCM outputs (forecasts for the whole season issued in September) were compared with high-resolution observed gridded rainfall data obtained from the India Meteorological Department for the period 1982–2010. Rainfall, interannual variability (IAV), correlation coefficients, and index of agreement were examined for the outputs of eight GCMs and compared with observation. It was found that the models are able to reproduce rainfall and IAV to different extents. The predictive power of GCMs was also judged by determining the signal-to-noise ratio and the external error variance; it was noted that the predictive power of the models was usually very low. To examine dominant modes of interannual variability, empirical orthogonal function (EOF) analysis was also conducted. EOF analysis of the models revealed they were capable of representing the observed precipitation variability to some extent. The teleconnection between the sea surface temperature (SST) and northeast monsoon rainfall was also investigated and results suggest that during OND the SST over the equatorial Indian Ocean, the Bay of Bengal, the central Pacific Ocean (over Nino3 region), and the north and south Atlantic Ocean enhances northeast monsoon rainfall. This observed phenomenon is only predicted by the CCM3v6 model. 相似文献
12.
—The study presents the results of the statistical relationship between seasonal northeast monsoon rainfall over Tamil Nadu state of India (TNR) and southeast India (SER) and mid-latitude circulation indices viz., zonal index (ZON) meridional index (MER) and the ratio of meridional to zonal index (M/Z) between the geographical area 35°N to 70°N at 500 hPa level over three sectors and hemisphere, based on 19 years (1971–1989) of data. The results indicate that northeast monsoon rainfall over India shows a strong antecedent relationship with the strength of ZON over all the sectors and hemisphere. The best association is observed during antecedent March over sector I (45°W–90°E) where direct and strong correlation coefficients of 0.69 and 0.64 are obtained with TNR and SER, respectively. Antecedent MAM (spring) season over sector I also shows a significant positive correlation with TNR/SER. Thus, the mid-latitude zonal circulation index may have possible use for the long-range forecasting of northeast monsoon rainfall over India. 相似文献
13.
Teleconnection between the Indian summer monsoon onset and the Meiyu over the Yangtze River Valley 总被引：11，自引：0，他引：11
Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data, the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the telecon- nection mode which is from the northwest of India via the Tibetan Plateau to northern China. The for- mer mode is defined as the "south" teleconnection of the Asian summer monsoon, forming in the pe- riod of ISM onset; while the latter mode is called the "north" teleconnection, mainly occurring in the Asian monsoon culminant period. During the process of the "south" teleconnection’s formation, the Asian monsoon circulation has experienced a series of important changes: ISM onset, the northward movement of the south Asia high (SAH), the onset vortex occurrence, the eastward extension of the stronger tropical westerly belt, and the northeastward jump of the western Pacific subtropical high (WPSH), etc. Consequently, since ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH after about two weeks, while in the mid- and lower troposphere, a strong wind belt forms from the Arabian Sea via the southern India, BOB and the South China Sea (SCS), then along the western flank of WPSH, to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams, the upper westerly jet stream and the low level jet have been coupled ver- tically over east Asia, while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet stream and the low level jet, i.e. right of the entrance of the upper jet stream and left of the low level jet. Such a structure of the vertical circulation can trigger the Meiyu onset over the Yangtze River Valley. 相似文献
14.
Porathur V. Joseph 《Surveys in Geophysics》2014,35(3):723-738
Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active–break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30–60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active–break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and the monsoon LLJ which has been related to the observed rapid decreasing trend in the seasonal number of monsoon depressions. 相似文献
15.
本文应用欧洲中期预报中心（ECMWF,European Centre for Medium\|Range Weather Forecasts—ERA\|40）资料和美国国家环境预测中心和国家大气研究中心(NCEP/NCAR, National Centers for Environmental Prediction/National Center for Atmospheric Research)资料,研究了青藏高原雪深变化对南海夏季风爆发的影响和ENSO对青藏高原降雪的影响.结果表明：（1）ECMWF的雪深资料是可信的,可以用来研究青藏高原雪深变化对南海夏季风爆发的影响;（2）青藏高原的积雪异常影响到500 hPa以上的温度异常和印度洋与大陆间的气温对比,一方面使上层的南亚高压移动速度发生变化,另一方面也影响到低层大气的运动和东西向风异常,在青藏高原少雪年,东印度洋产生西风异常和一个气旋对,而在青藏高原多雪年,东印度洋产生东风异常和一个反气旋对;（3）ENSO与青藏高原春季积雪关系密切.东太平洋SST正异常时,东印度洋和南海气压偏高,从而导致该区海陆经向压强梯度增强和西风异常.另外,此时青藏高原北部气压偏高,北风偏强,副热带锋面增强,同时,印度洋的SST偏高,为青藏高原降雪提供了水汽保障,这些都有利于青藏高原的降雪. 相似文献
16.
R. P. Kane 《Annales Geophysicae》1995,13(2):211-216
Stratospheric temperatures show distinct trends, not necessarily monotonically upward or downward. At the North Pole, trends were large only during winter and spring and were different for different months; downward for November, December, mixed for January and upward for February, March and April. For the 10°-90°N belt, the trends were variable, viz., downward during 1971-1975, upward during 1975–1978 and downward again from 1978 onwards up to date, opposite to the upward trend of ground temperature in the Northern hemisphere in recent years. Twelve-monthly running averages revealed strong QBO (quasi-biennial oscillation). For the North Pole, the QBO showed colder (lower) temperatures during 50-mb wind QBO westerly phase maxima. For the 10°-90°N belt, the QBO was similar for 30 mb and 50 mb but the QBO phases did not match well with 50-mb wind QBO phases. 相似文献
17.
Huawu Wu Xiao‐Yan Li Jianming Zhang Jing Li Jinzhao Liu Lihui Tian Congsheng Fu 《水文研究》2019,33(23):2997-3009
Stable water isotopes (δ18O and δ2H) are an important source signature for understanding the hydrological cycle and altered climate regimes. However, the mechanisms underlying atmospheric water vapour isotopes in the northeast Qinghai‐Tibetan Plateau of central Asia remain poorly understood. This study initially investigated water vapour isotopic composition and its controls during the premonsoon and monsoon seasons. Isotopic compositions of water vapour and precipitation exhibited high variability across seasons, with the most negative average δ18O values of precipitation and the most positive δ18O values of water vapour found during the premonsoon periods. Temperature effect was significant during the premonsoon period but not the monsoon period. Both a higher slope and intercept of the local meteoric water line were found during the monsoon period as compared with in the premonsoon period, suggesting that raindrops have been experienced a greater kinetic fractionation process such as reevaporation below the cloud during the premonsoon periods. The δ2H and δ18O signatures in atmospheric water vapour tended to be depleted with the occurrence of precipitation events especially during the monsoon period and probably as a result of rainout processes. The monthly average contribution of evaporation from the lake to local precipitation was 35.2%. High d‐excess values of water vapour were influenced by the high proportion of local moisture mixing, as indicated by the gradually increasing relative humidity along westerly and Asian monsoon trajectories. The daily observation (observed ε) showed deviations from the equilibrium fractionation factors (calculated ε), implying that raindrops experienced substantial evaporative enrichment during their descent. The average fraction of raindrops reevaporation was estimated to be 16.4± 12.9%. These findings provide useful insights for understanding the interaction between water vapour and precipitation, moisture sources, and help in reconstructing the paleoclimate in the alpine regions. 相似文献
18.
Arabian Peninsula-North Pacific Oscillation and its association with the Asian summer monsoon 总被引：2，自引：0，他引：2
Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnec- tion pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast China via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern China. All these changes of circulations and moisture conditions finally result in an anoma- lous Asian summer monsoon and monsoon rainfall over India and northern China. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly corre- lated with Asian summer monsoon variability. The spring APNPO might therefore provide valuable in- formation for the prediction of Asian summer monsoon. 相似文献
19.
Water vapour transport of the pre-monsoon period and the general performance of the Indian summer monsoon 总被引：1，自引：0，他引：1
S. N. Bavadekar 《Pure and Applied Geophysics》1982,120(1):67-78
The advective monthly mean transfer of water vapour in the layer below 700 mbar is investigated for India for the years 1962 to 1972 and for the months January to September. The average zonal and meridional components of the transfer of water vapour for India are obtained. They are further averaged for different combinations of the pre-monsoon months from January to May and are correlated with the summer monsoon rainfall. The correlation coefficients for zonal transfer of water vapour are either negative or small positive for different combinations of the months mentioned above. The correlation coefficients for the meridional transfer of water vapour are positive. The maximum value is 0.74 for the March to May combination and is statistically significant at the 1% level.An extensive investigation is, therefore, made for the March to May averages of water vapour transfer for four broad regions of India. The parameters of water vapour transfer for these regions are compared with the threshold values and the prediction category, normal or drought, for the subsequent summer monsoon season is determined for all years. The correlation coefficient between the index of drought, as determined from parameters of water vapour transport and rainfall departure, is statistically significant at the 2% level. 相似文献
20.
Some aspects of the monsoon circulation and monsoon rainfall 总被引：1，自引：0，他引：1
R. Ananthakrishnan 《Pure and Applied Geophysics》1977,115(5-6):1209-1249
Summary The south Asian summer monsoon from June to September accounts for the greater part of the annual rainfall over most of India and southeast Asia. The evolution of the summer and winter monsoon circulations over India is examined on the basis of the surface and upper air data of stations across India. The salient features of the seasonal reversals of temperature and pressure gradients and winds and the seasonal and synoptic fluctuations of atmospheric humidity are discussed. The space-time variations of rainfall are considered with the help of climatic pentad rainfall charts and diagrams. The rainfall of several north and central Indian stations shows a minimum around mid-August and a maximum around mid-February which seem to be connected with the extreme summer and winter positions of the ITCZ and the associated north-south shifts in the seasonal circulation patterns. Attention is drawn to the characteristic features of the monsoon rainfall that emerge from a study of daily and hourly rainfall of selected stations. Diurnal variations of temperature, pressure, wind and rainfall over the monsoon belt are briefly treated. 相似文献