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1.
M. R. Ramesh Kumar S. Sathyendranath N. K. Viswambharan L. V. Gangadhara Rao 《Journal of Earth System Science》1986,95(3):435-446
Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali and Arabian coasts are associated with good monsoon rainfall over India. The strong monsoonal cooling in these regions can be attributed to strong low level winds and intense upwelling. The reappearance of 27°C isotherm off Somali coast in May/June coincides with the onset of southwest monsoon over India. Further, the influence of zonal anomaly of SST off Somalia Coast (SCZASST) and Central Indian Ocean Zonal Anomaly of SST (CIOZASST) with monsoon rainfall over India is brought out. The former is negatively related to the monsoon rainfall over western and central parts of India, whilst CIOZASST is positively related. 相似文献
2.
D. R. Pattanaik 《Natural Hazards》2007,40(3):635-646
Between 1941 and 2002 there has been a decreasing trend in the frequency of monsoon disturbances (MDs) during the summer monsoon
season (June–September). This downwards trend is significant at the 99.9% level for the main monsoon phase (July–August) and
the withdrawal phase (September); however, it is not significant during the onset phase (June). The variability in rainfall
over the homogeneous regions of India on the sub-seasonal scale also shows a significant decreasing trend with respect to
the amount of rainfall over Northwest India (NWI) and Central India (CEI) during all three phases of the monsoon. Meteorological
observations reveal that there has been an eastward shift of the rainfall belt with time over the Indian region on the seasonal
scale and that this shift is more prominent during the withdrawal phase. This decreasing trend in MDs together with its restricted
westerly movement seem to be directly related to the decreasing trend in rainfall over CEI during both the main monsoon and
withdrawal phases and over NWI during the withdrawal phase. The low-level circulation anomalies observed during two periods
(period-I: 1951–1976; period-ii: 1977–2002) are in accordance with the changes in rainfall distribution, with comparatively
more (less) rainfall falling over NWI, CEI and Southern Peninsular India (SPI) during period-I (period-ii), and are accompanied
by a stronger (weaker) monsoon circulation embedded with an anomalous cyclonic (anti-cyclonic) circulation over CEI during
the main monsoon and withdrawal phases. During the onset phase, completely opposite circulation anomalies are observed during
both periods, and these are associated with more (less) rainfall over NWI, CEI and SPI during period-ii (period-I). 相似文献
3.
Some characteristics of very heavy rainfall over Orissa during summer monsoon season 总被引:1,自引:0,他引:1
Orissa is one of the most flood prone states of India. The floods in Orissa mostly occur during monsoon season due to very
heavy rainfall caused by synoptic scale monsoon disturbances. Hence a study is undertaken to find out the characteristic features
of very heavy rainfall (24 hours rainfall ≥125 mm) over Orissa during summer monsoon season (June–September) by analysing
20 years (1980–1999) daily rainfall data of different stations in Orissa. The principal objective of this study is to find
out the role of synoptic scale monsoon disturbances in spatial and temporal variability of very heavy rainfall over Orissa.
Most of the very heavy rainfall events occur in July and August. The region, extending from central part of coastal Orissa
in the southeast towards Sambalpur district in the northwest, experiences higher frequency and higher intensity of very heavy
rainfall with less interannual variability. It is due to the fact that most of the causative synoptic disturbances like low
pressure systems (LPS) develop over northwest (NW) Bay of Bengal with minimum interannual variation and the monsoon trough
extends in west-northwesterly direction from the centre of the system. The very heavy rainfall occurs more frequently with
less interannual variability on the western side of Eastern Ghat during all the months and the season except September. It
occurs more frequently with less interannual variability on the eastern side of Eastern Ghat during September. The NW Bay
followed by Gangetic West Bengal/Orissa is the most favourable region of LPS to cause very heavy rainfall over different parts
of Orissa except eastern side of Eastern Ghat. The NW Bay and west central (WC) Bay are equally favourable regions of LPS
to cause very heavy rainfall over eastern side of Eastern Ghat. The frequency of very heavy rainfall does not show any significant
trend in recent years over Orissa except some places in north-east Orissa which exhibit significant rising trend in all the
monsoon months and the season as a whole. 相似文献
4.
Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models. 相似文献
5.
Sulochana Gadgil 《Journal of Earth System Science》2018,127(1):1
For well over 300 years, the monsoon has been considered to be a gigantic land–sea breeze driven by the land–ocean contrast in surface temperature. In this paper, this hypothesis and its implications for the variability of the monsoon are discussed and it is shown that the observations of monsoon variability do not support this popular theory of the monsoon. An alternative hypothesis (whose origins can be traced to Blanford’s (1886) remarkably perceptive analysis) in which the basic system responsible for the Indian summer monsoon is considered to be the Intertropical Convergence Zone (ITCZ) or the equatorial trough, is then examined and shown to be consistent with the observations. The implications of considering the monsoon as a manifestation of the seasonal migration of the ITCZ for the variability of the Indian summer monsoon and for identification of the monsoonal regions of the world are briefly discussed. 相似文献
6.
Spatio-temporal variability of summer monsoon rainfall over Orissa in relation to low pressure systems 总被引:2,自引:0,他引:2
The summer monsoon rainfall over Orissa occurs mostly due to low pressure systems (LPS) developing over the Bay of Bengal
and moving along the monsoon trough. A study is hence undertaken to find out characteristic features of the relationship between
LPS over different regions and rain-fall over Orissa during the summer monsoon season (June-September). For this purpose,
rainfall and rainy days over 31 selected stations in Orissa and LPS days over Orissa and adjoining land and sea regions during
different monsoon months and the season as a whole over a period of 20 years (1980-1999) are analysed. The principal objective
of this study is to find out the role of LPS on spatial and temporal variability of summer monsoon rainfall over Orissa.
The rainfall has been significantly less than normal over most parts of Orissa except the eastern side of Eastern Ghats during
July and hence during the season as a whole due to a significantly less number of LPS days over northwest Bay in July over
the period of 1980-1999. The seasonal rainfall shows higher interannual variation (increase in coefficient of variation by
about 5%) during 1980-1999 than that during 1901-1990 over most parts of Orissa except northeast Orissa. Most parts of Orissa,
especially the region extending from central part of coastal Orissa to western Orissa (central zone) and western side of the
Eastern Ghats get more seasonal monsoon rainfall with the development and persistence of LPS over northwest Bay and their
subsequent movement and persistence over Orissa. The north Orissa adjoining central zone also gets more seasonal rainfall
with development and persistence of LPS over northwest Bay. While the seasonal rainfall over the western side of the Eastern
Ghats is adversely affected due to increase in LPS days over west central Bay, Jharkhand and Bangladesh, that over the eastern
side of the Eastern Ghats is adversely affected due to increase in LPS days over all the regions to the north of Orissa. There
are significant decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during June and
decreasing trends in rainy days over some parts of north interior Orissa and central part of coastal Orissa during July over
the period of 1980-1999 相似文献
7.
Ashish Sinha Lowell Stott Max Berkelhammer Hai Cheng R. Lawrence Edwards Brendan Buckley Mark Aldenderfer Manfred Mudelsee 《Quaternary Science Reviews》2011,30(1-2):47-62
Proxy reconstructions of precipitation from central India, north-central China, and southern Vietnam reveal a series of monsoon droughts during the mid 14th–15th centuries that each lasted for several years to decades. These monsoon megadroughts have no analog during the instrumental period. They occurred in the context of widespread thermal and hydrologic climate anomalies marking the onset of the Little Ice Age (LIA) and appear to have played a major role in shaping significant regional societal changes at that time. New tree ring-width based reconstructions of monsoon variability suggest episodic and widespread reoccurrences of monsoon megadroughts continued throughout the LIA. Although the El-Niño Southern Oscillation (ENSO) plays an important role in monsoon variability, there is no conclusive evidence to suggest that these megadroughts were associated with anomalous sea surface temperature anomalies that were solely the result of ENSO-like variability in the tropical Pacific. Instead, the causative mechanisms of these megadroughts may reside in protracted changes in the synoptic-scale monsoon climatology of the Indian Ocean. Today, the intra-seasonal monsoon variability is dominated by ‘active’ and the ‘break’ spells – two distinct oscillatory modes of monsoon that have radically different synoptic scale circulation and precipitation patterns. We suggest that protracted locking of the monsoon into the “break-dominated” mode – a mode that favors reduced precipitation over the Indian sub-continent and SE Asia and enhanced precipitation over the equatorial Indian Ocean, may have caused these exceptional droughts. Impetus for periodic locking of the monsoon into this mode may have been provided by cooler temperatures at the extratropical latitudes in the Northern Hemisphere which forced the mean position of the Inter-Tropical Convergence Zone (ITCZ) further southward in the Indian Ocean. 相似文献
8.
Shared nearest neighbour (SNN) cluster algorithm has been applied to seasonal (June–September) rainfall departures over 30 sub-divisions of India to identify the contiguous homogeneous cluster regions over India. Five cluster regions are identified. Rainfall departure series for these cluster regions are prepared by area weighted average rainfall departures over respective sub-divisions in each cluster. The interannual and decadal variability in rainfall departures over five cluster regions is discussed. In order to consider the combined effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO), an index called effective strength index (ESI) has been defined. It has been observed that the circulation is drastically different in positive and negative phases of ESI-tendency from January to April. Hence, for each phase of ESI-tendency (positive and negative), separate prediction models have been developed for predicting summer monsoon rainfall over identified clusters. The performance of these models have been tested and found to be encouraging. 相似文献
9.
Having recognized that it is the tropospheric temperature (TT) gradient rather than the land–ocean surface temperature gradient that drives the Indian monsoon, a new mechanism of El Niño/Southern Oscillation (ENSO) monsoon teleconnection has been unveiled in which the ENSO influences the Indian monsoon by modifying the TT gradient over the region. Here we show that equatorial Pacific coralline oxygen isotopes reflect TT gradient variability over the Indian monsoon region and are strongly correlated to monsoon precipitation as well as to the length of the rainy season. Using these relationships we have been able to reconstruct past Indian monsoon rainfall variability of the first half of the 20th century in agreement with the instrumental record. Additionally, an older coral oxygen isotope record has been used to reconstruct seasonally resolved summer monsoon rainfall variability of the latter half of the 17th century, indicating that the average annual rainfall during this period was similar to that during the 20th century. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
区域海气耦合模式研究进展 总被引:4,自引:0,他引:4
区域海气耦合模式是进行区域尺度气候模拟和预估的重要工具,近年来得到快速发展。在阐述区域海气耦合过程重要性的基础上,对当今国内外主要的区域海气耦合模式研究进展进行总结,归纳区域海气耦合模拟所关注的核心科学问题,介绍区域海气耦合模式的技术特点。发展基于耦合器且无通量订正的区域海气耦合模式是区域海气耦合模式发展的主流方向。当前国际上区域海气耦合模拟所关注的主要科学问题,包括区域海气耦合模式对区域海洋过程的模拟、区域海气耦合模式对区域大气过程的模拟、亚洲—西北太平洋季风模拟及其耦合模拟海表面温度(SST)冷偏差问题、热带海气相互作用过程模拟,以及区域海气耦合模式对未来气候变化的预估研究等。对上述5个方面科学问题的研究思路和主要科学结论进行总结,重点关注针对亚洲—西北太平洋季风区的区域海气耦合模拟研究,对区域海气耦合过程改进亚洲—西北太平洋地区降水模拟的物理机制,及在该区域模拟SST冷偏差的成因亦进行相关归纳和总结。最后提出当前区域海气耦合模拟亟待解决的关键科学问题。 相似文献
11.
The summer monsoon rainfall over Orissa, a state on the eastern coast of India, is more significantly related than Indian
summer monsoon rainfall (ISMR) to the cyclonic disturbances developing over the Bay of Bengal. Orissa experiences floods and
droughts very often due to variation in the characteristics of these disturbances. Hence, an attempt was made to find out
the inter-annual variability in the rainfall over Orissa and the frequencies of different categories of cyclonic disturbances
affecting Orissa during monsoon season (June–September). For this purpose, different statistical characteristics, such as
mean, coefficient of variation, trends and periodicities in the rainfall and the frequencies of different categories of cyclonic
disturbances affecting Orissa, were analysed from 100 years (1901–2000) of data. The basic objective of the study was to find
out the contribution of inter-annual variability in the frequency of cyclonic disturbances to the inter-annual variability
of monsoon rainfall over Orissa.
The relationship between summer monsoon rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa shows
temporal variation. The correlation between them has significantly decreased since the 1950s. The variation in their relationship
is mainly due to the variation in the frequency of cyclonic disturbances affecting Orissa. The variability of both rainfall
and total cyclonic disturbances has been above normal since the 1960s, leading to more floods and droughts over Orissa during
recent years. The inter-annual variability of seasonal rainfall over Orissa and the frequency of cyclonic disturbances affecting
Orissa during monsoon season show a quasi-biennial oscillation period of 2–2.8 years. There is least impact of El Nino southern
oscillation (ENSO) on inter-annual variability of both the seasonal rainfall over Orissa and the frequencies of monsoon depressions/total
cyclonic disturbances affecting Orissa. 相似文献
12.
Changes in Global Monsoon Circulations Since 1950 总被引:6,自引:0,他引:6
We examined changes in several independent intensity indices of four majortropical monsoonal circulations for the period 1950–1998. Theseintensity indices included observed land surface precipitation andobserved ocean surface pressure in the monsoon regions aswell as upper-level divergence calculated at severalstandard levels from the NCAR/NCEP reanalysis. These values wereaveraged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. Asa consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from theNCEP reanalysis.We find that in each of the four regions examined, a consistentpicture emerges indicating significantly diminished monsoonalcirculations over the period of record, evidence of diminished spatialmaxima in the global hydrological cycle since 1950. Trends since 1979,the period of strongest reported surface warming, do not indicate any change inmonsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduction of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening.Most previously reported model simulations of theeffects of rising CO2 show an increase in monsoonal activity withrising global surface temperature. We find no support in these datafor an increasing hydrological cycle or increasing extremes as hypothesized bygreenhouse warming scenarios. 相似文献
13.
青藏高原近地层及北侧气压系统的季节性振荡变化 总被引:3,自引:1,他引:2
基于ERA-Interim逐日4次600 hPa位势高度再分析资料, 以及青藏高原和周边地区75个气象站日平均温度、降水和相对湿度资料, 对高原近地层及北侧气压系统的季节性振荡变化进行了分析. 结果表明: 高原近地层及北侧气压系统强度在围绕中心点顺时针运动时不断加强, 逆时针运动时不断减弱. 两气压系统呈明显的跷跷板式变化, 在600 hPa上表现为高度场空间结构沿经向上的调整; 低高压差负值的开始和结束时间与高原季风起讫时间吻合. 高原夏季降水的起讫不仅与高原及北侧气压系统结构密切相关, 而且与高原东南或南部水汽输送条件息息相关. 相似文献
14.
Trends of pre-monsoon, monsoon and post-monsoon rainfall pattern were studied on decadal basis over different homogeneous monsoon regions in India for the period 1871–2008. It is attempted to understand the relation of monsoon rainfall with the global teleconnections of El Niño and La Niña, for which the correlation analysis has been carried out with Darwin pressure and Niño 3.4 sea surface temperature (Niño 3.4 SST). The correlation analysis inferred that the significant correlations were observed when monsoon rainfall is related to ENSO indices on decadal scale than on annual ones. The study also found that the north-west region is more affected by the moderate El Niño years compared to strong El Niño years. The regions Central North-East and North-East could not make any difference among weak, moderate and strong La Niña events. The authors also have carried out the extreme value analysis over different homogeneous monsoon regions of India as well as for whole India. The results show that the return values of rainfall are increasing with the return periods for the forthcoming 10, 20, 50 and 100 years. The heterogeneity in number of threshold years that were recorded for the extreme rainfall over north-east (humid climatic type) and north-west (arid climatic type) described the climate variability. The results of the present study may be useful for the policy makers in understanding the rainfall exceedance in different return periods for planning the risk management strategies. 相似文献
15.
Characteristics of certain surface meteorological parameters in relation to the interannual variability of Indian summer monsoon 总被引:1,自引:0,他引:1
With an objective to understand the influence of surface marine meteorological parameters in relation to the extreme monsoon activity over the Indian sub-continent leading to flood/drought, a detailed analysis of the sea level pressure over the Southern Hemisphere and various surface meteorological parameters over the Indian seas is carried out. The present study using the long term data sets (Southern Hemispheric Sea Level Pressure Analysis; Comprehensive Ocean Atmospheric Data Set over the Indian Seas; Surface Station Climatology Data) clearly indicates that the sea surface temperature changes over the south eastern Pacific (El Ninõ/La Niña) have only a moderate impact (not exceeding 50% reliability) on the Indian summer monsoon activity. On the other hand, the sea level pressure anomaly (SOI) over Australia and the south Pacific has a reasonably high degree of significance (more than 70%) with the monsoon activity over India. However, these two parameters (SLP and SST) do not show any significant variability over the Indian seas in relation to the summer monsoon activity. Over the Indian seas, the parameters which are mainly associated with the convective activity such as cloud cover, relative humidity and the surface wind were found to have a strong association with the extreme monsoon activity (flood/drought) and thus the net oceanic heat loss over the Indian seas provides a strong positive feed-back for the monsoon activity over India. 相似文献
16.
On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall 总被引:3,自引:0,他引:3
The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June–September) monsoon rainfall at
sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded
rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used.
The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact
on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan,
and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events.
The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student
t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO
events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly
scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related
correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from
July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming
that strong IOD events indeed affect the Indian summer monsoon.
相似文献
Karumuri AshokEmail: |
17.
Some statistical properties of the summer monsoon seasonal rainfall for India during the last 100 years (1881–1980) are presented.
The most recent decade of 1971–1980 shows the lowest value of standard-decadal average monsoon rainfall (86.40 cm) and is
also characterised by the second highest value of coefficient of variation in monsoon rainfall (12.4 %). The combined last
two standard-decadal period of 1961–1980 was the period of the largest coefficient of variation and the lowest average monsoon
rainfall for India.
The possible influence of global climatic variability on the performance of the monsoon is also examined. Analyses of correlation
coefficient show that a statistically significant positive relationship with a time-lag of about six months exists between
monsoon rainfall and northern hemispheric surface air temperature. A cooler northern hemisphere during January/February leads
to a poor monsoon.
All the major drought years during the last 3 decades had much cooler January/February periods over the northern hemisphere—1972
having the coldest January/February with a temperature departure of −0.94°C and the most disastrous monsoon failure. 相似文献
18.
G. Nageswara Rao 《Journal of Earth System Science》1999,108(4):327-332
Rainfall variability over a river basin has greater impact on the water resource in that basin. With this in view, the variability
of the monsoon rainfall over the Godavari river basin has been studied on different time scales. As expected, the monsoon
rainfall in Godavari basin is more variable (17%) than the all-India monsoon rainfall (11%) during the period of study (1951–90).
Similarly, inter-annual variability of the monsoon rainfall on smaller time scales is found to be still higher and increases
while going on from seasonal to daily scales. An interesting observation is that the intra-seasonal variability of the monsoon
rainfall has a significant negative relationship (CC= −0.53) with the total seasonal rainfall in the basin. 相似文献
19.
Hamza Varikoden Hilal Sulthan Ali Al-shukaili C. A. Babu A. A. Samah 《Arabian Journal of Geosciences》2016,9(8):520
The Sultanate of Oman is located in the south-eastern part of the Arabian Peninsula and covers the larger part of the southern coasts of the Arabian Peninsula in both arid and semi-arid environments except for the southern part which is swept by the monsoon affecting the Arabian Sea during the period from June to September. The summer rainfall over Oman shows year-to-year variability, and this is caused by oceanic and atmospheric influences. In the present study, we tried to explore the influence of El Niño on the rainfall over Oman using different data sets. The empirical orthogonal function (EOF) technique employed to the zonal wind at 850 hPa for the 30-year period shows that the second and third modes of EOF are showing high variability over the Oman regions. The corresponding PCs were subjected to FFT analysis, and it showed a peak about 5–6 years. In addition to this, the zonal wind over the Oman regions is correlated with the global zonal wind and found a significant correlation (1 % significant level). It has already been proved that the wind and rainfall during summer monsoon is in phase. Moreover, the spectral analysis of rainfall at Masirah station and the Niño3.4 index show the similar mode of variability indicating a direct relationship. The correlation between rainfall and the Niño3.4 index is also showing a positive significant value, and therefore, it can be concluded that the El Niño in the Pacific favours rainfall over the Oman region. 相似文献
20.
P. L. S. Rao U. C. Mohanty P. V. S. Raju Gopal Iyengar 《Journal of Earth System Science》2003,112(1):95-111
In this study, we present the mean seasonal features of the Indian summer monsoon circulation in the National Centre for Medium
Range Weather Forecasting (NCMRWF) global data assimilation and forecast system. The large-scale budgets of heat and moisture
are examined in the analyzed and model atmosphere. The daily operational analyses and forecasts (day 1 through day 5) produced
for the summer seasons comprising June, July and August of 1995 and 1993 have been considered for the purpose. The principal
aim of the study is two-fold. Primarily, to comprehend the influence of the systematic errors over the Indian summer monsoon,
secondarily, to analyze the performance of the model in capturing the interseasonal variability.
The heat and moisture balances show reduction in the influx of heat and moisture in the model forecasts compared to the analyzed
atmosphere over the monsoon domain. Consequently, the diabatic heating also indicates reducing trend with increase in the
forecast period. In effect, the strength of Indian summer monsoon, which essentially depends on these parameters, weakens
considerably in the model forecasts. Despite producing feeble monsoon circulation, the model captures interseasonal variability
realistically. Although, 1995 and 1993 are fairly normal monsoon seasons, the former received more rainfall compared to the
latter in certain pockets of the monsoon domain. This is clearly indicated by the analyzed and model atmosphere in terms of
energetics. 相似文献