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1.
Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal)
were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up
over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies
were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared
to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have
resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and
Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would
have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea
(EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen
in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003.
The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods
of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm
over EAS during entire July and hence less rainfall.
The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen
that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation
in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence
less rainfall compared to July 2003. 相似文献
2.
Medha Khole 《Meteorology and Atmospheric Physics》2000,75(1-2):1-9
Summary The year 1997 witnessed one of the most severe El-Ni?o events of the century. However, the All-India Summer Monsoon Rainfall
(AISMR) was 102% of its long period average. In view of recent studies (Tourre and White, 1995, 1997) of detection of ENSO
signal over Indian Ocean, the Sea-Surface Temperature (SST) variation over Indian Ocean (20° N–10° S/50° E–100° E), concurrent
to El-Ni?o event of 1997 is examined. It is observed that during the developing, mature and decaying stages of El-Ni?o, the
North Indian Ocean was abnormally warm. This anomalous warming may be one of the factors responsible for anomalous precipitation
over India during October to December of 1997.
Received August 24, 1999/Revised February 15, 2000 相似文献
3.
Prediction of summer monsoon rainfall over India using the NCEP climate forecast system 总被引：1，自引：0，他引：1
The performance of a dynamical seasonal forecast system is evaluated for the prediction of summer monsoon rainfall over the
Indian region during June to September (JJAS). The evaluation is based on the National Centre for Environmental Prediction’s
(NCEP) climate forecast system (CFS) initialized during March, April and May and integrated for a period of 9 months with
a 15 ensemble members for 25 years period from 1981 to 2005. The CFS’s hindcast climatology during JJAS of March (lag-3),
April (lag-2) and May (lag-1) initial conditions show mostly an identical pattern of rainfall similar to that of verification
climatology with the rainfall maxima (one over the west-coast of India and the other over the head Bay of Bengal region) well
simulated. The pattern correlation between verification and forecast climatology over the global tropics and Indian monsoon
region (IMR) bounded by 50°E–110°E and 10°S–35°N shows significant correlation coefficient (CCs). The skill of simulation
of broad scale monsoon circulation index (Webster and Yang; WY index) is quite good in the CFS with highly significant CC
between the observed and predicted by the CFS from the March, April and May forecasts. High skill in forecasting El Nino event
is also noted for the CFS March, April and May initial conditions, whereas, the skill of the simulation of Indian Ocean Dipole
is poor and is basically due to the poor skill of prediction of sea surface temperature (SST) anomalies over the eastern equatorial
Indian Ocean. Over the IMR the skill of monsoon rainfall forecast during JJAS as measured by the spatial Anomaly CC between
forecast rainfall anomaly and the observed rainfall anomaly during 1991, 1994, 1997 and 1998 is high (almost of the order
of 0.6), whereas, during the year 1982, 1984, 1985, 1987 and 1989 the ACC is only around 0.3. By using lower and upper tropospheric
forecast winds during JJAS over the regions of significant CCs as predictors for the All India Summer Monsoon Rainfall (AISMR;
only the land stations of India during JJAS), the predicted mean AISMR with March, April and May initial conditions is found
to be well correlated with actual AISMR and is found to provide skillful prediction. Thus, the calibrated CFS forecast could
be used as a better tool for the real time prediction of AISMR. 相似文献
4.
Role of the southern Indian Ocean in the transitions of the monsoon-ENSO system during recent decades 总被引：1，自引：0，他引：1
The focus of this study is to document the possible role of the southern subtropical Indian Ocean in the transitions of the monsoon-ENSO system during recent decades. Composite analyses of sea surface temperature (SST) fields prior to El Niño-Southern Oscillation (ENSO), Indian summer monsoon (ISM), Australian summer monsoon (AUSM), tropical Indian Ocean dipole (TIOD) and Maritime Continent rainfall (MCR) indices reveal the southeast Indian Ocean (SEIO) SSTs during late boreal winter as the unique common SST precursor of these various phenomena after the 1976–1977 regime shift. Weak (strong) ISMs and AUSMs, El Niños (La Niñas) and positive (negative) TIOD events are preceded by significant negative (positive) SST anomalies in the SEIO, off Australia during boreal winter. These SST anomalies are mainly linked to subtropical Indian Ocean dipole events, recently studied by Behera and Yamagata (Geophys Res Lett 28:327–330, 2001). A wavelet analysis of a February–March SEIO SST time series shows significant spectral peaks at 2 and 4–8 years time scales as for ENSO, ISM or AUSM indices. A composite analysis with respect to February–March SEIO SSTs shows that cold (warm) SEIO SST anomalies are highly persistent and affect the westward translation of the Mascarene high from austral to boreal summer, inducing a weakening (strengthening) of the whole ISM circulation through a modulation of the local Hadley cell during late boreal summer. At the same time, these subtropical SST anomalies and the associated SEIO anomalous anticyclone may be a trigger for both the wind-evaporation-SST and wind-thermocline-SST positive feedbacks between Australia and Sumatra during boreal spring and early summer. These positive feedbacks explain the extraordinary persistence of the SEIO anomalous anticyclone from boreal spring to fall. Meanwhile, the SEIO anomalous anticyclone favors persistent southeasterly wind anomalies along the west coast of Sumatra and westerly wind anomalies over the western Pacific, which are well-known key factors for the evolution of positive TIOD and El Niño events, respectively. A correlation analysis supports these results and shows that SEIO SSTs in February–March has higher predictive skill than other well-established ENSO predictors for forecasting Niño3.4 SST at the end of the year. This suggests again that SEIO SST anomalies exert a fundamental influence on the transitions of the whole monsoon-ENSO system during recent decades. 相似文献
5.
Summary The interannual variability of North-West India Winter Precipitation (NWIWP) has been examined in association with the variability
of sea surface temperature (SST), surface air temperature (SAT) and upper tropospheric (200 hPa) wind patterns over India
and the surrounding regions. We have considered data for a period of 54 years (1950–2003). During the years of excess NWIWP,
the SST was above normal over the equatorial Indian Ocean, SAT was below normal over east Mediterranean Sea and over the Himalayan
region and upper tropospheric westerlies strengthen and shift southwards. Upper tropospheric westerlies over north and central
India was found to be related with the SST anomalies over the equatorial Indian Ocean. The decrease of SAT over north India
and surroundings may largely be a manifestation of cooling brought about by excessive precipitation and sweep of cold air
advection in rear of the storms. The intensifying of upper troposphere westerlies embedded with a jet increases the upper
level divergence over north India due to increased horizontal shear resulting in intense anticyclone at upper troposphere. 相似文献
6.
During FGGE year 1979, low-level air flow over the western Indian Ocean was determined from the analysis of GOES images (5－20 June). The wind pattern shows sudden change in low-level air circulation over western Indian Ocean during the initial burst of summer monsoon. The burst of monsoon is characte-rized by sudden establishment of low-level jet and strong cross-equatorial flow. This abrupt change signals the beginning of southwest monsoon over India and it is associated with the first monsoon rainfall over the southern part of western coast of India. Sudden change in low-level air flow is followed by the burst of monsoon within 3－5 days. 相似文献
7.
Using 20 models of the Coupled Model Intercomparison Project Phase 5 (CMIP5), the simulation of the Southwest Indian Ocean (SWIO) thermocline dome is evaluated and its role in shaping the Indian Ocean Basin (IOB) mode following El Niño investigated. In most of the CMIP5 models, due to an easterly wind bias along the equator, the simulated SWIO thermocline is too deep, which could further influence the amplitude of the interannual IOB mode. A model with a shallow (deep) thermocline dome tends to simulate a strong (weak) IOB mode, including key attributes such as the SWIO SST warming, antisymmetric pattern during boreal spring, and second North Indian Ocean warming during boreal summer. Under global warming, the thermocline dome deepens with the easterly wind trend along the equator in most of the models. However, the IOB amplitude does not follow such a change of the SWIO thermocline among the models; rather, it follows future changes in both ENSO forcing and local convection feedback, suggesting a decreasing effect of the deepening SWIO thermocline dome on the change in the IOB mode in the future. 相似文献
8.
Located at the southern boundary of the tropical rainfall belt within the South Africa monsoon regime, Rodrigues Island, ～2500 km east of East Africa, is ideally located to investigate climatic changes over the southwest Indian Ocean(SWIO). In this study, we investigate the climatic controls of its modern interannual rainfall variability in terms of teleconnection and local effects. We find that increased rainfall over the SWIO tends to occur in association with anomalously warm(cold) SSTs over the equatorial central Pacific(Maritime Continent), resembling the central Pacific El Ni?o, closely linked with the Victoria mode in the North Pacific. Our analyses show that the low-level convergence induced by warm SST over the equatorial central Pacific leads to anomalous low-level divergence over the Maritime Continent and convergence over a large area surrounding the Rodrigues Island, which leads to increased rainfall over the SWIO during the rainy season. Meanwhile, the excited Rossby wave along the tropical Indian Ocean transports more water vapor from the tropical convergence zone into the SWIO via intensified northwest wind. Furthermore, positive feedback induced by the Rossby wave response to the increased rainfall in the region contributes to the large interannual variations over the SWIO. 相似文献
9.
本文利用30~60天带通滤波资料, 考察了不同季节印度洋—西太平洋区域对流活动季节内尺度变率的主要模态, 发现在不同季节赤道东印度洋(5°S~10°N, 70°E~100°E)和西北太平洋(5°N~20°N, 110°E~160°E)对流活动均存在反相变化的关系, 将之称为季节内尺度的印度洋—西太平洋对流涛动(Indo-West Pacific Convection Oscillation), 简称IPCO。对IPCO两极子区域对流活动进行超前滞后相关分析, 发现IPCO事件形成—发展—消亡的生命周期是由对流活动季节内振荡及其传播造成的。对流扰动首先在赤道中西印度洋形成, 随后逐渐向东发展变强, 在其继续变强的过程中将分两支传播:一支由赤道印度洋向北传播, 至印度半岛南部后逐渐减弱消失;另一支沿赤道继续东传, 在海洋大陆受到抑制, 快速越过海洋大陆到达赤道西太平洋后又开始发展变强, 随后北传至西北太平洋区域逐渐减弱, 最终至我国长江流域中下游到日本区域消失。将这一过程划分为8个位相, 详细分析了不同位相对应的环流场和降水场特征, 最后给出了IPCO事件演化示意图。 相似文献
10.
The southwestern Indian Ocean (SWIO) is characterized by significant climate variability and frequent tropical cyclones (TC). Year-to-year fluctuations of TC and associated oceanic and atmospheric fields in the period 1961–2002 are studied with reanalysis data as composites and cross-correlations, with wavelet filtering and cross-modulus analysis, and by hovmoller analysis and multi-variate statistical modeling. Observational limitations in the early part of the record are recognized. An intense TC-days index is formed and is characterized by quasi-biennial to decadal cycles that relate to ocean Rossby waves and high latitude atmospheric circulations, respectively. New variables are uncovered that significantly improve the seasonal prediction of SWIO TC. One predictor is the geopotential height in the SE Pacific, which explains 31% of SWIO TC variability. It foretells of downstream oscillations in the sub-tropical jet stream, which govern wind shear, an equatorial duct and attendant circulation anomalies over the SWIO. An anti-phase association between Amazon convection and intense TCs is found to be related to the Atlantic Zonal Circulation. Drought across the Amazon is related to an increase in TC activity in the SWIO, when zonal wind anomalies over the Atlantic become upper easterly/lower westerly. This feature is related to Pacific Ocean El Niño Southern Oscillation phase. A La Niña signal favors TC development through a westward propagating cyclonic circulation and downweling Rossby wave in the South Indian Ocean that enhances thermodynamic energy. It is recommended to repeat this analysis every few years to determine whether teleconnections evolve due to climate drift or improving observations. 相似文献
11.
Daily rainfall variability over southern Africa (SA) and the southwest Indian Ocean (SWIO) during the austral summer months
has recently been described objectively for the first time, using newly derived satellite products. The principle mode of
variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region.
These represent the location of cloud bands associated with tropical temperate troughs (TTT). This study objectively identifies
major TTT events during November to February, and on the basis of composites off NCEP reanalysis data describes the associated
atmospheric structure. The two phases of the rainfall dipole are associated with markedly contrasting circulation patterns.
There are also pronounced intra-seasonal variations. In early summer the position of the temperate trough and TTT cloud band
alternates between the SWIO and southwest Atlantic. In late summer the major TTT axis lies preferentially over the SWIO, associated
with an eastward displacement in the Indian Ocean high. In all months, positive events, in which the TTT cloud band lies primarily
over the SWIO, are associated with large-scale moisture flux anomalies, in which convergent fluxes form a pronounced poleward
flux along the cloud band. This suggests that TTT events are a major mechanism of poleward transfer of energy and momentum.
Moisture transport occurs along three principle paths: (1) the northern or central Indian Ocean (where anomalous fluxes extend
eastward to the Maritime Continent), (2) south equatorial Africa and the equatorial Atlantic, (3) from the south within a
cyclonic flow around the tropical-temperate trough. The relative importance of (2) is greatest in late summer. Thus, synoptic
scale TTT events over SA/SWIO often result from large-scale planetary circulation patterns. Hovmoeller plots show that TTT
development coincides with enhanced tropical convection between 10°–30°E (itself exhibiting periodicity of around 5 days),
and often with convergence of eastward and westward propagating convection around 40°E. Harmonic analysis of 200 hPa geopotential
anomalies show that TTT features are forced by a specific zonally asymmetric wave pattern, with wave 5 dominant or significant
in all months except February when quasi-stationary waves 1, 2 and 3 dominate. These findings illustrate the importance of
tropical and extratropical dynamics in understanding TTT events. Finally, it is suggested that in November–Januar TTT rainfall
over SA/SWIO may be in phase with similar rainfall dipole structures observed in the South Pacific and South Atlantic convergence
zones.
Received: 11 August 1998 / Accepted: 28 May 1999 相似文献
12.
Tropical cyclones (TCs) over Southeast Indian Ocean (SEIO) have the notable interannual variability caused by ENSO and Indian Ocean Dipole (IOD). In the September–November of El Niño and October–November of positive IOD (PIOD), SEIO TCs is far less than its climatology. However, it is hard to separately understand El Niño and PIOD's impact on SEIO TCs due to their similar occurrence time and time scale. Unlike El Niño and PIOD, SEIO TCs is remarkably more than its climatology only in September–November of negative IOD (NIOD) instead of La Niña. Consequently, it is concluded NIOD mainly affects SEIO TCs’ increase. Diagnose results suggest the relative humidity (RH) contributes mostly to the TCs’ increase, vertical wind shear provides the secondary positive contribution, vorticity term also makes a weak positive contribution and PI term's contribution even may be negligible. The study still uncovers the process of RH change: NIOD reaches its peak period and changes atmosphere circulation to make a positive low-level vorticity anomaly over SEIO. Vorticity anomaly strengthens upward motion. The vertical velocity anomaly and climatogical specific humidity (SH) work together to make vertical advection play a dominant role in SH variation. SH's change mainly reflects in RH variation. Eventually, all of these associates with NIOD lead to more SEIO TCs in September–November and the significance of difference is above 99%. 相似文献
13.
D. R. Kothawale A. A. Munot H. P. Borgaonkar 《Theoretical and Applied Climatology》2008,92(1-2):31-45
Summary The present study examines the long term trend in sea surface temperatures (SSTs) of the Arabian Sea, Bay of Bengal and Equatorial
South India Ocean in the context of global warming for the period 1901–2002 and for a subset period 1971–2002. An attempt
has also been made to identify the relationship between SST variations over three different ocean areas, and All-India and
homogeneous region summer monsoon rainfall variability, including the role of El-Ni?o/Southern Oscillation (ENSO). Annual
sea surface temperatures of the Arabian Sea, Bay of Bengal and Equatorial South India Ocean show a significant warming trend
of 0.7 °C, 0.6 °C and 0.5 °C per hundred years, respectively, and a relatively accelerated warming of 0.16 °C, 0.14 °C and
0.14 °C per decade during the 1971–2002 period.
There is a positive and statistically significant relationship between SSTs over the Arabian Sea from the preceding November
to the current February, and Indian monsoon rainfall during the period 1901–2002. The correlation coefficient increases from
October and peaks in December, decreasing from February to September. This significant relationship is also found in the recent
period 1971–2002, whereas, during 1901–70, the relationship is not significant. On the seasonal scale, Arabian Sea winter
SSTs are positively and significantly correlated with Indian monsoon rainfall, while spring SSTs have no significant positive
relationship. Nino3 spring SSTs have a negative significant relationship with Indian monsoon rainfall and it is postulated
that there is a combined effect of Nino3 and Arabian Sea SSTs on Indian monsoon. If the Nino3 SST effect is removed, the spring
SSTs over the Arabian Sea also have a significant relationship with monsoon rainfall. Similarly, the Bay of Bengal and Equatorial
South Indian Ocean spring SSTs are significantly and positively correlated with Indian monsoon rainfall after removing the
Nino3 effect, and correlation values are more pronounced than for the Arabian Sea.
Authors’ address: Dr. D. R. Kothawale, A. A. Munot, H. P. Borgaonkar, Climatology and Hydrometeorology divisions, Indian Institute
of Tropical Meteorology, Pune 411008, India. 相似文献
14.
Interdecadal change in the relationship of southern China summer rainfall with tropical Indo-Pacific SST 总被引：1，自引：0，他引：1
Renguang Wu Song Yang Zhiping Wen Gang Huang Kaiming Hu 《Theoretical and Applied Climatology》2012,108(1-2):119-133
The present study investigates the interdecadal change in the relationship between southern China (SC) summer rainfall and tropical Indo-Pacific sea surface temperature (SST). It is found that the pattern of tropical Indo-Pacific SST anomalies associated with SC summer rainfall variability tends to be opposite between the 1950–1960s and the 1980-1990s. Above-normal SC rainfall corresponds to warmer SST in the tropical southeastern Indian Ocean (SEIO) and cooler SST in the equatorial central Pacific (ECP) during the 1950–1960s but opposite SST anomalies in these regions during the 1980–1990s. A pronounced difference is also found in anomalous atmospheric circulation linking SEIO SST and SC rainfall between the two periods. In the 1950–1960s, two anomalous vertical circulations are present between ascent over SEIO and ascent over SC, with a common branch of descent over the South China Sea that is accompanied by an anomalous low-level anticyclone. In the 1980–1990s, however, a single anomalous vertical circulation directly connects ascent over SC to descent over SEIO. The change in the rainfall–SST relationship is likely related to a change in the magnitude of SEIO SST forcing and a change in the atmospheric response to the SST forcing due to different mean states. A larger SEIO SST forcing coupled with a stronger and more extensive western North Pacific subtropical high in recent decades induce circulation anomalies reaching higher latitudes, influencing SC directly. Present analysis shows that the SEIO and ECP SST anomalies can contribute to SC summer rainfall variability both independently and in concert. In comparison, there are more cases of concerted contributions due to the co-variability between the Indian and Pacific Ocean SSTs. 相似文献
15.
Theoretical and Applied Climatology - Large intraseasonal rainfall variations are identified over the southern South China Sea (SSCS), tropical southeastern Indian Ocean (SEIO), and east coast of... 相似文献
16.
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
17.
Nicolas Fauchereau B. Pohl C. J. C. Reason M. Rouault Y. Richard 《Climate Dynamics》2009,32(4):575-591
A cluster analysis of daily outgoing longwave radiation (OLR) anomalies from 1979 to 2002 over the Southern Africa/Southwest
Indian Ocean (SWIO) region for the November to February season reveals seven robust and statistically well separated recurrent
patterns of large-scale organized convection. Among them are three regimes indicative of well defined tropical–temperate interactions
linking the hinterland parts of Southern Africa to the mid-latitudes of the SWIO. Preferred transitions show a tendency for
an eastward propagation of these systems. Analysis of daily rainfall records for South Africa shows that six of the OLR regimes
are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country. Atmospheric
anomalies from the NCEP/DOE II reanalysis dataset show that the OLR regimes are associated with either regional or near-global
adjustments of the atmospheric circulation, the three regimes representative of tropical–temperate interactions being in particular
related to a well-defined wave structure encompassing the subtropical and temperate latitudes, featuring strong vertical anomalies
and strong poleward export of momentum in the lee of the location of the cloud-band. The time-series of OLR regimes seasonal
frequency are correlated to distinctive anomaly patterns in the global sea-surface-temperature field, among which are shown
to be those corresponding to El Nino and La Nina conditions. The spatial signature of El Nino Southern Oscillation’s (ENSO)
influence is related to the combination of an increased/decreased frequency of these regimes. It is shown in particular that
the well-known “dipole” in convection anomalies contrasting Southern Africa and the SWIO during ENSO events arises as an effect
of seasonal averaging and is therefore not valid at the synoptic scale. This study also provides a framework to better understand
the observed non-linearities between ENSO and the seasonal convection and rainfall anomalies over the region. 相似文献
18.
Summary One of the major forcings for the interannual variability of the Asian Summer Monsoon is the Sea Surface Temperature (SST)
distribution in the tropical Pacific Ocean. El Ni?o years are characterized by a negative Southern Oscillation Index (SOI)
and decreased monsoon rainfall over India leading to drought conditions. On the other hand, La Nina years are characterized
by a positive SOI and generally good monsoon conditions over India.
The monsoon ENSO relation is not a consistent one. The monsoons of 1991 and 1994 are good examples. The spring SOI was the
same (−1.3) during both years. However, the All India Summer Monsoon Rainfall (AISMR) was 91.4% of normal in 1991 and 110%
in 1994. Though the SOI was same during the spring of both years, the spatial distribution of SSTs was different.
In the present study, the impacts of different SST distributions in the tropical Pacific Ocean, on the monsoons of 1991 and
1994 have been examined, to assess the UKMO-unified model’s sensitivity of SST. It is observed that the simulated monsoon
was much stronger in 1994 than in 1991, in terms of precipitation and circulation. The wind and the Outgoing Long-wave Radiation
(OLR) simulated by the model are compared with NCEP/NCAR reanalyses data, while precipitation is compared with Xie-Arkin merged
rainfall data.
Received November 26, 1998 相似文献
19.
YANG Mingzhu DING Yihui LI Weijing MAO Hengqing HUANG Changxing 《Acta Meteorologica Sinica》2008,22(1):31-41
The Indian Ocean （IO） sea surface temperature （SST） was analyzed by using empirical orthogonal function （EOF）, and the leading mode of Indian Ocean （LMIO） SST was extracted. The major spatial and temporal characters of LMIO were discussed, and the relationships between LMIO with Indian summer monsoon （ISM） and with China summer rainfalls （CSR） were investigated, then the impacts of LMIO on Asian summer monsoon （ASM） circulation were explored. Some notable results are obtained： The significant evolutional characters of LMIO are the consistent warming trend of almost the whole IO basin, the distinctive quasi-3- and quasi-ll-yr oscillations and remarkably interdecadal warming in 1976/1977 and 1997/1998, respectively. The LMIO impaired the lower level circulation of ISM and was closely related with the climate trend of CSR. It was associated with the weakening of South Asian high, the easterly winds south of the Tibetan Plateau, and the cross-equatorial flows over 10°-20°N, 40°-110°E at the upper level; with the strengthening of Somali cross-equatorial jet but the weakening of the circulation of ISM in the sector of India, the strengthening of south wind over the middle and lower reaches of Yangtze River and South China but the weakening of southwesterly winds over North China at lower level and with the increasing of surface pressure over the Asian Continent. Changes in the moisture flux transports integrated vertically over the whole troposphere associated with LMIO are similar to those in the lower level circulation. To sum up, the significant SST increasing trend of IO basin was one of the important causes for weakening of the ASM circulation and the southwards shifting of China summer rainband. 相似文献
20.
夏季中国华北降水、印度降水与太平洋海表面温度的耦合关系 总被引：1，自引：0，他引：1
本文基于1951~2014年的站点观测资料以及再分析资料,应用多变量经验正交分解法（MEOF）研究了年际尺度上华北夏季降水、印度夏季降水与海表面温度之间的耦合关系（主要模态）。结果表明:当印度夏季降水偏强时,若同期夏季赤道中东太平洋海温表现为La Ni?a位相,则西太平洋暖池对流加强,副热带高压偏西偏北,有利于华北夏季降水与印度夏季降水一致增强。反之,当印度大部降水偏弱时,若同期夏季赤道中东太平洋海温表现为El Ni?o位相,则华北夏季降水和印度夏季降水一致减弱。然而,两地夏季降水的协同变化关系并不总是成立。当赤道中东太平洋海温异常随时间演变表现为冬春El Ni?o衰减型时,伴随着印度洋偶极子（IOD）正位相的衰减过程,这会减弱东亚夏季风,使得华北夏季降水偏少。此时印度半岛夏季降水增强区集中在其西部,无法形成连接印度和华北夏季降水异常的环半球遥相关（CGT）波列,可能使得华北夏季降水异常与全印度夏季降水异常成相反形势。这些结论揭示了中国华北夏季降水、印度夏季降水和海表面温度之间的耦合关系,有助于进一步理解海温外强迫对两地夏季降水之间相关关系的作用,从而对华北夏季降水的预测具有参考意义。 相似文献