首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献，搜索用时 562 毫秒
1.
This paper provides evidence that the variation of boreal winter sea level pressure (SLP) over the North Pacific is out-of-phase with SLP fluctuation over the tropical Indian Ocean on both the interdecadal and interannual time scales.Subsequently,a SLP between tropical Indian Ocean and North Pacific (TIO-NP) oscillation index is defined to indicate the variation of such out-of-phase fluctuation.Moreover,the simultaneous surface air temperature and precipitation anomalies in China are closely related to TIO-NP oscillations.Below-normal surface air temperature anomalies in the northern and the eastern part of China,and less rainfall in southern China,correspond to positive TIO-NP oscillation phase with negative SLP anomalies in tropical Indian Ocean and positive anomalies in North Pacific.The TIO-NP oscillation affects China’s winter climate anomalies,possibly through modulating the northeast East Asia winter monsoon.  相似文献   

2.
Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.  相似文献   

3.
Based on multiple datasets, correlation and composite analyses, and case studies, this paper investigated possible influences of the Indian Ocean dipole （IOD） mode on the eastward propagation of intraseasonal oscillation in the tropical atmosphere. The results showed that （1） the 30-60 day outgoing longwave radiation anomalies in the southeastern Indian Ocean and the 30-60 day 850-hPa zonal wind anomalies over the equatorial central Indian Ocean were significantly correlated with the IOD index; （2） during positive IOD years, the anomalously cold water in the southeastern Indian Ocean and the 850-hPa anomalous easterlies over the equatorial central Indian Ocean might act as barriers to the continuously eastward propagation of the intraseasonal convection, which interrupts the Madden-Julian oscillation （MJO） propagation in the eastern equatorial Indian Ocean and western Pacific; and （3） during negative IOD years, the anomalously warm water in the southeastern Indian Ocean and the low-level westerly anomalies over the equatorial central Indian Ocean favor the eastward movement of MJO.  相似文献   

4.
It is necessary to study the tropical western Pacific SST in association with variations of other parts of the globe. Two basic compositions are revealed of long-term variation in SST over three major tropical oceans since the 1950's (linear warming and El Nino-La Nina oscillations) and typical patterns with which they are displayed over the oceans are compared. On the basis of it, difference in long-term variation of SST over western, central and eastern tropical Pacific is analyzed in details. It is pointed out that the El Nino-La Nina oscillations are relatively weak in the long-term variation of SST in the tropical western Pacific and linear warming trend there is replaced by interdecadal oscillations. Further understanding of the peculiarity over the region helps improve short-term climatic predictions in China.  相似文献   

5.
The NOAA daily outgoing longwave radiation (OLR) and the Global Precipitation Climatology Project （GPCP） daily precipitation data are used to study the variation of dominant convection modes and their relationships over Asia, the Indian Ocean, and the western Pacific Ocean during the summers from 1997 to 2004. Major findings are as follows: (1) Regression analysis with the OLR indicates the convective variations over Asian monsoon region are more closely associated with the convective activities over the western subtropical Pacific (WSP) than with those over the northern tropical Indian Ocean (NTIO). (2) The EOF analysis of OLR indicates the first mode (EOF1) exhibits the out-of-phase variations between eastern China and India, and between eastern China and the WSP. The OLR EOF1 primarily exhibits seasonal and even longer-term variations. (3) The OLR EOF2 mostly displays in-phase convective variations over India, the Bay of Bengal, and southeastern China. A wavelet analysis reveals intraseasonal variation (ISV) features in 2000, 2001, 2002, and 2004. However, the effective ISV does not take place in every year and it seems to occur only when the centers of an east--west oriented dipole reach enough intensity over the tropical Indian and western Pacific Oceans. (4) The spatial patterns of OLR EOF3 are more complicated than those of EOF1 and EOF2, and an effective ISV is noted from 1999 to 2004. The OLR EOF3 implies there is added complexity of the OLR pattern when the effective ISV occurs. (5) The correlation analysis suggests the precipitation over India is more closely associated with the ISV, seasonal variations, and even longer-term variations than precipitation occurring over eastern China.  相似文献   

6.
Impacts of the MJO on Winter Rainfall and Circulation in China   总被引：10，自引：0，他引：10  
Impacts of the MJO on winter rainfall and circulation in China are investigated using a real-time multivariate MJO index.Composite results using the daily rainfall anomalies and "rainy day" anomalies according to eight different MJO phases show that the MJO has considerable influence on winter rainfall in China. Rainfall anomalies show systematic and substantial changes(enhanced/suppressed) in the Yangtze River Basin and South China with the eastward propagation of the MJO convective center from the Indian Ocean to the western Pacific.When the MJO is in phase 2 and 3(MJO convective center is located over the Indian Ocean),rainfall probability is significantly enhanced.While in phase 6 and 7(MJO convective center is over the western Pacific),rainfall probability is significantly reduced. MJO in winter influences the rainfall in China mainly through modulating the circulation in the subtropics and mid-high latitudes.For the subtropics,MJO influences the northward moisture transport coming from the Bay of Bengal and the South China Sea by modulating the southern trough of the Bay of Bengal and the western Pacific subtropical high.For the mid-high latitudes,the propagation of the low frequency perturbations associated with the eastward-propagating MJO convection modulate the circulation in the mid-high latitudes,e.g.the East Asian winter monsoon and the low trough over central Asia.  相似文献   

7.
In this paper,the p-σ five layer primitive equation model segmented by mountains and physical parameterizations including short wave radiation; long wave radiation; large-scale and convective condensation;heat and moisture transport from surface to the first model level is used.The horizonial resolution is 5° lat.×5° long.with the integration region from 25°S to 55°N and from 5°W eastward to 175°W.The model was spun up with perpetual June boundary conditions and forcing starting with June zonal mean heights and geostrophic wind field.In order to investigate the effects of SST (sea surface tempefuture) over the equatorial Western Pacific and the Indian Ocean on the Asian summer monsoon,four sets of numerical experments with positive anomalies over the equatorial Western Pacific,and positive and negative anomalies over the Western Indian Ocean,and zonal mean SST (the control case) are performed.The experimental results show that the South Asian low in the lower troposphere and the anticyclone over the South Asia in the uppet troposphere intensified when positive SST anomalies over the equatorial Western Pacific is included.A statistical test method for simulations is proposed.Finally,the influence mechanism of the SST anomalies over the equatorial oceans is discussed.It is worth stressing that the effects of the SST over the equatorial oceans on the Asian summer monsoon can arise as a result of interaction of SST anomalies,atmospheric flow field and heat sources and sinks in the atmosphere.  相似文献   

8.
The characteristics of 30-60 day oscillation (hereafter called LFO ) of the outgoing longwave radiation data (OLR) and its relations to the interannual oscillations of the sea surface temperature (SST) are investigated by using the daily OLR data for the period from January, 1979 to December, 1987 and the corresponding monthly SST data. It is found that the LFO the band the interannual oscillations of the SST monthly anomaly (SSTA) interact each other and they all relate to the occurrence and development of El Nino events closely. Before El Nino event happens, it contributes to the SST's wanning up and to the SST's quasi-biennial oscillation (called QBO for brevity) and three and half years oscillation (called SO for short) being in warm water phase in the equatorial central and eastern Pacific (ECP and EEP) that the LFO in the equatorial western Pacific (EWP) enhances and propagates eastward; When El Nino event takes place, the LFO, SSTA and SSTA's QBO and SO in the EEP interact and strengthen each oth  相似文献   

9.
By using the upper-wind data from July 1980 to June 1983,the variations of the low-frequency oscillation(LFO)in the atmosphere before and during 1982 El Nino have been investigated.Before the El Nino,the LFOpropagates from west to east over the equator of the Eastern Hemisphere and from east to west over 20°N.The eastward propagating LFO over the equator consists of zonal wavenumber 1 propagating eastward andzonal wavenumber 2 with a character of stationary wave.The oscillation of zonal wavenumber 2 can modulatethe oscillation strength.After the onset of the El Nino,the propagating directions of the LFO over the equatorand 20°N of the Eastern Hemisphere change to be westward and eastward,respectively.The LFO over thewestern Pacific weakens rapidly and one coming from middle and high latitudes propagates to the equator.From the phase compositions of streamline fields for the zonal wavenumber 1 of equatorial westward propa-gatirg LFO,it is found that the atmospheric heat source in the equator of the eastern Pacific(EEP)excites aseries of the equatorial cyclones and anticyclones which move northward and westward and form the westwardpropagating LFO over the equator.With the wavelength of 20000km,this kind of equatorial wave is similarto the mixing Rossby-gravity wave.In its westward and northward movement,the circulation in East Asiais modified.This may be the mechanism of the influence of El Nino on the climate of China.  相似文献   

10.
Increased evidence has shown the important role of Atlantic sea surface temperature(SST) in modulating the El Nio-Southern Oscillation(ENSO). Persistent anomalies of summer Madden-Julian Oscillation(MJO) act to link the Atlantic SST anomalies(SSTAs) to ENSO. The Atlantic SSTAs are strongly correlated with the persistent anomalies of summer MJO, and possibly affect MJO in two major ways. One is that an anomalous cyclonic(anticyclonic) circulation appears over the tropical Atlantic Ocean associated with positive(negative) SSTA in spring, and it intensifies(weakens) the Walker circulation. Equatorial updraft anomaly then appears over the Indian Ocean and the eastern Pacific Ocean, intensifying MJO activity over these regions. The other involves a high pressure(low pressure) anomaly associated with the North Atlantic SSTA tripole pattern that is transmitted to the mid-and low-latitudes by a circumglobal teleconnection pattern, leading to strong(weak) convective activity of MJO over the Indian Ocean. The above results offer new viewpoints about the process from springtime Atlantic SSTA signals to summertime atmospheric oscillation, and then to the MJO of tropical atmosphere affecting wintertime Pacific ENSO events, which connects different oceans.  相似文献   

11.
In this paper, interactions between the 30-60 day oscillation, the Walker circulation and the convective activities in the tropical western Pacific during the Northern Hemisphere summer are analyzed by using the observed data of wind fields and high-cloud amounts for the period from 1980 to 1989.The analyzed results show that the 30-60 day oscillation (hereafter called LFO) may be largely affected by the convective activities in the tropical western Pacific. The LFO in the tropical western Pacific during the strong convective activities around the Philippines stronger than those during the weak convective activities around the Philippines. Moreover, in the case of strong convective activities around the Philippines, the LFO in the tropical west-ern Pacific and tropical eastern Indian Ocean generally propagates westward, and it is intensified by the LFO with a westward propagating center of maximum oscillation from the east to 140oE. However, in the case of weak convective activities around the Philippines, the LFO gradually becomes stronger with a eastward propagating center of maximum oscillation from the eastern Indian Ocean to the tropical western Pacific.Corresponding to the 30-60 day oscillation, the Walker circulation is also in oscillation over the tropical Pacific and its circulation cell seems to shift gradually westward from the tropical western Pacific to the tropical eastern In-dian Ocean with strong convective activities around the Philippines. This may maintain the intensification of convective activities there. However, during the weak convective activities around the Philippines, the Walker circula-tion gradually moves eastward and an ascending flow may appear in the equatorial central Pacific. This may cause convective activities to be intensified over the equatorial central Pacific.The analyzed results also show that the LFO in the tropical western Pacific and East Asia may be associated with the interannual oscillation of the SST anomaly in the tropical western Pacific.  相似文献   

12.
The relationships between the tropical Indian Ocean basin(IOB)/dipole(IOD) mode of SST anomalies(SSTAs) and ENSO phase transition during the following year are examined and compared in observations for the period 1958–2008.Both partial correlation analysis and composite analysis show that both the positive(negative) phase of the IOB and IOD(independent of each other) in the tropical Indian Ocean are possible contributors to the El Nio(La Nia) decay and phase transition to La Nia(El Nio) about one year later. However, the influence on ENSO transition induced by the IOB is stronger than that by the IOD. The SSTAs in the equatorial central-eastern Pacific in the coming year originate from subsurface temperature anomalies in the equatorial eastern Indian and western Pacific Ocean, induced by the IOB and IOD through eastward and upward propagation to meet the surface. During this process, however the contribution of the oceanic channel process between the tropical Indian and Pacific oceans is totally different for the IOB and IOD. For the IOD, the influence of the Indonesian Throughflow transport anomalies could propagate to the eastern Pacific to induce the ENSO transition. For the IOB, the impact of the oceanic channel stays and disappears in the western Pacific without propagation to the eastern Pacific.  相似文献   

13.
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   

14.
The present study reveals cross-season connections of rainfall variability in the South China Sea (SCS) region between winter and summer. Rainfall anomalies over northern South China Sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern South China Sea in boreal winter (denoted as in-phase relation) and succeeded by opposite sign rainfall anomalies over southern South China Sea in the following winter (denoted as out-of-phase relation). Analysis shows that the in-phase relation from winter to summer occurs more often in El Niño/La Niña decaying years and the out-of-phase relation from summer to winter appears more frequently in El Niño/La Niña developing years. In the summer during the El Niño/La Niña decaying years, cold/warm and warm/cold sea surface temperature (SST) anomalies develop in tropical central North Pacific and the North Indian Ocean, respectively, forming an east–west contrast pattern. The in-phase relation is associated with the influence of anomalous heating/cooling over the equatorial central Pacific during the mature phase of El Niño/La Niña events that suppresses/enhances precipitation over southern South China Sea and the impact of the above east–west SST anomaly pattern that reduces/increases precipitation over northern South China Sea during the following summer. The impact of the east–west contrast SST anomaly pattern is confirmed by numerical experiments with specified SST anomalies. In the El Niño/La Niña developing years, regional air-sea interactions induce cold/warm SST anomalies in the equatorial western North Pacific. The out-of-phase relation is associated with a Rossby wave type response to anomalous heating/cooling over the equatorial central Pacific during summer and the combined effect of warm/cold SST anomalies in the equatorial central Pacific and cold/warm SST anomalies in the western North Pacific during the mature phase of El Niño/La Niña events.  相似文献   

15.
Present work compares impacts of El Niño Modoki and El Niño on anomalous climate in the Pacific rim during boreal winters of 1979–2005. El Niño Modoki (El Niño) is associated with tripole (dipole) patterns in anomalies of sea-surface temperature, precipitation, and upper-level divergent wind in the tropical Pacific, which are related to multiple “boomerangs” of ocean-atmosphere conditions in the Pacific. Zonal and meridional extents of those “boomerangs” reflect their independent influences, which are seen from lower latitudes in the west to higher latitudes in the east. In the central Pacific, more moisture is transported from the tropics to higher latitudes during El Niño Modoki owing to displacement of the wet “boomerang” arms more poleward toward east. Discontinuities at outer “boomerang” arms manifest intense interactions between tropical and subtropical/extratropical systems. The Pacific/North American pattern and related climate anomalies in North America found in earlier studies are modified in very different ways by the two phenomena. The seesaw with the dry north and the wet south in the western USA is more likely to occur during El Niño Modoki, while much of the western USA is wet during El Niño. The moisture to the southwestern USA is transported from the northward shifted ITCZ during El Niño Modoki, while it is carried by the storms traveling along the southerly shifted polar front jet during El Niño. The East Asian winter monsoon related anticyclone is over the South China Sea during El Niño Modoki as compared to its position over the Philippine Sea during El Niño, causing opposite precipitation anomalies in the southern East Asia between the two phenomena.  相似文献   

16.
The interannual variability of the Madden– Julian Oscillation (MJO) is investigated in an ensemble of 15 experiments performed with the ECHAM4 T30 general circulation model (GCM). The model experiments have been performed with AMIP conditions from January 1979 to December 1993. The MJO signal has been identified applying a principal oscillation pattern (POP) analysis to the 200-mb tropical velocity potential. The results obtained from the model ensemble are compared with 15?y of ECMWF re-analysis and OLR observations. The results suggest that the warm and cold phases of El Niño have some influence on the spatial propagation of the oscillation. Both in the re-analysis and in the model ensemble, the results indicate that during La Niña conditions the MJO is mostly confined west of the date line, with the largest activity located over the Indian Ocean and the western Pacific. In warm El Niño conditions, the convective anomalies associated with the oscillation appear to penetrate farther into the central Pacific. These changes in the MJO convective forcing seem to affect the zonal mean of the rotational component of the flow anomaly, which tends to weaken during warm El Niño periods. Some weak reproducibility of the interannual variability of the MJO activity is found. The results obtained from four-member and eight-member subsamples of the ensemble indicate that the reproducibility of the interannual behaviour of the MJO can be detected by choosing an ensemble of a larger size. Corresponding to the emergence of reproducibility with the increasing size of the sample, the correlation between the MJO activity and the Niño-3 SST anomaly appears to in-tensify.  相似文献   

17.
The role of tropical Atlantic sea surface temperature (SST) anomalies during ENSO episodes over northeast Brazil (Nordeste) is investigated using the CPTEC/COLA Atmospheric General Circulation Model (AGCM). Four sets of integrations are performed using SST in El Niño and La Niña (ENSO) episodes, changing the SST of the Atlantic Ocean. A positive dipole (SST higher than normal in the tropical North Atlantic and below normal in the tropical South Atlantic) and a negative dipole (opposite conditions), are set as the boundary conditions of SST in the Atlantic Ocean. The four experiments are performed using El Niño or La Niña SST in all oceans, except in the tropical Atlantic where the two phases of the SST dipole are applied. Five initial conditions were integrated in each case in order to obtain four ensemble results. The positive SST dipole over the tropical Atlantic Ocean and El Niño conditions over the Pacific Ocean resulted in dry conditions over the Nordeste. When the negative dipole and El Niño conditions over the Pacific Ocean were applied, the results showed precipitation above normal over the north of Nordeste. When La Niña conditions over Pacific Ocean were tested together with a negative dipole, positive precipitation anomalies occurred over the whole Nordeste. Using the positive dipole over the tropical Atlantic, the precipitation over Nordeste was below average. During La Niña episodes, the Atlantic Ocean conditions have a larger effect on the precipitation of Nordeste than the Pacific Ocean. In El Niño conditions, only the north region of Nordeste is affected by the Atlantic SST. Other tropical areas of South America show a change only in the intensity of anomalies. Central and southeast regions of South America are affected by the Atlantic conditions only during La Niña conditions, whereas during El Niño these regions are influenced only by conditions in the Pacific Ocean.  相似文献   

18.
Winter-spring precipitation in southern China tends to be higher (lower) than normal in El Niño (La Niña) years during 1953–1973. The relationship between the southern China winter-spring precipitation and El Niño-Southern Oscillation (ENSO) is weakened during 1974–1994. During 1953–1973, above-normal southern China rainfall corresponds to warmer sea surface temperature (SST) in the equatorial central Pacific. There are two anomalous vertical circulations with ascent over the equatorial central Pacific and ascent over southern China and a common branch of descent over the western North Pacific that is accompanied by an anomalous lower-level anticyclone. During 1974–1994, above-normal southern China rainfall corresponds to warmer SST in eastern South Indian Ocean and cooler SST in western South Indian Ocean. Two anomalous vertical circulations act to link southern China rainfall and eastern South Indian Ocean SST anomalies, with ascent over eastern South Indian Ocean and southern China and a common branch of descent over the western North Pacific. Present analysis shows that South Indian Ocean SST anomalies can contribute to southern China winter-spring precipitation variability independently. The observed change in the relationship between southern China winter-spring rainfall and ENSO is likely related to the increased SST variability in eastern South Indian Ocean and the modulation of the Pacific decadal oscillation.  相似文献   

19.
The composite analysis of the structure of anomalies of vertical motions revealed disturbances in the Walker and Hadley circulations in the whole tropical zone associated with the two types of El Niño. The Eastern Pacific El Niño is characterized by the suppressed convection over the Maritime Continent and by the intensification of ascending motions in the central and eastern Pacific. The Central Pacific El Niño is characterized by the double Walker circulation cell with ascending motions in the central Pacific and descending motions in the western and eastern Pacific. Significant differences in the pattern of vertical circulation anomalies outside the Pacific region are also found in the north and west of the Indian Ocean and in the area of South America and the Caribbean.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号