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1.
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
2.
气候平均状况下亚洲夏季风的季节内演变过程 总被引：5，自引：0，他引：5
根据1979—1995年美国NOAA的向外长波辐射逐日资料,用功率谱分析和带通滤波方法,对气候平均状况下亚洲夏季风的季节内演变过程进行分析,归纳得到亚洲季风区各个子系统季节内变化的8个关键阶段。利用1979—1999年NCEP/NCAR的大气环流再分析资料及中国气象局降水资料CMAP,对每个关键阶段亚洲夏季风的环流和降水的时空演变特征进行分析,得到亚洲季风区环流和降水季节内变化的物理图像。研究表明,在不同的季节内演变阶段,亚洲夏季风各个子系统成员的环流系统的变化特征可以将亚洲夏季风系统的季节内演变过程较好地描述出来。 相似文献
3.
This study focuses on deep convection anomalies in tropical regions in winter-spring period and
their possible influence on the following summer rainfall in Shandong province. On the basis of monthly
precipitation wet and dry summers in Shandong are defined according to a precipitation index. Then monthly OLR
data, observed by NOAA satellites, are used to diagnose the features of deep convection for both wet and dry
summers. It is found that negative anomalies seem dominant prior to wet summers, while large areas of positive
anomalies appear prior to dry summers in tropical oceans. The differences are remarkable especially in the western,
middle and eastern tropical Pacific as well as in the tropical Indian Ocean. Correlative analysis confirms the
relations between OLR and precipitation. Subtropical High, which plays an essential role in summer rainfall, is also connected with the deep conviction. Altogether eight EOF-CCA forecast models are established on the basis of
the above study. The assessment of the models relies on the gauge observing precipitation in 1997 and 1998. The
results show that models using spring OLR data appear to be more practicable than those using winter OLR data,
and the models established with OLR in western Pacific and the Indian Ocean perform better than the others. 相似文献
4.
Sub-seasonal variability of summer (May–October) rainfall over the ChangJiang Valley exhibits two dominant timescales, one with a quasi-biweekly (QBW) period (10–20 days) and the other with an intraseasonal oscillation (ISO) period (20–60 days). A significant positive correlation (at a 99% confidence level) was found between the summer precipitation anomaly and the intensity of the QBW and ISO modes in the region. By examining the composite structure and evolution characteristics, we note that the QBW mode is characterized by a northwest–southeast oriented wave train pattern, moving southeastward. The perturbations associated with the ISO mode propagate northwestward in strong ISO years but southeastward in weak ISO years. A marked feature is the phase leading of low-level moisture to convection in both the QBW and ISO mode. When the summer rainfall is strong in the ChangJiang Valley, large-scale atmospheric conditions in the strong QBW/ISO activity region are characterized by deeper moist layer, convectively more unstable stratification and greater ascending motion. Such mean conditions favor the growth of the QBW and ISO perturbations. Thus, a significant positive correlation between the summer precipitation and the strength of sub-seasonal variability arises from the large-scale control of the summer mean flow to perturbations. 相似文献
5.
R. Justin Small Shang-Ping Xie Eric D. Maloney Simon P. de Szoeke Toru Miyama 《Climate Dynamics》2011,36(5-6):867-890
Intraseasonal variability in the eastern Pacific warm pool in summer is studied, using a regional ocean?Catmosphere model, a linear baroclinic model (LBM), and satellite observations. The atmospheric component of the model is forced by lateral boundary conditions from reanalysis data. The aim is to quantify the importance to atmospheric deep convection of local air?Csea coupling. In particular, the effect of sea surface temperature (SST) anomalies on surface heat fluxes is examined. Intraseasonal (20?C90?day) east Pacific warm-pool zonal wind and outgoing longwave radiation (OLR) variability in the regional coupled model are correlated at 0.8 and 0.6 with observations, respectively, significant at the 99% confidence level. The strength of the intraseasonal variability in the coupled model, as measured by the variance of outgoing longwave radiation, is close in magnitude to that observed, but with a maximum located about 10° further west. East Pacific warm pool intraseasonal convection and winds agree in phase with those from observations, suggesting that remote forcing at the boundaries associated with the Madden?CJulian oscillation determines the phase of intraseasonal convection in the east Pacific warm pool. When the ocean model component is replaced by weekly reanalysis SST in an atmosphere-only experiment, there is a slight improvement in the location of the highest OLR variance. Further sensitivity experiments with the regional atmosphere-only model in which intraseasonal SST variability is removed indicate that convective variability has only a weak dependence on the SST variability, but a stronger dependence on the climatological mean SST distribution. A scaling analysis confirms that wind speed anomalies give a much larger contribution to the intraseasonal evaporation signal than SST anomalies, in both model and observations. A LBM is used to show that local feedbacks would serve to amplify intraseasonal convection and the large-scale circulation. Further, Hovm?ller diagrams reveal that whereas a significant dynamic intraseasonal signal enters the model domain from the west, the strong deep convection mostly arises within the domain. Taken together, the regional and linear model results suggest that in this region remote forcing and local convection?Ccirculation feedbacks are both important to the intraseasonal variability, but ocean?Catmosphere coupling has only a small effect. Possible mechanisms of remote forcing are discussed. 相似文献
6.
The timing of the South Asian High (SAH) establishment over the Indochina Peninsula (IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-central China in summer are investigated by using NCEP/NCAR daily reanalysis data, outgoing longwave radiation (OLR) data and the daily precipitation data from 753 weather stations in China. It is found that the transitions of the zonal wind vertical shear and convection establishment over tropical Asia are earlier (later) in the years of early (late) establishment of SAH. In the lower troposphere, anti-cyclonic (cyclonic) anomaly circulation dominates the equatorial Indian Ocean. Correspondingly, the tropical Asian summer monsoon establishes earlier (later). Furthermore, the atmospheric circulation and the water vapor transport in the years of advanced SAH establishment are significantly different from the delayed years in Asia in summer. Out-of-phase distribution of precipitation in eastern-central China will appear with a weak (strong) SAH and western Pacific subtropical high, strong (weak) ascending motion in the area south of Yangtze River but weak (strong) ascending motion in the area north of it, and cyclonic (anti-cyclonic) water vapor flux anomaly circulation from the eastern-central China to western Pacific. Accordingly, the timing of the SAH establishment at the upper levels of IP is indicative of the subsequent onset of the tropical Asian summer monsoon and the flood-drought pattern over eastern-central China in summer. 相似文献
7.
利用美国国家环境预测中心与国家大气研究中心（NCEP/NCAR）逐日再分析资料,针对北大西洋多年代际振荡（AMO）两个不同位相,对逐候200 hPa经向风异常进行EOF分析,发现在AMO正、负位相期间,欧亚副热带波列的季节内活动存在明显差异。利用超前—滞后回归,对比了不同AMO位相下副热带波列及其相联系的印度夏季降水的季节内活动演变特征,分析有关的大气环流,探究波列影响降水的机制。结果表明:在AMO负位相期间,由格陵兰岛以南北大西洋经大不列颠岛、地中海、黑海—里海向南亚北部传播的副热带波列的季节内演变,在印度中部引起下沉,导致中部及西北部季节内降水减少,波列负位相相反;在AMO正位相期间,副热带波列西起冰岛以南北大西洋经丹麦南部、俄罗斯西部、中亚向南亚东北部传播,对应该波列的季节内演变,辐合上升区在印度中部和东西两侧,使得该区域季节内降水增加,波列负位相相反。于是,AMO通过调制夏季欧亚副热带波列的季节内活动,可以对印度夏季降水的季节内变化空间型及演变发挥显著影响。 相似文献
8.
M. I. Vitorino P. L. da Silva Dias N. J. Ferreira 《Meteorology and Atmospheric Physics》2006,93(1-2):17-35
Summary Atmospheric variability in outgoing long-wave radiation (OLR) and tropospheric relative vorticity (VOR) over the South American
region was studied from 1979 to 1996 using the complex Morlet wavelet function. The analyses focus on spatial variation in
intraseasonal and submonthly scales. Scalograms were used to measure submonthly intraseasonal oscillations in convection,
which were found to be predominant in the tropical regions. However, 7-day and 15-day oscillations were observed at tropical
and extratropical latitudes in spring and winter, indicating that transient disturbances play a more prominent role. Regarding
VOR, tropical energy intensities were highest in the spring and summer, whereas subtropical and extratropical energy intensities
were highest in the autumn and winter. The dynamics of the 25-day and 45-day VOR oscillations indicates a possible correlation
with Rossby waves over the eastern tropical Pacific Ocean, mainly during the summer. During winter, the 7-day and 15-day VOR
oscillations are more frequent at higher latitudes and are enhanced along storm tracks. It was also observed that convection
amplitudes in the regions of maximum intensity change appreciably from year to year and from season to season, showing that
the behavior of the submonthly and intraseasonal oscillations is nonperiodic and correlates strongly with El Ni?o/Southern
Oscillation years. These results confirm the efficiency of wavelet analysis for time-scale studies of atmospheric variability. 相似文献
9.
A dipole pattern in convection between the South Atlantic convergence zone and the subtropical plains of southeastern South America characterizes summer intraseasonal variability over the region. The dipole pattern presents two main bands of temporal variability, with periods between 10 and 30 days, and 30 and 90 days; each influenced by different large-scale dynamical forcings. The dipole activity on the 30–90-day band is related to an eastward traveling wavenumber-1 structure in both OLR and circulation anomalies in the tropics, similar to that associated with the Madden–Julian oscillation. The dipole is also related to a teleconnection pattern extended along the South Pacific between Australia and South America. Conversely, the dipole activity on the 10–30-day band does not seem to be associated with tropical convection anomalies. The corresponding circulation anomalies exhibit, in the extratropics, the structure of Rossby-like wave trains, although their sources are not completely clear. 相似文献
10.
ENSO循环在夏季的不同位相对东亚夏季风的影响 总被引：20，自引：6，他引：14
采用ＳＳＴＡ、风场、ＯＬＲ以及中国１６０站降水、气温等资料,根据赤道中东太平洋ＳＳＴＡ的逐季变化,将ＥＮＳＯ循环过程在夏季的位相分为５种型。对其相应的Ｗａｌｋｅｒ环流的显著性检验发现,Ａ型与Ｃ型夏季的差别最为显著。夏季要素场合成分析发现。Ａ型与Ｃ型的情形差别最明显。Ａ型夏季的要素场与弱夏季风年的相似;Ｃ型夏季的要素场与强夏季风年的相似。 相似文献
11.
热带西太平洋暖池上空对流活动对东亚夏季风季节内变化的影响 总被引：40，自引：8，他引：40
本文通过1978—1989年热带西太平洋暖池上空的OLR资料、500 hPa高度场和降水的逐旬资料分析了热带西太平洋暖池上空对流活动对东亚夏季风季节内变化的影响。分析结果表明:在菲律宾周围对流活动强的夏季，西太平洋副热带高压在初夏向北突跳明显，即6月突跳明显，并且往往有两次向北突跳，这使得东亚夏季风降水雨带向北突跳明显，因此，雨带不可能在江淮流域维持；相反，在菲律宾周围对流活动弱的夏季，西太平洋副热带高压在初夏向北突跳不明显，即6月突跳不明显，它长期在江南上空维持，这样，东亚夏季风降水雨带往往在长江中、下 相似文献
12.
1998年我国东部大陆夏季风特征研究 总被引：4，自引：1，他引：4
利用NCEP／NCAR再分析资料和OLR资料，研究了1998年我国东部大陆夏季风的特征。结果指出，1998年夏季副高脊线的平均位置偏南，华南地区和长江流域的夏季风较强，强对流维持时间长；华北地区的夏季风较弱，对流比常年偏弱；我国东部大陆夏季风存在明显的低频振荡现象。 相似文献
13.
The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century 总被引：4，自引：0，他引：4
K. R. Sperber H. Annamalai I.-S. Kang A. Kitoh A. Moise A. Turner B. Wang T. Zhou 《Climate Dynamics》2013,41(9-10):2711-2744
The boreal summer Asian monsoon has been evaluated in 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 GCM simulations of the late twentieth Century. Diagnostics and skill metrics have been calculated to assess the time-mean, climatological annual cycle, interannual variability, and intraseasonal variability. Progress has been made in modeling these aspects of the monsoon, though there is no single model that best represents all of these aspects of the monsoon. The CMIP5 multi-model mean (MMM) is more skillful than the CMIP3 MMM for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations. Additionally, for rainfall/convection the MMM outperforms the individual models for the time mean, the interannual variability of the East Asian monsoon, and intraseasonal variability. The pattern correlation of the time (pentad) of monsoon peak and withdrawal is better simulated than that of monsoon onset. The onset of the monsoon over India is typically too late in the models. The extension of the monsoon over eastern China, Korea, and Japan is underestimated, while it is overestimated over the subtropical western/central Pacific Ocean. The anti-correlation between anomalies of all-India rainfall and Niño3.4 sea surface temperature is overly strong in CMIP3 and typically too weak in CMIP5. For both the ENSO-monsoon teleconnection and the East Asian zonal wind-rainfall teleconnection, the MMM interannual rainfall anomalies are weak compared to observations. Though simulation of intraseasonal variability remains problematic, several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from India to the equatorial west Pacific. The MMM also well represents the space–time evolution of intraseasonal outgoing longwave radiation anomalies. Caution is necessary when using GPCP and CMAP rainfall to validate (1) the time-mean rainfall, as there are systematic differences over ocean and land between these two data sets, and (2) the timing of monsoon withdrawal over India, where the smooth southward progression seen in India Meteorological Department data is better realized in CMAP data compared to GPCP data. 相似文献
14.
热带大气季节内振荡对西南地区东部夏季降水的影响及其可能机制 总被引：3，自引：2，他引：1
利用1979~2013年6~8月的西南地区东部20个台站日降水量资料、逐日MJO(Madden-Julian Oscillation)指数、全球OLR(Outgoing Longwave Radiation)逐日格点资料以及NCEP/NCAR再分析日资料,采用合成分析和线性回归等方法,对夏季MJO不同位相活动影响西南地区东部夏季降水的原因及其可能机制进行了初步分析。研究表明,MJO与西南地区东部夏季降水之间存在着显著的关系,当MJO处于第4(第6)位相时,由于西太平洋副高位置偏南(偏北)、向西南地区东部的水汽输送偏多(偏少),在异常上升(下沉)气流影响下,西南地区东部夏季降水偏多(偏少)。MJO影响西南地区东部夏季降水的可能原因是:当MJO处于第4位相时,赤道东印度洋地区上空大气释放凝结潜热,其激发东北向传播的异常波动,进而影响东亚环流,使得西南地区东部出现夏季降水偏多的环流形势,西南地区东部夏季降水增多;但在第6位相时,西太平洋地区上空对流释放的凝结潜热,其激发PJ(太平洋-日本)型Rossby波列,出现不利于西南地区东部夏季降水的环流形势,西南地区东部夏季降水偏少。 相似文献
15.
Influence of the intraseasonal variability on heat waves in subtropical South America 总被引：1，自引：1，他引：0
The influence of the intraseasonal variability on heat wave development over subtropical South America during austral summer is analyzed. The role of the South Atlantic Convergence Zone (SACZ) on this development is documented. Results show that intraseasonal variability can explain on average at least 32% of summer temperature variance. Moreover, 73% of the heat waves in subtropical South America develop in association with an active SACZ. The analysis of pentad maps shows that warm conditions in the region under study develop in association with the strengthening of an anticyclonic anomaly, which is discernible over the subtropical regions at least 15?days before temperature peak occurrence. That circulation anomaly is embedded in a large-scale Rossby wave train extending along the South Pacific Ocean that is linked to convection anomalies at the equatorial western and central Pacific Ocean. In addition, the development of the anticyclonic circulation over subtropical South America appears to be strengthened by the subsidence conditions promoted by the active SACZ, which result in temperature rise in the subtropical region under relatively dry conditions. On the other hand, during the last 2?days of evolution, SACZ activity weakens and the progressive temperature rise in the region is dominated by warmer and moister air being anomalously advected from the north. Results confirm the important role that SACZ activity on intraseasonal time scales has in inducing persistent circulation anomalies at the subtropical regions that can result in the development of persistent heat waves, and very extreme daily temperature. 相似文献
16.
利用1979—2018年夏季逐日观测和再分析数据，对北半球夏季热带季节内振荡影响我国夏季降水的规律和预测方法开展了研究。首先，利用非传统滤波即异常相对倾向（Anomalous Relative Tendency，ART）方法获取了气象要素的次季节变化分量，并采用EOF分析方法提取了北半球夏季热带主要季节内振荡信号，结果表明向外长波辐射（Outgoing Longwave Radiation，OLR）异常相对倾向EOF前两个模态共同反映了北半球夏季起源于印度洋并向东和向北传播的、具有30~60 d周期的季节内振荡（Boreal Summer Intraseasonal Oscillation，BSISO）信号。回归分析表明，该季节内振荡信号能够导致当地及其北面地区低层风场和位势高度场异常，影响该地区及其北面地区的水汽辐合辐散，从而能引起我国尤其是我国南方地区季节内旱涝变化，并一定程度上反映了我国异常雨带的向北推进过程。而后，将提取的热带主要季节内振荡信号作为预测因子，将降水异常相对倾向作为先行预板对象，利用多元线性回归方法构建了我国夏季旬降水异常相对倾向的预报模型，将预报的旬降水异常相对倾向加上观测已知的降水近期背景距平，从而得到旬降水距平的预报结果。通过历史回报和交叉检验，评估了该模型对梅雨期我国江淮流域降水（包括2020年梅汛期异常降水）的次季节预测能力。 相似文献
17.
18.
The spatio-temporal variability in summer rainfall within eastern China is identified based on empirical orthogonal function
(EOF) analysis of daily rain-gauge precipitation data for the period 1979–2003. Spatial coherence of rainfall is found in
the Yangtze Basin, and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal
oscillation (ISO) of Yangtze rainfall. The ensemble mean wavelet spectrum, representing statistically significant intraseasonal
variability, shows a predominant oscillation in summer Yangtze rainfall with a period of 20–50 days; a 10–20-day oscillation
is pronounced during June and July. This finding suggests that the 20–50-day oscillation is a major agent in regulating summer
Yangtze rainfall. Composite analyses reveal that the 20–50-day oscillation of summer Yangtze rainfall arises in response to
intraseasonal variations in the western North Pacific subtropical high (WNPSH), which in turn is modulated by a Rossby wave-like
coupled circulation–convection system that propagates northward and northwestward from the equatorial western Pacific. When
an anomalous cyclone associated with this Rossby wave-like system reaches the South China Sea (SCS) and Philippine Sea, the
WNPSH retreats northeastward due to a reduction in local pressure. Under these conditions, strong monsoonal southwesterlies
blow mainly toward the SCS–Philippine Sea, while dry conditions form in the Yangtze Basin, with a pronounced divergent flow
pattern. In contrast, the movement of an anomalous anticyclone over the SCS–Philippine Sea results in the southwestward extension
of the WNPSH; consequently, the tropical monsoonal southwesterlies veer to the northeast over the SCS and then converge toward
the Yangtze Basin, producing wet conditions. Therefore, the 20–50-day oscillation of Yangtze rainfall is also manifest as
a seesaw pattern in convective anomalies between the Yangtze Basin and the SCS–Philippine Sea. A considerable zonal shift
in the WNPSH is associated with extreme dry (wet) episodes in the Yangtze Basin, with an abrupt eastward (westward) shift
in the WNPSH generally leading the extreme negative (positive) Yangtze rainfall anomaly by a 3/8-period of the 20–50-day oscillation.
This finding may have implications for improving extended-range weather forecasting in the Yangtze Basin. 相似文献
19.
20.
利用四川省132个气象观测站降水资料和NOAA的逐日向外长波辐射(OLR)资料,分析了主汛期热带东印度洋MJO活动异常年低频对流传播的显著差异,及其影响四川盆地主汛期降水的物理过程。探讨了热带东印度洋MJO活跃年低频振荡向四川盆地传播的路径和源头,以及孟加拉湾西南季风系统、东亚副热带季风系统的低频振荡分别对四川盆地主汛期低频对流活动的影响。结果表明:热带印度洋的低频对流激发了孟加拉湾西南季风ISO进入活跃期,并在西南气流的引导下继续向四川盆地传播;低频对流先从热带印度洋东传至菲律宾群岛南部的热带洋面,并向东亚副热带地区北传,激发了东亚副热带季风ISO的活跃加强,进而向四川盆地西传。热带印度洋MJO活动异常对四川盆地降水的调制,正是通过两支季风系统(孟加拉湾夏季风和东亚副热带夏季风)的共同作用,影响了四川盆地主汛期异常的对流活动以及降水的多寡。 相似文献