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1.
Guojun Gu 《Climate Dynamics》2009,32(4):457-471
Intraseasonal (30–80 days) variability in the equatorial Atlantic-West African sector during March–June is investigated using
various recently-archived satellite measurements and the NCEP/DOE AMIP-II reanalysis daily data. The global connections of
regional intraseasonal signals are first examined for the period of 1979–2006 through lag-regression analyses of convection
(OLR) and other dynamic components against a regional intraseasonal convective (OLR) index. The eastward-propagating features
of convection can readily be seen, accompanied by coherent circulation anomalies, similar to those for the global tropical
intraseasonal mode, i.e., the Madden–Julian oscillation (MJO). The regressed TRMM rainfall (3B42) anomalies during the TRMM
period (1998–2006) manifest similar propagating features as for the regressed OLR anomalies during 1979–2006. These coherent
features hence tend to suggest that the regional intraseasonal convective signals might be mostly a regional response to,
or closely associated with the MJO, and probably contribute to the MJO’s global propagation. Atmospheric and surface intraseasonal
variability during March–June of 1998–2006 are further examined using the high-quality TRMM Microwave Imager (TMI) sea surface
temperature (SST), columnar water vapor, and cloud liquid water, and the QuikSCAT oceanic winds (2000–2006). Enhanced (suppressed)
convection or positive (negative) rainfall anomalies approximately cover the entire basin (0°–10°N, 30°W–10°E) during the
passage of intraseasonal convective signals, accompanied by anomalous surface westerly (easterly) flow. Furthermore, a unique
propagating feature seems to exist within the tropical Atlantic basin. Rainfall anomalies always appear first in the northwestern
basin right off the coast of South America, and gradually extend eastward to cover the entire basin. A dipolar structure of
rainfall anomalies with cross-equatorial surface wind anomalies can thus be observed during this evolution, similar to the
anomaly patterns on the interannual time scale discovered in past studies. Coherent intraseasonal variations and patterns
can also be found in other physical components.
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| Guojun GuEmail: |
2.
热带对流和环流季内振荡强度与海表温度关系对比研究 总被引：2，自引：1，他引：1
利用外逸长波辐射(OLR）、风场和海表温度(SST)资料, 研究了热带大气季节内振荡(ISO)强度的季节变化特征, 发现热带印度洋和热带西太平洋区域是OLR和风场季内振荡最主要的共同活跃区。对比分析了OLR和风场季内振荡强度与海表温度异常之间的年际异常关系, 发现OLR季内振荡强度异常与海表温度异常之间存在显著局地正相关关系, 即在热带中东太平洋区域、热带西北太平洋区域和热带西南太平洋区域, 当海表温度正(负)异常时, OLR季内振荡增强(减弱),特别在冬春季节这一关系更清楚。除个别区域外, 风场季内振荡强度异常与海表温度异常不存在类似OLR的局地关系。OLR和风场季内振荡强度异常与海表温度异常之间局地和非局地关系的差异, 体现了两种要素特性的本质差异。但两种要素季内振荡强度在El Niño事件发展过程中的变化基本一致, 即在气候场中季内振荡活跃的区域, 事件发生之前季内振荡会增强, 并逐渐向东传播, 事件发生之后这些区域振荡减弱。 相似文献
3.
Circulation Variability Reflected in Ice Core and Lake Records of the Southern Tropical Andes 总被引：2，自引：0，他引：2
The circulation mechanisms of climate anomalies in the southern tropical Andes are of particular interest for the January–February core of the precipitation season. With this focus, we evaluate in context upper-air and surface analyses, water level measurements of Lake Titicaca, and records of net balance and 18O from ice cores. Precipitation is more abundant with enhanced and southward expanded easterlies through a deep layer of the troposphere over the southern tropical Andes. Concomitant with this is a southward displaced circulation system over the equatorial Atlantic, entailing reduced interhemispheric gradient of sea surface temperature (SST; cold/warm anomalies in the North/South), more southerly position of the surface wind confluence and Intertropical Convergence Zone, and thus more abundant rainfall in Northeast Brazil. Such ensemble of circulation departures in boreal winter is common to the high phase of the Southern Oscillation.18O in the ice cores from Peru's Quelccaya Icecap, as wellas the cores from Sajama and Ilimani in Bolivia is more negative with more abundant precipitation, both in the same annual cycle and on interannual timescales. The large-scale circulation departures associated with the more negative 18O are in the sense as for anomalously abundant precipitation activity over the southern tropical Andes. The variability of 18O seasonally and interannually appears to be controlled mainly by the fate of the water vapor along its trajectory and over the Andes, rather than by the SST of the South Atlantic source region. 相似文献
4.
Summary This study investigates the circulation anomalies associated with the intraseasonal evolution of wet and dry years over western Tanzania (29–37° E, 11.5–4.75° S) and how the onset and withdrawal of the rainy season as well as its wet spell characteristics are modified. It is found that for wet years, the rains begin earlier and end later, with strong wet spells occurring during the season, and there tend to be a greater number of moderate wet spells (although not necessarily more intense wet spells) than in dry years. In dry years, late onset and early cessation of the rainy season occur, often with an extended dry spell soon after the onset, and there tend to be a greater number of dry spells within the season. Large negative outgoing long wave radiation (OLR) anomaly values tend to be located between 20° and 40° E with anomalous westerly flow at 850 hPa occurring across the continent from 10° E to the tropical western Indian Ocean during wet spells in the anomalously wet seasons. Anomalously dry seasons are characterised by large positive OLR anomalies over 30–50° E as well as easterly anomalies at 850 hPa and westerly anomalies at 200 hPa. Eastward propagating intraseasonal anomalies are slower during the wet years implying that the convection remains over Tanzania longer. On the intraseasonal scale, Hovmoeller analyses of OLR and 850 and 200 hPa zonal wind indicate that convection over western Tanzania may be associated with a flux of moisture from the tropical southeast Atlantic and Congo basin followed by weak easterlies from the tropical western Indian Ocean.On interannual scales, wet (dry) years are characterized over the Indian Ocean by weaker (stronger) equatorial westerlies and weaker (stronger) trades that lead to less (more) export of equatorial moisture away from East Africa and increased (decreased) low-level moisture flux convergence over southern Tanzania, respectively. These anomalies arise from an anticyclonic (cyclonic) anomaly over the tropical western Indian Ocean during wet (dry) austral summers that may be related to cool (warm) SST anomalies there. Large scale modulation of the Indian Ocean Walker cell is also evident in both cases, but particularly for the dry years.Current affiliation: Tanzania Meteorological Agency, P.O. Box 3056, Dar es Salaam, Tanzania 相似文献
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6.
POSSIBLE INFLUENCES OF THE TROPICAL INDIAN OCEAN DIPOLE ON THE EASTWARD PROPAGATION OF MJO 总被引：1，自引：0，他引：1
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
7.
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
8.
本文从赤道β平面近似下的线性化扰动方程组出发,基于第二类条件不稳定(CISK)理论,研究了热带对流层大气准40天低频振荡的动力机制。研究发现,当对流层中、上层存在较大的对流凝结加热时可激发出纬向波数为1、周期为40天左右的不稳定Kelvin波,它以每天8到11个经度的相速缓慢向东移动。由此指出,观测到的热带对流层大气30—50天的低频振荡可能正是这种由对流凝结加热所驱动的缓慢东移的Kelvin波的具体表现。这可对热带对流层大气30—50天低频振荡现象的动力机制给以初步的物理解释。 相似文献
9.
2010年华南前汛期持续性降水异常与准双周振荡 总被引：3，自引：1，他引：3
利用中国台站逐日降水资料以及NCEP-DOE逐日再分析资料,分析了2010年华南汛期降水异常的低频特征及大气环流的影响。结果表明,2010年华南汛期降水异常呈显著的低频振荡特征,其中前汛期以10~20天振荡（准双周振荡）为主,后汛期以20~50天振荡（季节内振荡）为主。重点讨论了准双周尺度上前汛期持续性降水异常与中高纬和热带地区大气低频振荡的关系。中高纬地区的低频环流可通过Rossby波能量沿着低频遥相关波列的频散影响华南低频环流的变化。波活动通量分析显示,西西伯利亚作为Rossby波源,其波能量沿着横跨欧亚大陆的低频遥相关波列向我国东部地区频散,引起该地扰动加强,从而引起华南低频环流及垂直运动的变化进而造成华南降水的异常。热带东印度洋的准双周振荡是影响华南前汛期降水的另一低频来源。当赤道东印度洋对流旺盛（抑制）,其上空为强上升（下沉）气流,低层辐合（辐散）高层辐散（辐合）,而华南上空盛行下沉（上升）运动,不利于（有利于）华南降水。来自中高纬和低纬的低频信号的叠加并配合低频水汽输送共同影响了华南环流异常的低频变化,从而引起华南的低频降水异常,有利于华南持续性降水异常的发生。 相似文献
10.
利用１９８０年１月～１９８３年１２月已滤波的ＯＬＲ资料，采用经验正交函数分析方法，对１９８０～１９８１年（正常年）和１９８２～１９８３年（异常年）低纬西太平洋和印度洋地区低频振荡的空间分布及遥相关特征进行了研究．结果表明：正常年与异常年，这些地区低频振荡的强度、空间型及时间系数的变化有较大的差异．此外，还发现正常年这些地区存在３种低频遥相关，即赤道西太平洋型，北热带西太平洋型和赤道印度洋型；异常年则仅存在２种低频遥相关，即赤道西太平洋型和南热带西太平洋型．由于受厄尔尼诺事件的影响，东西向偶极型低频振荡中心的位置和强度都有很大的变化 相似文献