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关于热带大气低频振荡的一个简单模式与数值模拟 总被引：1，自引：0，他引：1
本文首先从观测事实分析了热带大气的低频振荡现象，然后从理论上加以研究。为此，本文建立了一个包括触发热源和CISK机制的三维线性模式，用此模式讨论了热带大气低频振荡的性质、结构、传播和动力学机制。从模式的计算结果得到了周期为30d左右以大约9 m/s的速度向东传播的低频振荡现象，这种振荡为Kelvin波型的响应和向西传播的Rossby波型的响应的结合。计算还表明，这种振荡的周期与触发热源的周期关系不大，这说明了热带大气的低频振荡是大气自身的固有振荡，它是大尺度运动与对流凝结加热相互作用的结果。 相似文献
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运用一个包含Wave-CISK机制的斜压半地转8层模式和本征函数展开方法，研究了三种不同的对流凝结加热廓线对低纬大气的30—60天低频振荡的影响。研究表明，不同的加热廓线分布时30～60天低频振荡具有不同的相速和周期，并且低频振荡特征相速的量级都是o(10m／s)，由Wave-CISK机制激发的低频CISK—Kelvin波和CISK—Rossby波都是稳定的。同时，还进一步揭示了不同加热廓线对低纬大气30～60天低频振荡垂直结构的影响。 相似文献
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大气对热带热源低频响应的数值研究 总被引：3，自引：0，他引：3
本文设计—关于基本气流线性化的二层球面模式研究大气对不同类型赤道热源的低频响应,分析了全球大气40—50天低频振荡的结构和传播特点。结果表明:全球大气对热带热源响应特征是在热带地区表现为东西向非对称的热源东侧的Kelvin响应和西侧的Rossby响应,高低层反位相;在中高纬响应是具有低频振荡的二维Rossby波列,且具有相当正压结构。低频振荡的传播特征表明热带大气对移动性热源的响应更有利于振荡的向东传播,且该振荡可以沿波列路径向中高纬度传播,然后再折向低纬。二维Rossby波列是联系着热带和中高纬度地区低频振荡的基本动力学途径。该波列的形成取决于基本气流的分布,冬半球波列振幅较大。因此本文认为40—50天低频振荡是全球尺度的现象,它是一涉及到热带对流加热、赤道Kelvin波、亦道Rossby波、二维Rossby波列以及基本气流等动力学相互作用的过程。 相似文献
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1大气低频振荡的一般概念一些气象因子具有10～90天的准周期变化规律，这种振荡常在30～60天具有较大的振幅，通常将大气中一些气象因子具有的10～20天和30～60天准周期性变化称为大气低频振荡。现在发现具有低频振荡特性的气象因子主要有：纬向风速。气压。云量、降水、南亚季风槽位置、地气系统的射出（外逸）长波辐射等。2大气低频振荡的研究动态七十年代初Madden－J；11tan发现热带岛屿上的风场和地面气压场存在40～50天的准周期性变化，最早提出热带大气低频振荡的现象。此后由于EINino现象和海一气相互作用的深入研究，大气低频振荡… 相似文献
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青藏高原感热加热异常与夏季低频环流的数值研究 总被引：5，自引：1，他引：5
使用科学院大气物理研究所两层大气环流模式，就青藏高原地表感热通量异常减少对夏季东半球大气环流及亚洲季风低频变化的影响进行了数值试验研究。结果表明：高原地区感热通量异常减少时，南海及西太平洋地区低频振荡方差百分率增大；高原感热异常加热对东亚和印度季风子系统具有不同的影响，季风区低频扰动的位相，中高纬低频扰动的结构，强度和经向传播速度都发生改变，ＥＡＰ波列变得更为清楚典型，大圆上的低频涡旋一直传播到我 相似文献
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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
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热带积云对流加热在全球大气遥响应中的重要作用──数值试验结果 总被引：5，自引：1，他引：5
利用ＩＡＰ两层大气环流模式模拟研究了热带地区积云对流加热在大气对赤道东太平洋海温正异常响应中的作用。通过对积分结果进行分析发现：热带地区积云对流在大气对赤道东太平洋海温正异常的响应过程中起着非常重要的作用。若热带地区的积云对流加热减弱则大气中的遥响应（相关）型也减弱。同时我们还发现，热带地区的积云对流加热加强则响应场的３０—６０ｄ低频振荡也得到加强。 相似文献
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Considering the multiscale character of LFO (low-frequency oscillation) in the tropical atmosphere, the effects of SST on LFO in the tropical atmosphere are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies (SSTAs). Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive (negative) SSTAs can make waves decay (grow). 相似文献
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Impacts of SST and SST Anomalies on Low-Frequency Oscillation in the Tropical Atmosphere 总被引：4，自引：0，他引：4
Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）. 相似文献
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A DYNAMICAL ANALYSIS OF BASIC FACTORS OF LOW-FREQUENCY OSCILLATION IN THE TROPICAL ATMOSPHERE* 
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下载免费PDF全文 Based on dynamical characteristics of the tropical atmosphere,a mathematical model of low-frequency oscillation (LFO hereinafter) in low-latitudes has been developed.The analysis shows that the distributive features (shear of wind speed) of easterlies and westerlies in low-latitudes,the divergence and convergence of meridional and zonal flow,the vertical structure of diabatic heating and the Coriolis parameter f are the basic factors resulting in the LFO,while quasi-periodical baroclinity development or index cycle of westerly waves in middle-latitudes of the Southern Hemisphere is an external forcing to the LFO in the tropical atmosphere.The resonance on adequate condition makes LFO suddenly enhanced. 相似文献
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1991年江淮特大暴雨与东亚大气低频振荡 总被引：42，自引：3，他引：42
本文分析了１９９１年江淮特大暴雨期间东亚大气低频振荡活动。从低频振荡特征看，江淮雨量和东亚风场中低频振荡现象是普遍存在的，风场的振荡周期具有显著的地域和频域分布特征。从低频波的传播看，这一梅雨过程的两个异常阶段（５月下半月和７月上半月），东亚风场低频波的水平传播方向发生了显著的变化。分析指出，低纬地区低频波虽有不同传播方向，但都将暖湿空气以低频形式输送到江淮以南，它与北侧的低频冷空气在江淮地区相互作用，从而导致该地区以低频形式出现的３场特大暴雨。 相似文献
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An equatorial β-plane model which includes realistic non-uniform land-sea contrast and the underlying surface temperature distribution is used to simulate the 30-60 day oscillation (LFO) processes in tropical atmosphere, with emphasis on its longitude-dependent evolution and convective seesaw between Indian and the western Pacific oceans.The model simulated the twice-amplification of the disturbances over Indian and the western Pacific oceans while they are travelling eastward. It reproduced the dipole structure caused by the out-of-phase oscillation of the active centres in these two areas and the periodical transition between the phases of LFO. It is suggested that the convective seesaw is the result of interaction of the internal dynamics of tropical atmosphere with the zonally non-uniform thermal forcing from underlying surface. The convective activities are suppressed over Indonesia mari-time continents whilst they are favoured over the Indian Ocean and western Pacific warm waters, so there formed two active oscillation centres. The feedback of convection with large-scale flow slows down the propagation of disturb-ances when they are intensifying over these two areas, therefore they manifest a kind of quasi-stationary component to favor the ‘dipole’ structure. Whereas the disturbances weaken and speed up over the eastern Pacific cold water re-gion due to the interaction of sensible heating and evaporation with perturbational wind. Therefore the two major centers just show out-of-phase oscillation during onecycle around the latitudinal beltBy introducing the SST anomalies in El Ni?o and La Ni?a years into the surface temperature, we also show that they have significant influence on LFO processes. In an anomalously warm year, the LFO disturbances dissipate more slowly over the central-eastern Pacific region and can travel farther eastward; whilst in an anomalously cold year, the opposite is true. 相似文献
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LOW FREQUENCY OSCILLATION IN EAST ASIA DURING THE 1991 EXCESSIVELY HEAVY RAIN OVER THE CHANGJIANG-HUAIHE RIVER BASIN 下载免费PDF全文
下载免费PDF全文 The activity of low frequency oscillation (LFO) widely exists in East Asia during the period of1991 excessively heavy rain over the Changjiang-Huaihe River Basin (Jianghuai).Both the rainfallamount of Jianghuai and the atmosphere from subtropical area to mid-high latitudes have thedominant period of 10—20 d,while the atmospheres in tropical area and high latitudes have thedominant period of 30—60 d.Compared with normal Meiyu season,the anomaly of the 1991 Meiyu process may be reflectedin the following two low frequency synoptic events:(a) The Meiyu process onsets extremely early(in the second dekad of May,which is nearly one month earlier than in normal Meiyu) and isimmediately followed by the first episode of heavy rain.(b) In the first dekad of July,there occursthe heaviest episode of rainfall of the whole Meiyu season,and it is even the heaviest rainfall forthe recent 30 years in China.For these two periods,corresponding to the adjustment of large-scalesituation from“double blocking high”to“bipolar blocking high”,the propagation direction of LFOin East Asia has a distinct seasonal variation,from eastward/northward propagation (passingthrough Jianghuai) during the first episode to westward/southward propagation during the thirdepisode.Oscillations of different frequency bands are superposed in phase.The LFO activity of thecold and warm/moist airs over Jianghuai can be strengthened through those LFO propagationprocesses in East Asia,although they may have different directions in three episodes.Particularly,the eastward (westward) propagation in low latitudes makes the southwest (southeast) airflowtransport intensively the low frequency warm/moist air to the south of Jianghuai from the IndianOcean (tropical West Pacific Ocean) in the first (third) episode.Such warm/moist airs meet andinteract with the cold air which vigorously invades Jianghuai persistently,and finally three episodesof heavy rain occur in mode of LFO. 相似文献
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In the context of 1980-1992 JMA(Japan Meteorological Agency) GMS TBB gridded dataset,study is undertaken of annual cycle features of FFT-derived window power spectrum averaged over the record length,with localized space/time characteristics of low-frequency oscillation(LFO) in the tropical atmosphere investigated alongside possible causes.It turns out that the LFO takes on surprisingly noticeable annual cycle features marked by a wider variable range of the LFO periods over northern tropics than the southern counterpart and equatorial vicinity.In addition,on the whole,the signals are more intense in the Northern Hemisphere during summer/autumn and at equatorial/southern latitudes when northern winter/spring occur as well.Also,not all these features are identical for different segments at the same latitudes,displaying signatures on a local basis,and the spatial/temporal locality can be qualitatively interpreted in terms of nonlinear interaction between tropical waves,and modulation of diabatic heating on the LFO periods. 相似文献
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Ma Jingxian 《Acta Meteorologica Sinica》1990,4(5):613-619
Low-frequency oscillation(LFO) of a large-scale flow pattern is an important observational characteristic feature. In this paper, under the forcing of annual periodic variation a two-layer quasi-geostrophic low-spectrum model is used for carrying out a prolonged numerical integration of more than 30 model years. In the model atmosphere, the interannual time-scale LFO is implicitly reproduced. The result is quite agreeable with the observational evidence. 相似文献