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1.
针对江苏夏季旱涝和高温热浪等异常气候的预测难题，以江苏夏季站点降水和气温为预测目标，建立了一种基于全球动力模式BCC_CSM1.1（m）和最优可预测气候模态和异常相对倾向（SMART）原理结合的统计降尺度季节气候预测方法。利用历史观测资料和SVD方法提取决定中国夏季降水异常相对倾向的同期热带地区向外长波辐射（Outgoing Longwave Radiation，OLR）和北半球中高纬500 hPa位势高度场异常相对倾向的最优可预测气候模态，并利用逐步回归法构建其与同期江苏站点降水和气温异常相对倾向同期关系的统计降尺度模型；将动力模式对最优可预测气候模态的预测带入统计降尺度模型，实现对区域降水和气温异常相对倾向的预测；最后通过引入观测的近期背景异常实现对降尺度的降水和气温总距平的预测。通过对1991—2019年江苏夏季降水和气温的回报检验表明，本文建立的统计降尺度模型效果较BCC_CSM1.1（m）动力模式的直接预测效果有显著提高，为区域精细化季节气候预测提供了一种有效的手段。 相似文献
2.
夏季亚洲对流层温度异常与中国东部夏季降水紧密相关并可能作为降水的有效预报因子。基于欧盟ENSEMBLES计划的季节预测试验耦合模式每年5月1日开始的回报试验，分析了其对1960～2005年夏季亚洲对流层中上层温度（以200～500 hPa厚度替代，简称对流层温度）年际变率的预测结果，发现模式集合平均对夏季亚洲对流层温度年际变率具有较高的预报技巧，可以合理回报其前两个EOF（Empirical Orthogonal Function）主导模态（EOF1、EOF2），只是未能回报出EOF2高纬度的温度异常，模式集合平均预测的第一模态主成分（PC1）和第二模态主成分（PC2）与再分析资料的时间相关系数分别达到0.63和0.77。再分析资料中前两个EOF模态分别由ENSO（El Ni?o–Southern Oscillation）发展年印度夏季降水异常所激发的丝绸之路遥相关波列和ENSO衰减年西北太平洋夏季降水异常对应的太平洋—日本遥相关波列导致。ENSEMBLES计划可以合理预测出相应的海温异常及遥相关波列，进而合理预测出前两个EOF模态。对流层温度PC1和PC2分别表征了欧亚大陆与周围海洋之间的纬向和经向热力对比异常，模式对由PC1的预报技巧远高于前人定义的纬向热力对比的东亚夏季风指数，对前人定义的经向热力对比指数的预测技巧与PC2相当。将PC1和前人定义的经向热力对比指数作为预报因子，建立了中国夏季降水的动力—统计降尺度预测模型，交叉检验的结果表明该预报模型显著提高了东北和长江流域上游夏季降水的预报技巧。本文提出的亚洲对流层温度年际变率的EOF1及PC1，既能较好表征纬向热力对比与中国东部夏季降水显著相关，又能被模式合理预测，可以作为我国中高纬度地区，特别是东北地区降水的重要预测因子之一。 相似文献
3.
利用NCEP的第二代气候预测系统(CFSv2)提供的2000-2009年降水场历史回报试验资料以及川渝182个测站的降水实况资料。采用时间相关系数、均方根误差、距平相关系数、距平符号一致率以及PS评分等方法,对模式在川渝地区夏季降水以及夏季降水异常的次季节尺度预测技巧进行检验,并进一步分析了模式在概率密度和降水频次方面的预报偏差特征。结果表明：该模式对川渝夏季降水的可用预报时效为3候左右,能够较好地模拟出夏季降水的高值中心,但量级偏大。预报技巧高值区主要位于四川盆地西北部及渝东北地区,对攀西地区南部及川西高原部分地区也有一定的预报技巧。该模式也能够较好地把握川渝地区夏季降水异常偏少的趋势,有效预报技巧为2候以内。模式各时效预报与观测的降水概率密度主要集中在10 mm以下量级;模式预报各量级降水频次与实况相比均偏高得较为明显,且随着预报时效延长,偏差越大,其中偏高最为明显的是小雨频次。 相似文献
4.
SMIP2试验对亚洲夏季风的模拟能力及其可预报性的分析 总被引：4，自引：2，他引：2
利用参加第二次季节预测模式比较计划（Phase 2 of the Seasonal Prediction Model Intercomparison Project,简称SMIP2）的五个大气环流模式的输出结果,比较了这些模式对亚洲夏季降水的模拟能力,并讨论了大气环流模式在季节尺度上对亚洲夏季风的可预报性。结果表明,各模式能够较好地模拟亚洲夏季降水的大尺度分布特征。除了模拟的东亚夏季降水异常经验正交函数分解第一模态（EOF1）的时间系数与观测之间的相关系数较低之外,多数模式可以大致再现东亚、南亚和西太平洋夏季降水异常EOF1及其对应的时间系数。分析表明,热带地区有很好的可预报性,北半球副热带地区的可预报性尽管也较好,但比热带地区要低,南半球热带以外地区的可预报性较差,陆地上的可预报性比海洋上低。在热带和北半球副热带地区,由海温强迫所产生的较大外部方差对此地高可预报性有很大的贡献。与正常年份相比,模式在强El Ni?o年和强La Ni?a年表现出较高的可预报性,在南亚和印度洋地区大多数模式在El Ni?o年比La Ni?a年产生了更好的可预报性,在中西太平洋区域El Ni?o年可预报性的高值中心较La Ni?a年位置偏西。 相似文献
5.
BCC二代气候系统模式的季节预测评估和可预报性分析 总被引：6，自引：3，他引：3
本文利用国家气候中心（BCC）第二代季节预测模式系统历史回报数据,从确定性预报和概率预报两个方面系统地评估了该模式对气温、降水和大气环流的季节预报性能,并与BCC一代气候预测模式的结果进行了对比,重点分析了二代模式的季节可预报性问题。结果显示,BCC二代模式对全球气温、降水和环流的预报性能整体上优于一代模式,特别在热带中东太平洋、印度洋和海洋大陆地区的温度和降水的预报效果改进尤为明显。这些热带地区降水预报的改进,可以通过激发太平洋—北美型（PNA）、东亚—太平洋型（EAP）等遥相关波列提升该模式在中高纬地区的季节预报技巧。分析表明,厄尔尼诺和南方涛动（ENSO）信号在热带和热带外地区均是模式季节可预报性的重要来源,BCC二代模式能够较好把握全球大气环流对ENSO信号的响应特征,从而通过对ENSO预报技巧的改进有效地提升了模式整体的预报性能。从概率预报来看,BCC二代模式对我国冬季气温和夏季降水具备一定的预报能力,特别是对我国东部大部分地区冬季气温正异常和负异常事件预报的可靠性和辨析度相对较高。因此,进一步提高模式对热带大尺度异常信号和大气主要模态的预报能力、加强概率预报产品释用对提高季节气候预测水平具有重要意义。 相似文献
6.
本文采用1981～2010年夏季5～10月逐日的（10°S～50°N,40°E～160°E）范围内向外长波辐射OLR（Outgoing Longwave Radiation）资料和850 hPa层纬向风速资料（简称U850）作经验EOF（Empirical Orthogonal Function）分解,重新计算北半球夏季大气低频振荡BSISO（Boreal Summer Intraseasonal Oscillation）指数,并分析了其演变特征及其对华北夏季降水的影响规律。结果表明:（1）在北半球夏季印度洋—西北太平洋地区存在两种明显的低频信号,一种是BSISO1,空间分布呈西北—东南倾斜状,从热带印度洋向东北方向传播,振荡周期约为45 d;另一种是BSISO2,空间分布呈西南—东北倾斜状,从西北太平洋向西北方向传播,振荡周期约为20 d。（2）BSISO主要是通过影响大气环流和水汽输送来影响华北夏季降水过程。在500 hPa层,BSISO信号会造成华北地区东部副热带高压位置南北移动和强度发生变化来影响华北夏季降水;在850 hPa层,BSISO信号会通过伴随的气旋性或反气旋性异常环流影响向华北的水汽输送来影响华北夏季降水。（3）虽然热带大气季节内振荡MJO（Madden-Julian Oscillation）信号在全年都存在,但其变化在冬半年尤其冬季振幅最大,在夏季最小。BSISO信号变化在夏半年尤其夏季振幅最大。因此,利用热带大气低频信号开展延伸期降水过程预测,冬半年可以重点考虑MJO的影响,夏半年重点考虑BSISO的影响。 相似文献
7.
利用高原积雪信号改进我国南方夏季降水预测的新方法及其在2014年降水预测中的应用试验 总被引：1，自引：0，他引：1
2014年夏季我国南方出现严重洪涝、北方大部干旱,国内绝大多数预测模型在三月起报的汛期预测中均未能抓住位于南方地区的异常雨带,导致预测准确率明显偏低。基于模式对东亚地区夏季海平面气压场的高预报技巧和青藏高原冬季积雪与南方地区夏季降水的高相关性,本文提出一个针对我国夏季降水异常的组合统计降尺度预测新方法（Hybrid Statistical Downscaling Prediction,简称HSDP）,该方法综合利用了气候模式输出的高可预报性环流信息和前期观测的高原积雪异常信号,从而实现对我国南方夏季降水进行动力-统计相结合的改进预报。据此方法建立了一个基于国家气候中心气候预测模式的统计降尺度模型。对我国南方夏季降水进行跨季节预测的交叉检验结果显示,HSDP方法对于南方地区多年平均空间距平相关系数从模式原始预报的-0.006提高到0.24,且在大多数年份均有改进。基于HSDP方法于三月份制作的2014年夏季降水预测,能够很好地抓住南涝北旱的基本形势和我国南方的降水大值区,空间距平相关系数达到0.43。这表明,该方法对于我国夏季降水预测具有较好业务应用前景。 相似文献
8.
基于BCC第二代短期气候预测模式系统的中国夏季降水季节预测评估 总被引：1，自引：0，他引：1
利用BCC第二代气候预测模式系统1996-2015年提前1～3个月的回报试验结果,评估了模式在季节尺度上预测中国夏季降水空间分布和降水异常的能力,分析了模式预报效果的年际差异,并探讨了模式预测误差产生的可能原因。结果表明,模式对中国夏季降水的季节预测具有一定的技巧,西南至长江中下游南部、黄淮平原西部、东北北部及藏北高原等地区季节预测技巧较高,同时,模式对降水距平预报效果整体较好,其中在长江中下游、黄淮地区、华南地区、西北地区及东北北部距平符号一致率较高。而模式对降水季节预测的偏差主要表现为我国东部降水量强度预测偏小,对夏季降水异常的预报技巧有限,且不同年份模式的预测效果差异较大。模式对夏季西太平洋及印度洋高海温区范围预测偏小,对副热带高压和东亚地区低层水汽辐合的强度预测偏弱,从而导致风场与环流场的配置与观测不一致,使得模式对我国东部夏季降水预测显著偏少。从模式预测效果年际差异来看,当华南地区实况降水量偏多、长江中下游及东北地区降水量偏少时,模式具有较高的预测技巧,反之,模式的预报技巧较低。分析中国东部降水与海温的相关关系发现,夏季西北太平洋、热带西太平洋和北印度洋是影响中国东部夏季降水的关键区域,模式中西北太平洋海温偏低对模式预报技巧具有重要影响,海温场、高度场、风场及水汽通量散度场不同的相互配置导致中国东部夏季降水的分布及强度差异,而模式不能合理把握各物理量场间相互作用过程,从而影响模式的预报效果。因此,改进模式对外强迫因子与降水异常相关关系的预测能力是提高我国夏季降水季节预测技巧的主要途径。 相似文献
9.
中国夏季降水异常EOF模态的时间稳定性分析 总被引：4，自引：1，他引：3
本文基于1980~2012年中国160个台站降水资料,利用滑动交叉检验等方法讨论了中国夏季降水距平和距平百分率EOF各模态的时间稳定性,在此基础上探讨了EOF方法在中国夏季降水短期气候预测中的应用条件和潜在能力。研究表明,随机剔除一年样本,中国夏季降水距平场前四个EOF模态表现出显著的稳定性。若时间系数完全预测准确,则潜在的可预测站点主要位于黄河以南地区,理想预测与原始降水的距平相关系数为0.6左右。相对而言,降水距平百分率各模态的时间稳定性易受极端降水事件的影响,当人为削弱这种影响后,随机剔除一年样本,其前三个模态的稳定性得到提高,潜在的可预测站点均匀分布,理想预测与原始降水的距平相关系数为0.48。但是,伴随着预报时效的增加,降水距平和距平百分率后三个EOF模态的时间稳定性下降,预示着EOF方法对未来两年以上降水的预测能力将会明显下降。 相似文献
10.
利用1980～2012年Hadley中心的HadISST再分析海温资料、美国NCEP/NCAR月平均再分析资料和中国160站月平均降水资料,研究了前冬澳大利亚周边海温与长江流域夏季降水关系。研究表明,澳大利亚周边冬季逐月海表温度距平（SSTA）EOF分解第一模态具有全区一致模形式,澳大利亚周边海温一致模具有季节持续性,可从前一年冬季一直维持到当年的夏季。用Ni?o3.4指数剔除海温场中ENSO线性信号后,表明澳大利亚周边海温一致模可能是独立于ENSO位相的区域局地现象。基于冬季澳大利亚周边海温一致模形式,定义了表征长江流域夏季降水一致模指数（CMI）,对长江流域夏季降水具有一定的短期预测意义。澳大利亚周边海温一致模与长江流域夏季降水显著相关,一方面是因为澳大利亚周边海温异常能激发南北半球遥相关,造成西太平洋副热带高压异常,从而影响长江流域夏季降水;另一方面,澳大利亚周边海温异常导致热带地区南北半球对流异常,尤其使得菲律宾周边地区的对流活动异常,进而造成长江流域夏季降水异常。 相似文献
11.
In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies. 相似文献
12.
The boreal summer intraseasonal oscillation simulated by four Chinese AGCMs participating in the CMIP5 project 总被引：1，自引：0，他引：1
The performances of four Chinese AGCMs participating in the Coupled Model Intercomparison Project Phase 5 （CMIP5） in the simulation of the boreal summer intraseasonal oscillation （BSISO） are assessed. The authors focus on the major characteristics of BSISO： the intensity, significant period, and propagation. The results show that the four AGCMs can reproduce boreal summer intraseasonal signals of precipitation; however their limitations are also evident. Compared with the Climate Prediction Center Merged Analysis of Precipitation （CMAP） data, the models underestimate the strength of the intraseasonal oscillation （ISO） over the eastern equatorial Indian Ocean （IO） during the boreal summer （May to October）, but overestimate the intraseasonal variability over the western Pacific （WP）. In the model results, the westward propagation dominates, whereas the eastward propagation dominates in the CMAP data. The northward propagation in these models is tilted southwest-northeast, which is also different from the CMAP result. Thus, there is not a northeast-southwest tilted rain belt revolution off the equator during the BSISO＇s eastward journey in the models. The biases of the BSISO are consistent with the summer mean state, especially the vertical shear. Analysis also shows that there is a positive feedback between the intraseasonal precipitation and the summer mean precipitation. The positive feedback processes may amplify the models＇ biases in the BSISO simulation. 相似文献
13.
Real-time multivariate indices for the boreal summer intraseasonal oscillation over the Asian summer monsoon region 总被引：3，自引：0，他引：3
June-Yi Lee Bin Wang Matthew C. Wheeler Xiouhua Fu Duane E. Waliser In-Sik Kang 《Climate Dynamics》2013,40(1-2):493-509
The boreal summer intraseasonal oscillation (BSISO) of the Asian summer monsoon (ASM) is one of the most prominent sources of short-term climate variability in the global monsoon system. Compared with the related Madden-Julian Oscillation (MJO) it is more complex in nature, with prominent northward propagation and variability extending much further from the equator. In order to facilitate detection, monitoring and prediction of the BSISO we suggest two real-time indices: BSISO1 and BSISO2, based on multivariate empirical orthogonal function (MV-EOF) analysis of daily anomalies of outgoing longwave radiation (OLR) and zonal wind at 850 hPa (U850) in the region 10°S–40°N, 40°–160°E, for the extended boreal summer (May–October) season over the 30-year period 1981–2010. BSISO1 is defined by the first two principal components (PCs) of the MV-EOF analysis, which together represent the canonical northward propagating variability that often occurs in conjunction with the eastward MJO with quasi-oscillating periods of 30–60 days. BSISO2 is defined by the third and fourth PCs, which together mainly capture the northward/northwestward propagating variability with periods of 10–30 days during primarily the pre-monsoon and monsoon-onset season. The BSISO1 circulation cells are more Rossby wave like with a northwest to southeast slope, whereas the circulation associated with BSISO2 is more elongated and front-like with a southwest to northeast slope. BSISO2 is shown to modulate the timing of the onset of Indian and South China Sea monsoons. Together, the two BSISO indices are capable of describing a large fraction of the total intraseasonal variability in the ASM region, and better represent the northward and northwestward propagation than the real-time multivariate MJO (RMM) index of Wheeler and Hendon. 相似文献
14.
延伸期预报是无缝隙预测系统中的薄弱环节,如何提高灾害天气过程的延伸期预报技巧是国际热点及前沿问题。本研究基于2005年12月—2014年8月的观测/再分析资料,通过奇异值分解方法,揭示了与中国南方低频降水变化高度耦合的热带对流和中纬度波列信号。利用中国气象局参加国际次季节至季节预报计划模式（BCC-CPS-S2Sv2模式,简称BCC S2S模式）的回报数据,对中国南方低频降水异常场进行统计降尺度,构建了一套动力-统计相结合的延伸期降水预测模型。独立预测时段（2014年12月—2019年8月）的结果表明,BCC S2S模式可以提前10—15 d预报中国南方大部分区域的异常降水;提前15—20 d以上预报时,动力-统计结合预报模型对冬季（夏季）华南沿海地区（长江以北地区）的降水时间演变、降水空间分布及极端强降水事件的预报技巧均优于BCC S2S模式。文中提出的思路和方法可广泛应用于其他区域气象要素和极端天气事件的延伸期预报。 相似文献
15.
R. S. Ajayamohan H. Annamalai Jing-Jia Luo Jan Hafner Toshio Yamagata 《Climate Dynamics》2011,37(5-6):851-867
The study compares the simulated poleward migration characteristics of boreal summer intraseasonal oscillations (BSISO) in a suite of coupled ocean?Catmospheric model sensitivity integrations. The sensitivity experiments are designed in such a manner to allow full coupling in specific ocean basins but forced by temporally varying monthly climatological sea surface temperature (SST) adopted from the fully coupled model control runs (ES10). While the local air?Csea interaction is suppressed in the tropical Indian Ocean and allowed in the other oceans in the ESdI run, it is suppressed in the tropical Pacific and allowed in the other oceans in the ESdP run. Our diagnostics show that the basic mean state in precipitation and easterly vertical shear as well as the BSISO properties remain unchanged due to either inclusion or exclusion of local air?Csea interaction. In the presence of realistic easterly vertical shear, the continuous emanation of Rossby waves from the equatorial convection is trapped over the monsoon region that enables the poleward propagation of BSISO anomalies in all the model sensitivity experiments. To explore the internal processes that maintain the tropospheric moisture anomalies ahead of BSISO precipitation anomalies, moisture and moist static energy budgets are performed. In all model experiments, advection of anomalous moisture by climatological winds anchors the moisture anomalies that in turn promote the northward migration of BSISO precipitation. While the results indicate the need for realistic simulation of all aspects of the basic state, our model results need to be taken with caution because in the ECHAM family of coupled models the internal variance at intraseasonal timescales is indeed very high, and therefore local air?Csea interactions may not play a pivotal role. 相似文献
16.
El Ni?o对东亚夏季风和夏季降水季节内变化的影响 总被引：3，自引：0，他引：3
基于1979~2012年候平均再分析资料,合成分析了El Ni?o对东亚夏季风和夏季降水季节内变化的影响。结果表明,在El Ni?o衰减年夏季,西太平洋副热带高压(副高)明显偏强,位置偏向西南。副高的这种异常特征随夏季的季节进程有明显变化,初夏异常较弱,盛夏期间异常达到最强。此外,根据东亚夏季风降水呈现阶段式北进的特征,将夏季分为华南前汛期、江淮梅雨期、华北和东北雨期以及华南后汛期来分析东亚夏季风和降水的季节内变化。在上述各个时期,大气对流层低层表现为一致的环流异常型,副高及其以南区域为异常反气旋,其北部为异常气旋。这种异常环流型加强了副高南部偏东风及其北部偏北风,增强了热带水汽输送和高纬度地区冷空气的入侵,二者结合造成主汛期地区降水增加。需要强调的是,上述环流异常型随东亚夏季风逐步向北推移,导致东亚各地区的主汛期降水增加,非主汛期降水减少,降水分布更为集中。 相似文献
17.
This study investigates the influences of boreal summer intraseasonal oscillation (BSISO), which originates from the equatorial Indian Ocean and prevails over the Indo-Pacific region, on precipitation over Southeast China, including South China and Yangtze River Valley. The results indicate that the BSISO-related precipitation anomalies are remarkably different between early summer (May–June) and late summer (July–August). The BSISO-related precipitation anomalies tend to appear more northward in late summer in comparison with early summer. Accordingly, the BSISO is significantly related to precipitation anomalies over South China during many phases in early summer but related to very weak anomalies during all the phases in late summer. Such northward shifts of precipitation anomalies from early summer to late summer are clearest during phases 4 and 7, when the lower-tropospheric anticyclonic and cyclonic circulation anomalies dominate over the subtropical western North Pacific, respectively. Finally, we explain the differences between early and late summers through the seasonal northward migration of climatological equivalent potential temperature gradient, which is located in the South China during early summer but migrates northward to the YRV during late summer. 相似文献
18.
This study investigates the roles of the boreal summer intraseasonal oscillation (BSISO) in the diurnal rainfall cycle over Hainan Island during the warm season (April-September) using 20-year satellite-based precipitation, ERA5 and the outgoing longwave radiation data with the phase composite analysis method. Results show that the spatial distributions of the hourly rainfall anomaly significantly change under the BSISO phases 1-8 while no clear variations are found on the daily and anomaly daily area-averaged rainfall over the island. During the BSISO phase 1, the rainfall anomaly distinctly increases in the morning over the southwest and late afternoon over the northeast of the island, while suppressed convection occurs in the early afternoon over the southwest area. Under this circumstance, strong low-level westerly winds bring abundant moisture into the island, which helps initiate the nocturnal-morning convection over the south coastal area, and drives the convergence region of sea breeze fronts to concentrate into the northwest. Opposite to Phase 1, an almost completely reversed diurnal cycle of rainfall anomaly is found in Phase 5, whereas a positive anomalous rainfall peak is observed in the early afternoon over the center while negative peaks are found in the morning and late afternoon over the southwest and northeast, owing to a strong low-level northeasterly anomaly flow, which causes relatively low moisture and enlarges a sea-breeze convergence area over the island. During Phase 8, strongest moisture is found over the island all through the day, which tends to produce highest rainfall in the afternoon with enhanced anomalous northerly. These results further indicate that multiscale interactions between the large-scale circulations and local land-sea breeze circulations play important roles in modulating diurnal precipitation cycles over the tropical island. 相似文献
19.
The Madden-Julian oscillation (MJO) skeleton model is a low-order model for intraseasonal oscillations that, in an extended form, includes off-equatorial and antisymmetric components. Previous studies of this extended model have used an idealized background state and forcing terms. In the current study, observation-based estimates of these forcing terms and background state are used. Linear solutions to the extended model with this observation-based forcing consist of both equatorially-symmetric convective events and events with a meridional tilt reminiscent of composites of the boreal summer intraseasonal oscillation (BSISO) in observational studies. Solutions to a nonlinear stochastic form of the model exhibit realistic precipitation mean and variance and intraseasonal variability throughout much of the tropics. These solutions contain several types of events, including meridionally-tilted convective activity that moves both northward and eastward. Solutions to both forms of the model also indicate that this BSISO-like convective activity is coupled to activity over the eastern Pacific. A discussion of these features and their agreement with previous observational studies of the BSISO is given. 相似文献
20.
The impact of initialization and perturbation methods on the ensemble prediction of the boreal summer intraseasonal oscillation was investigated using 20-year hindcast predictions of a coupled general circulation model. The three perturbation methods used in the present study are the lagged-averaged forecast (LAF) method, the breeding method, and the empirical singular vector (ESV) method. Hindcast experiments were performed with a prediction interval of 10 days for extended boreal summer (May–October) seasons over a 20 year period. The empirical orthogonal function (EOF) eigenvectors of the initial perturbations depend on the individual perturbation method used. The leading EOF eigenvectors of the LAF perturbations exhibit large variances in the extratropics. Bred vectors with a breeding interval of 3 days represent the local unstable mode moving northward and eastward over the Indian and western Pacific region, and the leading EOF modes of the ESV perturbations represent planetary-scale eastward moving perturbations over the tropics. By combining the three perturbation methods, a multi-perturbation (MP) ensemble prediction system for the intraseasonal time scale was constructed, and the effectiveness of the MP prediction system for the Madden and Julian oscillation (MJO) prediction was examined in the present study. The MJO prediction skills of the individual perturbation methods are all similar; however, the MP‐based prediction has a higher level of correlation skill for predicting the real-time multivariate MJO indices compared to those of the other individual perturbation methods. The predictability of the intraseasonal oscillation is sensitive to the MJO amplitude and to the location of the dominant convective anomaly in the initial state. The improvement in the skill of the MP prediction system is more effective during periods of weak MJO activity. 相似文献