Modeling of the Teleconnections in the African Climate

大量经验研究表明，大陆尺度的气候异常在决定非洲气候的可变性方面发挥着重要作用。其中一个十年尺度的气候异常制度涉及赤道非洲和热带非洲之间降水异常分布的同时位相逆转。尽管大陆上每个纬度带的雨季处于年度周期的不同阶段，但这种大陆规模的重叠还是会发生。显然，大陆尺度的遥相关机制似乎参与了这些气候条件的发展和维持。由稳态多层线性模式得到的PI解表明，非洲大尺度地形与基态气候波动之间的相互作用有助于产生观测到的非洲气候遥相关。PI将通过基于NCAR社区气候模式(CCM)进行一系列数值模拟来扩展他之前的研究。这项调查将针对两个截然不同但密切相关和相辅相成的目标，具体内容如下。(1)利用美国国家大气研究中心(NCAR)的社区气候模式(CCM)，研究观测到的全球海温(SST)、非洲大陆尺度遥相关和区域萨赫勒干旱之间的三向联系。数值积分将基于NCAR GCM的两个版本，一个是早期的CCM1模型，另一个是新版本的CCM2，其中已实施了广泛的增强。(2)提出并检验一个新的假设，即非洲大尺度地形和平均纬向气流之间的相互作用在促进观测到的非洲气候遥相关中所起的作用。通过这项调查，国际和平研究所希望澄清非洲气候中大陆尺度遥相关的一些重要物理机制。此外，这项研究还将有助于评估CCM1和CCM2在模拟热带气候变率方面的相对表现，从而有助于进一步改进模式。

A Significant body of empirical studies indicated that continental-scale climate anomalies play an important part in determining the variability of the African climate. One of these decadal-scale climate anomaly regimes concerns the simultaneous phase reversal, in the precipitation anomaly distribution, between equatorial and tropical Africa. This continental-scale concurrence happens despite the fact that the rainy season in each latitudinal band over the continent comes at different phases of the annual cycle. Clearly, a continental-scale teleconnection mechanism appears to be involved in the development and maintenance of these climatic conditions. The PI's solutions obtained form a steady-state multi-level linear model, indicate that the interaction between the large-scale African orography and the climatic fluctuations in the basic state could help to produce the observed teleconnections in the African climate. The PI will extend his previous investigations by performing a series of numerical simulations based on the NCAR Community Climate Model (CCM). This investigation will be aimed at two distinct but closely related and complementary objectives which may be stated as follows. (1) Employ the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) to investigate the observed three-way connection between the global sea surface temperature (SST), the continental-scale teleconnections in the African climate, and the regional Sahelian droughts. The numerical integrations will be based on two versions of the NCAR GCM, an earlier model designated CCM1, and a new version CCM2, in which extensive enhancements have been implemented. (2) Introduce and test a new hypothesis concerning the role of the interaction between the large-scale orography of Africa and the mean zonal flow in promoting the observed teleconnections in the African climate. Through this investigation the PI hopes to clarify some of the important physical mechanisms responsible for the continental- scale teleconnections in the African climate. In addition this study will help to assess the relative performances of CCM1 and CCM2 in simulating the variability of the tropical climate, thus contributing toward further improvements in the models.