Climate variability over the Greater Horn of Africa based on NCAR AGCM ensemble
Climate variability over the Greater Horn of Africa based on NCAR AGCM ensemble
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DOI：
10.1007/s00704-005-0203-7
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发表时间：
2006-09-01
影响因子：
3.4
通讯作者：
Semazzi, F. H. M.
中科院分区：
文献类型：
--
作者：
Anyah, R. O.;Semazzi, F. H. M.
利用美国国家大气研究中心（NCAR）AGCM集合多年资料，研究了非洲之角（GHA）气候的变率和极端湿异常。虽然GCM集合平均再现现实的年际变化的降雨模式在GHA次区域的观测相比，有一个明显的北移，在整个季节的降雨量最大的模拟区域。然而，与观测和许多先前的研究一致，由ENSO分析的主导模式得出的年际变化主要是由ENSO相关的波动。另一方面，对应于第二种模式（EOF 2）的空间格局表现出独特的偶极子降雨异常模式（湿/干条件）在我们的域的北方/南半部在所有三个月的短雨季。当从集合平均资料的40年EOF 2时间序列中滤除3-10年周期时，月平均和季平均降水异常存在三种明显的准年代际变化，地面异常和中期异常的结合是降水异常的主要原因。来自大西洋西北部和东部的对流层气流以及来自印度洋的东风气流在形成与ENSO无关的1961年洪水中发挥了重要作用。隐蔽地，在ENSO相关的1997年洪水期间，中热带气流的特征是来自刚果雨林的异常西风气流与来自印度洋的气流沿着东非海岸和肯尼亚东部/东北部汇合。在集合和NCEP再分析中的异常水汽通量辐合/辐散也与与两次湿事件相关的对流层中层气流异常一致。
The variability and extreme wet anomalies in the Greater Horn of Africa (GHA) climate are investigated based on a multi-year National Center for Atmospheric Research (NCAR) AGCM ensemble data. While the GCM ensemble average reproduces realistic inter-annual variability of rainfall pattern over the GHA sub-region compared to observations, there is a distinct northward shift in the simulated regions of rainfall maxima throughout the season. However, in agreement with observations and many previous studies, the inter-annual variability derived from leading mode of EOF analysis is dominated by ENSO-related fluctuations. On the other hand, the spatial pattern corresponding to the second mode (EOF2) exhibits a unique dipole rainfall anomaly pattern (wet/dry conditions) over the northern/southern halves of our domain during all the three months of the short rains season. When the 3-10 year periodicity is filtered out from the 40-year EOF2 time series of the ensemble mean data, three distinct quasi-decadal regimes in the rainfall anomalies is exhibited for both monthly and seasonal mean data.It is also evident from our results that a combination of anomalous surface and mid-tropospheric flow from northwestern and eastern Atlantic Ocean and easterly flow from the Indian Ocean played a significant role in setting up the non-ENSO related 1961 floods. Coversely, during the ENSO-related 1997 floods, the mid-troposheric flow was characterized by anomalous westerly flow originating from the Congo rainforest that converged with the flow from Indian Ocean along the East Africa coast and over eastern/northeastern Kenya. The anomalous moisture flux convergence/divergence in both the ensemble and NCEP reanalysis is also consistent with the mid-trospheric flow anomalies that are associated with the two wet events.