Spatial Coherence of Monsoon Onset over Western and Central Sahel (1950-2000)
Spatial Coherence of Monsoon Onset over Western and Central Sahel (1950-2000)
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DOI：
10.1175/2008jcli2383.1
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发表时间：
2009-03-01
影响因子：
4.9
通讯作者：
Philippon, Nathalie
中科院分区：
文献类型：
--
作者：
Marteau, Romain;Moron, Vincent;Philippon, Nathalie
通过分析1950 - 2000年103个测站的日降雨量资料，研究了萨赫勒西部和中部（塞内加尔、马里、布基纳法索）北方季风爆发的空间相干性。开始日期使用当地农学定义来定义，即连续1或2天的第一个潮湿日（> 1毫米）至少接收20毫米，而在接下来的20天内没有7天的干旱期接收不到5毫米。改变初始湿期的长度或幅度，或两者兼而有之，或随后的干旱期的长度修改本地尺度的发病日期的长期平均值，但只有一个微弱的影响，无论是其年际变化或其空间一致性。发病日期呈现出从布基纳法索南部（5月中旬）到塞内加尔西北部和撒哈拉边缘（8月初）的季节性进展。地方尺度的发病日期的年际变化似乎没有很强的空间连贯性。在年际时间尺度上，跨台站的共变信号远弱于站间噪声。特别是，在整个萨赫勒西部和中部几乎没有观察到系统的空间一致的提前或延迟。因此，对萨赫勒西部和中部地区局部规模爆发的季节性预测，例如与大规模海面温度相关的预测，充其量也很弱。
The spatial coherence of boreal monsoon onset over the western and central Sahel (Senegal, Mali, Burkina Faso) is studied through the analysis of daily rainfall data for 103 stations from 1950 to 2000. Onset date is defined using a local agronomic definition, that is, the first wet day (> 1 mm) of 1 or 2 consecutive days receiving at least 20 mm without a 7-day dry spell receiving less than 5 mm in the following 20 days. Changing either the length or the amplitude of the initial wet spell, or both, or the length of the following dry spell modifies the long-term mean of local-scale onset date but has only a weak impact either on its interannual variability or its spatial coherence. Onset date exhibits a seasonal progression from southern Burkina Faso (mid-May) to northwestern Senegal and Saharian edges (early August). Interannual variability of the local-scale onset date does not seem to be strongly spatially coherent. The amount of common or covariant signal across the stations is far weaker than the interstation noise at the interannual time scale. In particular, a systematic spatially consistent advance or delay of the onset is hardly observed across the whole western and central Sahel. In consequence, the seasonal predictability of local-scale onset over the western and central Sahel associated, for example, with large-scale sea surface temperatures, is, at best, weak.