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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Seasonal cycle and interannual variability of the Sahelian rainfall at hydrological scales - art. no. 8389
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Seasonal cycle and interannual variability of the Sahelian rainfall at hydrological scales - art. no. 8389

机译：水文尺度上萨赫勒降雨的季节周期和年际变化-艺术。没有。 8389

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1] Sahelian rainfall is characterized both by a strong interannual variability and by periods of long-lasting droughts, such as the years 1970 - 1997. The controlling factors of this variability have been the subject of a significant amount of research, but most of this research is carried out using low-resolution averages, typically, monthly to seasonal in time and over 5degrees x 5degrees grid boxes (or larger) in space. This paper is an attempt at characterizing the Sahelian rainfall regime at finer scales, with the objective of establishing links between the seasonal cycle and the interannual variability. To that end, high space-time resolution data sets are analyzed. One is composed of around three hundred daily rain gauges covering a 1,700,000 km(2) area for the period 1951 - 1990. The second is a set of full resolution Meteosat images covering the years 1989 - 1999, allowing for a systematic tracking of the mesoscale convective systems (MCSs). The third data set was produced from an experimental network of recording rain gauges covering 16,000 km 2 in the region of Niamey, Niger, during the years 1990-2000. The analysis of the regional daily rainfall data set tends to revisit the common vision of the seasonal cycle of the Sahelian rainfall. It is shown that the average regime is in fact composed of two subregimes. One is an oceanic regime characterized by a progressive increase of the moist air flow from the ocean into the continent, associated with the seasonal migration of the ITCZ from its southern position in the boreal winter to its northern position in the boreal summer. The second regime is a continental regime in which rain is mostly produced by large convective systems embedded in the easterly circulation. This continental regime sets in abruptly during the second half of June, and 90% of the Sahelian rainfall is then produced by a small number (12% of the total number) of large and organized mesoscale convective systems. The mean event rainfall associated with these systems is larger than the mean event rainfall observed in the oceanic regime. The average proportion of the Sahelian rainfall occurring during the continental regime represents between 75% and 90% of the total annual rainfall. It is thus necessary to study this regime in order to understand the interannual rainfall variability of the region better. It is shown, for instance, that the main factor of interannual variability is the variability of the number of the large convective systems from year to year. It is also shown, using NCEP/NCAR reanalysis, that the easterly waves, which are a major synoptic feature of the region, are not systematically associated with rain-efficient convective systems and that further studies are needed to understand the differences between wet and dry waves. [References: 35
机译：1]萨赫勒地区的降雨既具有强烈的年际变化特征，又具有长期干旱时期，例如1970年至1997年。这种变化的控制因素已成为大量研究的主题，但其中大多数研究是使用低分辨率的平均值进行的，通常是按时间到月度到季节，并且在空间上超过5度x 5度（或更大）的网格框。本文试图在更细的尺度上刻画萨赫勒地区的降雨状况，目的是建立季节周期与年际变化之间的联系。为此，对高时空分辨率数据集进行了分析。一个由约三百个每日雨量计组成，覆盖了1951年至1990年的1,700,000 km（2）区域。第二个是一套涵盖1989年至1999年的全分辨率Meteosat影像，可以对中尺度进行系统跟踪对流系统（MCS）。第三个数据集来自1990-2000年尼日尔尼亚美地区一个记录雨量计的实验网络，该雨量计覆盖了16,000 km 2。对区域每日降雨量数据集的分析倾向于重新审视萨赫勒地区降雨的季节性周期。结果表明，平均政权实际上由两个子政权组成。一种是海洋体制，其特征是从海洋进入大陆的湿气流逐渐增加，这与ITCZ从北方冬季的南部位置到北方夏季的北部季节迁移有关。第二种状态是大陆性状态，其中降雨主要由嵌入在东风环流中的大型对流系统产生。这种大陆性政权在6月下半月突然成立，然后由少量（占总数的12％）大型且有组织的中尺度对流系统产生了萨赫勒地区的降雨量。与这些系统相关的平均事件降雨量大于在海洋状态下观测到的平均事件降雨量。大陆地区发生的萨赫勒地区降雨的平均比例占全年总降雨量的75％至90％。因此，有必要研究这种状况，以便更好地了解该地区的年际降雨变化。例如，表明年际变化的主要因素是大型对流系统数量逐年变化。使用NCEP / NCAR的再分析还显示，作为该区域主要天气特征的东风波与有效利用雨水的对流系统没有系统关联，需要进一步研究以了解干湿之间的差异波浪。 [参考：35

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