Multi‐scale analysis of the 25–27 July 2006 convective period over Niamey: Comparison between Doppler radar observations and simulations
Multi‐scale analysis of the 25–27 July 2006 convective period over Niamey: Comparison between Doppler radar observations and simulations
复制标题
2006年7月25日至27日尼亚美对流期的多尺度分析：多普勒雷达观测与模拟之间的比较
DOI：
10.1002/qj.539
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发表时间：
2010
影响因子：
8.9
通讯作者：
F. Cazenave
中科院分区：
文献类型：
--
作者：
C. Barthe;N. Asencio;J. Lafore;M. Chong;B. Campistron;F. Cazenave
本研究调查了与 2006 年 7 月 25 日至 26 日期间尼亚美上空发生的一系列对流事件相关的多尺度过程。这一时期对应于 2006 年萨赫勒地区第一次强烈季风涌动的活跃阶段。在这两天的时间里，两个连续的中尺度对流系统 (MCS) 序列位于非洲东风波 (AEW) 波谷之前并与之同相。随后在槽后面和山脊附近出现抑制或孤立的对流。大型 AMMA-SOP 数据集，特别是尼亚美的 UHF 雷达和 MIT 多普勒雷达，与低分辨率（5 公里）云解析模型结合使用，以了解对流组织及其与环境的相互作用。已经测试了多个初始条件和边界条件，但只有从 ECMWF AMMA 再分析开始的模拟才能成功再现观察到的特征；这强调了初始状态的重要性。从模拟的 MCS 中，发现对流引起的表观动量源的沿线分量高达 1 m s−1h−1。看来，MCS在全球范围内减少了季风流量，并在中层产生南风，这可以加强低压槽通过时的风的旋转。 7月26日下午，尼亚美上空局地对流是由一些有利因素（湿度、CAPE、CIN）引发对流，而抑制因素（中层干燥层、偏北的低层风切变较弱、700 hPa流线反气旋曲率）阻止其自行组织和传播。特别是，低空风切变似乎至关重要。版权所有 © 2010 英国皇家气象学会
The present study investigates the multi‐scale processes associated with a sequence of convective events that occurred over Niamey during the period 25–26 July 2006. This period corresponds to the active stage of the first intense monsoon surge over Sahel for 2006. During this two‐day period, two successive sequences of mesoscale convective systems (MCSs) were located ahead of and in phase with the trough of an African Easterly Wave (AEW). They were followed by suppressed or isolated convection behind the trough and in the vicinity of the ridge. The large AMMA‐SOP dataset, in particular the UHF radar and the MIT Doppler radar in Niamey, are used in combination with a low‐resolution (5 km) cloud‐resolving model to understand the convection organization and its interaction with the environment. Several initial and boundary conditions have been tested, but only the simulation starting with the ECMWF AMMA reanalysis succeeds in reproducing the observed features; this emphasizes the importance of the initial state. From the simulated MCSs, the along‐line component of the apparent source of momentum due to the convection is found to be up to 1 m s−1h−1. It seems that MCSs globally reduce the monsoon flow and generate southerlies at mid levels which can reinforce the rotation of the wind at the passage of the trough. During the afternoon of 26 July, the local convection over Niamey resulted from some favourable factors (humidity, CAPE, CIN) that triggered convection, while inhibiting factors (mid‐level dry layer, weaker low‐level wind shear pointing to the north, anticyclonic curvature of the streamlines at 700 hPa) prevented it organizing itself and propagating. In particular, the low‐level wind shear seems of critical importance. Copyright © 2010 Royal Meteorological Society