Characteristics of Low-level Jets in Shanghai during the 2008-2009 Warm Seasons as Inferred from Wind Profiler Radar Data
Characteristics of Low-level Jets in Shanghai during the 2008-2009 Warm Seasons as Inferred from Wind Profiler Radar Data
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根据风廓线雷达资料推断2008-2009年暖季上海低空急流特征
DOI：
10.2151/jmsj.2012-603
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发表时间：
2012-12
影响因子：
3.1
通讯作者：
Yang, Yinming
中科院分区：
文献类型：
--
作者：
Du, Yu;Zhang, Qinghong;Ying, Yue;Yang, Yinming
为了了解中国大陆沿海低空急流的特征及其与暖季降水的联系，利用2008年和2009年青浦地区风廓线雷达的半小时资料，以及非梅雨期前后一个月的资料，研究了上海中国低空急流的气候学特征。在海拔500~800m和2100~2200m有两个发病高峰。因此，我们将观测到的低空急流分为两类：(1)边界层急流(BLJ，1公里以下)和(2)天气系统相关低空急流(SLLJ，1-3公里内)。BLJ和SLJ在发生频率、风向以及与降水的关系等时间变化上表现出不同的行为。BLJ表现出比SLLJ更明显的日周期，最大的发病率出现在夜间和清晨。黑斑潜蝇在梅雨期比非梅雨期出现的频率更高，而黑斑潜蝇的发生频率在整个暖季都有所增加，在梅雨期没有出现高峰。BLJ主要是由惯性振荡引起的南风，由于东西陆地-海洋热力差异，背景强的南地转风。SLLJ最常见的表现为嵌入东亚季风环流的西南风和西风。通过比较雨天(个例)、日(4小时)累积降雨量在1~10 mm范围内的日降雨量(个例)和非雨天(个例)(因为暴雨期间WPR资料的缺失率较高)的低空夹层与降水的关系，研究了低层夹层与降水的关系。BLJ和SLLJ在雨天比非雨天发生得更多。在较短的时间尺度上(4h)，除雨季前的SLLJ外，BLJ和SLLJ均倾向于在雨季期间、雨前和雨后频繁发生。
In order to understand the characteristics of low-level jets (LLJs) over coastal areas of China Continent and its linkages with rainfall during the warm seasons, half-hourly data from a wind profiler radar (WPR) at the Qingpu site during the Meiyu periods of 2008 and 2009 in addition to data from one month prior to and after (non-Meiyu periods) were used to develop a climatology of the LLJs over Shanghai, China. Two peaks in LLJ incidence were revealed at 500–800 m and 2100–2200 m altitudes. Thus, we classified the observed LLJs into two types: (1) boundary-layer jets (BLJs, below 1 km) and (2) synoptic-system-related LLJs (SLLJs, within 1–3 km). BLJs and SLJs showed different behavior in their temporal variation of the occurrence frequency, wind direction, and relation to rainfall. The BLJs displayed a more evident diurnal cycle than the SLLJs, with maximum incidence occurring in nighttime and early morning. The SLLJs occurred more frequently during Meiyu periods than non-Meiyu periods, whereas the occurrence frequency of BLJs increased throughout the warm seasons with no peak during Meiyu periods. BLJs are mostly southerly winds that might be induced by inertial oscillation with a strong background southerly geostrophic wind due to the west-east land-ocean thermal difference. SLLJs most frequently appeared as southwesterly and westerly winds embedded in the East Asian monsoon circulation. The relation between LLJs and precipitation was examined by comparing the frequency of LLJs occurrence on rainy days (cases), with daily (4-hourly) accumulated rainfall within 1 to 10 mm, and non-rainy days (cases) because the missing rate of WPR data is high during heavy rainfall events. Both BLJs and SLLJs occur more often on rainy days than on non-rainy days. In shorter time scales (4 hours), both BLJs and SLLJs tend to occur frequently during, before and after rainy cases, except SLLJs before rainy cases.
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