Sensitivity study of the seasonal mean circulation in the northern South China Sea

A study of the circulation in the northern South China Sea （SCS） is carried out with the aid of a three-dimensional, high-resolution regional ocean model. One control and two sensitivity experiments are performed to qualitatively investigate the effects of surface wind forcing, Kuroshio intrusion, and bottom topographic influence on the circulation in the northern SCS. The model results show that a branch of the Kuroshio in the upper layer can intrude into the SCS and have direct influence on the circulation over the continental shelf break in the northern SCS. There are strong southward pressure gradients along a zonal belt largely seaward of the continental slope. The pressure gradients are opposite in the southern and northern parts of the Luzon Strait, indicating inflow and outflow through the strait, respectively. The sensitivity experiments suggest that the Kuroshio intrusion is responsible for generating the imposed pressure head along the shelf break and has no obvious seasonal variations. The lateral forcing through the Luzon Strait and Taiwan Strait can induce the southwestward slope current and the northeastward SCS Warm Current in the northern SCS. Without the lateral forcing, there is the continental slope. The wind forcing mainly causes the The wind-induced water pile-up results in the southward no high-pressure-gradient zonal belt seaward of seasonal variation of the circulation in the SCS. high pressure gradient along the northwestern boundary of the basin. Without the blocking of the plateau around Dongsha Islands, the intruded Kuroshio tends to extend northwest and the SCS branch of the Kuroshio becomes wider and stronger. The analyses presented here are qualitative in nature but should lead to a better understanding of the oceanic responses in the northern SCS to these external influence factors.     

气流的垂直分布对地形雨落区的影响

从大气运动的基本方程出发,讨论了华北地区太行山东侧低空东风气流背景下不同垂直分布气流对降水落区的影响。认为：当垂直于山体的气流随高度减小时,地形的作用表现为迎风坡上水平辐合,造成气旋式涡度增加,产生风场切变,因此对迎风坡降水产生明显的增幅作用。当气流的垂直分布随高度增加时,迎风坡方向表现为反气旋涡度增强,而在背风坡方向产生辐合作用,造成气旋式涡度增加,发生风场切变。     

Retrieving atmospheric temperature profiles from AMSU-A data with neural networks

Back propagation neural networks are used to retrieve atmospheric temperature profiles from NOAA-16 Advanced Microwave Sounding Unit-A (AMSU-A) measurements over East Asia. The collocated radiosonde observation and AMSU-A data over land in 2002-2003 are used to train the network, and the data over land in 2004 are used to test the network. A comparison with the multi-linear regression method shows that the neural network retrieval method can significantly improve the results in all weather conditions. When an offset of 0.5 K or a noise level of ±0.2 K is added to all channels simultaneously, the increase in the overall root mean square (RMS) error is less than 0.1 K. Furthermore, an experiment is conducted to investigate the effects of the window channels on the retrieval. The results indicate that the brightness temperatures of window channels can provide significantly useful information on the temperature retrieval near the surface. Additionally, the RMS errors of the profiles retrieved with the trained neural network are compared with the errors from the International Advanced TOVS (ATOVS) Processing Package (IAPP). It is shown that the network-based algorithm can provide much better results in the experiment region and comparable results in other regions. It is also noted that the network can yield remarkably better results than IAPP at the low levels and at about the 250-hPa level in summer skies over ocean. Finally, the network-based retrieval algorithm developed herein is applied in retrieving the temperature anomalies of Typhoon Rananim from AMSU-A data.     

西风爆发时赤道西太平洋的热量平衡：个例分析

The responses of sea surface temperature (SST) in the western equatorial Pacific warm pool to the west erly wind bursts (WWBs) play an important role in the relationship between WWB and ENSO. By using da ta collected from eight buoys of TOGA (Tropical Ocean-Global Atmosphere)-COARE (Coupled Ocean-Atmosphere Response Experiment), the heat balances of the upper ocean in the western equatorial Pacific around 0°. 156°E during two WWB events were calculated according to Stevenson and Niiler＇s (1983) method. In both events, SST increased before and after the WWBs, while decreased within the WWBs. The SST amplitudes approximated to l℃. Although sometimes the horizontal heat advections may become the biggest term in the heat balance, the variation of SST was dominated by the surface heat flux. On the other aspect, some different features of the two events are also revealed. The two cases have different variation of mixed layer depth. The depth of mixed layer is almost double in the first case (35 m to 70 m), which is caused by Ekman convergence, while only 10m increments due to entrainment in the second one. There are also differences in the currents structure. The different variations of thermal and currents struc ture in the mixing layers accounted for the different variation of the heat balance during the two events, es pecially the advection and residue terms. The seasonal variation of SST in this area is also investigated sim ply. The first WWB event happened just during the seasonal transition. So we considered that it is a normal season transition rather than a so-called anomaly. That also suggested that the seasonal distinction of the WWB is worthy of more attention in the researches of its relationship to ENSO.     

梅雨锋对引发暴雨的中尺度对流系统发生发展影响的研究

针对梅雨锋(湿度锋)上或附近偏南暖湿气流一侧中尺度对流系统不断发生发展和长时间维持而引发长江流域暴雨的观测事实,利用中尺度数值预报模式WRF(V3.1.1)设计了一系列三维理想数值试验,研究了梅雨锋两侧自身水汽差异效应,探讨了基本气流和风垂直切变对梅雨锋上中尺度对流系统发生发展的影响,揭示了梅雨锋对中尺度对流系统的组织...     

基于多普勒雷达VAD算法的业务应用讨论

多普勒天气雷达垂直风廓线（V WP ）产品在业务预报中已有较广泛的应用,并得到了风廓线的某些特征结构与雷暴及强对流之间的对应关系。由于对多普勒径向速度反演得到风廓线产品的VAD算法缺乏了解,目前对VWP 及速度方位显示（VAD）产品的应用还存在一些误区。文章由单多普勒雷达反演水平风场的基本原理入手,回顾了VWP 及VAD产品在暴雨与强对流临近预报中的应用,并重点对VWP及VAD产品的业务应用误区进行了讨论。     

温度,盐度和风应力对南海海流模拟的影响

用美国普林斯顿大学海洋模式（ＰＯＭ）对南中国海的年平均海流进行了数值模拟,对温盐结构和风应力在海流形成中的作用进行了较详细的讨论。结果表明,仅有温盐水平不均匀分布也可以驱动海水而生成南海海流,但此种海流的结构较乱,最大流速只有３０～４０ｃｍ·ｓ－１。若温盐无水平结构,则在风应力驱动下,南海海流的结构较为有序,且最大流速可增至６０～７０ｃｍ·ｓ－１。在温盐水平分布不均匀并有风应力的作用时,生成的南海海流与仅有风应力作用时的海流场较相似,说明在南海海流的形成中,风应力的作用更为重要。海面自由高度的分析也证明了上述结论。     

元数据技术在MDSS实时气象数据库系统建设中的应用

元数据是关于数据的数据,目前被越来越多的应用于系统建设过程中。利用元数据,可以记录整个系统中数据的来龙去脉,这样可以把整个业务的工作流、信息流有效地管理起来,提高系统的可扩展性;此外元数据还具有数据发现和数据搜索的功能,能够提高系统的灵活性。介绍了国家级气象资料存储检索系统(MDSS)中实时气象数据库设计的元数据种类及其存储管理方式,以及元数据技术在实时气象数据库系统建设中的应用,详细描述了如何通过元数据提高软件的灵活性、可维护性。     

张掖国家气候观象台常规气象资料检验分析

选取2007年建成的张掖国家气候观象台梯度塔2007年9月至2008年8月5层风速、温度、湿度和水汽压观测资料,统计了这段时期内资料的缺测率,分析了张掖地区不同季节的气候要素变化特征,通过与其他观测台站资料比较,验证了资料的可靠性。     

伴随同化系统中用云导风修正模式地形的试验

以2002年7月23日的天气过程为例,利用中尺度模式MM5伴随模式同化系统,进行了修正模式地形高度的试验研究。结果发现,MM5伴随模式同化系统可以对地形进行修正,并得到与资料更为协调一致的地形高度。另外,利用非常规云导风资料能够比仅使用常规资料更有效地修正模式地形高度。将修正后的地形场作为模式地形,所得的预报结果比未经修正的地形有所改进。