2009年中国东北夏季低温及其与前期海气系统变化的联系

依据中国东北地区拥有百年地面观测记录的长春和哈尔滨测站气温资料、NCEP/NCAR再分析资料和英国哈得来中心海表温度资料,揭示2009年东北地区发生的迄今已有15年没有出现的夏季低温事件成因.结果表明:发生东北夏季低温时的水平和垂直环流结构均为低值系统,东北冷涡异常活动是其最直接的影响因子;有利的年代际变化背景是,哈尔滨和长春6-8月平均气温年代际尺度(≥9 a)的振荡值1999-2008年约-O.8℃/10 a,显著低于全球变暖东北区域响应的线性增暖值0.2℃/10 a(1961-2000年),与长春和哈尔滨夏季气温呈正相关的前一年冬季太平洋极涡面积指数年代际振荡亦呈显著下降趋势.与1994-2008年东北夏季高温的500 hPa平均环流距平场显著不同,北极涛动呈强的负位相分布,东北亚、阿留申和北大西洋上空为显著负距平区;2009年前一年冬季与明显低温的1972年的前一年冬季北太平洋涛动均呈显著的负位相,春季仍持续,且2009年前一年冬季赤道中东太平洋SSTA为拉尼娜位相,2009年春季明显减弱;2009年6-7月夏季东北冷涡活动异常强与4-5月500 hPa北太平洋地区超长波扰动转为定常波扰动槽有关;SVD和谐波分析表明,北太平洋涛动的异常位相不仅是东北夏季气温变化的重要前期信号,还是大气中除了天气尺度的混沌分量外可提取的一种行星尺度稳定分量.     

2013年初桂北寒潮天气过程分析

运用Micaps资料和地面观测实况资料,对2013年1月3-5日桂北寒潮天气过程进行了诊断分析,结果表明：（1）此次寒潮天气过程的特点是降温快、回温慢,且过程日平均气温低;（2）此次寒潮过程的冷空气堆积过程完成后,是由横槽转竖引导槽后冷空气大举南下入侵广西,造成的桂北寒潮天气;（3）中暖下冷的逆温层结维持时间与降雪冻雨时段对应较好,逆温层结被破坏后,桂北的持续雨雪天气也宣告结束,气温开始逐步回升;（4）中低层水汽辐合及较强的槽前正涡度平流也是产生降雪的必要条件之一。     

Copula-based risk evaluation of droughts across the Pearl River basin, China

Daily precipitation data for the period of 1960–2005 from 42 precipitation gauging stations in the Pearl River basin were analyzed using the Mann–Kendall trend test and copula functions. The standardized precipitation index method was used to define drought episodes. Primary and secondary return periods were also analyzed to evaluate drought risks in the Pearl River basin as a whole. Results indicated that: (1) in general, the drought tendency was not significant at a 95 % confidence level. However, significant drought trends could be found in November, December, and January and significant wetting trends in June and July. The drought severity and drought durations were not significant at most of the precipitation stations across the Pearl River basin; (2) in terms of drought risk, higher drought risk could be observed in the lower Pearl River basin and lower drought risk in the upper Pearl River basin. Higher risk of droughts of longer durations was always corresponding to the higher risk of droughts with higher drought severity, which poses an increasing challenge for drought management and water resources management. When drought episodes with higher drought severity occurred in the Pearl River basin, the regions covered by higher risk of drought events were larger, which may challenge the water supply in the lower Pearl River basin. As for secondary return periods, results of this study indicated that secondary return periods might provide a more robust evaluation of drought risk. This study should be of merit for water resources management in the Pearl River basin, particularly the lower Pearl River basin, and can also act as a case study for determining regional response to drought changes as a result of global climate changes.     

The Effects of Line-Wing Cutoff in LBL Integration on Radiation Calculations

There are three basic methods in radiative transfer calculations, i.e., line-by-line (LBL) integration, correlated k-distribution method, and band model. The LBL integration is the most accurate of all, in which, there are two quadrature algorithms named in this paper as integration by lines and by sampling "points when calculating atmospheric transmittance in the considered wavenumber region. Because the LBL integration is the most expensive of all, it is necessary and important to save calculation time but increase calculation speed when it is put into use in the daily operation in atmospheric remote sensing and atmospheric sounding. A simplified LBL method is given in this paper on the basis of integration by lines, which increases computational speed greatly with keeping the same accuracy. Then, we discuss the effects of different cutoff schemes on atmospheric absorption coefficient, transmittance, and cooling rate under both of accurate and simplified LBL methods in detail. There are four cutoff schemes described in this paper, i.e., CUTOFFs 1, 2, 3, and 4. It is shown by this numerical study that the way to cut off spectral line-wing has a great effect on the accuracy and speed of radiative calculations. The relative errors of the calculated absorption coefficients for CUTOFF 2 are the largest under different pressures, while for CUTOFF 1, they are less than 2% at most of sampling points and for CUTOFFs 3 or 4, they are ahnost less than 5% in the calculated spectral region, however, the calculation time is reduced greatly. We find in this study that the transmittance in the lower atmosphere is not sensitive to different LBL methods and different cutoff schemes. Whereas for the higher atmosphere, the differences of transmittance results between CUTOFF 2 and each of other three cutoff schemes are the biggest of all no matter for the accurate LBL or for the simplified LBL integrations. By comparison, the best and optimized cutoff scheme is given in this paper finally.     

CTL-713C天气雷达DVIP电路浅析及故障判断

阐述了CTL-713C天气雷达视频积分处理器(DVIP)的工作原理,分析了CTL-713C天气雷达视频积分处理器信号工作流程,给出了视频积分处理器重要测量点参数和主要时序产生电路波形,得出视频积分处理器的故障判断和检修方法,并通过实例分析进行了检验,最后对视频积分处理器的故障检修方法进行了小结,指出掌握DVIP工作电路各关键点参数和相关时序波形的重要性.     

微型无人驾驶飞机探空初步试验研究

对具有自动导航，自动驾驶功能的微型无人驾驶飞机探空的可行性进行了初步研究。设计了水平空速归零测风方式，利用全球定位系统测风，进行了微型无人驾驶飞机探测试验。研究表明，微型无人驾驶飞机可成为一种方便，经济，灵活的探空工具。     

An Observational Study of the Mesoscale Mistral Dynamics

We investigate the mesoscale dynamics of the mistral through the wind profiler observations of the MAP (autumn 1999) and ESCOMPTE (summer 2001) field campaigns. We show that the mistral wind field can dramatically change on a time scale less than 3 hours. Transitions from a deep to a shallow mistral are often observed at any season when the lower layers are stable. The variability, mainly attributed in summer to the mistral/land–sea breeze interactions on a 10-km scale, is highlighted by observations from the wind profiler network set up during ESCOMPTE. The interpretations of the dynamical mistral structure are performed through comparisons with existing basic theories. The linear theory of R. B. Smith [Advances in Geophysics, Vol. 31, 1989, Academic Press, 1–41] and the shallow water theory [Schär, C. and Smith, R. B.: 1993a, J. Atmos. Sci. 50, 1373–1400] give some complementary explanations for the deep-to-shallow transition especially for the MAP mistral event. The wave breaking process induces a low-level jet (LLJ) downstream of the Alps that degenerates into a mountain wake, which in turn provokes the cessation of the mistral downstream of the Alps. Both theories indicate that the flow splits around the Alps and results in a persistent LLJ at the exit of the Rhône valley. The LLJ is strengthened by the channelling effect of the Rhône valley that is more efficient for north-easterly than northerly upstream winds despite the north–south valley axis. Summer moderate and weak mistral episodes are influenced by land–sea breezes and convection over land that induce a very complex interaction that cannot be accurately described by the previous theories.     

Comparative analysis of different underlying surfaces using a high-resolution assimilation dataset in semi-arid areas in China

To study the land surface and atmospheric meteorological characteristics of non-uniform underlying surfaces in the semi-arid area of Northeast China, we use a “High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC)”. The grid points of three different underlying surfaces were selected, and their meteorological elements were averaged for each type (i.e., mixed forest, grassland, and cropland). For 2009, we compared and analyzed the different components of leaf area index (LAI), soil temperature and moisture, surface albedo, precipitation, and surface energy for various underlying surfaces in Northeast China. The results indicated that the LAI of mixed forest and cropland during the summer is greater than 5 m² m^?2 and below 2.5 m² m^?2 for grassland; in the winter and spring seasons, the Green Vegetation Fraction (GVF) is below 30%. The soil temperature and moisture both vary greatly. Throughout the year, the mixed forest is dominated by latent heat evaporation; in grasslands and croplands, the sensible heat flux and the latent heat flux are approximately equal, and the GVF contributed more to latent heat flux than sensible heat flux in the summer. This study compares meteorological characteristics between three different underlying surfaces of the semi-arid area of Northeast China and makes up for the insufficiency of purely using observations for the study. This research is important for understanding the water-energy cycle and transport in the semi-arid area.     

Verification of Carbon Sink Assessment: Can We Exclude Natural Sinks?

Any human-induced terrestrial sink is susceptible to the effects of elevated atmospheric CO₂ concentration, nitrogen deposition, climate variability and other natural or indirect human-induced factors. It has been suggested in climate negotiations that the effects of these factors should be excluded from estimates of carbon sequestration used to meet the emission reduction commitments under the Kyoto Protocol. This paper focuses on the methodologies for factoring out the effects of atmospheric and climate variability/change. We estimate the relative magnitude of the non-human induced effects by using two biosphere models and discuss possibilities for narrowing estimate uncertainty.     

近50 a全球和三大洋海温距平的时空变化特征

利用49a(1950-1998年)NCEP/NCAR逐月SSTA资料和EOF方法,分别对太平洋、大西洋、印度洋和全球海洋SSTA主要特征向量的空间分布和相应的时间变化进行了讨论。利用Morlet小波进一步分析了要素场的周期变化和能量变化。发现经EOF分解后的SSTA场具有很好的空间整体性和明显的年际和年代际变化。各大洋海温变化存在明显的同期和时滞相关关系,很好地体现了大洋间的协同作用和太平洋的主导作用。从不同的空间分布模态中选择海温变化显著的区域作为关键区,进行同期和时滞相关分析,结果发现各关键区之间具有明显的同期和时滞相关关系。