辽宁省夏季降水的日变化特征

文章利用辽宁省25个气象观测站1961—2008年夏季6—8月的逐时降水自记资料,分析了辽宁省夏季降水日变化的基本特征。发现：降水日变化特征地域性较强,沿海站与内陆站存在差异。总体来说,沿海站降水量的最大值基本出现在午前04-08时,内陆站点则呈双峰值的形式,峰值分别出现在午前和午后,午后1 4—20时为降水量最大值出现的时间;降水频次的日变化特征和降水量基本相同;持续时间长的降水多在午前达到峰值,持续时间短的降水多在午后达到峰值;沿海站点午前的降水峰值区基本是由持续时间在6 h以上的长时间降水造成,内陆站点午后最大降水峰值则为持续时间6 h以内的短时降水,这与内陆下午对流能量强相适应。研究表明,降水日变化的存在能够影响到降水预报的评分。     

大气中的水汽滞留函数

水分从蒸发进入大气到变成雨雪再降落大约在空中滞留(存活)9天,而9天只是水汽在大气中的平均寿命。我们应当知道在大气里现存的总水汽量中已经在大气里滞留(存活)1天、2天或者n天的水汽分别占有的百分比是多少。描述这个问题需要引入大气中的水汽滞留函数概念。本文阐明了水汽滞留函数的物理含义并且指出它应当是一个负指数方程。     

基于局部线性嵌入的人工智能台风强度集合预报模型

利用局部线性嵌入算法通过学习挖掘高维数据集的内在几何结构,高效地实现维数约简和特征提取的能力,论文以2001—2012年共12年6—9月西北太平洋海域内生成的台风样本为基础,将气候持续因子作为台风强度的基本预报因子,采用局部线性嵌入的特征提取与逐步回归计算相结合的预报因子信息数据挖掘技术,以进化计算的粒子群算法,生成期望输出相同的多个神经网络个体,建立了一种新的非线性人工智能集合预报模型,进行了分月台风强度预报模型的建模研究。在建模样本、独立预报样本相同的情况下,分别采用人工智能集合预报方法和气候持续法进行预报试验。试验对比结果表明,前者较后者在6、7、8和9月24 h台风强度预报中,平均绝对误差分别下降了23.34%、24.46%、19.41%和27.45%,4个月的平均绝对误差下降了23.10%;48 h台风强度预报中,6—9月平均绝对误差分别下降了44.82%、16.73%、0.89%和49.26%,4个月的平均绝对误差下降了25.54%。进一步研究发现,在变动局部线性嵌入算法忌近邻个数的情况下,建立的台风强度集合预报模型,其预报结果稳定可靠,相对于气候持续法均为正的预报技巧水平,为台风强度客观预报提供了新的预报工具和预报建模方法。     

2012-2019年昌吉州冬季降雪日变化特征分析

利用2012—2019年冬季昌吉州11个国家级台站逐时降水资料,运用常规统计方法,对昌吉州冬季降雪日变化特征进行分析。结果表明：昌吉州冬季降雪量空间分布与海拔高度呈正相关,与纬度呈显著的负相关,降雪强度与纬度关系密切。全州逐时累积降雪量呈双峰型分布,主峰出现在下午17:00,次峰出现在上午08:00;西部呈三峰型特征,主次峰值分别出现在17:00、14:00、08:00;东部呈准单峰单谷型,峰值发生在19:00,谷值出现在中午13:00。昌吉州冬季降水事件以短时降水事件为主,对冬季降水量贡献为64%,12 h以上长持续性降水事件发生概率很小,仅在部分台站偶有发生。西部和东部冬季降水日循环与降水持续性关系较密切,其中持续3～4 h降水事件对西部和东部冬季降水量贡献最大,但随着持续时间增长对降水量的贡献却越来越小。     

From small scales to the big picture: persistence mechanisms of planktonic grazers in the oligotrophic ocean

In this review we evaluate whether universal behavioral and metabolic mechanisms exist, which permit marine proto‐ and metazooplankton to persist in continuously food‐limited environments such as the North Pacific Subtropical Gyre and other oligotrophic ocean systems. We re‐visit the issue of what processes account for low steady‐state abundance of the dominant groups of planktonic grazers: phagotrophic protists and copepods, by examining evidence for the four processes proposed by Strom et al. (2000) : grazing thresholds, behavioral response to prey patchiness, top–down control of grazers, and mixotrophy (combination of photosynthesis and phagotrophy in protists) and/or omnivory (switching between alternate prey types). Published observations reveal that grazing thresholds, below which feeders reduce their feeding efforts and, with that, their metabolic expenditures, do exist. There are also studies suggesting that both protistan and small metazoan plankton feeders may take advantage of patchiness of food particles and are frequently mixotrophic and/or omnivorous. Predator patchiness in response to prey patches may facilitate top–down control of grazers. Finally, we discuss processes, which may lead to low quasi steady‐state abundances of food particles and feeders.     

东亚季风边缘区气候代用指标的分形比较及其意义

利用R/S分析东亚季风边缘区祁连山教德冰心、树木车轮、黄土磁化率、CaCO3含量曲线,得到其分维值分别为1．29、1．30、1．19和1．15,证实近百万年来东亚率风演变的特征是长期持续的,即季风边缘区具有干净化趋势,且旱化趋势的成分更为明显。其中,冰心δ18O比率、年轮指数的分维数与乌鞘岭年平均温度记录的分维值1．25接近,黄土磁化率和CaCO3含量的分维数与年降水量记录的分维值1．19一致。虽然这些气候指标是用不同物理单位测量并在不同时间尺度记录的,但分形分析可对它们进行数学比较,从而揭示出不同信息源所包含的气候意义。     

海南东方近岸海域海浪观测特征研究

利用海南东方近岸海域2014年至2015年间一整年的海浪观测资料, 分析了海浪的时间变化特征。观测时间段内, 有效波高最大值为4.03m, 平均值0.79m; 平均周期最大值为6.32s, 平均值为3.58s。该海域冬季波高较大, 秋季最小, 常浪向为SSW方向, 强浪向为WSW向。基于该长期观测数据, 文章亦研究了平均周期、有效波高之间的关系, 同时还确立了该海域波高与平均持续时间之间的关系。最后讨论了观测时间段内波浪能流密度的变化特征, 发现一年中能流密度大于2kW·m^-1的频率为26%, 且从全年的计算结果来看, 观测位置处12月的波浪能较适宜开发, 但总体波浪能资源不够丰富。文章对于认识海南东方近岸海域波浪特征以及工程设计都具有重要的意义。     

Trends in hydrological and climatic variables affected by four variations of the Mann-Kendall approach in Urmia Lake basin,Iran

ABSTRACT

The trends in hydrological and climatic time series data of Urmia Lake basin in Iran were examined using the four different versions of the Mann-Kendall (MK) approach: (i) the original MK test; (ii) the MK test considering the effect of lag-1 autocorrelation; (iii) the MK test considering the effect of all autocorrelation or sample size; and (iv) the MK test considering the Hurst coefficient. Identification of hydrological and climatic data trends was carried out at monthly and annual time scales for 25 temperature, 35 precipitation and 35 streamflow gauging stations selected from the Urmia Lake basin. Mann-Kendall and Pearson tests were also applied to explore the relationships between temperature, precipitation and streamflow trends. The results show statistically significant upward and downward trends in the annual and monthly hydrological and climatic variables. The upward trends in temperature, unlike streamflow, are much more pronounced than the downward trends, but for precipitation the behaviour of trend is different on monthly and annual time scales. Furthermore, the trend results were affected by the different approaches. Specifically, the number of stations showing trends in hydrological and climatic variables decreased significantly (up to 50%) when the fourth test was considered instead of the first and the absolute value of the Z statistic for most of the time series was reduced. The results of correlations between streamflow and climatic variables showed that the streamflow in Urmia Lake basin is more sensitive to changes in temperature than those of precipitation. The observed decreases in streamflow and increases in temperature in the Urmia Lake basin in recent decades may thus have serious implications for water resources management under the warming climate with the expected population growth and increased freshwater consumption in this region.

Editor Z. W. Kundzewicz; Associate editor Q. Zhang     

喜河水电站坝址区缓倾角结构面综合分析研究

喜河水电站坝型为混凝土重力坝,重力坝对地基岩体的抗剪强度有较高的要求。前期勘查成果表明喜河水电站坝址区存在较多的缓倾角结构面,缓倾角结构面的存在是影响坝基抗滑稳定的关键,因此要对坝基作出抗滑稳定性评价。首先要研究坝址区缓倾角结构面的分布规律及连通情况,通过对坝址区缓倾角结构面的综合分析研究提出合理的坝基岩体的综合抗剪强度。