1998年夏季长江流域大气季节内振荡的结构演变及其对降水的影响

利用中国逐日降水格点资料和NCAR/NCEP再分析资料,对1998年发生在我国东部长江中下游流域的夏季持续性强降水过程中显著的大气季节内振荡(ISO)的三维结构演变等活动特征进行了分析。1998年夏季长江及江南地区的异常强降水对应着该地区强的ISO活动。利用位相合成方法,对长江流域两个典型的季节内循环周期的ISO降水、850 hPa水平风场以及水汽和垂直速度等循环过程的时空分布特征进行了诊断分析。在低频环流场上,对流层低层的低频气旋和反气旋环流表现出交替在热带西北太平洋增强并向西偏北方向移动发展的特征,当异常气旋环流移动到长江流域上空时,长江流域正好位于气旋环流西南侧的东北风异常和西北太平洋上向西移动的反气旋环流西北侧的西南风异常环流汇合处的下方,引起该地区强降水的发生。在强降水阶段的ISO的垂直结构上,上升运动和水汽表现出从华南到长江流域自南向北移动的特征,强烈的垂直上升运动以及来自南方充足的水汽为增强长江流域地区的降水起到了重要作用。     

Analysis of lower-boundary climate factors contributing to the summer heatwave frequency over eastern Europe using a machine-learning model

A machine-learning (ML) model, the light gradient boosting machine (LightGBM), was constructed to simulate the variation in the summer (June–July–August) heatwave frequency (HWF) over eastern Europe (HWF_EUR) and to analyze the contributions of various lower-boundary climate factors to the HWF_EUR variation. The examined lower-boundary climate factors were those that may contribute to the HWF_EUR variation—namely, the sea surface temperature, soil moisture, snow-cover extent, and sea-ice concentration from the simultaneous summer, preceding spring, and winter. These selected climate factors were significantly correlated to the summer HWF_EUR variation and were used to construct the ML model. Both the hindcast simulation of HWF_EUR for the period 1981–2020 and its real-time simulation for the period 2011–2020, which used the constructed ML model, were investigated. To evaluate the contributions of the climate factors, various model experiments using different combinations of the climate factors were examined and compared. The results indicated that the LightGBM model had comparatively good performance in simulating the HWF_EUR variation. The sea surface temperature made more contributions to the ML model simulation than the other climate factors. Further examination showed that the best ML simulation was that which used the climate factors in the preceding winter, suggesting that the lower-boundary conditions in the preceding winter may be critical in forecasting the summer HWF_EUR variation.摘要本文使用LightGBM机器学习模型模拟了欧洲东部夏季热浪频率的变化, 并分析了多个底边界层气候因子的贡献. 所选取的气候因子包括前期冬季, 前期春季以及同期夏季的下垫面海温, 土壤湿度, 积雪以及海冰. 分析结果说明LightGBM模型能够较好的模拟出欧洲东部夏季热浪频率的变化, 其中海温因子对模拟的贡献最大. 进一步的分析研究显示, 使用前期冬季的气候因子进行的模拟可以获得最佳模拟结果, 意味着前期冬季的下垫面气候因子可能对夏季欧洲东部热浪频率变化的预报能起到关键作用.     

Characteristics of diurnal variations of warm-season precipitation over Xinjiang Province in China

降水日变化受大气热力,动力过程以及复杂地形影响,演变特征复杂且区域差异显著.本文采用中国气象局发布的中国地面与CMORPH融合逐小时降水产品(2008-2019年),分析了新疆省暖季降水日变化特征.研究结果表明:(1)新疆大部分地区降水主峰值发生在清晨;(2)持续时间超过三小时的降水事件是新疆地区主要降水事件,贡献了南...     

The role of rare rainstorms in the formation of calcic soil horizons on alluvial surfaces in extreme deserts

Soils in similar geomorphic settings in hyperarid deserts (< 50 mm yr⁻¹) should have similar characteristics because a negative moisture balance controls their development. However, Reg soils in the hyperarid southern Negev and Namib deserts are distinctly different. Soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics. Annual rainfall amount can be similar (15-30 mm), but storm duration can drastically alter Reg soil properties in deserts. The cooler fall/winter and dry hot summers of the southern Negev Desert with a predominance brief (≤ 1 day) rainstorms result in gypsic-saline soils without any calcic soil horizon. Although the Namib Desert receives only 50-60% of the southern Negev annual rainfall, its rainstorm duration is commonly 2-4 days. This improves leaching of the top soil under even lower annual rainfall amount and results in weeks-long grass cover. The long-term cumulative effect of these rare rain-grass relationships produces a calcic-gypsic-saline soil. The development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil-moisture regime in deserts, and has important implications for the use of key desert soil properties as proxies in paleoclimatology.     

汶川地震后四川省绵竹市清平乡文家沟泥石流灾害调查研究

在2008年5月12日汶川地震后的地震灾区暴发了许多泥石流灾害,其中以四川省绵竹市清平乡文家沟泥石流最为显著。文家沟原来不是泥石流沟,在汶川地震时由于滑坡形成的巨大的滑坡-碎屑流堆积体改变了文家沟的泥石流形成条件,在此后的3个雨季内,文家沟先后暴发了5次大规模和特大规模的泥石流灾害,其中以8.13文家沟泥石流规模和危害最大。8.13文家沟泥石流暴发时的总降雨量为227mm,泥石流持续时间约2.5h,泥石流总量约310×104m3;泥石流造成7人死亡,5人失踪,39人受伤,479户农房被掩埋,直接经济损失4.3亿元。5次大规模和特大规模的泥石流以及洪水仅带走了16%的可以很容易形成泥石流的滑坡-碎屑流堆积物,文家沟如再遭遇较大降雨还会暴发泥石流。即使在今后的雨季中暴发几次规模如8.13泥石流一样大的特大规模泥石流,文家沟在较大降雨下仍然可能暴发泥石流灾害,因此对文家沟泥石流的防治工作将是一个长期的工作。     

Univariate modelling of summer-monsoon rainfall time series: Comparison between ARIMA and ARNN

The present article reports studies to develop a univariate model to forecast the summer monsoon (June–August) rainfall over India. Based on the data pertaining to the period 1871–1999, the trend and stationarity within the time series have been investigated. After revealing the randomness and non-stationarity within the time series, the autoregressive integrated moving average (ARIMA) models have been attempted and the ARIMA(0,1,1) has been identified as a suitable representative model. Consequently, an autoregressive neural network (ARNN) model has been attempted and the neural network has been trained as a multilayer perceptron with the extensive variable selection procedure. Sigmoid non-linearity has been used while training the network. Finally, a three-three-one architecture of the ARNN model has been obtained and after thorough statistical analysis the supremacy of ARNN has been established over ARIMA(0,1,1). The usefulness of ARIMA(0,1,1) has also been described.     

南极中山站DPS-4电离层测高仪的中层夏季回波统计分析

The vertical temperature profiles of snow and sea ice have been measured in the Arctic during the 2nd Chinese National Arctic Research Expedition in 2003(CHINARE2003).The high-resolution temperature profile in snow is solved by one-dimensional heat transfer equation.The effective heat diffusivity,internal heat sources are identified.The internal heat source refers to the penetrated solar radiation which usually warms the lower part of the snow layer in summer.By temperature gradient analysis,the zero level can be clarified quantitatively as the boundary of the dry and wet snow.According to the in situ time series of vertical temperature profile,the time series of water content in snow is obtained based on an evaluation method of snow water content associated with the snow and ice physical parameters.The relationship of snow water content and snow temperature and temporal-spatial distribution of snow water content are presented     

Effectiveness of Teaching Pedagogical Content Knowledge Through Summer Geography Institutes

Abstract

Research presented in this paper addresses two fundamental questions: how effective have state geographic alliance summer geography institutes (ASGIs) been in changing the classroom teaching behaviors of participants, and to what extent do the institutes reflect characteristics of effective inservice training? Both questions are grounded in Shulman's concept of pedagogical content knowledge—the notion that effective teaching requires knowledge of how specific ideas and procedures in a particular content domain can best be taught. On-site evaluations and four follow-up evaluations provided data regarding the strengths and weaknesses of the institutes as well as evidence regarding the institutes' long-term effectiveness in promoting change in geography instruction. Results of the study indicate that ASGI graduates not only make substantive changes in how they teach geography, but also conduct high-quality inservices that lead to changes in the teaching practices of their colleagues.     

东亚夏季风系统与青藏高原冬季植被的关系

用1982年1月—2001年12月NDVI资料、台站日降水资料和NCEPⅠ/NCAR再分析资料,首先利用SVD方法分析了青藏高原冬季NDVI与我国降水的关系,指出青藏高原冬季NDVI与我国夏季降水相关系数从南到北呈"+-+-"相间分布,高原冬季NDVI增大(减小),随后夏季降水在华南和华北地区增加(减少),而长江流域和东北地区降水减少(增加)。然后通过合成法,分析了高原冬季NDVI大、小值年东亚夏季风系统的变化,得到在青藏高原冬季NDVI大值年时,夏季马斯克林高压偏弱,而澳大利亚高压偏强。赤道辐合带强度偏强,有利于越赤道气流的加强,使南海夏季风爆发偏早。同时南亚高压偏弱位置偏西,副热带高压位置偏东偏北。副热带西风急流的位置也偏西偏北。     

我国夏季暴雨气候学的研究进展与科学问题

我国夏季暴雨频发并导致洪涝灾害,严重影响着社会和经济的发展。基于对我国夏季降水和暴雨天气学的大量研究,从气候学的角度综述了我国夏季暴雨的研究进展,特别是关于我国暴雨的年际和年代际变化及趋势、与暴雨发生相关联的大尺度环流特征及年际和年代际变化成因以及全球气候变暖背景下今后我国夏季暴雨的演变趋势等方面的主要研究进展。此外,还指出了我国夏季暴雨气候学亟待进一步研究的若干科学问题。