夏季黄河流域降水气候特征及其与大气环流的关系

本文基于1958—2015年夏季黄河流域55个观测站降水量和NCEP/NCAR再分析1高度场等资料,使用MannKendall突变检验、合成分析和Monte Carlo检验等气候统计方法,分析了黄河流域58年夏季降水量的气候变化特征,以及导致其变化的大气环流成因。58年期间,黄河流域夏季降水量总体呈减少趋势,尤其在河套北部有显著性减少趋势,其主要原因是欧亚中高纬度等压面升高、西风带减弱所致;1975年和1996年是黄河流域夏季降水的两个明显年代际气候变化转折点,在1958—1975年期间,黄河流域夏季降水量年际变化大,异常偏多和偏少年出现频次较高,期间欧亚中高纬度及其以南包括黄河流域地区高度场偏低,主要受高空低压系统和较强冷空气影响;在1976—1995年期间,黄河流域大部降水偏多,其主要环流成因为乌拉尔山阻塞高压发展、贝加尔湖到东北亚一带受负高度距平控制高空槽加深,同时,来自南方的暖湿气流输送增强;到1996—2015年最近20年间,乌拉尔山北部环流高度场偏低、里海至贝加尔湖再到东北亚一带高度场一致偏高,黄河流域一带西风带强度和冷空气势力均较弱,流域受高压影响导致大部区域降水偏少。不同时期黄河各流域段降水量与中高纬度阻塞高压以及与西北太平洋副热带高压的相关关系分析进一步说明了上述结论。     

北大西洋多年代际振荡正、负位相期间欧亚夏季副热带波列季节内活动特征及与印度降水的联系

利用美国国家环境预测中心与国家大气研究中心（NCEP/NCAR）逐日再分析资料,针对北大西洋多年代际振荡（AMO）两个不同位相,对逐候200 hPa经向风异常进行EOF分析,发现在AMO正、负位相期间,欧亚副热带波列的季节内活动存在明显差异。利用超前—滞后回归,对比了不同AMO位相下副热带波列及其相联系的印度夏季降水的季节内活动演变特征,分析有关的大气环流,探究波列影响降水的机制。结果表明:在AMO负位相期间,由格陵兰岛以南北大西洋经大不列颠岛、地中海、黑海—里海向南亚北部传播的副热带波列的季节内演变,在印度中部引起下沉,导致中部及西北部季节内降水减少,波列负位相相反;在AMO正位相期间,副热带波列西起冰岛以南北大西洋经丹麦南部、俄罗斯西部、中亚向南亚东北部传播,对应该波列的季节内演变,辐合上升区在印度中部和东西两侧,使得该区域季节内降水增加,波列负位相相反。于是,AMO通过调制夏季欧亚副热带波列的季节内活动,可以对印度夏季降水的季节内变化空间型及演变发挥显著影响。     

鲁西北连续两次强降水过程对比分析

利用各种观测资料和NCEP/NCAR 1×1°再分析资料,对2012年7月30日夜间和31日夜间鲁西北连续两天强降雨天气进行诊断和对比分析。结果表明:强降水产生在西风槽前和副热带高压边缘的偏南暖湿气流中,西风槽稳定少动,台风在东南沿海北上,副高加强北抬,为鲁西北连续两天的强降水提供了天气尺度背景。925hPa及以下的低层,来自于渤海的偏东气流和来自于华东沿海的东南气流同时向鲁西北强降水区输送水汽,低层比湿大,CAPE和K指数较高。第1次强降水产生在偏南气流的暖区中,降水强度大,维持时间短。第2次强降水期间,低层有冷空气锲入,把暖湿气流抬升,前期为对流性降水,中后期转为稳定性降水,降水强度小,维持时间较长。850hPa及以下倒槽式切变线和中尺度低涡环流是造成强降水的中尺度影响系统,近地面层来自于渤海的东北气流与来自于东南沿海的东南暖湿气流形成中尺度涡旋,产生气旋式辐合上升,触发对流不稳定能量释放。对流云团在鲁西北形成长形的中尺度对流系统(MCS),稳定少动,有明显的列车效应和后向传播特征。强降水具有较强的日变化,夜间发展增强,白天减弱。     

副高外围影响下遵义市区域性暴雨的高空形势场特征研究

利用常规观测资料和NCEP1°×1°再分析资料,发现2007-2016年6～8月有8次区域性暴雨天气过程是由副高东退、引导高空槽东移的大尺度背景条件下,配合低层系统造成的,将其分类后得到三种类型：低涡槽型、高空槽气旋旋转型和高空槽低涡切变型;对每种类型的高空形势进行合成分析,找出了暴雨落区与高空系统、物理量配置之间的关系。     

试从土壤物质迁移与积累论亚热带北界的划分--以河南省伏牛山为例

对伏牛山中段南坡不同海拔高度7 个土壤剖面进行了野外调查和室内土壤理化分析,选择土壤氧化物迁移系数、硅铝铁率、活性铁与全铁之比、活性锰与全锰之比、Ba值、β值等指标,运用聚类分析等方法,从土壤物质迁移和积累角度深入探讨了河南省伏牛山南坡亚热带北界的划分。研究结果表明,该界线大约在海拔950 m左右。     

华北和北京的酷暑天气 Ⅱ. 模拟实验和机理分析

利用Ｐｅｎｎ／ＮＣＡＲ 的ＭＭ５ 中尺度模式对１９９９ 年６ 、７ 月华北的两段高温过程进行了模拟研究, 并利用模拟输出量对高温形成的机理进行了一些探讨。结果表明, 在利用了Ｎｕｄｇｉｎｇ 同化以后, 中尺度模式能对整个过程作较长时间的模拟, 对高压的移动过程、强度和维持能较好的复制出来。分析结果表明, 大陆副热带高压中的下沉增温和辐射增温是造成此高温酷暑天气的主要原因。     

Improved Method for Calculating Anthropogenic CO2 in the Upper Layer of the North Pacific Subtropical Gyre along 175°E

Seawater samples were collected in the North Pacific along 175°E during a cruise of the Northwest Pacific Carbon Cycle Study (NOPACCS) program in 1994. Many properties related to the carbonate system were analyzed. By using well-known ratios to correct for chemical changes in seawater, the CO₂ concentration at a given depth was back calculated to its initial concentration at the time when the water left the surface in winter. We estimated sea-surface CO₂ and titration alkalinity (TA) in present-day winter, from which we evaluated the degree of air-sea CO₂ disequilibrium in winter was. Using a correction factor for air-sea CO₂ disequilibrium in winter, we reconstructed sea-surface CO₂ in pre-industrial times. The difference between the back-calculated initial CO₂ and sea-surface CO₂ in pre-industrial times should correspond to anthropgenic CO₂ input. Although the mixing of different water masses may cause systematic error in the calculation, we found that the nonlinear effect induced by the mixing of different water masses was negligible in the upper layer of the North Pacific subtropical gyre along 175°E. The results of our improved method of assessing the distribution of anthropogenic CO₂ in that region show marked differences from those obtained using the previous back-calculation method.     

舟山冬季暴雨的特征

文章分析了冬季暴雨发生时的环流形势和物理量场分布特征,揭示了冬季暴雨的发生与厄尔尼诺现象有着一定的相关。同时,分析了单站要素的变化,为以后的冬季暴雨预报提供参考。     

Discussion of Some Problems as to the East Asian Subtropical Monsoon

Based on NCEP/NCAR gridded reanalysis, TRMM precipitation data, CMAP, and rainfall observations in East China, a study is conducted with focus on the timing and distinctive establishment of the rainy season of the East Asian subtropical monsoon （EASM） in relation to the South China Sea （SCS） tropical summer monsoon （SCSM）. A possible mechanism for the EASM is investigated. The results suggest that 1） the EASM rainy season begins at first over the south of the Jiangnan region to the north of South China in late March to early April （i.e., pentads 16-18）, and then the early flooding period in South China starts when southerly winds enhance and convective rainfall increases pronouncedly; 2） the establishment of the EASM rainy season is earlier than that of its counterpart, the SCSM. The EASM and the SCSM each is featured with its own independent rain belt, strong southwesterly wind, intense vertical motion, and robust low-level water vapor convergence. The SCSM interacts with the EASM, causing the EASM rainy belt to move northward. The two systems are responsible for the floods/droughts over the eastern China; and 3） in mid-late March, the eastern Asian landmass （especially the Tibetan Plateau） has its thermal condition changing from a cold to a heat source for the atmosphere. A reversal of the zonal thermal contrast and related temperature and pressure contrasts between the landmass and the western Pacific happens. The argument about whether or not the dynamic and thermal effects of the landmass really act as a mechanism for the earlier establishment of the EASM rain belt is discussed and to be further clarified. Finally, the article presents some common understandings and disagreements regarding the EASM.     

Contrasting hydrography and phytoplankton distribution in the upper layers of cyclonic eddies in the Mozambique Basin and Mozambique Channel

Hydrographic data collected in cyclonic eddies in the Mozambique Channel and Basin revealed notable differences in temperature and salinity at a depth of 100 m, the upper mixed layer, the nitracline depths, and vertical distribution of chlorophyll-a (Chl-a). Differences in temperature and salinity did not show any consistent patterns. In contrast, the differences in the upper mixed layer, nitracline depths and the vertical Chl-a profile appeared to be driven by combined effects of eddy dynamics (i.e. shoaling of isopleths) and the seasonal variation in light availability and mixing conditions in the upper layers. Cyclonic eddies studied during austral spring and summer in the Mozambique Channel exhibited shallower upper mixed layers and nitracline depths, and deeper euphotic zones. Distinct subsurface Chl-a maxima (SCM) were associated with the stratified conditions in the upper layers of these eddies. In contrast, a cyclonic eddy studied during mid-austral winter in the Mozambique Basin had a shallower euphotic zone, deeper upper mixed layer and uniform Chl-a profiles. Another eddy sampled in the Mozambique Basin toward the end of winter showed a less pronounced SCM and roughly equal euphotic zone and upper mixed layer depths, suggestive of a transition from a well-mixed upper layer during winter to stratified conditions in summer.