中纬度海气相互作用研究进展

回顾了中纬度海气相互作用的研究现状,分析了长期以来该项研究进展缓慢的原因和近十几年来的研究成果,结果指出:中纬度海洋在全球气候变化中有着重要的作用;冬季中纬度海气相互作用的强信号是冷空气强度;中纬度海洋强暖流区海气能量交换异常对同期和后期(半年至一年)北半球范围内的大气环流型有重要影响;当冬季黑潮和湾流海域海洋对大气同时异常多或异常少加热时,易形成夏季长江中下游偏旱或偏涝的环流形势。最后还提出,深入研究中纬度海气能量系统异常对大气环流影响及其物理机制,是今后海气相互作用研究的重要内容,其结果将为短期气候预测提供理论依据。     

晚第四纪以来中纬度北太平洋古生产力记录

综合论述了晚第四纪以来北太平洋中纬度地区海洋古生产力变化特征及其影响因素。晚第四纪以来,北太平洋中纬度地区海洋古生产力变化表现出明显的冰期-间冰期尺度波动特征,冰期条件下海洋古生产力增加,而间冰期条件下古生产力较低。在综合考虑影响北太平洋古生产力变化的各种因素后,初步认为：冰期气候条件下,亚洲粉尘携带的浮游生物生长所必需养分的增加促进了浮游生物的生长,可能是导致本区冰期时古生产力增加的主要原因。     

一种适合MSNA区域的单站TEC经验模型:以ohi3站为例

中纬度夏季夜间异常(midlatitude summer nighttime anomaly, MSNA)区域内的总电子含量(total electron content, TEC)的日变特性存在季节性差异,能否有效描述MSNA的特征是检验电离层TEC经验模型精度的关键指标之一.针对MSNA现象,提出了一种适合MSNA...     

南半球风暴轴对冬夏季中纬度海温异常的响应特征

利用HadISST(Hadley Centre Global Sea Ice and Sea Surface Temperature)和20CRv2(Twentieth-Century Reanalysis dataset version 2)数据集,对1951—2000年南半球中纬度海表面温度(Sea Surface Temperature; SST)进行了经验正交函数分解(EOF),结合回归分析方法,分析了南半球风暴轴对冬夏季中纬度海温异常的响应特征。结果表明:南半球夏季SST第一模态表现为三极子型,南大西洋、南印度洋和南太平洋的SST暖异常能够使对流层低层涡动活动增强,体现在850 hPa涡动热量极向热通量增加,其最大值出现在南太平洋西部。南半球冬季SST第一模态表现为在南大西洋、南印度洋分布暖异常,在南太平洋中西部出现弱偶极子型SST异常,分别能够在局地增强和减弱对流层低层涡动活动,体现在增强和减弱,其大值区出现在南印度洋。进一步对大气斜压性和斜压能量转换的诊断结果表明,上述中纬度海温异常的存在能导致对流层低层出现一致性的斜压增强(减弱),进而加强(削弱)大气涡动活动。     

Numerical Simulation of Torrential Rainfall and Vortical Hot Towers in a Midlatitude Mesoscale Convective System

A cloud-resolving model simulation of a mesoscale convective system （MCS） producing torrential rainfall is performed with the finest horizontal resolution of 444 m. It is shown that the model reproduces the observed MCS, including its rainfall distribution and amounts, as well as the timing and location of leading rainbands and trailing stratiform clouds. Results show that discrete convective hot towers, shown in Vis5D at a scale of 2-5 kin, are triggered by evaporatively driven cold outflows converging with the high-θe air ahead. Then, they move rearward, with respect to the leading rainbands, to form stratiform clouds. These convective towers generate vortical tubes of opposite signs, with more intense cyclonic vorticity occurring in the leading convergence zone. The results appear to have important implications for the improvement of summertime quantitative precipitation forecasts and the understanding of vortical hot towers, as well midlevel mesoscale convective vortices.     

末次冰期40 ka以来阿拉善高原地区的环境演变与地貌演化

阿拉善高原末次冰期（40 ka）以来的环境演变研究是揭示中纬度沙漠的发展变化与物质来源的重要依据,为不同尺度区域乃至全球气候变化间的比较提供依据,进一步揭示气候要素的发展变化。目前已有大量的研究工作及成果见诸文献报道,但缺乏系统性的总结与对比分析,尤其是40 ka以来的环境演变过程及其原因。本文通过对中西方已有文献的系统总结和对比研究,从末次冰期、全新世早、中、晚期的古气候变化记录、地貌演化记录及环境变化的原因、可能存在的问题等方面,分析了阿拉善高原地区末次冰期以来的环境演变历史。指出约40 ka到末次盛冰期结束时的环境比现在湿润,之后至更新世结束环境普遍干旱,风沙活动增强;但是乌兰布和沙漠的环境演变与区域总体的变化结果不同,即整个末次冰期均表现为干旱的环境;全新世早期和中期环境普遍湿润,湖泊、植被等进一步发育,风沙活动弱,全新世晚期环境干旱,沙漠或进一步扩大。但是,腾格里沙漠全新世早期表现为干旱的环境,并且存在争议最大的是巴丹吉林沙漠全新世中期的干旱事件,这些问题仍需要进一步研究。此外,西风带、东亚季风在不同时期对研究区气候变化的影响不同,关于研究区与全球气候变化的具体关系的研究很少,缺少代表性事件的证据。沙源的研究结果存在不一致性,由于研究方法的局限性和地貌营力作用的复杂性,沙源的定性和量化分析具有一定的难度;沙丘的形态、分布与风的方向、能量具有相互指示性,适当的风能才是沙丘建造的关键;从气候变化的全球尺度分析,沙漠的形成普遍与冰期或者气候寒冷干燥时期相对应。     

Analysis of Stationary-Wave Nonstationarity in the Northern Hemisphere 500-hPa Height Field

In this paper, the concept of stationary-wave nonstationarity is presented and elucidated in the framework of the Lorenz circulation decomposition. This concept indicates the relative magnitude of the zonal nonuniform abnormity to the intensity of stationary waves on the monthly mean scale. Based on the Lorenz circulation decomposition, the nonstationarity degree Ius(Ilus) of the global (local) stationary waves is defined, and then used to analyze the stationary-wave nonstationarity at 30° 60°N, where the intensity of stationary waves at 500 hPa in the Northern Hemisphere, as is well known, is very high. The following findings are obtained: (1) There exist seasonal southward and northward movements in the position of the nonstationarity zones of the global stationary waves. The steady stationary waves occur in midlatitudes (35°-55°N) in winter and in the subtropical region (south of 35°N) in summer, associated with the major troughs over East Asia and North America and the weak European trough in winter, and with the relatively steady subtropical high system in summer. A high value center of Ius is at 35°N in spring and 50°N in summer, which might be caused by the seasonal variation of stationary-wave intensity, particularly in association with the interannual variability of trough ridge positions of stationary waves on the monthly mean maps. (2) There exists obvious asymmetry in Ilus, with the steady zones always located in the areas controlled by strong troughs/ridges and the unsteady ones in the areas where the stationary-wave intensity is low. The Ilus in the subtropics (south of 35°N) is larger in winter than in summer, and vice versa in the midlatitude region (north of 35°N). The summertime distribution of Ilus on the whole shows a rather complicated structure. However, North Europe is the most unsteady area for local stationary waves, as represented by high values of Ilus in both summer and winter, while over the North American continent (about 120°E-60°W), the °Ilus is slightly less than 1 in summer, indicating that the stationary waves in this region are more steady than those over other mid and high latitude regions. (3) From North China to Northwest Pacific, there is a high value zone of Ilus in summer, with its center (45°N, 130°E) located in the east of Heilongjiang Province. This influences the summer climate of northern China, including Northeast, North, and Northwest China. It is obvious that the nonstationarity is an intrinsic attribute of stationary waves, and can be regarded as being of the same importance as the intensity and energy-spectrum structure of stationary waves in the studies of the general circulation system.     

2006年川渝地区高温干旱特征及其成因分析

2006年夏季,四川、重庆发生了50年一遇的高温大旱.利用中国730站中川渝地区58个测站2006年1月1日～9月8日的逐日降水、日最高气温和NCEP再分析资料,探讨了这次高温干旱的特征及成因机理,重点分析了西太平洋副热带高压和大陆副热带高压的异常活动以及西风带与热带环流的特征.研究指出,东亚西风带扰动偏弱、偏北,青藏高原低涡活动减弱,使得川渝地区上空长时间受强大的副热带高压控制;2006年夏季副热带高压的加强和维持与菲律宾以东洋面及南海地区的对流加强、孟加拉湾地区降水异常增多导致的加热场异常密切相关.