Effects of urbanization on daily temperature extremes in North China简   总被引：1，自引：0，他引：1  

SI Peng  ZHENG Zuofang  REN Yu  LIANG Dongpo  LI Mingcai  SHU Wenjun 《地理学报(英文版)》2014,24(2):349-362

The regional changes of daily temperature extremes in North China caused by ur- banization are studied further from observed facts and model estimates on the basis of ho- mogenized daily series of maximum and minimum temperature observations from 268 mete- orological stations, NCEP/DOE AMIP- Ⅱ reanalysis data （R-2）, and the data of simulations by regional climate model （RegCM3）. The observed facts of regional warming on long time scales are obtained by analyzing the indices of temperature extremes during two time periods of 1961-2010 and 1951-2010. For urbanization effect, the contributions to decreases in an- nual and winter diurnal temperature range （DTR） are 56.0% and 52.9%, respectively, and increases in the lowest minimum temperature （TNn） are 35.7% and 26.2% by comparison of urban and rural observations. Obtained by R-2 data with observations for contrast, on the other hand, increase in the number of annual warm nights （TN90p） contributed by urbaniza- tion is 60.9%. And observed facts of regional warming in daily temperature extremes are also reflected in the simulations, but what difference is urbanization progress at rural areas in North China would be prominent in the next few years relative to urban areas to some extent from model estimates.  相似文献   

Assessment of future drought in Southwest China based on CMIP5 multimodel projections   总被引：3，自引：0，他引：3  

Lin Wang  Wen Chen  Wen Zhou 《大气科学进展》2014,31(5):1035-1050

In the last decade, a series of severe and extensive droughts have swept across Southwest China, resulting in tremendous economic losses, deaths, and disruption to society. Consequently, this study is motivated by the paramount importance of as- sessing future changes in drought in Southwest China. Precipitation is likely to decrease over most parts of Southwest China around the beginning of the century, followed by widespread precipitation increases; the increase in potential evapotran- spiration （PET）, due to the joint effects of increased temperature and surface net radiation and decreased relative humidity, will overwhelm the whole region throughout the entire 21st century. In comparative terms, the enhancement of PET will outweigh that of precipitation, particularly under Representative Concentration Pathway （RCP） 8.5, resulting in intensified drought. Generally, the drying tendency will be in the southeast portion, whereas the mountainous region in the northwest will become increasingly wetter owing to abundant precipitation increases. Droughts classified as moderate/severe according to historical standards will become the norm in the 2080s under RCP4.5/RCP8.5. Future drought changes will manifest different characteristics depending on the time scale： the magnitude of change at a time scale of 48 months is nearly twice as great as that at 3 months. Furthermore, we will see that not only will incidences of severe and extreme drought increase dramatically in the future, but extremely wet events will also become more probable.  相似文献   

Mean properties of mesoscale eddies in the Kuroshio recirculation region     

马利斌  王强 《中国海洋湖沼学报》2014,32(3):681-702

Using a 19-year altimetric dataset, the mean properties and spatiotemporal variations of eddies in the Kuroshio recirculation region are examined. A total of 2 001 cyclonic tracks and 1 847 anticyclonic tracks were identifi ed using a geometry-based eddy detection method. The mean radius was 57 km for cyclonic eddies and was 61 km for anticyclonic eddies, respectively, and the mean lifetime was about 10 weeks for both type eddies. There were asymmetric spatial distributions for eddy generation and eddy termination, which were domain-dependent. Mean eddy generation rates were 2.0 per week for cyclonic eddies and were 1.9 per week for anticyclonic eddies. Both type eddies tended to deform during their lifetime and had different propagation characteristics, which mainly propagated westward and southwestward with velocities 4.0–9.9 cm/s, in the Kuroshio recirculation region. Further discussion illustrates that the eddy westward speed maybe infl uenced by the combined effect of vertical shear of horizontal currents and nonlinearity of eddy. To better understand the evolution of eddy tracks, a total of 134 long-lived tracks(lifetime ≥20 weeks) were examined. Comparison between short-span eddies(lifetime ≥4 weeks and 20 weeks) and long-lived eddies is also conducted and the result shows that the short-span and long-lived eddies have similar time evolution. Finally, eddy seasonal variations and interannual changes are discussed. Correlation analysis shows that eddy activity is sensitive to the wind stress curl and meridional gradient of sea surface temperature on interannual timescales. Besides, the strength and orientation of background fl ows also have impacts on the eddy genesis.  相似文献   

夏季越南东北外海暖水的时空变化特征及其机理研究   总被引：1，自引：1，他引：0  

YAN Yunwei  CHEN Changlin  LING Zheng 《海洋学报(英文版)》2014,33(11):55-63

Due to orographic blockage, a weak wind wake occurs in summer off northeast Vietnam in the South China Sea. Under the wind wake, warm water is observed from both high-resolution satellite data and hydrographic observations. The wake of warm water forms in June, continues to mature in July and August, starts to decay in September, and disappears in October. The warm water wake also shows robust diurnal variation – it intensifies during the day and weakens in the night. Warm water wakes can be generated through wind-induced mixing and thermal(latent heat flux) processes. In this paper, a mixed layer model is used to evaluate the relative importance of the two processes on seasonal and diurnal timescales, respectively. The results demonstrate that thermal processes make a greater contribution to the wake than wind-induced mixing processes on a seasonal timescale, while the warm water wake is dominated by wind-induced mixing processes on a diurnal timescale.  相似文献   

Spatial and Temporal Variations of Atmospheric Angular Momentum and Its Relation to the Earth Length of Day          下载免费PDF全文

YANG Ping  SHI Wenjing  XIAO Ziniu  DONG Shi  REN Juzhang 《Acta Meteorologica Sinica》2014,28(1):150-161

The characteristics of atmospheric-angular-momentum （AAM） and length-of-day （LOD） on different timescales are investigated in this paper, on the basis of the NECP/NCAR reanalysis data and an LOD dataset for 1962-2010. The variation and overall trend of the AAM anomaly （AAMA） at different latitudes are presented, and the relationship between AAMA and LOD is discussed. The AAMAs in different latitude regions exhibit different patterns of variation, and the AAMA in the tropics makes a dominant contribution to the global AAMA. In the tropics, the AAMA propagates poleward to the extratropical regions. It is confirmed that a downward propagation of the AAMA occurs in the lower stratosphere. Correlation analysis shows that the relationship between AAMA and LOD varies significantly on different timescales. Specifically, the tropical AAMA is positively correlated with LOD on short timescales, but they are not obviously correlated on long timescales. This indicates that the interaction between AAM and the earth＇s angular momentum follows the conservative restriction on short timescales, but the influence of the earth angular momentum on that of the atmosphere depends on the interaction process on long timescales.  相似文献   

月内尺度北半球环状模水平和垂直活动特征分析   总被引：2，自引：1，他引：1  

李晓峰  李建平 《气象学报》2011,69(6):1046-1061

采用李建平等定义的更好表征北半球环状模变化的指数,利用NCEP/NCAR逐日再分析资料,从对流层的角度分析了北半球环状模在月内时间尺度上的相关环流的垂直和水平传播特征.结果表明,在水平方向上,温度异常在对流层,尤其是近地层,表现为由极区和高纬度地区向中低纬度地区强的南传特征,而在平流层则为由中低纬度地区向高纬度地区弱的...  相似文献   

内蒙古阴山北麓农牧交错带风蚀气候侵蚀力特征   总被引：5，自引：0，他引：5  

邹春霞  申向东  李夏子  李彰俊 《吉林大学学报(地球科学版)》2011,41(4):1172-1178

为了解内蒙古阴山北麓农牧交错带的风蚀气候侵蚀力变化特征及规律,在收集多年风速、降水、气温、相对湿度和沙尘暴气象站观测数据的基础上,计算了典型区域风蚀气候侵蚀力。引入MHF小波函数,对该时间序列进行小波分析,揭示了区域风蚀气候侵蚀力变化的多时间尺度的复杂结构,分析了其在不同时间尺度下的周期性和突变诊断点。结合沙尘暴发生日数的观测资料,进一步分析风蚀气候指数与沙尘暴发生日数的尺度变化关系。研究表明:内蒙古阴山北麓农牧交错带风蚀气候侵蚀力具有明显的阶段性特征,以16 a的周期振动最强;在整个时间域上,区域风蚀气候侵蚀因子与沙尘暴日数的变化具有较好的对应关系,即风蚀气候指数偏大期对应沙尘暴日数偏多期,风蚀气候指数偏小期对应沙尘暴日数偏少期;并预测在未来一段时间内风蚀气候侵蚀力较大时间尺度变化处于增强的偏小期,但较小尺度表现出由大到小的过渡。  相似文献   

海气通量涡相关法计算中的时间尺度分析     

黄艳松  宋金宝  范聪慧 《海洋科学》2011,35(11):114-119

基于黄海上连续14 d 的浮标观测资料, 采用多尺度分解法确定了海气通量涡相关法计算中的截断时间尺度, 并分析了该截断时间尺度的特征及其对感热通量计算的影响。研究结果是： 由多尺度分解法获得的湍通量截断时间尺度可将总通量中湍通量和中尺度通量分离开来, 截断时间尺度随着湍流强度或水平风速的增加而增加, 且感热通量的截断时...  相似文献   

东北夏季降水预测技巧偏低的原因探讨     

赵俊虎  熊开国  陈丽娟 《大气科学》2020,44(5):913-934

1978～2018年全国夏季降水实时业务预测技巧显示东北地区明显偏低,尤其是近几年在对全国夏季旱涝的总体分布预测效果明显提高的情况下,对东北地区的预测却与实况相反,因此有必要分析该区域预测技巧偏低的原因。利用站点资料、再分析格点数据、实时预测历史数据及统计诊断等方法,探讨了动力气候模式预测能力以及东北夏季降水预测的认识缺陷。通过系统地回顾东北夏季旱涝的气候特征、影响因子及预测方法等方面的研究进展,以及东北夏季降水实时预测检验,得出预测技巧偏低的可能原因:（1）东北初夏降水主要受东北冷涡活动的影响,盛夏主要受西太平洋副热带高压、东北南风和中高纬环流型的共同作用,而业务常用的国内外主要动力气候模式无法准确反映与东北初夏和盛夏降水相联系的关键环流系统;（2）东北夏季降水与全球海温的关系较弱且不稳定,尤其是与ENSO的关系较为复杂,年际关系随年代际变化而波动,即ENSO不是预测东北夏季降水的强信号;（3）东北夏季降水具有明显的季节内、年际和年代际等多时间尺度变率,夏季降水受到多种时间尺度信息的叠加和调控,不同尺度变率的贡献相当,且影响系统不同,导致预测难度较大。最后,进一步探讨了东北夏季降水预测存在的科学问题及可能的解决途径,以期为夏季业务预测提供参考。  相似文献   

淮河流域稻麦轮作农田生态系统CO2通量多时间尺度变化特征     

段春锋  田红  黄勇  曹雯  凌新锋 《气象科学进展》2020,10(5)

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