中山站高频雷达观测结果初步分析

中山站高频相干散射雷达于2010年4月建成投入观测,并加盟SuperDARN雷达观测网,成为我国探测电离层对流的重要手段。首先简要介绍中山站高频雷达的工作原理及工作模式,然后利用该雷达第一年的观测数据,给出了每个波束观测的电离层回波总数随距离和回波强度、多普勒速度及谱宽的分布,以及电离层回波发生率随频率的变化特性。观测结果和射线追踪的模拟计算表明,由于波束指向不同,电波波矢方向与地磁场形成正交条件的区域有所不同,因此会造成不同频率下,不同波束观测的电离层回波发生率的差别。     

Bringing the other into political ecology: Reflecting on preoccupations in a research field

For all its vitality political ecology often appears to be a project in which work by Anglo‐Americans in particular, if it is not privileged, certainly predominates. This trend reflects wider language and intellectual tendencies in human geography and the social sciences that distort the development of the field by downplaying or obscuring the contributions of many non‐Anglo‐Americans and by naturalizing Anglo‐American assumptions at the heart of research. The latter in turn determine what constitutes ‘good’ work – even as there is no single definition of political ecology. Arguing against this tendency, this paper draws on postcolonial thinking to emphasize the need to reassess and reorient the field as ‘other’ political ecologies are feasible and desirable.     

淮北地区2010年4月异常低温气候特征及成因分析

利用1961—2010年NCEP/NCAR再分析资料和4月淮北地区气温资料,用累积距平(CA)法、合成分析法对淮北地区气温的时空分布特征以及2010年4月淮北地区持续冷气候背景进行分析。文章分析了淮北地区4月冷、暖年的大气环流异常及要素场的空间分布特征。结果表明:淮北地区4月气温的年代际变化特征明显,在1990年前后发生了突变。贝加尔湖南部,100°E以东的华北地区中低层的冷空气活动与淮北地区4月气温高低存在很好的相关性,该地中低层冷空气强(弱),淮北地区4月气温低(高)。冷暖年,乌拉尔山暖脊、东亚大槽、西伯利亚高压等差异显著,说明以上是影响淮北地区4月气温异常的关键系统。另据分析,El Nino与淮北地区4月气温异常也具有很好的相关性。     

1951—2010年长沙市极端气温事件的变化特征

利用1951-2010年长沙最高和最低气温资料,运用国际上通用的百分位阈值法确定暖日、暖夜和冷日、冷夜数,采用线性倾向估计法和M-K突变检测等方法,研究长沙市60 a来极端气温事件的时空变化特征。结果表明,暖日和暖夜数分别以3.48个.（10a）-1和3.06个.（10a）-1的速率显著增加,冷日和冷夜数分别以-2.13个.（10a）-1和-1.78个.（10a）-1的速率显著减少,白天增暖幅度大于夜间增暖幅度。研究还表明,阶段性特征明显,近60 a来暖日和冷日、冷夜数发生了明显的突变。暖日数增加秋季最显著,春季次之;暖夜数增加夏季最显著,冬季次之。冷日（夜）数减少的季节主要是春季和冬季;四季都在变暖,但以春季、冬季变暖最明显。7月暖日（暖夜）数增加最显著,4月和2月冷日（冷夜）数减少最显著。     

An Integrated Analysis of Dry-Wet Variability in Western China for the Last 4-5 Centuries

The dry-wet variability in western China and its spatiotemporal structure during the last 4-5 centuries was examined using 24 climate proxies from sediments, ice cores, historical documents, and tree rings. Spatial patterns and temporal evolutions of dryness and wetness were not only extracted from the proxy data using rotated empirical orthogonal function (REOF) analysis for the last 4 centuries, but also for instrumental data in the last 40 years. The leading five REOF modes indicate that 5 dry-...     

Effects of the low-frequency zonal wind variation on the high frequency atmospheric variability over the tropics

Recently, there is increasing evidence on the interaction of atmospheric high-frequency (HF) variability with climatic low-frequency (LF) variability. In this study, we examine this relationship of HF variability with large scale circulation using idealized experiments with an aqua-planet Atmospheric GCM (with zonally uniform SST), run in different zonal momentum forcing scenarios. The effect of large scale circulation changes to the HF variability is demonstrated here. The HF atmospheric variability is enhanced over the westerly forced region, through easterly vertical shear. Our study also manifests that apart from the vertical wind shear, strong low-level convergence and horizontal zonal wind shear are also important for enhancing the HF variance. This is clearly seen in the eastern part of the forcing, where the HF activity shows relatively maximum increase, in spite of similar vertical shear over the forced regions. The possible implications for multi-scale interaction (e.g. MJO–ENSO interaction) are also discussed.     

An analysis on observed and simulated PNA associated atmospheric diabatic heating

This study examines the PNA associated atmospheric diabatic heating by linearly isolating the influence of ENSO. The analysis is based on the NCEP–NCAR and ERA-40 reanalyses and a 1,000-year-long integration of the CCCma coupled climate model. Both the vertically integrated and three-dimensional diabatic heating are examined. The Rossby wave sources in association with the PNA are also diagnosed. The PNA-related heating is confined outside the tropics and is dominated by anomalies in the eastern Pacific, with a north–south dipole structure in mid-latitudes and the northern subtropics. The heating anomalies change sign with height in mid-latitudes but have the same sign throughout the troposphere in the northern subtropics. Relatively weak heating anomalies also appear in mid-latitudes, downstream of the heating dipole over North America and the western North Atlantic. The heating anomalies are largely supported by the advections related to the mean state throughout the troposphere, and partially damped by the advections related to the eddy effect, particularly at the upper troposphere over the North Pacific. Broadly similar patterns are seen from the NCEP–NCAR and ERA-40 reanalyses. Yet anomalous heating centers are generally located at relatively lower troposphere for the ERA-40 with respect to the NCEP–NCAR. The tropical heating anomalies are rather weak, remarkably different from those related to ENSO variability. In addition, the Rossby wave source collocates with the atmospheric diabatic forcing in the mid-high latitudes over the PNA sector, and shows no forcing source in the tropics. The results demonstrate possible forcing in the mid-high latitudes, regardless of tropical heating for the PNA teleconnection. The modeled heating and wave forcing anomalies in association with the modeled PNA compare reasonably well with the reanalysis-based estimates, increasing confidence in the observational results. The analysis provides further evidence of the independence of the PNA on ENSO from the diabatic heating point of view.     

热通量和风应力影响北太平洋SST年际和年代际变率的数值模拟

利用一个大洋环流模式LICOM, 通过1958～2001年风应力 (ERA40) 和热通量驱动下的两组模拟试验, 检验了二者在北太平洋年际和年代际变率形成中的作用。结果表明, 尽管在年际尺度上热带太平洋变率主要受风应力影响, 但合理考虑热通量异常的强迫作用能够显著改进模式对El Niño的模拟效果, 包括对El Niño周期非规则性的成功模拟; 北太平洋SST的年际和年代际异常主要受热通量异常的影响, 合理考虑热通量强迫的年代际变化能够改善模式对北太平洋年代际变率的模拟效果。在北太平洋海盆的不同区域, 导致SST变率异常的因子不同: 在加利福尼亚沿岸, 冬季平均海温的变率异常主要由热通量的异常决定; 在北太平洋中部, 温度趋势异常主要受热通量和水平平流的作用影响; 在黑潮及其延伸体区域, 对温度趋势异常起主导作用的是热通量和海洋非线性作用, 与此同时, 水平平流和扩散的作用亦不容忽视。     

Simulated Change in the Interannual Variability of South Asian Summer Monsoon in the 21st Century

This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO-monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 (CMIP3) coupled models. The dynamical monsoon index (DMI) was adopted to describe the interannual variability of South Asian summer monsoon, and the standard dev...