Simulated impacts of the South Atlantic Ocean Dipole on summer precipitation at the Guinea Coast

An intermediate complexity atmospheric general circulation model has been used to investigate the influence of the South Atlantic Ocean (SAO) dipole (SAOD) on summer precipitation over the Guinea Coast of West Africa. Two ensemble integrations in which idealized but realistic SAOD-type sea surface temperature (SST) anomaly is prescribed only in the SAO, and then globally are performed and inter-compared. Consistently, above (below) the average precipitation is simulated over the Guinea Coast during the positive (negative) phase of the SAOD. Comparison of the two set of experiments reveal that in its active years, the SAOD is a dominant mechanism that shapes the spatial character of summer precipitation at the Guinea coast, the global SST variability merely slightly moderate its effects. During the SAOD, cool SST anomaly in the extra-tropical SAO off the Brazil–Uruguay–Argentina coast gives rise to suppressed convection and mass divergence. In turn, the subsidence tends to amplify the sub-tropical arm of anomalous Hadley-type circulation and consequently large scale convection and mass flux convergence in the equatorial Atlantic Ocean/Gulf of Guinea region bordering on the coastal fringes of West Africa. Precipitation is therefore increased at the Guinea Coast.     

影响我国北方冬半年气旋的气候特征及年际变率

本文首先对气旋进行了客观定义,实现了气旋的自动识别与跟踪算法,利用NCEP/NCAR再分析资料建立了近60年(1951～2010)我国北方冬半年气旋活动数据集。对气旋的气候特征与年际变率进行了探讨。结果表明:蒙古国中西部、雅布洛诺夫山脉东麓等为主要气旋源地;蒙古国东南部、内蒙古东南部、松嫩平原是气旋活跃区;内蒙古东南部、东北地区中北部为气旋消亡区与快速填塞区;初春、仲秋季节气旋较活跃,冬季气旋最少;随季节推移,气旋活动区域向南、向东推进;气旋移动以偏东路径居多,其次是东南、东北路径;700 hPa风场对气旋移动趋势具有较好的指示意义;24 h标准加深率大于0.5 Bergeron的快速发展气旋,位于内蒙古东部、东北地区中北部、日本海中部等地;爆发性气旋则主要位于日本海附近,我国大陆极少;极端最强气旋主要集中在1980年代以前的仲秋与初春;1980年代以来,气旋频次相对较少,强气旋有逐渐增加的趋势;气旋频次减少与东亚中高纬度大气低层斜压性减弱有关。     

Possible relationship between North Korean total rainfall and Arctic Oscillation in May

In this study, a negative correlation between the rainfall over North Korea in May and the Arctic Oscillation (AO) in the same month is analyzed. The reasons for rainfall declines in the positive AO phase are as follows: (a) the strengthening of anomalous anticyclone in the Maritime Province of Siberia, (b) the weakening of the subtropical western North Pacific high, and (c) the stabilization across all the atmospheric layers in North Korea. Anomalous anticyclone strengthened in the Maritime Province of Siberia plays a critical role in placing the North Korean region under the influence of anomalous northeasterlies. In addition, the development of the anomalous northeasterlies results in the supply of a large amount of cold and dry air into North Korea. This consequently stabilizes the atmosphere in North Korea. Moreover, the reinforcement of anomalous cold sea surface temperature in the mid-latitude region of East Asia is found to be another reason for the atmospheric stabilization.     

Interdecadal change in North Korean winter mean rainfall

In the present study, it was found that there was a significant climate regime shift in 1993 from average rainfall amounts in winter (December of a year and January and February of the next year) in North Korea over the last 30 years (1982–2011). This significant climate regime shift in 1993 also appeared in empirical orthogonal function analysis conducted using the winter mean rainfall amounts observed at 26 weather observation stations in North Korea. The reason why winter mean rainfall amounts in North Korea were smaller during the period of 1994–2011 than during the period of 1982–1994 was that anomalous anticyclone was reinforced in regions near Lake Baikal while anomalous cyclone was reinforced on the sea on the east of Japan so that the winter pressure system pattern (west high-east low pattern) appeared and thus anomalous cold and dry northerlies were reinforced in most East Asian regions including North Korea. To figure out the reason why anomalous anticyclone was reinforced further in the East Asian continent in winters during the period of 1994–2011, differences in water equivalent of accumulated snow depths between the two periods were analyzed. As a result, more snow was observed in most East Asian regions during the period of 1994–2011. Therefore, anomalous anticyclone could be further reinforced in the East Asian continent because surface air temperature dropped further due to snow-albedo effect. The surface air temperature cooling deepened further in the East Asian continent during the period of 1994–2011 due to snow-albedo effect was identified through differences in sensible heat net flux between the two periods.     

一种双向测距与时间同步系统的设计与分析

在研究双向单程伪距测量原理的基础上,设计了双向测距与时间同步（DRTS）终端系统总体构架,阐述了在系统中使用的技术,并搭建了基于DSP＋FPGA的双向测距与时间同步系统软硬件平台。实验结果表明,此系统的码速率为5MHz、中心频率为15MI-Iz时,测距和时间同步的分辨率可达0．15cm和5ps（@1S）,采用不同频率源时测距和时间同步的精度分别为1．038m和3．46ns,采用相同频率源时分别为0．28cm和9．43ps（参考频率稳定度1×10^-10／d量级）。与国外同类产品相比具有测量精度优势,但考虑通用性,此系统的硬件仍需进一步优化,软件上需要做到码速率可调。     

鲁东地区主要副矿物晶体化学特征的研究

岩石中副矿物的晶体形态主要受岩石化学及形成时的物理化学条件所控制。矿物晶体化学成分的变化反映了岩性的差异。由于不同的岩石形成时,介质的酸度和碱度有所不同,其中副矿物晶面生长速度也就不同,从而形成不同的晶体形态。因此,研究副矿物的晶体化学     

近江牡蛎3个种群生化遗传变异的研究

用同工酶电泳方法研究广东省官渡、阳江和汕尾的近江牡蛎(Ostea rivularis)的遗传变异。分析了11种同工酶20个的位点,其中出现13个位点显示为多态。结果表明官渡、阳江、汕尾种群的多态位点比例分别为0.200、0.200、0.500。官渡和阳江种群间,官渡和汕尾种群间以及阳江和汕尾种群间的遗传距离(D)分别为0.0451,0.1125,0.1088。     

Runoff and sediment loss responses to rainfall and land use in two agricultural catchments on the Loess Plateau of China

Soil erosion is a severe problem hindering sustainable agriculture on the Loess Plateau of China. Plot experiments were conducted under the natural rainfall condition during 1995–1997 at Wangdongguo and Aobao catchments in this region to evaluate the effects of various land use, cropping systems, land slopes and rainfall on runoff and sediment losses, as well as the differences in catchment responses. The experiments included various surface conditions ranging from bare soil to vegetated surfaces (maize, wheat residue, Robinia pseudoacacia L., Amorpha fruticosa L., Stipa capillata L., buckwheat and Astragarus adsurgens L.). The measurements were carried out on hill slopes with different gradients (i.e. 0 ° to 36 °). These plots varied from 20 to 60 m in length. Results indicated that runoff and erosion in this region occurred mainly during summer storms. Summer runoff and sediment losses under cropping and other vegetation were significantly less than those from ploughed bare soil (i.e. without crop/plant or crop residue). There were fewer runoff and sediment losses with increasing canopy cover. Land slope had a major effect on runoff and sediment losses and this effect was markedly larger in the tillage plots than that in the natural grass and forest plots, although this effect was very small when the maximum rainfall intensity was larger than 58·8 mm/h or smaller than 2·4 mm/h. Sediment losses per unit area rose with increasing slope length for the same land slope and same land use. The effect of slope length on sediment losses was stronger on a bare soil plot than on a crop/plant plot. The runoff volume and sediment losses were both closely related to rainfall volume and maximum intensity, while runoff coefficient was mainly controlled by maximum rainfall intensity. Hortonian overland flow is the dominant runoff process in the region. The differences in runoff volume, runoff coefficient and sediment losses between the catchments are mainly controlled by the maximum rainfall intensity and infiltration characteristics. The Aobao catchment yielded much larger runoff volume, runoff coefficient and sediment than the Wangdongguo catchment. Copyright © 2001 John Wiley & Sons, Ltd.     

星系形成的半解析模型研究进展

基于目前流行的冷暗物质等级成团理论的星系形成的半解析模型取得了很大进展．在引入一系列合理的关于重子物质物理过程的假设，如气体冷却、恒星形成率、超新星能量反馈以后，结合N体数值模拟，星系形成的半解析模型一方面能较成功地预言许多与观测符合的近邻星系的性质，如光度函数、星系的两点相关函数、Thlly-Fisher关系、星系团中椭圆星系的颜色一星等关系等；另一方面还能较成功地预言宇宙的恒星形成历史，以及一部分高红移星系的性质，如Lyman-Break星系的数目随红移的分布．但是最近一些观测表明，半解析模型在高红移预言的大质量星系较少，且红星系数目也较观测少．重点讨论半解析模型成功与不足之处，并指出解决这些问题可能的途径。