The effect of surface friction on the development of tropical cyclones

When tropical cyclones (hereafter referred as TCs) are over the ocean, surface friction plays a dual role in the development of TCs. From the viewpoint of water vapor supply, frictional convergence and Ekman pumping provide a source of moisture for organized cumulus convection and is propitious to the spin-up of TCs. On the other hand, surface friction leads to a dissipation of kinetic energy that impedes the intensification of TCs. Which role is dominant in the developing stage of TCs is a controversial issue. In the present work, the influence of surface friction on the growth of TCs is re-examined in detail by conducting two sets of numerical experiments initialized with different cyclonic disturbances. Results indicate that, because of the inherent complexities of TCs, the impact of surface friction on the evolution of TCs can not be simply boiled down to being positive or negative. In the case that a TC starts from a low-level vortex with a warm core, surface friction and the resultant vertical motion makes an important contribution to the convection in the early developing stage of the TC by accelerating the build-up of convective available potential energy (CAPE) and ensuring moisture supply and the lifting of air parcels. This effect is so prominent that it dominates the friction-induced dissipation and makes surface friction a facilitative factor in the spin-up of the TC. However, for a TC formed from a mesoscale convective vortex (MCV) spawned in a long-lasting mesoscale convective system (MCS), the initial fields, and especially the low-level humidity and cold core, enable the prerequisites of convection (i.e., conditional instability, moisture, and lifting), to be easily achieved even without the help of boundary-layer pumping induced by surface friction. Accordingly, the reliance of the development of TCs on surface friction is not as heavy as that derived from a low-level vortex. The positive effect of surface friction on the development of TCs realized through facilitating favorable conditions for convection is nearly cancelled out by the friction-induced dissipation. However, as SST is enhanced in the latter case, the situation may be changed, and different development speeds may emerge between model TCs with and without surface friction considered. In short, owing to the fact that TC development is a complicated process affected by many factors such as initial perturbations, SST, etc., the importance of surface friction to the intensification of TCs may vary enormously from case to case.     

对流有效位能计算的新方案

对流有效位能是强对流天气分析预报的重要参数。本文通过理论推导,提出了载水气块和非载水气块两种情况下,对流有效位能的两个新的计算方案,分别记作CAPEw和CAPE。该方案与以往的方案有很大的不同和根本的区别,更加合理和符合实际。编制了相应的计算程序,可以计算两种情况下的对流抑制能量CINw、CIN,对流有效位能CAPEw、CAPE,抬升凝结高度LCL(二者相同),自由对流高度LFCw、LFC,对流凝结高度CCL(二者相同)以及平衡高度ELw、EL;可以预报对流温度Tg(二者相同);可以分析地面和高空温度、湿度、等压面高度发生变化时,CINw、CIN和CAPEw、CAPE等的数值变化情况,便于业务应用和理论研究。还讨论了影响对流有效位能局地变化的因子和预报思路。     

阿克苏河流域无站控制区地表水资源及可利用量评价

阿克苏河是"四源一干"中最大的源流,多年平均地表径流总量为80.6×108m3,入塔里木河水量34.2×108m3,占阿拉尔站以上3条源流输水量的73.5%,对塔里木河的形成、发展、演变和生态环境起着决定作用.无站控制区调查面积7 110 km2,占流域总面积的14.2%.2005—2007年对中国境内阿克苏河无站控制区主要19条河(沟)洪水水量、洪水沟基流和17条泉水水量野外调查计算,阿克苏河流域无站控制区间地表水资源总量为6.68×108m3.其中,洪水沟总洪量0.6050×108m3,洪水沟基流总量2.0569×108m3,泉水天然补给量4.0185×108m3.在6.68×108m3的地表水资源总量中,可利用量为3.2×108m3.     

中尺度暴雨云团发生发展前的一些征兆

利用湿有效能量方法找出了盛夏午后北京地区中尺度暴雨云团发生发展的一些征兆：（１）北京地区已贮存着大量能量；（２）湿有效能量正在北京地区积聚；（３）低层流场结构有利于出现强迫抬升；（４）北京地区与河套地区之间午后将出现非绝热加热形成的巨大水平温差。     

克拉玛依地区土壤速效微量养分空间变异特征

用地统计学方法研究了克拉玛依地区土壤速效微量养分的空间变异特征 ,并绘制了微量养分空间分布图。结果表明 :土壤速效微量养分在整个研究区内均表现出中等变异水平 ,其变异性大小表现为 :速效Mo >速效B >速效Mn >速效Zn。除速效硼外 ,其它微量元素都表现出很强的空间结构性 ,速效Zn、Mn变程较短 ,分别为 8.7km和 5 .2km ,速效Mo、B变程较长 ,分别为 4 1km和 6 6 .4km。基于半方差函数模型 ,用普通克里格法对研究区土壤速效微量养分进行了克里格插值 ,结果表明 :速效Zn在研究区内普遍缺乏 ,速效B、速效Mn含量较丰富 ,而速效Mo含量在整个研究区表现出明显的差异性。     

云南哀牢山中山湿性常绿阔叶林土壤氮矿化季节变化

为了揭示哀牢山中山湿性常绿阔叶林土壤有效氮的季节动态特征,我们用封顶埋管法对徐家坝地区典型的中山湿性常绿阔叶林进行了研究。结果表明:1)土壤有效氮含量季节变化为22.96～68.20mgN·kg-1,其中氨态氮的含量(10.89～47.85mgN·kg-1)大于硝态氮含量(1.48～31.74mgN·kg-1),是有效氮的主体;2)一年的净有效氮矿化总量为310.32mgN·kg-1·hm-2(土壤层0～15cm),有效氮总量和NO3N干湿季节变化极显著,NH4N的干湿季节变化不显著,NH4N在湿季末(200409)最高,干季末(200404)最低,NO3N湿季初(200405)最高,湿季末(200310)最低;3)净矿化速率、净氨化速率、净硝化速率的干湿季节变化均不显著,原因在于土壤内部的干湿季节变化平缓,且这种变化滞后于大气的降雨量变化。     

Development and propagation of equatorial waves

Development and propagation of equatorial waves are investigated with the model which includes convection -wave convergence feedback and convection-frictional convergence feedback. Two experiments with an initial Kelvin wave (Exp. K) and with an initial Rossby wave (Exp. R) are carried out. The equatorial waves in Exp. R grow much faster than those in Exp. K. The equatorial waves in both experiments follow zonal (eastward / westward) and meridional (poleward) propagation. The equatorial waves can be partitioned into two meridional modes using Parabolic Cylinder Function. An equa?tor mode denotes a wave component with a positive precipitation center at the equator and an off-equator mode rep?resents a wave component with positive precipitation centers off the equator. The equator mode dominates in Exp. K whereeas the off-equator mode dominates in Exp. R. The rapid wave growth in Exp. R is interpreted by analyzing the eddy available potential energy (EAPE) generation. Stronger off-equator mode in Exp. R obtains more EAPE through convection-frictional convergence feedback which results in more rapid wave growth. The relative vorticity tendency is determined by interactions between Earth’s vorticity and lower-troposphere convergence (divergence effect) and between the meridional gradient and lower-troposphere circulation (beta effect). The eastward and poleward propagation of equatorial waves is a result of the divergence effect, and the westward movement is caused by the beta effect.     

新世纪地球科学视野中的新技术和新方法

评价和区分大型矿床 ,一直是近年矿产勘查活动的焦点。最新研究表明 ,大型、巨型矿床与一般矿床的主要并可以量化的区别 ,在于大型、巨型矿床有着巨量的成矿元素供应与聚集。这种巨量的成矿元素供应 ,不是传统意义上元素的全量 ,而是能被成矿过程所利用的活动态分量。文中提出了基于元素立体分散模式和成矿可利用金属分量评价和区分矿床规模的一种定量地球化学模型和方法。     

敦煌西土沟沙漠洪水资源开发利用模式及成效分析

收集研究区域内雨量站历年降水量资料,水文站历年径流系列资料以及历年最大洪峰流量、洪水总量成果资料及西土沟敦煌沙漠水文实验研究站实测水文资料,调查该区域内洪水沟道的历史最大洪水。用水文学原理和方法对洪峰流量和洪水总量变化规律进行统计分析,结合敦煌西土沟流域灾害综合治理工程实施情况估算区域水资源可利用量,提出沙漠洪水资源开发利用新模式。结果表明:西土沟流域洪水灾害综合治理工程的实施探索出导流+分洪+工程防护的洪水资源开发利用模式、拦蓄洪水产生地下径流利用模式和沙漠冷水虹鳟鱼养殖到葡萄种植的区域水资源重复利用模式;有效遏制了研究区内沙漠的进一步推进并可显著增加流域内可利用水资源量,实现了区域生态治理与经济发展的良性循环。     

四种浸提剂对果园与菜地土壤有效硒浸提效果的对比研究

有效硒是评价土壤中硒对植物供给能力的重要指标,我国目前尚无测试有效硒的国家标准方法。浸提剂的选择对于准确测定有效硒的含量至关重要,本文根据浸提的有效硒与硒形态的关联性来确定最优浸提剂种类。实验中选取了碳酸氢钠、磷酸二氢钾、硝酸和盐酸四种浸提剂,对天津果园和菜地的土壤进行有效硒浸提,采用原子荧光光谱法测定各形态硒的含量,并分别对浸提的有效硒与水溶态+离子交换态+碳酸盐结合态硒的最小值、25%处数据值、中位数、75%处数据值和最大值进行比较分析和差异性检验。结果表明:采用碳酸氢钠和磷酸二氢钾提取菜地土壤有效硒的平均含量均约为0.039mg/kg,高于硝酸和盐酸的提取量;采用碳酸氢钠、磷酸二氢钾、硝酸和盐酸提取果园土壤有效硒的含量依次降低。两种土壤中,磷酸二氢钾浸提有效硒的最小值、25%处数据值、中位数、75%处数据值和最大值与水溶态+离子交换态+碳酸盐结合态硒的含量最为接近,而且无显著差异性。研究认为,0.1mol/L磷酸二氢钾适合作为天津果园和菜地土壤有效硒的浸提剂。