A model for solar radio pulsations at short centimetric band

In this paper, the observed solar radio pulsations during the bursts at 9.375 GHz are considered to be excited by some plasma instability. Under the condition of the conservation of energy in the wave-particle interaction, the saturation time of plasma instabilities is inversely proportional to the initial radiation intensity, which may explain why the repetition rate of the pulsations is directly proportional to the radio burst flux at 9.375 GHz as well as 15 GHz and 22 GHz. It is also predicted that the energy released in an individual pulse increases with increasing the flux of radio bursts, the modularity of the pulsations decreases with increasing the flux of radio bursts, these predictions are consistent with the statistical results at 9.375 GHz in different events. The energy density of the non-thermal particles in these events is estimated from the properties of pulsation. For the typical values of the ambient plasma density (10⁹ cm^–3) and the ratio between the nonthermal and ambient electrons (10^–4), the order of magnitude of the energy density and the average energy of the nonthermal electrons is 10^–4 erg/cm³ and 10 kev, respectively. It is interesting that there are two branches in a statistical relation between the repetition rate and the radio burst flux in a special event on March 11–17, 1989, which just corresponds to two different orders of magnitude for the quasi-quantized energy released in these five bursts. This result may be explained by the different ratios between the thermal and the nonthermal radiations.     

气象信息微信公众服务平台设计与应用开发

为了进一步拓宽气象信息的发布手段和发布渠道,提升气象服务能力和水平,使社会公众能够便捷地获取到丰富的气象信息。研究依托天津滨海新区气象信息Web服务端,以微信为基础平台,应用Java编程语言、Oracle数据库,Hibernate和Spring框架等技术,通过对微信公众平台API进行开发,以图表、文字、GIS图等展现方式,开发了基于微信网络社区软件的公益气象信息服务平台。本研究充分利用了新型移动传媒发布气象信息的手段,实现了气象信息多形式服务于社会公众,可达到公众及时掌握气象信息的需求。     

环境场对西北太平洋热带气旋快速增强过程的影响

利用美国联合台风预警中心整编的西北太平洋1970—2012年热带气旋(TC)最佳路径数据集及ERA-Interim再分析资料,利用极端天气法确定TC快速增强(RI)的阈值为30 kn,分析了快速增强(RI)TC的时空分布特征;从RI的样本中选取9个个例,采用动态合成分析法,对TCRI过程的环境场进行比分析。研究表明:(1)菲律宾群岛以东(10~15°N,130°E)海域为RI发生频数最多的区域,南海地区发生RI的情况明显偏少。(2)RI在1972年发生的概率最大,而在2005年发生的概率最小,1997年后,RI发生的概率波动性较大。(3)西风与西南风水汽输送结合150h Pa附近的反气旋强辐散作用,有利于TCRI过程的进行。(4)RI发生前24 h至RI发生后的6 h,TC中心附近区域平均东风切变较快增大,其值由0.5 m·s~(-1)增加到2.5 m·s~(-1)左右,之后保持在2.0~3.0 m·s~(-1),使TC处于一个有利于其RI过程的纬向风切变环境。     

Numerical experiments on the impacts of surface evaporation and fractionation factors on stable isotopes in precipitation

The isotope enabled atmospheric water balance model is applied to examine the spatial and temporal variations of δ¹⁸O in precipitation, amount effect and meteoric water lines (MWL) under four scenarios with different fractionation nature and surface evaporation inputs. The experiments are conducted under the same weather forcing in the framework of the water balance and stable water isotope balance. Globally, the spatial patterns of mean δ¹⁸O and global MWLs simulated by four simulation tests are in reasonably good agreement with the Global Network of Isotopes in Precipitation observations. The results indicate that the assumptions of equilibrium fractionation for simulating spatial distribution in mean annual δ¹⁸O and the global MWL, and kinetic fractionation in simulating δ¹⁸O seasonality are acceptable. In Changsha, four simulation tests all reproduce the observed seasonal variations of δ¹⁸O in precipitation. Compared with equilibrium fractionation, the depleted degree of stable isotopes in precipitation is enhanced under kinetic fractionation, in company with a decrease of isotopic seasonality and inter-event variability. The alteration of stable isotopes in precipitation caused by the seasonal variation of stable isotopes in vapour evaporated from the surface is opposite between cold and warm seasons. Four simulations all produce the amount effect commonly observed in monsoon areas. Under kinetic fractionation, the slope of simulated amount effect is closer to the observed one than other scenarios. The MWL for warm and humid climate in monsoon areas are well simulated too. The slopes and intercepts of the simulated MWLs decrease under kinetic fractionation.     

泸沽湖地区晚全新世气候和环境演变

泸沽湖地区受人类活动影响较小、对气候变化较为敏感,是开展古气候研究的理想区域。本文以孢粉为重要研究手段,对采自泸沽湖草海地区103cm的浅钻沉积物开展研究,采样间距2cm,共取得52块样品用于孢粉分析。沉积物年龄采用AMS-~(14)C测定,经校正之后钻孔底部年龄为3455cal.a BP。经实验分析之后,所有样品均含有丰富的孢粉类群,反映的植被组成主要以松(Pinus)林为主,铁杉(Tsuga)也较为常见,被子植物中则以栎属(Quercus)占绝对优势,栗属(Castanea)和木犀科(Oleaceae)植物也频繁出现,而草本植物则以禾本科(Gramineae)为主,蓼科(Polygonaceae)、菊科(Asteraceae)和莎草科(Cyperaceae)植物也是重要的组成成分,林下生长有大量的蕨类的植物,主要以紫萁属(Osmunda)、石松属(Lycopodium)和膜蕨科(Hymenophyllaceae)等为主,另外,采样点草海为季节性湿地,水生植物主要以香蒲属(Typha)和藻类植物中的双星藻(Zygnema)和水绵(Spirogyra)最为常见。为了获得该地区晚全新世以来的气候变化曲线,本研究采用共存分析法分别对划分的四个孢粉带进行了古气候的定量重建,年均温和年均降水量分别为:3455cal.a BP至2585cal.a BP,MAT(mean annual temperature)=11.5~18.6℃,MAP(mean annual precipitation)=797.5~1484.3mm;2585cal.a BP至1699cal.a BP,MAT=11.7~18.6℃,MAP=617.9~1523.1mm;1699cal.a BP至595cal.a BP,MAT=8.5~18.6℃,MAP=797.5~1484.3mm;595cal.a BP至今,MAT=5.7~18.6℃,MAP=617.9~1484.3mm。结果显示该地区3455cal.a BP以来气候经历了略微变暖-变凉-持续变凉-回暖四个阶段。本研究还将变化曲线与其他地区同时代的研究结果进行了对比分析,显示年均温的变化趋势与格陵兰冰芯δ~(18)O以及祁连山敦德冰芯所反映的温度变化趋势基本一致,并可观察到中世纪暖期、晚全新世小冰期及现代温暖期。