北斗三号导航定位技术体制与服务性能

介绍了北斗三号系统的星座设计、服务类型、导航信号体制、时空基准以及轨道确定与时间同步机制等技术体制,分析提出了评估北斗三号导航定位服务性能的指标体系,指标涵盖时空基准、空间信号质量、空间信号精度和服务性能4个方面,综合利用全球数据资源对北斗三号基本系统的导航定位服务性能进行了评估。结果显示,各信号分量有效功率比偏差优于0.25dB,S曲线过零点偏差(SCB)优于0.3ns,满足设计要求;北斗三号基本系统当前全球位置精度因子(PDOP)可用性优于85.0%,空间信号测距误差0.48m(RMS),空间信号连续性99.99%,空间信号可用性99.78%,UTC偏差误差优于19.1ns(95%),均满足系统服务性能规范承诺的指标。相对于北斗二号而言,北斗三号在覆盖能力、空间信号精度、空间信号可用性、空间信号连续性等方面均有显著提升。     

2020年全球变暖会创新高吗?

近百年全球气候变暖已是既定事实。伴随着冰川的持续消融、多年积雪的不断融化、海平面的上升、极端事件的增加,气候系统正面临着严峻挑战。2020年是特殊的一年,澳洲山火持续数月,蝗灾肆虐,突破历史记录的洪涝和干旱频发,因而全球变暖问题备受关注。本文利用最新的再分析资料,预测了2020年全球年平均地表温度;2020年全球冬季温度年际增量出现较大正值,结合温室气体、海冰和海表温度距平信号,预测2020年全球变暖将持续。采用年际增量方法进行定量预测,结果显示,2020年全球地表温度很可能超过2016年而成为近百年来最热的一年。     

近几年我国霾污染实时季节预测概要

近些年,中国东部经历了严重的霾污染,对人体健康、交通安全、生态系统以及社会经济有巨大的危害。在1周以内的霾污染预报之外,季节尺度的霾污染预测可以给减排治污措施的制定提供更长时间尺度的科学支撑。本文以年际增量为预测对象,选取前期外强迫因子为自变量,分别针对京津冀和长三角区域建立逐月的冬季霾日数季节尺度预测模型,并开展了实时的季节预测。总体来看,京津冀和长三角区域预测模型的性能大体处于相似的水平,均方根误差在2 d左右,对距平符号的捕捉率在80%以上,对霾日数变化的长期趋势具有很好的再现能力。在2016/2017年冬季京津冀霾日数实时预测中,模型预测的结果相对于常年值的定性结论全部准确,相对于前一年污染状况的结论大多数准确。在2017/2018年冬季长三角霾日数实时预测中,12月和1月的预测误差较小,2月的预测误差在2 d左右。     

南黄海崂山隆起地层属性及油气地质

应用地震地层学研究方法,对近几年重新采集、处理的地震剖面进行综合解释,同时,结合与下扬子地块的区域地质对比,建立崂山隆起地层层序格架,确定其地层地质属性,分析其地层分布规律和油气地质特征。研究认为崂山隆起海相下构造层分布稳定,残留厚度较大,烃源丰富,保存条件较好,具备形成大型油气藏的油气地质条件,是潜在的油气勘探目标。     

鄱阳湖流域南昌市城市湖泊水体抗生素污染特征及生态风险分析

采用固相萃取-超高效液相色谱-质谱法对南昌市5个城市湖泊——艾溪湖、瑶湖、青山湖、象湖和东西湖水体的抗生素进行监测,并分析其污染来源和生态风险.结果表明,南昌市5个城市湖泊水体中四环素类、磺胺类、喹诺酮类、林可霉素及大环内酯类5类抗生素的检出浓度范围分别为ND~6.3、ND~32.0、ND~97.2、ND~54.7和ND~98.4 ng/L;红霉素和林可霉素是5个城市湖泊水体中的主要抗生素类型;相比于其他湖泊,南昌市城市湖泊水体中主要检出抗生素浓度总体处于中等水平,其中恩诺沙星的检出浓度高于其他对比湖泊.南昌市城市湖泊中6种主要抗生素的风险商均小于0.1,表明均为最低生态风险;5个城市湖泊的主要生态风险因子分别是艾溪湖为红霉素,瑶湖为磺胺二甲嘧啶,青山湖为罗红霉素,象湖为红霉素,东西湖为磺胺嘧啶.本研究可为南昌市城市湖泊水环境管理,特别是新型污染物的环境管理提供基础依据.     

神农架大九湖湿地浮游植物群落结构特征及营养状态评价

大九湖湿地是南水北调中线工程的重要水源涵养地之一.为了解实施生态修复工程后浮游植物群落结构特征及水质营养状态,于2014年11月-2015年9月进行了3次采样调查,综合营养状态指数表明水质处于中营养和轻度富营养化之间,水质富营化水平沿水流方向呈降低趋势;共采集浮游植物8门129种,11月优势种为绿藻门的四尾栅藻(Scenedesmus quadricauda)和硅藻门的颗粒直链藻(Melosira granulata)、短缝藻(Eunotia sp.);5月优势种为蓝藻门的纤细席藻(Phormidium tenue)、绿藻门的四尾栅藻(Scenedesmus quadricauda)和球衣藻(Chlamydomonas globosa Snow)、硅藻门的短线脆杆藻(Fragilaria brevistriata);9月优势种为蓝藻门的拟柱孢藻(Cylindrospermopsis raciborskii)、小形色球藻(Chroococcus minor)和泽丝藻(Limnothrix redekei),优势种主要为中污带指示种.冗余分析表明总磷和总氮浓度对浮游植物丰度变化有显著影响,温度和总磷浓度对浮游植物生物量有显著影响,蓝藻门和绿藻门的丰度和生物量均与总磷浓度呈正相关.     

Permafrost and climatic change in China

The permafrost area in China is about 2.15×10⁶ km², and is generally characterized by altitudinal permafrost. Permafrost in China can be divided into latitudinal and altitudinal types, the latter can be further divided into plateau and alpine permafrost. Altitudinal permafrost also can be divided into five thermal stability types. The permafrost environment has changed significantly since the Late Pleistocene. In northeastern China, the southern limit of permafrost extended to 41–42°N during the last glaciation maximum; in the Holocene megathermal, it retreated northward. The ice wedges and permafrost formed during the Late Pleistocene are still present in the northern part of the Da-Xing'anling Mountains. The inactive ice wedges at Yitulihe indicate a cooling and subsequent permafrost expansion during the Late Pleistocene. The lower limit of altitudinal permafrost in western China has elevated from 800 to 1500 m since the last glaciation maximum. Compared with that in northern Europe and North America, latitudinal permafrost in northeastern China is less sensitive to climatic warming, but altitudinal permafrost, especially permafrost on the Qinghai–Tibet Plateau (QTP), is sensitive to climatic warming. Since the early 20th century, significant permafrost degradation has occurred and is occurring in most permafrost regions in China. Due to the combined influence of climatic warming and increasing anthropogenic activities, substantial retreat of permafrost is expected on the QTP and in northeastern China during the 21st century. Permafrost degradation has and will cast great influence on engineering construction, water resources and environments in the cold regions of China. The wetlands in the cold regions of China emit significant amounts of CH₄ and N₂O to the atmosphere and uptake atmospheric CO₂ at a considerable rate, which might contribute to the global atmospheric carbon budget and feedback to climatic systems. However, uncertainties about permafrost changes, rates of changes and their environmental impacts are still large and call for intensive studying.     

Editorial Statement

At the request of Dr. Hideharu AKIYOSHI of the National Institute for Environmental Studies (NIES) of Japan and with the apology of Dr. ZHOU Libo for his misconduct, we hereby announce that the paper of "Middle-High Latitude N2O Distributions Related to the Arctic Vortex Breakup", authored by ZHOU Libo, ZOU Han, and GAO Yongqi, be retracted from Volume 23, No. 2, March 2006 of Advances in Atmospheric Sciences (AAS) on page number 215-223. This paper will not be considered as a published paper in AAS, and it will not appear in any future reference or record. In fact, this paper should not have been submitted for consideration for publication in AAS, because it was based on the scientific ideas and research previously     

The Seasonal Climate and Low Frequency Oscillation in the Simulated Mid-Holocene Megathermal Climate

l.IntroductionThegoalofPMIP(PaleoclimateModellingIntercomparisonProject)istocomparethestate-ofthe-artclimatemodels'simulationsforthepastclimateonthebasisofthepaleoclimatedata.Oneofthemostinterestingperiodsisthemid-Holoceneduring8.5-3.OkaBPwiththemaximumin7.2-6.OkaBP(beforepresent)inChina(Shietal.,l992).Itwasre-vealedthatthetemPeraturewasl-4'Chigherandtheprecipitationwas4O%-loO%largercomparedtothepresentoverChina(Shietal.,l992;Anetal..l99l;Kongetal.,l99O,l99l).Therehavebeensomesimula…     

古气候模拟与气候模式

本文概要地介绍了国内外近年来古气候模拟研究的若干进展.内容包括国际古气候模拟比较计划的研究工作和中国科学院大气物理研究所开展的古气候模拟研究.作为气候模拟研究的重要手段,气候模式是非常关键的,因此,文中也对古气候模拟中使用的各种气候模式作了扼要的介绍.