东亚冬季风的年代际变化及其与全球气候变化的可能联系

对近年来中外关于东亚冬季风(EAWM)年代际变化问题研究进展做了回顾和评述,主要包括以下3个方面内容:(1)东亚冬季风明显受到全球气候变化的影响,从20世纪50年代开始,中国冬季气温经历了一次冷期(从20世纪50年代延续到80年代初中期),一次暖期(从20世纪80年代初中后期延续到21世纪初)和近10-15年(约从1998年开始)出现的气候变暖趋缓期(也称气候变暖停顿期)。(2)东亚冬季风主要表现出强-弱-强3阶段的特征,即从1950年到1986/1987年,明显偏强;从1986/1987年冬季开始,东亚冬季风减弱;约2005年之后,东亚冬季风开始由弱转强。与东亚冬季风的年代际变化特征相对应,东亚冬季大气环流以及中国冬季气温和寒潮都表现出一致的年代际变化。(3)东亚冬季风的年代际变化与大气环流和太平洋海表温度(SST)的区域模态变化密切相关。当北半球环状模/北极涛动(NAM/AO)和太平洋年代际振荡(PDO)处于负(正)位相,东亚冬季风偏强(弱),中国冬季气温偏低(高)。此外,北大西洋年代尺度振荡(AMO)对东亚冬季风也有重要影响,在AMO负位相时,对应东亚冷期(强冬季风),正位相对应暖期(弱冬季风)。因而海洋的年代际变化是造成东亚冬季风气候脉动的主要自然原因,而全球气候变暖对东亚冬季风强度的减弱也有明显影响。     

1961 - 2018年河西走廊寒潮频次时空变化特征及其环流影响因素研究

寒潮是我国北方地区冬、 春、 秋季节常见气象灾害之一, 产生的危害严重影响社会经济发展和人们生产生活。河西走廊生态环境脆弱且处于寒潮影响的重要区域, 揭示河西走廊寒潮频次时空变化特征可以为农牧业防灾减灾提供参考。基于1961 - 2018年河西走廊12个气象站逐日最低气温数据, 采用数据统计和空间可视化表达方法, 分析近60 a河西走廊寒潮频次时空变化特征, 并探讨北极涛动（AO）异常与寒潮频次的响应关系。结果表明： 从时间上看, 河西走廊的寒潮主要发生在10月至4月, 其中11月、 12月、 4月为寒潮高发时期, 近60 a河西走廊寒潮频次呈现出下降的趋势, 其中在20世纪80年代出现明显的低值, 下降趋势在季节上表现为秋季>春季>冬季; 河西走廊寒潮发生频次具有显著的空间差异, 其中西部地区最多, 东部地区居中, 中部地区最少; 北极涛动（AO）强弱与河西走廊寒潮频次变化具有时空响应关系, 当AO处于负相位时, 河西走廊各气象站寒潮发生频次较多, 并且在河西走廊东部和西部表现的较为明显。     

北半球环状模波流相互作用动力学研究进展

总结了国内外学者对于北半球环状模（NAM：Northern Hemisphere Annular Mode）及其活动中心形成原因的研究成果。主要从NAM的天气、气候影响,波流相互作用原理对NAM形成的解释,NAM在北太平洋、北大西洋和北极3个区域活动中心的天气尺度波和行星尺度波活动等方面论述。NAM在对流层的变化与天气尺度波有关,北太平洋和北大西洋两个活动中心是天气尺度波活跃的区域,其峰值区表现为风暴轴,其中北大西洋天气尺度波破碎过程会使得NAM指数急剧变化。NAM在平流层的变化和准定常行星波关系密切,冬季准定常行星波会上传并与高纬平流层纬向流发生相互作用,从而引起北极极涡发生改变。准定常行星波将NAM 3个活动中心有机联系起来：对流层准定常行星波的纬向传播会影响北太平洋风暴轴的位置,而风暴轴的变化会影响下游北大西洋波破碎过程,同时准定常行星波的上传可以影响极涡活动。     

Physical Characteristics of Kazan Minor Showers as Determined by Correlations with the Arecibo UHF Radar

In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source areas where it is easiest to detect discrete showers with less confusion from the background.     

On the Differences and Climate Impacts of Early and Late Stratospheric Polar Vortex Breakup

The stratospheric polar vortex breakup (SPVB) is an important phenomenon closely related to the seasonal transition of stratospheric circulation. In this paper, 62-year NCEP/NCAR reanalysis data were employed to investigate the distinction between early and late SPVB. The results showed that the anomalous circulation signals extending from the stratosphere to the troposphere were reversed before and after early SPVB, while the stratospheric signals were consistent before and after the onset of late SPVB. Arctic Oscillation (AO) evolution during the life cycle of SPVB also demonstrated that the negative AO signal can propagate downward after early SPVB. Such downward AO signals could be identified in both geopotential height and temperature anomalies. After the AO signal reached the lower troposphere, it influenced the Aleutian Low and Siberian High in the troposphere, leading to a weak winter monsoon and large-scale warming at mid latitudes in Asia. Compared to early SPVB, downward propagation was not evident in late SPVB. The high-latitude tropospheric circulation in the Northern Hemisphere was affected by early SPVB, causing it to enter a summer circulation pattern earlier than in late SPVB years.     

冬季北极涛动对西伯利亚高压、东亚冬季风以及海冰范围的可能影响

利用NCEP／NCAR月平均再分析资料（1958－1997），月平均海表面温度资料（1950－1992）以及月的海冰密集度资料（1953－1995），研究了冬季北极涛动与西伯利亚高压、东亚冬季风以及巴伦支海海冰范围之间的联系。研究结果表明，冬季北极涛动不仅影响北极和北大西洋区域气候变化，并且可能影响冬季西伯利亚高压，进而影响东亚冬季风。当冬季北极涛动处于正位相时，冬季西伯利亚高压和东亚冬季风都偏弱，在西伯利亚南部和东亚沿岸，包括中国东部、韩国和日本，从地表面到对流层中部气温偏高0.5-2℃。当冬季北极涛动处于负位相时，结果正相反。研究结果还表明，冬季西伯利亚高压对北极以及北大西洋区域气候变化没有显的影响，与北极涛动的影响相比，西伯利亚的影响强度和范围明显偏弱。研究进一步揭示了冬季北极涛动可能影响西伯利亚高压的可能机理。冬季西伯利亚高压与动力过程以及从地表面到对流层中部的气温变化有密切的关系。西伯利亚高压的西部变化主要依赖于动力过程，而其东部与气温变化更为密切。冬季西伯利亚高压的维持主要依赖于对流层中的下沉气流，这种下沉气流源于北大西洋区域，其变化受到北极涛动的影响。当冬季北极涛动处于正（负）位相时，气流的下沉运动明显减弱（增强），进而影响冬季西伯利亚高压。此处，冬季北极涛动对同时期的巴伦支海海冰范围有显的影响。     

Ocean–atmosphere Teleconnections Play a Key Role in the Interannual Variability of Seasonal Gross Primary Production in China

Since the 1950s, the terrestrial carbon uptake has been characterized by interannual variations, which are mainly determined by interannual variations in gross primary production (GPP). Using an ensemble of seven-member TRENDY (Trends in Net Land–Atmosphere Carbon Exchanges) simulations during 1951–2010, the relationships of the interannual variability of seasonal GPP in China with the sea surface temperature (SST) and atmospheric circulations were investigated. The GPP signals that mostly relate to the climate forcing in terms of Residual Principal Component analysis (hereafter, R-PC) were identified by separating out the significant impact from the linear trend and the GPP memory. Results showed that the seasonal GPP over China associated with the first R-PC1 (the second R-PC2) during spring to autumn show a monopole (dipole or tripole) spatial structure, with a clear seasonal evolution for their maximum centers from springtime to summertime. The dominant two GPP R-PC are significantly related to Sea Surface Temperature (SST) variability in the eastern tropical Pacific Ocean and the North Pacific Ocean during spring to autumn, implying influences from the El Ni?o–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The identified SST and circulation factors explain 13%, 23% and 19% of the total variance for seasonal GPP in spring, summer and autumn, respectively. A clearer understanding of the relationships of China’s GPP with ocean–atmosphere teleconnections over the Pacific and Atlantic Ocean should provide scientific support for achieving carbon neutrality targets.     

BCC_CSM1.1气候模式年代际试验对北极涛动季节回报能力的初步评估

本文基于国家气候中心气候系统模式BCC_CSM1.1自1960—2004年每年起报的年代际预测试验结果,初步评估了该模式对北极涛动（AO）的预报技巧。同时,把该模式年代际预测结果与历史试验模拟比较,分析了气候模式初始化对年代际试验预测季节尺度AO及其年际变化的贡献。结果表明,年代际试验和历史试验均能反映出AO模态是北半球中高纬大气变率第一模态的特征,其中年代际预测试验回报的AO模态与观测的空间相关系数高于历史试验。两组试验基本能再现AO指数冬季最强、夏季最弱的特征。与历史试验相比,年代际预测试验回报月和冬季AO指数与观测的相关系数更高,特别是年代际试验与观测的月AO指数相关系数达到了0.1的显著性水平。年代际试验回报月、春季AO指数的变化周期更接近观测结果。因此,年代际试验中初始状态使用海温资料进行初始化,在一定程度上可以提高AO的回报能力。     

Mechanism of an Abrupt Decrease in Sea-Ice Cover in the Pacific Sector of the Arctic during the Late 1980s

The recent decline in Arctic sea-ice cover (SIC) shows seasonal and regional characteristics. The retreat of summer sea ice has occurred mainly in the Pacific sector of the Arctic. In this study, using the moving t-test, we found an abrupt change event in the long-term sea-ice area in the Pacific sector in summer 1989. This event was linked to the phase shift of the Arctic Oscillation (AO) or the Northern Annular Mode (NAM). Corresponding with the AO/NAM phase shift from negative to positive, the area of the northern hemisphere stratospheric polar vortex decreased abruptly in winter 1988/89. Comparisons of two periods before (1979–1988) and after (1989–1993) the abrupt decrease in sea ice show that an anomalous winter sea level pressure (SLP) was induced by changes in the polar vortex leading to an anomalous cyclonic ice drift in the Pacific sector. The changes in SLP and wind field persisted into the following spring, resulting in a decrease in SIC and warming of the surface air temperature (SAT). The influence of the spring SLP and SAT on ice persisted into the following summer. Meanwhile, the increased summer net surface heat flux over the ocean and sea ice as a result of the decreased spring ice cover further contributed to the summer sea-ice melt.     

Interdecadal correlation of solar activity with Tibetan Plateau snow depth and winter atmospheric circulation in East Asia

Studies on the impact of solar activity on climate system are very important in understanding global climate change. Previous studies in this field were mostly focus on temperature, wind and geopotential height. In this paper, interdecadal correlations of solar activity with Winter Snow Depth Index (WSDI) over the Tibetan Plateau, Arctic Oscillation Index (AOI) and the East Asian Winter Monsoon Index (EAWMI) are detected respectively by using Solar Radio Flux (SRF), Total Solar Irradiance (TSI) and Solar Sunspot Number (SSN) data and statistical methods. Arctic Oscillation and East Asian winter monsoon are typical modes of the East Asian atmospheric circulation. Research results show that on interdecadal time scale over 11-year solar cycle, the sun modulated changes of winter snow depth over the Tibetan Plateau and East Asian atmospheric circulation. At the fourth lag year, the correlation coefficient of SRF and snow depth is 0.8013 at 0.05 significance level by Monte-Carlo test method. Our study also shows that winter snow depth over the Tibetan Plateau has significant lead and lag correlations with Arctic Oscillation and the East Asian winter monsoon on long time scale. With more snow in winter, the phase of Arctic Oscillation is positive, and East Asian winter monsoon is weak, while with less snow, the parameters are reversed. An example is the winter of 2012/2013, with decreased Tibetan Plateau snow, phase of Arctic Oscillation was negative, and East Asian winter monsoon was strong.