气候系统与气候变化研究进展

气候系统与气候变化
Climate System and Climate Change

气候系统与气候变化研究进展

2014年，气候系统研究所在气候预测理论与方法、气候系统模式研发、东亚季风变异机理、古气候以及极地气候研究方面获得了显著进展。

1 气候预测理论与方法

1.1 夏季青藏高原积雪异常与同期梅雨降水的关联

高分辨率的卫星资料（EASE-grid）显示，在青藏高原西部、南部等高海拔地区夏季仍存在积雪。该地区的积雪异常可以调节青藏高原陆面加热，进而影响青藏高原西部的垂直运动，并通过经向垂直环流调节北印度洋地区的垂直上升运动。同时，通过热带地区的纬向垂直环流和开尔文波（Kelvin wave）响应，北印度洋异常垂直运动可以造成西北太平洋副热带高压异常，也对西太平洋暖池的对流活动具有重要的影响。因此，青藏高原高海拔地区的夏季积雪能够影响东亚-太平洋遥相关型（EAP）和相应的东亚梅雨区夏季降水异常（图1a）。

另外，青藏高原前期春季（5月）积雪异常可持续到夏季，进而影响东亚梅雨区的夏季降水（图1b）。青藏高原西部积雪异常从春至夏的持续性能够部分解释前春积雪对东亚夏季降水影响的季节延迟效应。这一机制不同于以往的高原东部的冬、春季积雪异常通过调节春、夏季土壤湿度等陆面状况来影响降水的机制，是关于青藏高原积雪对我国降水预测的一个较为重要的补充（图1）。(刘舸)

1.2 气候预测新方法研究

利用分数阶积分的相关理论，成功地将给定的气候时间序列分解为两部分：历史记忆性信息及当前扰动。换言之，对于某给定时刻气候状态的预测，可以首先计算由于历史信息持续性影响造成的变化，再对当前扰动进行预测。建立了分数阶随机气候模型，并成功给出了定量计算历史记忆性信号的方法。以北半球温度序列及PDO指数为例，估算了它们的历史记忆性信号。对于这两个序列，其历史记忆性信号所占方差比很大。掌握历史信息的持续影响可以很大程度上提高我们对当前时刻气候状态的模拟、预测能力。

对当前扰动的预测，考虑从多因子相互作用出发，通过评估不同预报因子在不同时间尺度上的不同作用，尝试建立分层预测模型。目前已提出了定量评估不同预报因子在不同时间尺度上相互作用强弱的新方法，即去趋势的偏相关分析方法（DPCCA）。以长江中下游夏季降水、前冬赤道东太平洋海温异常、前冬PDO指数三者之间的关系为例，介绍了该方法。可以看到，该方法可以成功地提取出不同因子的特征作用时间尺度（图2）。（袁乃明）

1.3 中国北方冬季温度的东北—西北偶极型模态及其前兆信号

基于中国北方71个站点、NCEP/ NCAR和NOAA的CIRES 20世纪再分析月平均气温（SAT）资料，对中国北方冬季温度的EOF主要模态进行了探讨。结果表明，除了第1模态一致寒冷（温暖），第2模态也占总方差相当大的比例，其特点是偶极子结构，中国西北冷（暖），则中国东北地暖（冷）。研究发现，欧亚大陆秋季气温异常与欧亚大陆积雪异常紧密相关，并对中国北方的冬季气候有延迟效应。进一步研究发现，上一年贝加尔湖（50°～60°N，85°～120°E）地区与蒙古高原（42°～52°N，80°～120°E）地区的秋季气温对我国东北、西北冬季气温有着重要的调节作用。（辛羽飞）

2 气候系统模式研发

气候系统研究所从2009年起成功建立了一个包括大气、陆面、海洋和海冰的气候系统模式。经数年持续发展改进，模式在去除通量订正、减小气候漂移、改进ENSO季节锁相模拟以及降水模拟等方面取得了重要进展。在自由耦合情况下，模式以T42和T63的大气水平分辨率、1°的海洋水平分辨率稳定积分超过1000年，显示了对全球气候平均态、季节变化以及年际变率良好的模拟性能以及对我国气候预测的潜在应用前景。

2014年模式研发在以下几个方面取得了进展：

（1）完成了ECHAM5模式与陆面模式CoLM的双向耦合工作。耦合CoLM陆面模式后模拟的地表温度偏差较之前版本在全球大部分地区均显示减小，特别是欧亚大陆北部的冷偏差得到明显改善。

（2）大气模式的水平分辨率提高至T255（约50 km)，海洋模式水平分辨率提高至0.5°，耦合模式水平分辨提高到大气模式T106、海洋模式0.5°。随着分辨率的增加，模式对东亚地区降水的模拟水平得到了显著提高。

（3）对ECHAM5的动力框架进行了改进。模式的水汽输送引入了“两步保形平流方案”（TSPAS）。模拟结果显示，新方案对东亚地区降水特别是青藏高原大地形周边降水有明显改善。（荣新尧）

3 东亚季风变异机理

3.1 青藏高原大气热源对高原低涡演变东移的影响

青藏高原低涡（简称“高原低涡”）是夏季青藏高原特有的天气系统，是高原地区的主要降水系统之一。它主要在青藏高原主体上生消，一般产生于高原西半部，消失于东半部。在一定条件下，高原低涡可以移出高原，进而造成我国东部甚至更广大地区的暴雨、雷暴等灾害天气，高原下游地区一些较大规模的降水都与青藏高原低涡的移出有关。

利用NCEP的FNL资料和常规探空资料，对比研究了移出型高原低涡和不移出型高原低涡的演变东移机制。结果显示，高原低涡的演变东移是加热场和环流场相互作用的结果。对于移出型低涡，500 hPa等压面上高原北部的高压脊和孟加拉湾附近的低压槽更强，来自北部高压脊的北风和来自低压槽的南风在低涡东部的辐合更强。同时，200 hPa等压面上高空西风急流入口区右侧的辐散区正好位于高原涡的上空。高层辐散低层辐合的配置有利于低涡的维持和降水的发生，伴随降水产生的凝结潜热加热对低涡的演变东移有重要影响。

通过对位势涡度收支方程的计算和对青藏高原大气热源空间分布特征的诊断分析发现，在低涡的发展阶段，无论是移出型低涡还是不移出型低涡，其发展东移的机制是相似的，即以凝结潜热加热为主的大气热源的垂直分布对低涡的发展东移起主导作用；在衰减阶段，对于移出型低涡，其东移主要依靠低涡东部南风和北风的辐合，对于不移出型低涡，位势涡度在垂直方向上的辐散导致低涡强度减弱，且不利于其东移。（李论）

3.2 中部型厄尔尼诺的激发和发展机理

利用海洋和大气观测再分析资料，分析了中部型厄尔尼诺事件的4次主要个例（1994，2002，2006，2009年）的激发和发展机理。混合层热量收支平衡诊断发现，与2000年之后的几次事件相比，1994年中部型厄尔尼诺的激发机制存在显著不同，但各次事件的发展机制大致相同。指出中部型厄尔尼诺事件的激发机制有两种：一种是（以1994年为例）赤道外侧的次表层暖水在海洋经向环流的输送下抵达赤道中太平洋，促进中太平洋变暖；一种是（以2000年后其他中部型事件为例）西太平洋暖池附近次表层暖水的堆积及其向东扩展，导致了中部型厄尔尼诺的发展。在1994年厄尔尼诺激发期，赤道太平洋海温增暖起因于太阳短波辐射的增加，这是由前期副热带太平洋暖海温异常引发的大气经向环流的改变所致。同时，副热带太平洋海洋异常能够促使赤道外侧形成反气旋式环流，这有利于赤道外侧次表层暖水的形成。赤道外侧次表层暖水能够在海洋次表层由海洋环流输运至赤道区域，形成赤道次表层暖水。受此影响赤道温跃层加深，进而增强平流反馈机制和温跃层反馈机制，因此海表温度异常得以发展。在2000年之后的几次中部型厄尔尼诺事件的激发期，海洋动力机制起到主要作用，而海表热通量异常很弱。此类厄尔尼诺前期赤道太平洋出现次表层海温异常，可增强东向的海流进而有利于海表温度增加。这种正的海流反馈机制和温跃层反馈机制可持续至发展期，使得海表温度得以不断增温。（苏京志）

3.3 印度夏季风对南亚高压的影响及其与中国夏季降水的关系

利用逐月的ERA-40再分析资料以及降水观测资料，分析了印度夏季风对200 hPa上南亚高压的影响，以及南亚高压对中国夏季降水异常的作用。在年际时间尺度上，发现南亚高压具有显著的东西偏向特征，高压中心位于伊朗高原或者青藏高原上空。当印度季风偏强（弱）时，南亚高压位置偏西（东），中心位于伊朗（青藏）高原上空。南亚高压的东西偏向与中国夏季降水之间也存在密切关系。位置偏西（东）的南亚高压对应着江淮流域降水偏少（多），华南、华北地区降水偏多（少）。进一步提出了印度季风通过影响南亚高压进而对中国夏季降水产生影响的物理过程。当印度夏季风偏强（弱）、降水偏多（少）时，印度半岛北部地区凝结潜热释放增加（减少），为异常热（冷）源。异常热（冷）源在对流层高层，其西北和东北侧分别激发位势高度的正（负）异常和负（正）异常，表现为南亚高压位置偏西（东），中心位于伊朗（青藏）高原上空。此时，在对流层上层，青藏高原东部至中国东部上空为异常气旋（反气旋）。与该异常环流相对应的垂直运动异常影响中国夏季降水。本研究提出，南亚高压在印度夏季风影响东亚夏季风的过程中起了重要作用。（温敏）

4 古气候研究

4.1 末次间冰期以来北大西洋深层海温与青藏高原气温的千年尺度位相关系及其演变

采用代用资料研究了北大西洋深层海温和青藏高原气温自末次间冰期以来在千年尺度上的位相关系及其变化。对比分析和小波交叉谱分析表明，自末次间冰期以来二者同位相和反位相关系交替出现，同位相的持续时间相对较短，而反位相的持续时间较长，并且二者同位相和反位相关系的转换在间冰期比在冰期频繁，北大西洋深层海温与青藏高原气温的位相关系大体被北大西洋气温(格陵兰冰芯氧同位素)与青藏高原气温所验证。此外，北大西洋海表温度可能是北大西洋深层海温在千年尺度上影响青藏高原气温的一个重要因子（图3）。（肖栋）

4.2 20世纪后半叶中国石笋氧同位素对大气环流的记录

由于缺乏定量的校准，关于中国石笋氧同位素（δ18Ocs）代表的意义争论激烈：δ18Ocs记录的是局地的还是大尺度的信号，是单一水汽源信息还是多水汽源信息？对所有的器测时段内δ18Ocs趋势的统计分析结果显示，大部分δ18Ocs在1960—1994年有线性增加趋势，表明δ18Ocs记录了大尺度大气环流。定量计算了来自不同源区的水汽输送。用NCEP-NCAR再分析资料计算了1960—1994年孟加拉湾、南海、西太平洋夏季水汽输送强度比例。定义RSCS/BOB为南海与孟加拉湾水汽输送强度比例，RWNP/ BOB为西太平洋和孟加拉湾水汽强度比例，RWNP/SCS为西太平洋和南海水汽输送强度比例。RWNP/ BOB和RWNP/SCS呈现了显著的年代际增强，可能是因为1970年代末西太平洋副热带高压西伸导致从西太平洋来的水汽输送加强。进一步分析表明，赤道中东太平洋处于El Niño位相，印度洋、孟加拉湾和南海SST偏高；北太平洋中纬度SST偏低时，RWNP/BOB和RWNP/SCS偏高。1970年代以后赤道中东太平洋经常处于El Niño位相，与δ18Ocs的趋势相符，说明δ18Ocs记录了20世纪后半叶的大气环流。（南素兰）

5 极地气候研究

5.1 东南极冰盖气候地带性研究新发现

自1996年起，我国南极内陆考察开始布设降雪观测点，用于观测南极年降雪量的时空分布；安装自动气象站，用于获取冰盖内陆气象信息；同时，在考察过程中对风成表面地貌形态也进行了统计。通过空间分析方法发现，东南极冰盖沿岸至内陆最高区域，共分为4个具有不同气候背景的气候带。这4个气候带大致以海拔2000 m、3000 m和3600 m为界。在分界点前后，不同地带的降雪时间变化具有相反的趋势。结合遥感和数值模拟手段发现，水汽来源的不同是造成该气候地带性的首要原因：海岸、内陆和冰穹区域具有明显不同的水汽来源，分别来自于近岸海洋、东南印度洋中高纬海洋和中低纬海洋。其次，不同天气条件下的沉积后过程，是造成内陆区域分为两个地带的重要原因。我们是国内外首个提出该地带性的团队，仍需更多的证据来证明。（丁明虎）

5.2 一种便携式大气水汽同位素连续监测装置

以往对氢氧稳定同位素的研究主要是针对液态水和固态水，其中一个主要原因是液态水和固态水的稳定性较强，易采集和保存。与这两个形态相比，气态氢氧稳定同位素比率的观测虽可以在不同季节和天气条件下进行，可提供更多的关于大气学、水文学和稳定同位素分馏过程等多方面的信息，但其样品的收集和测量甚为复杂。由于目前采样和分析技术的限制，对于大气水汽氢氧稳定同位素比率的研究，大都局限于粗空间和时间分辨率的条件。而对于海洋-大气边界层上的同位素分馏过程，也都集中于理论实验和物理过程模拟。因此，需要采用适当的装置和方法通过模拟野外自然移动条件下水汽稳定同位素比率梯度，实现水汽中δ18O和δ1D梯度和分馏过程的观测，从而实现在实时、实地、大范围、便携、低能耗等条件下大气水汽δ18O和δ1D同位素的测量与评价。本研究开发了一种可以快速、动态和准确测量野外自然条件下水汽中氢氧稳定同位素比率、梯度及其分馏过程的装置和方法。通过该装置和方法，可以客观评价并校正水汽δ18O和δ1D测量的精度，实现野外自然条件下大气水汽δ18O和δ1D的便携式观测并获取高质量数据。该发明专利于2014年12月得到授权，相应设备已经成功在我国南北极走航考察中应用，相关研究发表在Journal of Environmental Sciences、《冰川冻土》《地理科学进展》等杂志上（图4）。（丁明虎）

图1 夏季(a)和前期春季(b)(5月)青藏高原积雪面积异常与夏季降水的相关（阴影区超过90%统计置信度）Fig. 1 Spatial distribution of correlation coeff cients between the (a) summer and (b) preceding spring (May) snow cover area proportion (SCAP) index and summer precipitation for the period 1979–2006 (the shaded areas denote correlation signif cant at the 90% conf dence level)

图2 DPCCA在实际气候问题研究中的应用(SRYR代表长江流域夏季降水，红色点线为DPCCA结果，虚线为0.05显著性边界。可以看到，Niño3海温对长江流域夏季降水的影响主要在4～7年的尺度，而PDO的影响主要在35年的尺度)Fig. 2 Triple relations among summer rainfall over Yangtze River (SRYR), Niño3-SSTA, and PDO index, on different time scales. Red curves are results from DPCCA, where effects of PDO (Niño3-SSTA) on SRYR are removed in a (b)

图3 末次间冰期以来北大西洋底栖有孔虫类氧同位素记录(红线)和青藏高原古里雅冰芯氧同位素记录(绿线)(按照二者位相关系的变化, 将过去131 ka 划分为11个时段, 分别用阴影和数字标记)Fig. 3 Oxygen isotope (δ18O) records from the North Atlantic benthic foraminifera (red line) and from the ice core in Guliya Glacier (green line) since the Last Interglaciation. Based on their phase relationship, the past 131 ka is divided into 11 epochs, which are indicated by the color shading and the serial numbers at the bottom of this f gure

图4 大气水汽同位素实时高精度观测系统Fig. 4 A real time-high precision instrument for monitoring atmospheric water vapor isotopes

Progress in Climate System and Climate Change Research

1 Theory and methodology of climate prediction

1.1 The summer snow cover anomaly over the Tibetan Plateau and its association with simultaneous precipitation over the Meiyu–Baiu region

The satellite-derived Equal-Area Scalable Earth grid (EASE-grid) dataset shows that snow still exists in summer in the western part and along the southern f ank of the Tibetan Plateau (TP). The summer snow anomaly over the TP can directly modulate the land surface heating and, consequently, vertical motion over the western TP, and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation. Through a zonal vertical circulation over the tropics and a Kelvin wave-type response, anomalous vertical motion over the North Indian Ocean may result in the anomaly of the western North Pacif c subtropical high and modulate the convective activity in the western Pacif c warm pool, which stimulates the East Asia-Pacif c (EAP) pattern and eventually affects summer precipitation over the Meiyu-Baiu (MB) region (Fig. 1a).

The snow anomaly over the TP maintains from preceding spring (May) to summer, and therefore exerts an important effect on summer rainfall over the MB region (Fig. 1b). The persistence of snow anomaly over the western TP can partly explain the season-delayed effect of TP snow on summer rainfall over East Asia, which differs from the contribution of the soil moisture appearing over the eastern TP. Therefore, the western TP snow anomaly in preceding spring could be regarded as an important supplementary factor in the forecasting of summer precipitation over East Asia (Fig. 1). (Liu Ge)

1.2 Research progress in the climate prediction: Novel methods

In 2014, we mainly focused on the research on climate prediction. By using fractal integral techniques, we have decomposed a given climatic time series into two parts: (i) climate memory signals accumulated from historical information, and (ii) weather scale excitations. When making predictions (simulations) of climate states at a given time point, we can f rst calculate the climate memory signals, then try to predict (simulate) the weather scale excitations.

Up to now, we have established a Fractal Integral Stochastic Model, and proposed a method which can extract the climate memory signals quantitatively and successfully. We take the North Hemisphere temperature anomalies (black curve in a) and PDO index (black curve in c) as an example, and extract their memory signals (red curves). The memory signals account for a large proportion of the total variance, which indicates that extracting climate memory signals is important and can improve our ability in climate prediction.

As for the second part, the weather scale excitations, we plan to use multi-predictors for our prediction. By determining the typical time scales which different predictors may have significant influence on, we aim to establish a hierarchical prediction model. Now we have proposed a new method, detrended partialcross-correlation analysis (DPCCA), which can be used to diagnose quantitatively the typical time scales for different predictors. In Fig. 2, we analyzed the triple relations among the summer rainfall over Yangtze River (SRYR), the preceding winter time Niño3-SSTA, and the preceding winter time PDO index. As we can see, this method can provide us with the correlation information on different time scales, which is useful for the further development of a hierarchical model (Fig. 2). (Yuan Naiming)

1.3 Individual variations of winter surface air temperature over Northwest and Northeast China and their respective precursory signals

Based on the monthly mean surface air temperature (SAT) from 71 stations in northern China, the NCEP/NCAR and NOAA-CIRES 20th century reanalysis data, the dominant modes of winter SAT over northern China were explored. The results show that, apart from the first mode with a unanimously colder (warmer) northern China as a whole, the second mode, which is characterized by a dipole structure with a colder (warmer) Northwest China (NWC) and warmer (colder) Northeast China (NEC), also accounts for a fairly large proportion of total variance. The two components constituting the second mode, the individual variations of winter SAT over Northwest and Northeast China and their respective precursory signals were further investigated. It is found that the autumn SAT anomalies are intimately linked to persistent snow cover anomalies over Eurasia, showing the delayed effects on winter climate over northern China. Specif cally, the preceding autumn SAT anomalies over the Lake Baikal (LB; 50°–60°N, 85°–120°E) and Mongolian Plateau (MP; 42°–52°N, 80°–120°E) regions play an important role in adjusting the variations of winter SAT over NWC and NEC, respectively. The preceding autumn SAT anomaly over the MP region may exert an inf uence on winter SAT over Northeast China through modulating the strength and location of East Asian major trough. The preceding autumn SAT over the LB region may modulate winter westerlies at the middle and high latitudes of Asia and accordingly affects the invasion of cold air and associated winter SAT over Northwest China. (Xin Yufei)

2 Development of a climate system model

Via years of work since 2009, the Institute of Climate System has successfully developed a climate system model. By several years of continuous model development, signif cant improvement was achieved in terms of removal of model f ux correction, reduction of climate drift, and ENSO phase locking as well as precipitation bias. Both the T42 and T63 versions have steadily integrated over 1000 years without flux correction, displaying remarkable performance in simulating the global climatological mean state, seasonal cycle as well as interannual variability, hence a potential application to climate prediction in China.

In 2014, encouraging progress has been achieved in the following areas:

(1) We successfully conducted the two-way coupling between CoLM land model and ECHAM5 model. The version of the coupled CoLM land model showed notable improvement in reducing ground temperature bias for most areas of the globe, especially for the cold bias over the northern Asian-European continent.

(2) The horizontal resolutions of the atmosphere model and ocean model were increased to T255 (about 50 km) and 0.5 degree, respectively. The horizontal resolution of coupled model was also increased to T106 for the atmospheric model and 0.5 degree for the ocean model. With the model resolution increased, the simulation of precipitation over the East-Asian region was signif cantly improved.

(3) Modification of ECHAM5 dynamical core. The “Two-Step Shape-Preserving Advection Scheme”(TSPAS) was introduced for model vapor transportation. The result shows significant improvement in simulation of East-Asian precipitation, especially precipitation around the Tibetan Plateau. (Rong Xinyao)

3 Variability and mechanism of the East Asian monsoon

3.1 Effect of the atmospheric heat source on the development and eastward movement of the Tibetan Plateau vortices

In boreal summer, the low-level cyclonic vortices forming over the Tibetan Plateau (hereinafter the plateau vortices) are the major mesoscale rain-producing systems over the Tibetan Plateau. Most of the vortices originate over the central-western plateau, and decay over the eastern plateau, especially over the sloping terrain at the eastern edge of the Tibetan Plateau. Some of them can maintain a long time and move eastward out of the plateau (Wang et al., 2009). The vortices moving off the plateau often trigger heavy rainfall to the east of the Tibetan Plateau, and even give rise to disastrous weather events over eastern China.

Based on the final analyses data (FNL) of the Global Forecasting System of the National Centers for Environment Prediction (NCEP) and the radiosonde data over the Tibetan Plateau, evolutions of two types of the Tibetan Plateau vortices, moving-off the plateau (Type A) and dying-out on the plateau (Type B), are investigated respectively. Compared to Type B vortices, the large-scale circulations associated with Type A vortices show a stronger ridge to the north of the plateau and a deeper trough near the Bay of Bengal at 500 hPa, and the southwesterly flow from the trough and the northwesterly flow from the ridge converge more intensely to the east of Type A vortices. Meanwhile, at 200 hPa the divergence on the right-hand side of the upper westerly jet is just over the vortices. The convergence at 500 hPa and the divergence at 200 hPa provide favorable conditions for the development and eastward motion of the vortices as well as the rainfall to the east of the vortices. The condensation latent heat related to the rainfall has a close relationship with the eastward movement of the vortices. The diagnoses of the potential vorticity (PV) budgets and spatial features of the atmospheric heat source reveal that in the developing stages of the two types of vortices, the vertical distribution of the atmospheric heat source determines both their intensity and moving direction. In the decaying stage, the maintenance and eastward movement for Type A vortices mainly depend on the convergence of the strong northwesterly and southwesterly to the east of the vortices. For Type B vortices, the vertical PV f ux divergence caused by the ascending motion around the vortices reduces the intensity of the vortices and is unfavorable for their eastward motion. (Li Lun)

3.2 The initiation and development mechanisms of central Pacif c El Niños

The initiation and development mechanisms of four major central Pacif c (CP) El Niño events in 1994, 2002, 2006 and 2009 were investigated by analyzing oceanic and atmospheric reanalysis data. A mixed-layer heat budget analysis was conducted and the result shows that the initiation mechanism of the 1994 CP El Niño is very different from other CP El Niños in 2000s in spite that the development mechanisms are similar among these events. The initial sea surface temperature (SST) warming of the 1994 El Niño was caused by enhanced solar radiation, which was related to atmospheric meridional overturning circulation in association with the positive SST anomaly forced in the subtropical Pacif c. The subtropical SST anomalies also induced anticyclonic surface wind stress curl anomalies, which caused the formation of subsurface warmer water in the off-equatorial regions. The off-equatorial subsurface warmer water was further transported equatorward by the mean subsurface ocean currents, leading to the subsurface warming in the central equatorial Pacif c. The deepened thermocline anomaly at the equator further promoted a positive advective and thermocline feedback so that the SST anomaly grew. During the initiation phase of the 2000s El Niños, ocean dynamics played a dominant role while the effect of surface heat f ux anomalies was minor. Pre-existing subsurface warmer water appeared in the equatorial region during its initiation phases. Such subsurface anomalies can cause the SST warming in the central Pacif c through induced anomalous eastward zonal currents that transport high mean SST eastward. This positive zonal advective feedback, along with a positive thermocline feedback, continued to warm the local SST throughout the development phase of the 2000s El Niño events. (Su Jingzhi)

3.3 Impact of Indian summer monsoon on the South Asian high and its inf uence on summer rainfall over China

By using the monthly ERA-40 reanalysis data and observed rainfall data, we investigated the effect of the Indian summer monsoon (ISM) on the South Asian high (SAH) at 200 hPa, and the role played by the SAH in summer rainfall variation over China. It is found that in the interannual timescale the east-west shift is a prominent feature of the SAH, with its center being either over the Iranian Plateau or over the Tibetan Plateau. When the ISM is stronger (weaker) than normal, the SAH shifts westward (eastward) to the Iranian Plateau (Tibetan Plateau). The east-west position of SAH has close relations to the summer rainfall over China. A westward (eastward) location of SAH corresponds to less (more) rainfall in the Yangtze-Huai River Valleys and more (less) rainfall in North China and South China. A possible physical process that the ISM affects the summer rainfall over China via the SAH is proposed. A stronger (weaker) ISM associated with more (less) rainfall over India corresponds to more (less) condensation heat release and anomalous heating (cooling) in the upper troposphere over the northern Indian peninsula. The anomalous heating (cooling) stimulates positive (negative) height anomalies to its northwest and negative (positive) height anomalies to its northeast in the upper troposphere, causing a westward (eastward) shift of the SAH with its center being over the Iranian Plateau (Tibetan Plateau). As a result, an anomalous cyclone (anticyclone) is formed over the eastern Tibetan Plateau and eastern China in the upper troposphere. The anomalous vertical motions in association with the circulation anomalies are responsible for the rainfall anomalies over China. Our present study reveals that the SAH may play an important role in the effect of ISM on the East Asian summer monsoon. (Wen Min)

4 Palaeo-Climate

4.1 Millennial-scale phase relationship between North Atlantic deep-level temperature and Qinghai-Tibet Plateau temperature and its evolution since the Last Interglaciation

This study employed proxy data to investigate the phase relationship between the North Atlantic deeplevel temperature and the Qinghai-Tibet Plateau (TP) surface air temperature (TP temperature) and its evolution at the millennial scale since the Last Interglaciation. The results indicate the alternation of in-phase and antiphase relationships since the Last Interglaciation, with the in-phase relationships showing a shorter duration than the anti-phase relationships. Alternations between the in-phase and anti-phase relationships occurred more frequently during the Last Interglaciation than during the Last Glaciation. The phase relationship between the North Atlantic deep-level temperature and the TP temperature was broadly illustrated by that between the North Atlantic temperature (based on oxygen isotope data from the Greenland ice core) and TP temperature (Fig. 3). Furthermore, the North Atlantic deep-level temperature and the TP temperature may be connected through the North Atlantic sea surface temperature. (Xiao Dong)

4.2 Evaluation of the ability of the Chinese stalagmite δ18O to record the variation in atmospheric circulation during the second half of the 20th century

The Chinese stalagmite δ18O (δ18Ocs) has provoked debate worldwide over the past few years due to its lack of quantitative calibration, leading us to questions of whether δ18Ocs records a local or large-scale signal and whether δ18Ocs records the signal of a single remote water vapor source or multiple water vapor sources. In this study, we observe all of the δ18Ocs trends within the instrumental period to verify whether they possess a common trend, which could be used as a basis to determine whether the trends ref ect the large-scale signal together or whether each trend ref ects the local signal. The results show that most of the δ18Ocs experienced a linear increase from 1960 to 1994, which may indicate that the δ18Ocs could record a trend occurring in large-scale atmospheric circulations. We then quantitatively describe the proportion of water vapor transport (WVT) from different source regions. Using the NCEP/NCAR reanalysis data from 1960 to 1994, the ratios of the intensities of three WVTs from the Bay of Bengal, the South China Sea, and the western North Pacif c during the summer are calculated. We def ne RSCS/BOB as the ratio of the WVT intensities from the South China Sea to those from the Bay of Bengal, RWNP/BOB as the ratio of the WVT intensities from the western North Pacif c to those from the Bay of Bengal, and RWNP/SCS as the ratio of the WVT intensities from the western North Pacif c to those from the South China Sea. The signif cant decadal increase occurs in the time series of RWNP/BOB and RWNP/SCS, most likely resulting from the strengthened WVT from the western North Pacif c in the late 1970s due to the western Pacif c subtropical high that extended westward. A further analysis indicates that when the equatorial central and eastern Pacif c is in the El Niño phase, the sea surface temperature (SST) in the tropical Indian Ocean, the Bay of Bengal, and the South China Sea is high, and the SST at the middle latitudes in the North Pacif c is low, then the RWNP/BOB and RWNP/SCS values tend to be high. Since the late 1970s, the equatorial central and eastern Pacif c has often been in the El Niño phase. Therefore, we conf rm that the δ18Ocs indeed records the variation in atmospheric circulation during the second half of the 20th century. (Nan Sulan)

5 Polar Climate

5.1 New f nding on climatic zonation in East Antarctica

Since 1996, the Chinese National Antarctic Research Expedition has started to set up the stakes to monitor snowfall, deploy the Automatic Weather Stations to monitor the surface meteorology and measure the sastrugi to identify the wind erosion. Based on these data, we explored the climatic zonation by a spatial analysis and found that from the coast to the summit of East Antarctica, there are four sections with different surface mass balance patterns. These sections are divided into heights of ～2000 m, ～3000 m and 3600 m.

Combined with studies by remote sensing and simulation, we found the coast, inland and dome areas have different moisture sources: the precipitation at coast mainly comes from offshore, the precipitation at inland comes from the southeast Indian Ocean and the dome area comes from low-mid ocean surfaces. Secondly, the post-depositional processes by wind, could determine the loss of surface snow; this is the reason that the inland area is divided into two sections with different surface mass balance tendencies. This f nding has never been reported before this paper, and still needs more evidence. (Ding Minghu)

5.2 A novel instrument in monitoring atmospheric water vapor isotopes

Previously, the studies on water isotopes were mainly carried out on liquid or solid water. One of the most important reasons is that liquid or solid water is easily collected and transported. Compared with them, vapor isotopes exist in atmosphere and could be measured in all kinds of weather. It could also provide more information on global earth surface processes and hydrological cycles. During the past tens of years, the studies on atmospheric water vapor isotopes were restricted in coarse spatial and temporal resolutions for technical reasons. Besides, the isotopic fractionation processes above sea surface have been only carried out with theoretical and physical simulation experiments. So, it is necessary to develop a system, method or instrument to monitor the isotopic ratio and vertical prof le. Based on the laser spectrum, we have invented an instrument to achieve a real time-mobile-high precision measurement of atmospheric water vapor isotopes (Fig. 4).

This invention was authorized with a patent in December 2014 and the instrument has been successfully applied in the Chinese National Antarctic/Arctic Research Expedition. The papers related to the instrument have been published in Journal of Environmental Sciences, Journal of Glaciology and Geocryology, Progress in Geography, etc. (Ding Minghu)