Precipitation pattern of the mid-Holocene simulated by a high-resolution regional climate model

Early proxy-based studies suggested that there potentially occurred a ＂southern drought/northern flood＂ （SDNF） over East China in the mid-Holocene （from roughly 7000 to 5000 years before present）.In this study,we used both global and regional atmospheric circulation models to demonstrate that the SDNF-namely,the precipitation increases over North China and decreases over the the lower reaches of the Yangtze River Valley--could have taken place in the mid-Holocene.We found that the SDNF in the mid-Holocene was likely caused by the lower SST in the Pacific.The lowered SST and the higher air temperature over mainland China increased the land-sea thermal contrast and,as a result,strengthened the East Asian summer monsoon and enhanced the precipitation over North China.     

北大西洋年际变率的海气耦合模式模拟II：热带太平洋强迫

利用一个全球海气耦合模式(BCM),结合观测资料,讨论了热带太平洋强迫对北大西洋年际气候变率的影响。研究表明,BCM能够相对合理地模拟赤道太平洋的年际变率模态及相应的海温距平型和大气遥相关型,尽管其准3年的振荡周期过于规则。来自数值模式和观测上的证据都表明,北大西洋冬季海温的主导性变率模态,即自北而南出现的“- -”的海温距平型,受到来自热带太平洋强迫的显著影响,其正位相与赤道中东太平洋冷事件相对应。换言之,赤道太平洋暖事件的发生,在太平洋-北美沿岸激发出PNA遥相关型,进而通过在北大西洋产生类似NAO负位相的气压距平型,削弱本来与NAO正位相直接联系的三核型海温距平。北大西洋三核型海温距平对热带太平洋强迫的响应,要滞后2—3个月的时间。     

Stratospheric precursor of non-uniform variation in early spring surface temperature over Eurasia

The stratospheric influences on the non-uniform variation in early spring (March–April, MA) surface temperature over Eurasia is investigated based on the ERA-Interim, NCEP-1, and NCEP-2 reanalysis data for the period 1980–2016. A lead–lag correlation is found between preceding winter (December–February, DJF) stratospheric polar vortex displacements (SPVD) and the MA west–east seesaw pattern in surface temperature over Eurasia. Further analysis reveals that the East Asian jet stream may act as a bridge linking DJF SPVD and MA surface temperature over Eurasia. A positive change in SPVD is associated with a decelerated polar jet stream and an accelerated East Asian jet stream in the troposphere in DJF. The East Asian jet stream signal can persist into MA. As a result, anomalous southerly/northerly winds prevail over western/eastern Eurasia, accounting for the west–east surface temperature seesaw over Eurasia.     

60～70oS臭氧总量的QBO和ENSO信号

本文利用Ｎｉｍｂｕｓ－７上搭载的臭氧总量观测光谱仪（ＴＯＭＳ）得到的６０～７０ｏＳ纬圈中臭氧总量资料,分析研究了该地区臭氧总量准两年振荡（ＱＢＯ）和ＥＮＳＯ信号的纬向分布,指出在该纬圈臭氧总量的长期变化中包含着的ＱＢＯ和ＥＮＳＯ信号。同时,本文还分析研究了沿纬圈分布的大气臭氧总量季节变化和长期变化趋势,指出在该纬圈各个季节中臭氧总量呈下降趋势,以６０～１００ｏＷ十月份的下降最大,达到－９．３ＤＵ／ａ。研究同时表明：臭氧总量季节变化、长期变化趋势、以及ＱＢＯ信号的纬向分布都在西南极上空出现异常。本文对此进行了讨论,认为这是西南极海陆分布调整大气环流及大气波动造成对臭氧总量分布和变化的影响     

The Relationship between Melt Season Sea Ice over the Bering Sea and Summer Precipitation over Mid-Latitude East Asia

Independent datasets consistently indicate a significant correlation between the sea ice variability in the Bering Sea during melt season and the summer rainfall variability in the Lake Baikal area and Northeastern China. In this study, four sea ice datasets(Had ISST1, Had ISST2.2, ERA-Interim and NOAA/NSIDC) and two global precipitation datasets(CRU V4.01 and GPCP V2.3) are used to investigate co-variations between melt season(March-April-May-June, MAMJ)Bering Sea ice cover(BSIC) and summer(June-July-August, JJA) East Asian precipitation. All datasets demonstrate a significant correlation between the MAMJ BSIC and the JJA rainfall in Lake Baikal-Northeastern China(Baikal-NEC).Based on the reanalysis datasets and the numerical sensitivity experiments performed in this study using Community Atmospheric Model version 5(CAM5), a mechanism to understand how the MAMJ BSIC influences the JJA Baikal-NEC rainfall is suggested. More MAMJ BSIC triggers a wave train and causes a positive sea level pressure(SLP) anomaly over the North Atlantic during MAMJ. The high SLP anomaly, associated with an anti-cyclonic wind stress circulation anomaly,favors the appearance of sea surface temperature(SST) anomalies in a zonal dipole-pattern in the North Atlantic during summer. The dipole SST anomaly drives a zonally orientated wave train, which causes a high anomaly geopotential height at 500 h Pa over the Sea of Japan. As a result, the mean East Asian trough moves westward and a low geopotential height anomaly occurs over Baikal-NEC. This prevailing regional low pressure anomaly together with enhanced moisture transport from the western North Pacific and convergence over Baikal-NEC, positively influences the increased rainfall in summer.     

大尺度山地上空的臭氧低值及地面加热

首次利用Ｎｉｍｂｕｓ－７卫星上搭载的臭氧观测光谱仪（ＴＯＭＳ）资料,分析研究了大尺度山地（青藏高原、洛基山脉和安第斯山脉）上空臭氧总量的分布和季节变化规律,指出了大尺度山地对大气臭氧的减少作用。从全球大气臭氧总量分布和纬向偏差分布可以看出：在上述３个大尺度山地上空均存在着明显的臭氧低值扰动,该扰动区夏季强于冬季。在这３个区域中,青藏高原上空的臭氧低值扰动为最强。分析同时指出：上述大尺度山地上空臭氧季节变化的极小值在秋季,极大值在春季。但上述地区臭氧总量与同纬度其它地区臭氧总量的偏差在春季或初夏达到极小值。为分析这种大尺度山地对臭氧减少作用的原因,本文分析了青藏高原地面热源与臭氧总量的关系,指出：大尺度山地表面对大气的加热与该地区臭氧减少之间存在着良好的反相关;在地面对大气的感热加热、潜热加热和有效长波辐射加热中,以感热加热与臭氧减少的关系为最好。     

渭河盆地及邻区重力异常小波多尺度分解与解释

基于EGM2008重力场模型计算获得了渭河盆地及邻区布格重力异常。采用小波多尺度分解方法对布格重力异常进行了4阶小波逼近和小波细节分解,同时基于平均径向对数功率谱方法定量化地计算出1~4阶小波细节和小波逼近所对应的场源平均埋深。结合区域地质和地震资料,对获得的重力场结果进行分析,得到如下结论:①鄂尔多斯地块、渭河盆地、秦岭造山带3个一级构造单元的布格重力异常之间存在明显差异;构造区内部重力异常也存在横向的显著差异。布格重力异常的走向、规模、分布特征与二级构造区及主要的断裂具有一定的对应关系。②渭河盆地及邻区布格重力异常1~4阶细节对应4~23 km不同深度的场源信息,鄂尔多斯地块南缘东、西部的地壳结构存在明显的差异;渭河盆地凹陷、凸起构造区边界清晰,断裂边界与重力异常边界具有较好的一致性;秦岭造山带重力异常连贯性不好,东、西部重力异常变化特征表现出明显的差异。③渭河盆地及邻区布格重力异常分布与莫霍面埋深具有非常明显的镜像关系。渭河盆地及邻区地震主要分布在六盘山—陇县—宝鸡断裂带、渭河断裂与渭南塬前断裂交汇处、韩城断裂与双泉—临猗断裂交汇处。渭河盆地及邻区重力异常主要由中上地壳剩余密度体所影响,这可能是该区地震以浅源地震为主的主要原因。     

Sensitivity of East Asian climate to the progressive uplift and expansion of the Tibetan Plateau under the mid-Pliocene boundary conditions

A global atmospheric general circulation model has been used to perform eleven idealized numerical experiments, i.e., TP10, TP10, .., TP100, corresponding to different percentages of the Tibetan Plateau altitude. The aim is to explore the sensitivity of East Asian climate to the uplift and expansion of the Tibetan Plateau under the reconstructed boundary conditions for the mid-Pliocene about 3 Ma ago. When the plateau is progressively uplifted, global annual surface temperature is gradually declined and statistically significant cooling signals emerge only in the Northern Hemisphere, especially over and around the Tibetan Plateau, with larger magnitudes over land than over the oceans. On the contrary, annual surface temperature rises notably over Central Asia and most parts of Africa, as well as over northeasternmost Eurasia in the experiments TP60 to TP100. Meanwhile, the plateau uplift also leads to annual precipitation augmentation over the Tibetan Plateau but a reduction in northern Asia, the Indian Peninsula, much of Central Asia, parts of western Asia and the southern portions of northeastern Europe. Additionally, it is found that an East Asian summer monsoon system similar to that of the present initially exists in the TP60 and is gradually intensified with the continued plateau uplift. At 850 hPa the plateau uplift induces an anomalous cyclonic circulation around the Tibetan Plateau in summertime and two anomalous westerly currents respectively located to the south and north of the Tibetan Plateau in wintertime. In the mid-troposphere, similarto-modern spatial pattern of summertime western North Pacific subtropical high is only exhibited in the experiments TP60 to TP100, and the East Asian trough is steadily deepened in response to the progressive uplift and expansion of the Tibetan Plateau.     

鄂尔多斯南缘地区重力变化场源特征

以鄂尔多斯南缘地区布格重力异常数据及2014—2017年相对重力观测数据为基础,采用欧拉反褶积方法,对引起重力变化的场源深度进行反演,并对空间分布规律予以解释。通过构建理论模型,反演得到最优模型参数,并对实际数据进行计算和分析。为了减弱和消除欧拉解的发散性,利用水平梯度滤波法优化反演结果。结果表明:①构造指数为1时,适合对相对重力数据进行反演,当滑动窗口选择4—8倍测点间距时,可以获得较为可靠的场源参数;②在主要断裂附近,不同时间尺度的场源呈较好的一致性特征;③引起重力变化的场源深度集中在10—30 km,与鄂尔多斯南缘地区的震源深度基本一致;④不同时间尺度的场源位置相对分散,表明引起重力变化的物质流动具有随机性和波动性。     

内蒙古阿拉善左旗乌兰尚德地区志留系圆包山组笔石化石的发现及其地质意义

阿拉善盟阿拉善左旗杭乌拉山以北哈日奥布日格断凹陷盆地两侧,北东向出露770km2的哑地层,前人将其划为二叠系双堡塘组,但该套地层的岩性和岩石组合及层序特征,与内蒙古岩石地层所述的双堡塘组的现在定义和地质特征及区域变化完全相悖。采用现代沉积学理论和层序地层学方法,开展岩石组合、基本层序、沉积构造与沉积环境研究,划分出3个段级填图单元。根据发现的笔石化石和被晚泥盆世中粗粒黑云母花岗闪长岩侵入的关系,将地层时代确定为早志留世,改划为志留系圆包山组。泥盆纪区域变质变形作用使其发生浅变质和片理化变形,并形成轴向北东的复式向斜构造。后期叠加构造变形,形成紧闭倒转褶皱。志留系圆包山组的确定对本区地层划分和区域构造演化研究有重要意义。