北太平洋涛动的季节演变及其与我国冬春气候异常的联系

本文利用NCEP/NCAR再分析资料和我国160站的观测资料,首先定义了季节平均的北太平洋涛动(NPO)指数,在此基础上分析了不同季节中NPO的时空变化特征,特别对冬季和春季NPO与我国气温、降水异常的关系作了研究.结果表明,作为北太平洋地区海平面气压(SLP)年际变化的第二模态,NPO具有相当正压的结构,在地面表现为...     

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。     

Nature and stability of atoll island shorelines: Gilbert Island chain,Kiribati, equatorial Pacific

Islands rimming Pacific atolls typically form narrow, low‐lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea‐level rise. As these, low islands form the only habitable land for many island nations, understanding the character of shorelines, and the rates and controls that operate to bring about changes, is an issue of central importance. The purpose of this study is to unravel the characteristics of coastal change on atoll islands of the Gilbert Island chain of the equatorial Pacific nation of Kiribati, especially as they relate to autogenic shoreline processes and El Niño/Southern Oscillation variability. Integration of field observations, differential global positioning system data, historical aerial photographs and ultra‐high resolution remote sensing images demonstrates the nature, spatial patterns and rates of change from 17 islands on Maiana and Aranuka atolls. The results illustrate that, between 2005 and 2009, ca 50% of the shorelines on these islands displayed a discernable shift in position; some shorelines were accretionary (at net rates up to ca 8 m year^?1) and others were erosional (up to ca 18 m year^?1). Long‐term net rates of change on Maiana between 1969 and 2009 were lower than short‐term net rates measured between 2005 and 2009. Both short‐term and long‐term observations illustrate some of the greatest change occur near terminations of the largest, north–south oriented islands, associated with longshore movement of coarse sand and gravel. Direct hits by tropical depressions and marked seasonality, factors interpreted as being essential in island growth and shoreline dynamics elsewhere, do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics. Similarly, observations over four years suggested that shoreline variability probably is not influenced directly by marked sea‐level change, although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long‐term increase in the rate of sea‐level rise. Within this framework of global change, local anthropogenic effects, autogenic shoreline processes and El Niño/Southern Oscillation‐influenced wind and wave variability control many aspects of these dynamic shorelines. These results provide quantitative insights into the character and variability of rates of shoreline change, information essential for evaluating and mitigating the vulnerability of island nations such as Kiribati.     

Four thousand years of environmental change and human activity in the Cochabamba Basin, Bolivia

The Cochabamba Basin (Bolivia) is on the ancient road network connecting Andean and lowland areas. Little is known about the longevity of this trade route or how people responded to past environmental changes. The eastern end of the Cochabamba valley system constricts at the Vacas Lake District, constraining the road network and providing an ideal location in which to examine past human-environmental interactions. Multi-proxy analysis of sediment from Lake Challacaba has allowed a c. 4000 year environmental history to be reconstructed. Fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability (c. 4000-3370 and c. 2190-1020 cal yr BP) compared to adjacent wetter episodes (c. 3370-2190 and c. 1020 cal yr BP-present). The moisture fluctuations broadly correlate to El Niño/Southern Oscillation variations reported elsewhere. High charcoal abundance from c. 4000 to 2000 yr ago indicates continuous use of the ancient road network. A decline in charcoal and an increase in dung fungus (Sporormiella) c. 1340-1210 cal yr BP, suggests that cultural changes were a major factor in shaping the modern landscape. Despite undisputable impacts of human populations on the Polylepis woodlands today, we see no evidence of woodland clearance in the Challacaba record.     

Cyclone activity associated with the interannual seesaw oscillation of summer precipitation over northern Eurasia

This study describes surface cyclone activity associated with the interannual variability in summer precipitation in northern Eurasia and how that activity may be connected to other climate signals. An east–west seesaw oscillation of precipitation across Siberia is the primary mode of interannual variability in the summer hydrological cycle over northern Eurasia. This variation occurs at sub-decadal timescales of about 6–8 years. The spatial characteristics of cyclone frequency and cyclone tracks at the two poles in variability [eastern Siberia (ES)-wet–western Siberia (WS)-dry and WS-wet–ES-dry] were examined, and temporal variability in regional cyclone frequency was compared to basin-scale precipitation variability. The analysis period was from 1973 to 2002, when the precipitation variability signal was predominant.Cyclone behavior suggested that the regions of enhanced (reduced) cyclone activity coincided with regions of increased (decreased) precipitation in each phase of the oscillation. Such behavior reflects the zonal displacement of the track of frequent storm activity that accompanies the changes in precipitation. Comparisons of the temporal characteristics confirmed the importance of regional cyclone frequency on precipitation variability in both eastern and western Siberia. Low-frequency changes in regional cyclone activity may produce the precipitation oscillation. We used various climate signals to explore connections between regional precipitation and cyclone activity in Siberia. Results suggest that the North Atlantic Oscillation (NAO) from the preceding winter is significantly and negatively correlated with summer surface cyclone frequency and precipitation over western Siberia. Enhanced (reduced) summer cyclone activity and precipitation in western Siberia follows low- (high-) winter NAO. However, the physical mechanisms linking summer cyclone activity and precipitation over western Siberia with the preceding climate conditions associated with the winter NAO remain unclear.     

Some discussions on Arctic vortex

The Arctic vortex is a persistent large-scale cyclonic circulation in the middle and upper troposphere and the stratosphere. Its activity and variation control the semi-permanent active centers of Pan-Arctic and the short-time cyclone activity in the subarctic areas. Its strength variation, which directly relates to the atmosphere, ocean, sea ice and ecosystem of the Arctic, can affect the lower atmospheric circulation, the weather of subarctic area and even the weather of middle latitude areas. The 2003 Chinese Second Arctic Research Expedition experienced the transition of the stratosphereic circulation from a warm anticyclone to a cold cyclone during the ending period of Arctic summertime, a typical establishing process of the polar vortex circulation. The impact of the polar vortex： variation on the low-level circulation has been investigated by some scientists through studying the coupling mechanisms of the stratosphere and troposphere. The impact of the Stratospheric Sudden Warming （SFW） events on the polar vortex variation was drawing people＇s great attention in the fifties of the last century. The Arctic Oscillation （ AO）, relating to the variation of the Arctic vortex, has been used to study the impact of the Arctic vortex on climate change. The recent Arctic vortex studies are simply reviewed and some discussions on the Arctic vertex are given in the paper. Some different views and questions are also discussed.     

High resolution oxygen isotope and grayscale records of a medieval fossil giant clam (Tridacna gigas) in the South China Sea：physiological and paleoclimatic implications

Mollusks are well known for their detailed recording of paleoenvironmental and paleoclimatic changes in their carbonate shells. In this study, we constructed 18-year blue color intensity and oxygen isotope profiles of a 14 C dated(AD 990±40) fossil giant clam, Tridacna gigas, from Shidao Island, South China Sea. The δ18O profile of the T. gigas specimen displayed regular annual cycles and was probably controlled by seasonal variations of the climatic parameters. The blue color intensity profile showed good agreement with the δ18O series, and both had 18 clear annual cycles in accordance with the 18 visually identified annual growth bands. The annual shell growth rate determined from the blue color intensity and oxygen isotope profiles indicated that the annual shell increment of the Tridacna specimen was stable after the onset of sexual maturity. Spectral analysis of the δ18O and blue color intensity time series suggested that the El Nio–Southern Oscillation(ENSO) period observed in the instrumental temperature and precipitation records of the South China Sea during the past 50 years also existed in medieval times. Our results showed that fossil giant clams could provide a good archive of historical intra-seasonal to decadal climate variations.     

Influence of the Pacific Decadal Oscillation on regional sea level rise in the Pacific Ocean from 1993 to 2012

The rate of regional sea level rise(SLR) provides important information about the impact of human activities on climate change.However,accurate estimation of regional SLR can be severely affected by sea surface height(SSH) change caused by the Pacific Decadal Oscillation(PDO-SSH).Here,the PDOSSH signal is extracted from satellite altimeter data by multi-variable linear regression,and regional SLR in the altimeter era is calculated,before and after removing that signal.The results show that PDO-SSH trends are rising in the western Pacific and falling in the eastern Pacific,with the strongest signal confined to the tropical and North Pacific.Over the past 20 years,the PDO-SSH accounts for about 30%-40%of altimeter-observed SLR in the regions 8°-15°N,130°-160°E and 30°-40°N,170°-220°E.Along the coast of North America,the PDO-SSH signal dramatically offsets the coastal SLR,as the sea level trends change sign from falling to rising.     

Research Progress in China on the Tropical Atmospheric Intraseasonal Oscillation

Tropical intraseasonal oscillation (including the Madden-Julian oscillation) is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect weather and climate both inside and outside the tropical region. The study of these phenomena therefore represents one of the frontiers of atmospheric sciences. This review aims to synthesize and summarize studies of intraseasonal oscillation (ISO) by Chinese scientists within the last 5-10 years. We focus particularly on ISO's mechanisms, its numerical simulations (especially the impacts of diabatic heating profiles), relationships and interactions with ENSO (especially over the western Pacific), impacts on tropical cyclone genesis and tracks over the northwestern Pacific, and influences on the onset and activity of the South and East Asian monsoons (especially rainfall over China). Among these, focuses of ongoing research and unresolved issues related to ISO are also discussed.     

近50年中国大陆冬季气温和区域环流的年代际变化研究

利用中国大陆468 个站点1960～2013 年逐日气温资料,本文首先对中国冬季气温的年代际变化特征进行分析。通过气候跃变检验分析发现,中国冬季气温在整体变暖的趋势上叠加有年代际波动,可划分为冷期、暖期和停滞期三个时期。本文对比三个时期的冬季大气环流发现,冷/停滞期（暖）期西风环流减弱（增强）而东亚大槽增强（浅薄）,槽后的辐合下沉增强（削弱）,西伯利亚高压增强（减弱）,这加强（削弱）了东亚冬季风,冷空气更多（少）侵入中国大陆地区,冬季气温偏低（高）。北半球环状模/北极涛动（Northern Hemisphere Annular Mode,NAM/Arctic Oscillation,AO）正是通过东亚冬季风系统对中国冬季气温,尤其是冬季最低气温有很强的年代际影响。太平洋年代际振荡（Pacific Decadal Oscillation,PDO）与中国冬季气温在年代际上也有很好的正相关关系。进一步将PDO 的年代际变化分量作为背景,分析NAM/AO 和厄尔尼诺—南方涛动（El Nino Southern Oscillation,ENSO）不同配置下的东亚冬季风环流场可以发现,两者的配置作用不仅影响着中国冬季气温一致变化型的年代际波动,而且也可以影响到冬季气温南北反相振荡型的变化,这从一个方面解释了1980 年代和1990年代北方变暖较强及最近十年北方降温趋势较为明显的原因。