Low- and Mid-High Latitude Components of the East Asian Winter Monsoon and Their Reflecting Variations in Winter Climate over Eastern China

The present study defines a low-latitude component (regionally averaged winter 1000-hPa V-winds over 10 25°N, 105 135°E) and a mid-high-latitude component (regionally averaged winter 1000-hPa V-winds over 30 50°N, 110 125°E) of the East Asian winter monsoon (EAWM), which are denoted as EAWM-L and EAWM-M, respectively. The study examines the variation characteristics, reflecting variations in winter climate over eastern China, and associated atmospheric circulations corresponding to the two components. The main results are as follows: 1) the EAWM-L and EAWM-M have consistent variation in some years but opposite variations in other years; 2) the EAWM-M index mainly reflects the extensive temperature variability over eastern China, while the EAWM-L index better reflects the variation in winter precipitation over most parts of eastern China; and 3) corresponding to the variation in the EAWM-M index, anomalous winds over the mid-high latitudes of East Asia modulate the southward invasion of cold air from the high latitudes and accordingly affect temperatures over eastern China. In combination with the variation in the EAWM-L index, anomalous low-latitudinal winds regulate the water vapor transport from tropical oceans to eastern China, resulting in anomalous winter precipitation. These pronounced differences between the EAWM-L and the EAWM-M suggest that it is necessary to explore the monsoons' individual features and effects in the EAWM study.

Assessing the Impacts of Eurasian Snow Conditions on Climate Predictability with a Global Climate Model

On the basis of two ensemble experiments conducted by a general atmospheric circulation model(Institute of Atmospheric Physics nine-level atmospheric general circulation model coupled with land surface model,hereinafter referred to as IAP9L_CoLM),the impacts of realistic Eurasian snow conditions on summer climate predictability were investigated.The predictive skill of sea level pressures(SLP)and middle and upper tropospheric geopotential heights at mid-high latitudes of Eurasia was enhanced when improved Eurasian snow conditions were introduced into the model.Furthermore,the model skill in reproducing the interannual variation and spatial distribution of the surface air temperature(SAT)anomalies over China was improved by applying realistic(prescribed)Eurasian snow conditions.The predictive skill of the summer precipitation in China was low;however,when realistic snow conditions were employed,the predictability increased,illustrating the effectiveness of the application of realistic Eurasian snow conditions.Overall,the results of the present study suggested that Eurasian snow conditions have a significant effect on dynamical seasonal prediction in China.When Eurasian snow conditions in the global climate model(GCM)can be more realistically represented,the predictability of summer climate over China increases.

Response of Northern Hemispheric Air Temperature to Arctic Sea Ice Decline

Two numerical experiments were performed by using the Community Atmosphere Model version 3 （CAM3） with different sea ice datasets to assess the con- tribution of the decline of Arctic sea ice to warming in the Northern Hemisphere. One observed sea ice cover data; experiment was driven by for the other one, the authors used the sea ice data of the 4xCO2 scenario simulated by the fourth-generation European Centre Hamburg atmos- pheric general circulation Model of Istituto Nazionale di Geofisica e Vulcanologia, Italy （1NGV ECHAM4）. The comparison of the two experiments indicates that the de- cline of the Arctic sea ice leads to a dramatic wanning over the high latitudes of the Northern Hemisphere, char- acterized by a maximum warming of more than 26~C over the Arctic region. The significant warming is closely re- lated to the enhanced atmospheric heat source. A 40-60 W m-2 increase in the apparent heat source was simulated in winter due to the decline of Arctic sea ice. In contrast, no significant change was found in the atmospheric ap- parent heat source in summer. As a result, the summer temperature change induced by the decline of Arctic sea ice appears to be weak. This study suggests that accurate sea ice cover data is crucial for future climate projection of air temperature in high latitudes.

Abrupt Climate Changes of Holocene

This paper is a review of studies of abrupt climate changes(ACCs) during the Holocene published during the past ten years.North Atlantic cold events are indicators of ACCs.As indicated by North Atlantic ice-rafted debris(IRD),there were nine confirmed cold events during the Holocene,occurring at 11.1 kyr,10.3 kyr,9.4 kyr,8.1 kyr,5.9 kyr,4.2 kyr,2.8 kyr,1.4 kyr,and 0.4 kyr respectively according to most representative results from Bond et al.(1997).However,the identification of chronology has been made with some uncertainties.Considerable climatic proxy data have shown that,during the cold events,substantial climate abnormalities have occurred widely across the globe,particularly in the areas surrounding the North Atlantic.These abnormalities were in the form of high-latitude cold in the both hemispheres,expansion of the Westerlies to low latitudes,drought in the monsoon regions,recession of summer monsoons,and intensification of the winter monsoons.Studies have indicated that the four ACCs occurring in the early Holocene may be related to freshwater pulses from ice melting in the northern part of the North Atlantic,and the other five ACCs that occurred during the middle and late Holocene may be related to the decreased solar activity.

Zonal Mean Mode of Global Warming over the Past 50 Years

Zonal mean annual temperature trends were estimated using four reanalysis and three analysis grid datasets. The trends over land and for the entire globe were estimated from 1958-2001 and 1979-2007, respectively. Estimates of temperature trends over land from Climate Research Unit （CRU） analysis data indicate more intense wanning moving northward, at a rate of about 3.5℃ per century at 65°N, then declining further to the north. CRU estimates indicated dramatic warming over the latitudes of the Antarctic Peninsula, with a localized cooling trend at 45°S. A global estimate was conducted by comparing estimates of the reanalysis datasets. Temperature distribution trends of the reanalysis data were similar to those generated by land observations but with large bias in the Polar Regions. The bias could be reduced by comparing these estimates with those from the analysis data at high latitudes. Extreme warming trends were esti- mated at rates of 2.9℃-3.5℃ per century in the Arctic and 3.2℃-4.7℃ per century in the Antarctic for 1958-2001. Surface warming was even more intense in the Northern Hemisphere for 1979-2007, with extreme arctic warming rates ranging from 8.5℃-8.9℃ per century, as estimated by the analysis and reanalysis datasets. Trends over Antarctica for this period were contradictory, as Japan Meteorological Agency （JMA） reanalysis （JRA-25） indicated a cooling trend at about -7℃ per century, while other reanalysis datasets showed sharp warming over the continent.

Interannual Climate Variability of the Past Millennium from Simulations

The interannual variability of global temperature and precipitation during the last millennium is analyzed using the results of ten coupled climate models participating in the Paleoclimate Modelling Intercomparison Project Phase 3. It is found that large temperature(precipitation) variability is most dominant at high latitudes(tropical monsoon regions), and the seasonal magnitudes are greater than the annual mean. Significant multi-decadal-scale changes exist throughout the whole period for the zonal mean of both temperature and precipitation variability, while their long-term trends are indistinctive. The volcanic forcings correlate well with the temperature variability at midlatitudes, indicating possible leading drivers for the interannual time scale climate change.

新疆巴里坤湖全新世气候环境变化与高低纬间气候变化的关联

选择位于新疆东北部的封闭湖泊-巴里坤湖作为研究对象,采用常规14C测年建立了该湖一剖面约9400 cal a BP以来的时间序列,对该剖面沉积自生碳酸盐碳(δ13Ccar)、氧同位素(δ18Ocar)、有机碳(TOC)等多代用指标进行了连续小波变换、奇异谱分析.结果表明,全新世以来巴里坤湖地区的气候变化模式具有明显的阶段性变化:9400～8000 cal a BP期间气温偏低且较干旱;8000～6000 cal a BP期间气候环境温凉湿润;6000～2700 cal a BP期间,气候环境在总体上较为暖干,在向全新世晚期演变过程中呈现出降温、增湿的趋势;2700～800 cal a BP期间气温降低,湿润状况有所改善;800 cal a BP以来气候环境偏干.巴里坤湖全新世气候变化过程与周边区域古气候记录具有较好地一致性.研究发现,全新世以来研究区的气候环境不仅可能受到了北大西洋地区气候变化的影响,同样可能与来自热带低纬过程的海-气相互作用有关,特别是自全新世中期以来,逐渐增强的El Nio/La Nia-South Oscillation(ENSO)活动对研究区的气候环境变化可能具有一定的影响.研究还发现,在全新世期间,新疆东北部地区的气候演变可能并非简单地遵循某种单一的气候变化模式,不同气候系统(如西风、季风)在该地区的强弱对比状况可能对此地区气候环境变化模式有重要影响.