There has been a profound warming over East Asia during the winter months (November through to March) over the past few decades. The goal of this study is to address the question of whether the daily temperature has become more variable in conjunction with this warming by using observed temperature data obtained from 155 Chinese and Korean stations. Prior to the analysis, the annual cycle is removed to obtain daily temperature anomalies for each winter for each station. Results show that the intra-seasonal variance generally decreases, implying that the daily temperatures are becoming less variable. Considering all stations as a whole, the rate of change is −0.49℃2 per decade (equivalent to −3.59% per decade). The changes are more robust in the northeastern portion of China. In contrast, there are no dominant trends for the skewness coefficients, except for clear negatively skewed trends in northeastern China. These results are consistent with an increase in the number of extremely cold events. Over the region, the frequency of low-temperature extremes (as low as below minus two standard deviations) increases at a rate of change of 0.26 days per decade, significant at the 95% confidence level. Both the Siberian high and Arctic oscillation (AO) exert a notable influence on the temperature variance. Intra-seasonal variance of the Siberian high and AO are significantly correlated with the temperature variance, whereas the seasonal mean state of the AO affects the temperature variance by modulating the high-frequency components of theSiberian high. The intra-seasonal variance of the Siberian high tends to decline at a rate of change of −10.7% per decade, significant at the 99% level; meanwhile, the mean wintertime AOs have strengthened in the last few decades. These two climate features together make a considerable contribution to the changes in intra-seasonal temperature variance in East Asia. Copyright

Large-scale atmospheric systems, such as the Southern Oscillation, North Atlantic Oscillation, and so on, are important climatic change indicators over the northern hemisphere. These systems play essential roles in regional-tocontinental scale climate fluctuation and vegetation activity in response to global change. Using the Pathfinder AVHRR NDVI (Advanced Very High Resolution Radiometer Normalized Difference Vegetation Index) data for the period 1982-2000, the authors investigated the relationship of the inter-annual variations of spring NDVI to nine large-scale climate indices. On average, 57.2% of the satellite-sensed NDVI variance was explained. These climate indices also accounted for a large portion of the trends in NDVI as observed in five regions, namely, north-west North America (climate-related trend was 18.2%/10 years), south-eastern North America (5.8%/10 years), Europe (6.9%/10 years), highlatitude Asia (12.4%/10 years), and East Asia (8.0%/10 years). The results are useful for understanding and predicting the regional-to-continental NDVI variations in response to global climate change.

In this study, the connection between Arctic Oscillation (AO) and variability of East Asian winter mon-soon is investigated. Two indices are chosen to describe the winter monsoon. One is the intensity of the Siberian High, defined as the average SLP over the center region, and the other is the temperature of eastern China, averaged over 76 surface stations. These are two tightly related components, correlate at-0.62 for period 1951-99. Temperature drops by 0.64 degrees Celsius in association witha one standard de-viation increase in Siberian High intensity. It is found that there are significant out-of-phase relationships between the AO and the East Asian winter monsoon. The correlation coefficient between the AO and the Siberian High inten-sity index is-0.48 for period 1958-98. AO is also signifi-cantly correlated with the temperature of eastern China at 0.34. However, when the li'near trend is removed, the corre-lation between AO and temperature is no longer significant. But the strong connection between the AO and Siberian High, and between the Siberian High and temperature are still significant. These results reveal that the AO influences the East Asian winter monsoon through the impact on the Siberian High. Negative phase of the AO is concurrent with a stronger East Asian Trough and an anomalous anticyclonic flow over Urals at the middle troposphere (500hPa). Both the AO and the Eurasian pattern play important roles in changes of the Siberian High and/or East Asian winter mon-soon. They account for 13.0% and 36.0% of the variance in the Siberian High respectively.

利用1954～2001年我国150站日平均气温资料，分析了历年冬季期间（11月1日到次年3月31日）气温方差的变化与北极涛动的关系。发现北极涛动处于较强的正位相时，我国日平均气温方差偏小，反之则偏强。主要是通过影响西伯利亚高压中心区的海平面气压的高频变率而影响我国日气温的波动。季节尺度内异常低温事件（日气温距平<−2σ，σ为各站各冬季日气温距平的标准差）频次与气温方差之间存在反常的关系：温度方差大（小）时，异常低温事件频次下降（上升）。这与气温的非正态分布有关，也明显受北极涛动位相及强弱的影响。近50年来随着北极涛动指数的增强，西伯利亚高压中心区海平面气压方差显著下降（−10.7%/10a），我国日气温的变率也在显著减少（−4.1%/10a），而异常低温事件频次则显著增加（0.16d/10a）。