Surface and Upper-Level Features Associated with Wintertime Cold Surge Outbreaks in South Korea

The surface and upper-level features associated with a sharp drop ofwintertime daily temperature over South Korea is investigated in this study. This sharp drop indaily temperature is called a cold surge and is one of the most hazardous weather phenomena in EastAsian winters. An upper-level baroclinic wave of 60° wavelength propagating eastward at a phasespeed of 12° longitude per day across the continent of northern China from the west of Lake Baikaltoward the eastern coast of China causes the outbreak of cold air over South Korea. The coolingassociated with the upper-level baroclinic jvave is found at all altitudes under the geopotentialheight-fall center near the tropopause. The development in the ridge seems to derive the earlyevolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly withthe tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after theoutbreak of a cold surge is a response to the steep temperature gradient associated with thedeveloping baroclinic wave.

Comparison of Daily Extreme Temperatures over Eastern China and South Korea between 1996–2005

This paper examined the decadal mean, seasonal cycle, and interannual variations of mean and extreme temperatures using daily temperature and relative humidity data from 589 stations over eastern China and South Korea between 1996-2005. The results show that the decadal mean Tm （mean daily mean temperature） and the TNn （minimum daily minimum temperature） increase from north to south; the opposite spatial gradient is found in the DTR （diurnal temperature range）; the value of the DTR over South Korea is in- between that over North China and the mid-low Yangtze River valley; the TXx （maximum daily maximum temperature） has a unique spatial distribution, with the largest value over eastern China. The highest standard deviation （STD） is located over northern China and the TNn has the largest area coverage of the high STD. The peak of the seasonal cycle for the Tm, TXx and TNn over South Korea （August） occurs one month later than that over eastern China （July）. The seasonal cycle of the DTR has two peaks （April and October）; the value in the middle-lower reaches of the Yangtze River valley is larger than that in South Korea during July and August owing to the seasonal northward jump of the major monsoon rain band. The interannual variations of summertime temperature indices including the Tin, TXx, and DTR over South Korea are consistent （opposite） to that over northern （southern） China. For the wintertime temperature indices however, the variation over South Korea is consistent with that over eastern China.

Teleconnections:Summer Monsoon over Korea and India

This study investigates the relationship between the summer monsoon rainfall over Korea and India, by using correlation analysis and Singular Value Decomposition (SVD).Results reveal that summer monsoon rainfall over Korea is negatively (significant at the 99% level) cor-related with the rainfall over the northwest and central parts of India. In addition, coupled spatial modes be-tween the rainfall over Korea and India have been identified by the SVD analysis. The squared covariance fraction explained by the first mode is 70% and the correlation coefficient between the time coefficients of the two fields is significant at the 99% level, indicating that the coupled mode reflects a large part of the interaction between the summer monsoon rainfall over Korea and India. The first mode clearly demon-strates the existence of a significant negative correlation between the rainfall over the northwest and central parts of India and the rainfall over Korea.Possible mechanisms of this correlation are investigated by analyzing the variation of upper-level at-mospheric circulation associated with the Tibetan high using NCEP/NCAR Reanalysis data.

夏季东亚高空急流与天气尺度波动的气候特征之间的联系

利用NCEP／NCAR逐日资料（1979-2003年），分析了东亚夏季高空急流和天气尺度波动气候特征之间的联系。通过分析急流与天气尺度波动活动量Q（用于描述某一时间段内天气尺度波动活动强弱程度）、热量涡动输送（VT）的关系，发现：在气候平均意义下，天气尺度波动活动量在6、8月较大，这意味着在这两个月中，天气尺度波动较为剧烈。这和急流的强度变化是相对应的，即强的天气尺度波动活动量对应着强的急流，弱的天气尺度波动活动量对应着弱的急流。热量涡动输送也表现出与天气尺度波动活动量类似的特征。年际变化上，夏季平均和6、7、8各月平均的热量涡动输送和急流强度都存在显著的正相关。对强、弱急流年份条件下热量涡动输送合成分析的结果表明：热量涡动输送偏南时，对应着强的急流；热量涡动输送偏北时，对应着弱的急流。以上的研究结果说明，在气候平均意义和年际变化上夏季东亚高空急流和天气尺度波动之间有着密切的联系。

Validation of Sea Level Data in the East Asian Marginal Seas: Comparison between TOPEX/POSEIDON Altimeter and In-Situ Tide Gauges

In an effort to assess the reliability of satellite altimeter systems, the authors conduct a comparative analysis of sea level data that were collected from the TOPEX/POSEIDON (T/P) altimeter and 10 tide gauges (TG) near the satellite passing ground tracks. The analysis is made using datasets collected from marginal sea regions surrounding the Korean Peninsula at T/P cycles of 2 to 230, which correspond to October 1992 to December 1998. Proper treatment of tidal errors is a very critical step in data processing because the study area has very strong tide. When the T/P data are processed, the procedures of Park and Gamberoni (1995) are adapted to reduce errors associated with the tide. When the T/P data are processed in this way, the alias periods of M2, S2, and K1 constituents are found to be 62.1, 58.7, and 173 days repectively. The compatibility of the T/P and TG datasets are examined at various filtering periods. The results indicate that the low-frequency signals of the T/P data can be interpreted more safely with longer filtering periods (such as up to the maximum selected value of 200 days). When RMS errors for the 200-day low-pass filter period are compared with all 10 tidal stations, the values span the range of 2.8 to 6.7 cm. The results of a correlation analysis for this filtering period also show a strong agreement between the T/P and TG datasets across all stations investigated (e.g.,p- values consistently less than 0.001). Hence according to the analysis, the conclusion is made that the analysis of surface sea level using satellite altimeter data can be made safely with reasonably extended filtering periods such as 200 days.

伴随韩国雨季开始和结束早晚的关联场分析(英文)

分析了与韩国雨季开始和结束的年际变化相关联的一些要素场发生的变化。分别对雨季开始和结束早晚的个例进行了合成分析。６月月平均资料用来分析与雨季开始早晚相关联的要素场变化，而在分析与雨季结束早晚相关联的要素场变化时则利用７月月平均资料。结果表明，对应雨季开始（或结束）早晚，大气环流和表面温度等要素不仅在东亚地区、而且在远离东亚的地方具有显著的差异。在东亚地区的显著差异主要是高空急流和西太平佯副热带高压。远离东亚的显著差异主要是印度季风和ＥＮＳＯ现象。印度季风与韩国雨季开始和结束均有关联，但ＥＮＳＯ现象只与雨季开始显著相关、而与结束并没有显著的关联。

东亚夏季风降水和环流数值模拟对不同对流参数化方案的敏感性(英文)

应用一个５层大气环流谱模式（ＩｍＰＫＵ－５ＬＡＧＣＭ）分别考察在气候平均情况、弱和强亚洲夏季风情况下东亚地区夏季风降水和环流数值模拟结果对不同对流参数化方案的敏感性。利用 Ａｒａｋａｗａ－Ｓｃｈｕｂｅｒｔ（之后简称 Ａ－Ｓ）、 Ｋｕｏ和 Ｍａｎａｂｅ对流参数化方案模拟的结果表明：无论在气候平均情况或是在弱亚洲夏季风以及强亚洲夏季风情况下，所模拟的东亚夏季风降水和环流的分布非常依赖于对流参数化方案。模拟的结果也表明了虽然应用Ａ－Ｓ方案在热带地区降水的数值模拟结果要好一些，但在东亚地区，Ｋｕｏ方案比Ａ－Ｓ方案或Ｍａｎａｂｅ方案似乎更适合于夏季风降水和环流的模拟、这可能是由于东亚地区的夏季降水云系往往是积云和层云的混合， Ｋｕｏ的对流参数化方案能够反映东亚夏季风降雨云系的特征。

Monsoonal precipitation variation in the East Asia since A.D. 1840 ——Tree-ring evidences from China and Korea

Three tree-ring rainfall reconstructions from China and Korea are used in this paper to investigate the East Asian summer monsoon-related precipitation variation over the past 160 years. Statistically, there is no linear correlation on a year-by-year basis between Chinese and Korean monsoon rainfall, but region-wide synchronous variation on a decadal-scale was observed. More rainfall intervals were 1860-1890, 1910-1925, and 1940-1960, and dry or even drought peri-ods were 1890-1910, 1925-1940, and 1960-present. Reconstructions also display that the East Asian summer monsoon precipitation suddenly changed from more into less around mid-1920. These tree-ring precipitation records were also confirmed by Chinese historical dry-ness/wetness index and Korean historical rain gauge data.

A physically-based statistical forecast model for the middle-lower reaches of the Yangtze River Valley summer rainfall

A new approach to forecast the middle-lower reaches of the Yangtze River Valley summer rainfall in June―August(JJA) is proposed in this paper.The year-to-year increment of the middle-lower reaches of the Yangtze River Valley is forecasted and hence the summer precipitation could be predicted.In this paper,DY is defined as the difference of a variable between the current year and the preceding year(year-to-year increment).YR denotes the seasonal mean precipitation rate of the middle-lower reaches of the Yangtze River Valley summer rainfall.After analyzing the atmospheric circulation anomalies in winter and spring that were associated with the DY of YR,six key predictors for the DY of YR have been identified.Then the forecast model for the DY of YR is established by using the multi-linear regression method.The predictors for the DY of YR are Antarctic Oscillation,the meridional wind shear between 850hPa and 200hPa over the Indo-Australian region,and so on.The prediction model shows a high skill for the hindcast during 1997-2006,with the average relative root mean square error is at 18%.The model can even reproduce the upward and downward trends of YR during 1984―1998 and 1998―2006.Considering that the current operational forecast models of the summer precipitation over the China region have the average forecast scores at 60%―70% and that the prediction skill for the middle-lower reaches of Yangtze River Valley summer precipitation remains quite limited up to now,thus this new approach to predict the year-to-year increment of the summer precipitation over the Yangtze River Valley(and hence the summer precipitation itself) has the potential to significantly increase the operational forecast skill of the summer precipitation.