ABSTRACT:In this study, spatial and temporal patterns of changes in extreme events of temperature and precipitation at 143 weather stations in ten Asia-Pacific Network (APN) countries and their associations with changes in climate means are examined for the 1955-2007 period. Averaged over the APN region, annual frequency of cool nights (days) has decreased by 6.4 days/decade (3.3 days/decade), whereas the frequency of warm nights (days) has increased by 5.4 days/decade (3.9 days/decade). The change rates in the annual frequency of warm nights (days) over the last 20 years (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) have exceeded those over the full 1955-2007 period by a factor of 1.8 (3.4). Seasonally, the frequencies of summer warm nights and days are changing more rapidly per unit change in mean temperatures than the corresponding frequencies for cool nights and days. However, normalization of the extreme and mean series shows that the rate of changes in extreme temperature events are generally less than that of mean temperatures, except for winter cold nights which are changing as rapidly as the winter mean minimum temperature. These results indicate that there have been seasonally and diurnally asymmetric changes in extreme temperature events relative to recent increases in temperature means in the APN region.There are no systematic, regional trends over the study period in total precipitation, or in the frequency and duration of extreme precipitation events. Statistically significant trends in extreme precipitation events are observed at fewer than 30% of all weather stations, with no spatially coherent pattern of change, whereas statistically significant changes in extreme temperature events have occurred at more than 70% of all weather stations, forming strongly coherent spatial patterns.

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[1] The variations of wintertime surface air temperature (SAT) and the occurrences of cold surges over east Asia in association with the Madden and Julian Oscillation (MJO) are examined. The MJO is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hPa zonal winds and outgoing longwave radiation in the tropics. The spatial pattern and magnitude of SAT anomalies over east Asia significantly change with respect to MJO phases. Composite analysis reveals that the MJO-SAT relationship is mainly affected by strong temperature advection in the lower troposphere. In addition, occurrences of cold surges are identified using objectively determined synoptic criteria, and their relation to the MJO is analyzed. Most extreme cold surges occur when the MJO convection center is located over the Indian Ocean, and it is suggested that MJO-induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges.

This study investigates possible changes of extreme events in global warming over Korea with MM5 downscaling simulation during the period 1971–2100. Frequency distribution of daily temperatures over Korea shows an increase in the mean by about 5.5°C from 1971–2000 to 2071–2100 while change in the variance is negligible. Increasing temperature results in changes in the frequency and intensity of temperature extremes. Under the current climate change scenario, hot events are expected to be more frequent and intense, while cold events will be rare and weaker. The increasing trend of temperature is associated with an increasing trend of precipitation. The increasing trend produces an increase in the number of the days of heavy precipitation as well as the corresponding amount. Better resolved topography in MM5 produces bigger changes in local precipitation than in the temperature field. Consequently increasing tendency is obvious in the northern part of Korea.

We have investigated the spatial patterns of trends in summer precipitation amount, intensity, and heavy precipitation for South Korea between 1973 and 2005. All stations show increasing trends in precipitation amount during the summer months, with the highest percentage of significant increase in June precipitation for the northern and central western part of South Korea. There is a significant increase in August precipitation for stations in the southeastern part of South Korea. Only a few stations exhibited significant upward trends in September precipitation. There is a weak to moderate spatial autocorrelation with the highest Moran's I value in June precipitation amount and August precipitation intensity. The number of days with daily precipitation exceeding 50 and 30 mm during the summer has increased at all stations. Observed trends are likely to be associated with changes in large-scale atmospheric circulation, sea surface temperature anomalies, and orography, but detailed causes of these trends need further investigation.

This letter reports on a possible delayed impact of the winter North Atlantic Oscillation (NAO) on the following east Asian summer monsoon precipitation. An analysis of weather station data shows significant correlations between the December NAO index and precipitation over Korea and China in the subsequent summer. It appears that the correlation may be related to a wave train pattern which originates from the North Atlantic. The east Asian branch of this wave train can affect large‐scale circulation and the precipitation over east Asia in early summer. We also found a significant interdecadal change of this relationship, which is possibly linked to a climatological change of the east Asian jet stream.

To investigate the spatial and temporal relationships of drought occurrence and intensity between Korea and East Asia, the Standardized Precipitation Index (SPI), calculated from Climatic Research Unit (CRU) monthly precipitation data, was used from 1951 to 1996. It is found that the frequency of occurrence of droughts in Korea has significant time intervals of 2-3 and 5-8 years and has been increasing since the 1980s. Correlation and composite analyses showed that the occurrence of droughts over central eastern China, Manchuria, and the north coast of Japan was highly correlated with those in Korea. However, the time scales of occurrence of droughts over the three regions were different. Droughts in eastern China represented in-phase variations with those in Korea with a time interval of 5-8 years, whereas those in Manchuria occurred with a time interval of 15 years, and those in Japan had no coincident variations.To assess the feasibility of usage of proxy climate data in eastern China for the research of droughts in Korea during the pre-instrumental period, dry-wet indices in six regions of eastern China were correlated to the SPI values in Korea for the period of 1951-92 considering several time scales. Dry-wet indices of region V showed a larger correlation and the most similar trend to the droughts in Korea with a time scale of 5-11 years. This suggested an effective utilization of historical records and other proxy data in eastern China to understand extreme climatic events in Korea for the past 500 years.