Abstract
For the past few decades, daily winter temperatures over East Asia have been higher and less variable. Generally, these simple temperature-distribution shifts should lead to a decrease in the occurrence of cold extremes, but observations of the changes in the extremes are often complicated. In the present study, the change in the occurrence of relatively cold events (daily temperature anomaly, ≤-2σ for that season) in each winter monsoon over East Asia was examined using ground observations of daily temperature for the period 1954-2006. The time-mean temperature for each winter was subtracted to remove the interannual variability and long-term trend. Our analyses reveal that the intraseasonal temperature distribution over East Asia has changed with a negative skew, and the frequency of the relatively cold events has slightly increased (by 0.09 days per decade) over the past few decades, on an average, for the entire analysis domain (east of 1 05°E, 122 stations). In particular, the increase occurs more dominantly (82° o of the total stations) in regions north of 40°N where a stronger warming has progressed. The frequency of relatively cold events is found to be significantly correlated with the variance of the Siberian high and the mean of the Arctic Oscillation. The increasing trend in the frequency of relatively cold events may serve to partly countervail the decrease (-1.12 days per decade) in the frequency of absolute cold events (daily temperature anomaly, ≤2σ overall) across the entire observation period.
Highlights
The climatological mean temperature is usually defined as the average for 30 years at the end of each decade
It is found that the recent increase in variance occurred after the mid-1990 and was accompanied by the recent decrease in the frequency of relatively cold events. These results suggest that the change in the variance is associated with that in the frequency of relatively cold events in winter over East Asia
Previous studies have found that a considerable portion of the monthly seasonal-mean temperature variation in East Asia is related to the Siberian High (SH) and Arctic Oscillation (AO) (Gong et al 2001; Wu and Wang 2002; Jeong and Ho 2005, Jeong et al 2006; Park et al 2008)
Summary
The climatological mean temperature is usually defined as the average for 30 years at the end of each decade. They found that the variance has decreased as the mean temperature increased during the past several decades, whereas the skewness coefficients show tendencies toward negative values Their results suggest that a warming in East Asia may result in reduced up-and-down daily temperature variations, and more frequent “relatively” cold events (defined as daily temperature anomaly £ -2si, where si indicates the intraseasonal standard deviation) during each winter; the term ‘relatively’ emphasizes anomalous temperature only on intraseasonal time scales. Such events form the low tail of the temperature frequency distribution for a given season; this is an important notion from the viewpoint of studies on intraseasonal variability as well as socioeconomic climate adaptation related to bodily sensations in the living.
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