Showing papers by "Chang-Hoi Ho published in 2004"

Interdecadal Changes in Summertime Typhoon Tracks

Abstract: The present work examines interdecadal variations of typhoon tracks in the western North Pacific (WNP) during the boreal summer (June–September) for the period 1951–2001. Typhoon tracks are expressed as percentage values of the total number of typhoon passages into a 5° × 5° latitude–longitude grid box with respect to the total number of typhoons formed in the WNP. The analysis period is divided into two interdecadal periods: ID1 (1951–79) and ID2 (1980–2001). From ID1 to ID2, typhoon passage frequency decreased significantly in the East China Sea and Philippine Sea, but increased slightly in the South China Sea. The time series of typhoon passage frequency over the East China Sea and South China Sea further reveal a regime shift in the late 1970s, while those over the Philippine Sea indicate a continuous downward trend of −9% decade−1. The interdecadal changes in typhoon tracks are associated with the westward expansion of the subtropical northwestern Pacific high (SNPH) in the late 1970s. The e...

Upstream Subtropical Signals Preceding the Asian Summer Monsoon Circulation

Abstract: In this study, the authors address several issues with respect to the antecedent signals of the large-scale Asian summer monsoon that were earlier identified by Webster and Yang In particular, they revisit the changes in the subtropical upper-tropospheric westerlies preceding the monsoon, depict the detailed structure of the monsoon’s antecedent signals, and investigate the physical processes from the signals to the monsoon They also explore the teleconnection of these signals to various large-scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the Tibetan Plateau and the monsoon Before a strong (weak) Asian summer monsoon, the 200-mb westerlies over subtropical Asia are weak (strong) during the previous winter and spring A significant feature of these signals is represented by the variability of the Middle East jet stream whose changes are linked to the Arctic Oscillation, North Atlantic Oscillation, El

Intra-seasonal Variability of Wintertime Temperature over East Asia

Abstract: 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°C2 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 the Siberian 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 © 2004 Royal Meteorological Society

Influences of Tropical Western and Extratropical Pacific SST on East and Southeast Asian Climate in the Summers of 1993–94

Abstract: This study emphasizes the importance of sea surface temperature (SST) over the tropical western Pacific and the ocean–atmosphere coupling in the extratropical Pacific for the climate in East and Southeast Asia. Specifically, it demonstrates that the anomalies of tropical SST explain many features of the climate variability in those regions during the summers of 1993 and 1994. Very different atmospheric circulation patterns appeared in East and Southeast Asia between 1993 and 1994. Many regions including northern China, Korea, and Japan suffered from extremely high temperatures and severe droughts in the summer of 1994 but experienced reverse climate anomalies in the summer of 1993. To the south of these regions, the opposite climate patterns occurred. These climate features do not really resemble those associated with the El Nino–Southern Oscillation, which usually exerts a moderate impact on the East Asian climate. However, different SST anomalies have been observed in the tropical western and e...