Climatologically, June is usually the wettest month in Hong Kong. With significant interannual variation of the summer monsoon, the rainfall variability in June is also large. As Hong Kong is in close proximity to the...Climatologically, June is usually the wettest month in Hong Kong. With significant interannual variation of the summer monsoon, the rainfall variability in June is also large. As Hong Kong is in close proximity to the peripheries of different monsoon regions, the variability of June rainfall largely depends on the relative strength of various monsoon systems. In the present study, a new index comparing the relative condition of the western North Pacific summer monsoon and the South China Sea summer monsoon is developed based on the difference between the respective monsoon indices WNPMI （western North Pacific summer monsoon index） and UMI （unified monsoon index）. It is shown that June rainfall in Hong Kong and its vicinity is better correlated with this new index than either WNPMI or UMI alone. Based on the signs of the new index in conjunction with those of WNPMI and UMI, a framework to stratify the monsoon conditions into different configurations together with a simple scheme to summarize the associated rainfall responses is formulated. This study highlights how the rainfall variability on a local or regional scale can be quantified by the broad-scale conditions of different monsoon systems.展开更多
Tropical cyclones(TCs) moving across Luzon from east to west are likely to affect Hong Kong. As such, it is important for forecasters take into account the likely changes in intensity and movement characteristics of T...Tropical cyclones(TCs) moving across Luzon from east to west are likely to affect Hong Kong. As such, it is important for forecasters take into account the likely changes in intensity and movement characteristics of TCs crossing Luzon. 50 TCs in the period 1980-2014 were examined to determine the effect of Luzon’s terrain on their intensity and movement.The results indicated that TCs generally weakened as they passed through the terrain of Luzon. The decrease in the maximum sustained winds(MSW) for TCs with intensity of severe tropical storms or below was normally < 10 knot. For typhoons, the decrease in the MSW was usually ≥10 knot. The study also showed that TCs moving across Luzon were likely to accelerate(decelerate) as they approached(moved away) from Luzon. Furthermore, while there was a slight bias for TCs to defl ect leftwards on leaving Luzon, a signifi cant negative correlation was found between the defl ection tendency before and after crossing Luzon. A TC defl ected to the right(left) before landfall was likely to defl ect to the left(right) after leaving Luzon. Also, defl ection upon/near landfalling is found to be related to the intensity, moving speed and the direction of motion of a TC.展开更多
文摘Climatologically, June is usually the wettest month in Hong Kong. With significant interannual variation of the summer monsoon, the rainfall variability in June is also large. As Hong Kong is in close proximity to the peripheries of different monsoon regions, the variability of June rainfall largely depends on the relative strength of various monsoon systems. In the present study, a new index comparing the relative condition of the western North Pacific summer monsoon and the South China Sea summer monsoon is developed based on the difference between the respective monsoon indices WNPMI （western North Pacific summer monsoon index） and UMI （unified monsoon index）. It is shown that June rainfall in Hong Kong and its vicinity is better correlated with this new index than either WNPMI or UMI alone. Based on the signs of the new index in conjunction with those of WNPMI and UMI, a framework to stratify the monsoon conditions into different configurations together with a simple scheme to summarize the associated rainfall responses is formulated. This study highlights how the rainfall variability on a local or regional scale can be quantified by the broad-scale conditions of different monsoon systems.
文摘Tropical cyclones(TCs) moving across Luzon from east to west are likely to affect Hong Kong. As such, it is important for forecasters take into account the likely changes in intensity and movement characteristics of TCs crossing Luzon. 50 TCs in the period 1980-2014 were examined to determine the effect of Luzon’s terrain on their intensity and movement.The results indicated that TCs generally weakened as they passed through the terrain of Luzon. The decrease in the maximum sustained winds(MSW) for TCs with intensity of severe tropical storms or below was normally < 10 knot. For typhoons, the decrease in the MSW was usually ≥10 knot. The study also showed that TCs moving across Luzon were likely to accelerate(decelerate) as they approached(moved away) from Luzon. Furthermore, while there was a slight bias for TCs to defl ect leftwards on leaving Luzon, a signifi cant negative correlation was found between the defl ection tendency before and after crossing Luzon. A TC defl ected to the right(left) before landfall was likely to defl ect to the left(right) after leaving Luzon. Also, defl ection upon/near landfalling is found to be related to the intensity, moving speed and the direction of motion of a TC.
