Using the daily average of the NCEP/DOE AMIP-II reanalysis data from 1979 to 2005 and the characteristics of monsoon troughs in the western North Pacific,we established an intensity index and a location index to descr...Using the daily average of the NCEP/DOE AMIP-II reanalysis data from 1979 to 2005 and the characteristics of monsoon troughs in the western North Pacific,we established an intensity index and a location index to describe the activity of the monsoon troughs in three different regions and their impacts on tropical cyclones generated therein(MTTCs).The behavior of the monsoon troughs was analyzed.The following conclusions are obtained:(1)The established monsoon trough intensity index has a positive correlation to the location index,indicating that stronger monsoon trough intensity corresponds to more northward location.(2)Monsoon trough intensity exhibits significant interannual variation,with obvious periods of 4–5 years prior to 1994 and 2–3 years afterwards.(3)The affecting factors on monsoon trough intensity are different with areas.The preceding SST anomaly results in anomalous atmospheric circulation, leading to the anomaly of monsoon trough intensity in different areas.(4)The frequency of cyclogenesis and location anomalies of the MTTC are closely related to the intensity and location of the monsoon trough. Most of the anomalously less MTTC years coincide with the years with a weak general monsoon trough and weak regional monsoon troughs.The anomalously more MTTC years are associated with both a strong general monsoon trough and a weak general monsoon trough combined with a strong one over the South China Sea,though with a larger probability for the latter.(5)The interseasonal variation of the intensity of monsoon troughs provides favorable conditions for TC generation and development.The monsoon trough is in the active periods of both quasi-biweekly 10 to 20 day and 30 to 60 day oscillations,which is favorable for MTTC occurrence.展开更多
Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce ...Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.展开更多
Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130°—160°E, 10°—20°N, a composite analysis is performed on the fields of surface temp...Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130°—160°E, 10°—20°N, a composite analysis is performed on the fields of surface temperature, outgoing longwave radiation and 850 hPa zonal wind. The composite results show that the weaker (stronger) WNP convection is related to the El Nino (La Nina)—pattern sea surface temperature (SST) anomalies in the preceding winter and in spring. A comparison with previous results indicates that a similar spatial and temporal distribution of SST anomalies is also associated with the onsets of both the WNP and South China Sea (SCS) monsoons. The composite results also show that the weaker (stronger) convection over the WNP corresponds to the easterly (westerly) anomalies that extend westward from the WNP into the Bay of Bengal. A numerical experiment by an atmospheric general circulation model shows a similar result. In addition, during weaker (stronger) convection summer, the convection over the WNP and lower-level zonal winds over the SCS exhibit a small (large) extent of seasonal evolution.展开更多
Guangdong suffered from the most serious precipitation of its corresponding time during the dragon-boat race of 2008 since 1951.The relationship between the strong dragon-boat precipitation in 2008 and atmospheric low...Guangdong suffered from the most serious precipitation of its corresponding time during the dragon-boat race of 2008 since 1951.The relationship between the strong dragon-boat precipitation in 2008 and atmospheric low-frequency oscillation was analyzed with the methods of wavelet analysis,correlation and Lanczos filter.Results showed that the daily rainfall exhibits a significant 7 to 12-day quasi-periodic oscillation(namely quasi-10-day oscillation) during the precipitation,the daily 500 hPa height over Guangdong exhibits a significant 8 to 13-day quasi-periodic oscillation,and the daily 850 hPa zonal wind averaged over the north of the South China Sea presents a significant quasi-12-day periodic oscillation.The Guangdong rainfall during the annually first rainy season is most closely correlated with monsoon over the north of South China Sea,and less closely with an upper-level trough at 500 hPa affecting Guangdong.Strong monsoon surges induced two heavy rainfall processes in 2008.The monsoon surges joined with a westward-propagating quasi-10-day oscillation that originated from the central Pacific and was enhanced in a strong convective region east of the Philippines and a northward-propagating monsoon that originated from the southern South China Sea was enhanced.With composite analysis of typical phases,the common evolution characteristics of atmospheric circulation of the two heavy rainfall processes were analyzed for different phases.These features can be used as reference for medium prediction of heavy rainfall processes in Guangdong.展开更多
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
基金An open project of Key Laboratory for Meteorological Disasters for Jiangsu Province(KLME0708)Natural Science Foundation of China(90915002+2 种基金4077504740775058)A project of Young Talents for Fujian Province(2007F3019)
文摘Using the daily average of the NCEP/DOE AMIP-II reanalysis data from 1979 to 2005 and the characteristics of monsoon troughs in the western North Pacific,we established an intensity index and a location index to describe the activity of the monsoon troughs in three different regions and their impacts on tropical cyclones generated therein(MTTCs).The behavior of the monsoon troughs was analyzed.The following conclusions are obtained:(1)The established monsoon trough intensity index has a positive correlation to the location index,indicating that stronger monsoon trough intensity corresponds to more northward location.(2)Monsoon trough intensity exhibits significant interannual variation,with obvious periods of 4–5 years prior to 1994 and 2–3 years afterwards.(3)The affecting factors on monsoon trough intensity are different with areas.The preceding SST anomaly results in anomalous atmospheric circulation, leading to the anomaly of monsoon trough intensity in different areas.(4)The frequency of cyclogenesis and location anomalies of the MTTC are closely related to the intensity and location of the monsoon trough. Most of the anomalously less MTTC years coincide with the years with a weak general monsoon trough and weak regional monsoon troughs.The anomalously more MTTC years are associated with both a strong general monsoon trough and a weak general monsoon trough combined with a strong one over the South China Sea,though with a larger probability for the latter.(5)The interseasonal variation of the intensity of monsoon troughs provides favorable conditions for TC generation and development.The monsoon trough is in the active periods of both quasi-biweekly 10 to 20 day and 30 to 60 day oscillations,which is favorable for MTTC occurrence.
基金Project supported by the National Natural Science Foundation of China （Grant No 40505019） and the 0pen Research Fund of Laboratory of China Meteorological Administration （Grant No CMATG2006L03）.
文摘Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.
基金This study was supported by the " National Key Program for Developing Basic Sciences" G1998040900 Part 1 and the National Natura
文摘Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130°—160°E, 10°—20°N, a composite analysis is performed on the fields of surface temperature, outgoing longwave radiation and 850 hPa zonal wind. The composite results show that the weaker (stronger) WNP convection is related to the El Nino (La Nina)—pattern sea surface temperature (SST) anomalies in the preceding winter and in spring. A comparison with previous results indicates that a similar spatial and temporal distribution of SST anomalies is also associated with the onsets of both the WNP and South China Sea (SCS) monsoons. The composite results also show that the weaker (stronger) convection over the WNP corresponds to the easterly (westerly) anomalies that extend westward from the WNP into the Bay of Bengal. A numerical experiment by an atmospheric general circulation model shows a similar result. In addition, during weaker (stronger) convection summer, the convection over the WNP and lower-level zonal winds over the SCS exhibit a small (large) extent of seasonal evolution.
基金Specialized Research Project of Novel Meteorological Technologies for Forecasters from China Meteorological Administration (CMATG2007Y04)Science Bureau of Guangdong (2006B37202004)+1 种基金Guangdong Meteorological Bureau (2008A02)Specialized Project for Industries for Public Well-being(Meteorological Sector) (GYHY201006018)
文摘Guangdong suffered from the most serious precipitation of its corresponding time during the dragon-boat race of 2008 since 1951.The relationship between the strong dragon-boat precipitation in 2008 and atmospheric low-frequency oscillation was analyzed with the methods of wavelet analysis,correlation and Lanczos filter.Results showed that the daily rainfall exhibits a significant 7 to 12-day quasi-periodic oscillation(namely quasi-10-day oscillation) during the precipitation,the daily 500 hPa height over Guangdong exhibits a significant 8 to 13-day quasi-periodic oscillation,and the daily 850 hPa zonal wind averaged over the north of the South China Sea presents a significant quasi-12-day periodic oscillation.The Guangdong rainfall during the annually first rainy season is most closely correlated with monsoon over the north of South China Sea,and less closely with an upper-level trough at 500 hPa affecting Guangdong.Strong monsoon surges induced two heavy rainfall processes in 2008.The monsoon surges joined with a westward-propagating quasi-10-day oscillation that originated from the central Pacific and was enhanced in a strong convective region east of the Philippines and a northward-propagating monsoon that originated from the southern South China Sea was enhanced.With composite analysis of typical phases,the common evolution characteristics of atmospheric circulation of the two heavy rainfall processes were analyzed for different phases.These features can be used as reference for medium prediction of heavy rainfall processes in Guangdong.
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.
