To date, the intraseasonal variation of raindrop size distribution(DSD) in response to the Madden–Julian Oscillation(MJO) has been examined only over the Indonesian Maritime Continent, particularly in Sumatra. This p...To date, the intraseasonal variation of raindrop size distribution(DSD) in response to the Madden–Julian Oscillation(MJO) has been examined only over the Indonesian Maritime Continent, particularly in Sumatra. This paper presents the intraseasonal variation of DSD over the Indian Ocean during the Cooperative Indian Ocean experiment on Intraseasonal Variability in the Year 2011(CINDY 2011) field campaign. The DSDs determined using a Joss–Waldvogel disdrometer,which was installed on the roof of the anti-rolling system of the R/V Mirai during stationary observation(25 September to 30 November 2011) at(8°S, 80.5°E), were analyzed. The vertical structure of precipitation was revealed by Tropical Rainfall Measuring Mission Precipitation Radar(version 7) data. While the general features of vertical structures of precipitation observed during the CINDY and Sumatra observation are similar, the intraseasonal variation of the DSD in response to the MJO at each location is slightly different. The DSDs during the active phase of the MJO are slightly broader than those during the inactive phase, which is indicated by a larger mass-weighted mean diameter value. Furthermore, the radar reflectivity during the active MJO phase is greater than that during the inactive phase at the same rainfall rate. The microphysical processes that generate large-sized drops over the ocean appear to be more dominant during the active MJO phase, in contrast to the observations made on land(Sumatra). This finding is consistent with the characteristics of radar reflectivity below the freezing level, storm height, bright band height, cloud effective radius, and aerosol optical depth.展开更多
The modulation of twin tropical cyclogenesis in the Indian-western Pacific Oceans by the Madden-Julian Oscillation (MJO) during the onset period of 1997/98 ENSO is explored for the period of September 1996 to June 199...The modulation of twin tropical cyclogenesis in the Indian-western Pacific Oceans by the Madden-Julian Oscillation (MJO) during the onset period of 1997/98 ENSO is explored for the period of September 1996 to June 1997 based on daily OLR, NCEP/NCAR wind vector, and JTWC best track datasets. The MJO westerly wind burst associated with its eastward propagation can result in a series of tropical cyclogeneses in a multi-day interval. Only in the transition seasons are pairs of tropical cyclones observed in both the tropical sectors of the Indian-western Pacific Oceans. Two remarkable twin tropical cyclogeneses probably modulated by the MJO westerly wind burst are found: one is observed in the Indian Ocean in the middle of October 1996, and the other is observed in the Western Pacific Ocean in late May 1997. The twin tropical cyclogenesis in mid-October 1996 is observed when the super cloud cluster separates into two isolated clusters by the enhanced westerly wind, which is accompanied by two independent vortices in the equatorial tropical sectors. The other one, in late-May 1997, however, is characterized by one cyclonic flow that later results in another cyclonic cell in its opposite equatorial sector. Thus, there are two very important conditions for twin cyclogenesis: one is the MJO westerly wind straddling the equator, and the other is the integral super cloud cluster, which later splits into two cloud convective clusters with independent vortices.展开更多
Tropical intraseasonal oscillation （including the Madden-Julian oscillation） is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect ...Tropical intraseasonal oscillation （including the Madden-Julian oscillation） is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect weather and climate both inside and outside the tropical region. The study of these phenomena therefore represents one of the frontiers of atmospheric sciences. This review aims to synthesize and summarize studies of intraseasonal oscillation （ISO） by Chinese scientists within the last 5-10 years. We focus particularly on ISO＇s mechanisms, its numerical simulations （especially the impacts of diabatic heating profiles）, relation- ships and interactions with ENSO （especially over the western Pacific）, impacts on tropical cyclone genesis and tracks over the northwestern Pacific, and influences on the onset and activity of the South and East Asian monsoons （especially rainfall over China）. Among these, focuses of ongoing research and unresolved issues related to ISO are also discussed.展开更多
The characteristics of droughts and floods in China during the summers（May–August）of 2016 and 1998 were compared in great detail,together with the associated atmospheric circulations and external-forcing factors.Fo...The characteristics of droughts and floods in China during the summers（May–August）of 2016 and 1998 were compared in great detail,together with the associated atmospheric circulations and external-forcing factors.Following results are obtained.（1）The precipitation was mostly above normal in China in summer 2016,with two main rainfall belts located in the Yangtze River valley（YRV）and North China.Compared with 1998,a similar rainfall belt was located over the YRV,with precipitation 100%and more above normal.However,the seasonal processes of Meiyu were different.A typical＂Secondary Meiyu＂occurred in 1998,whereas dry conditions dominated the YRV in2016.（2）During May–July 2016,the Ural high was weaker than normal,but it was stronger than normal in 1998.This difference resulted from fairly different distributions of sea surface temperature anomalies（SSTAs）over the North Atlantic Ocean during the preceding winter and spring of the two years.（3）Nonetheless,tropical and subtropical circulation systems were much more similar in May–July of 2016 and 1998.The circulation systems in both years were characterized by a stronger than normal and more westward-extending western Pacific subtropical high（WPSH）,a weaker than normal East Asian summer monsoon（EASM）,and anomalous convergence of moisture flux in the mid and lower reaches of the YRV.These similar circulation anomalies were attributed to the similar tropical SSTA pattern in the preceding seasons,i.e.,the super El Ni？o and strong warming in the tropical Indian Ocean.（4）Significant differences in the circulation pattern were observed in August between the two years.The WPSH broke up in August 2016,with its western part being combined with the continental high and persistently dominating eastern China.The EASM suddenly became stronger,and dry conditions prevailed in the YRV.On the contrary,the EASM was weaker in August 1998 and the＂Secondary Meiyu＂took place in the YRV.The Madden–Julian Oscillation（MJO）was extremely active in August 2016 and stayed in western Pacific for 25 days.It triggered frequent tropical cyclone activities and further influenced the significant turning of tropical and subtropical circulations in August2016.In contrast,the MJO was active over the tropical Indian Ocean in August 1998,conducive to the maintenance of a strong WPSH.Alongside the above oceanic factors and atmospheric circulation anomalies,the thermal effect of snow cover over the Qinghai–Tibetan Plateau from the preceding winter to spring in 2016 was much weaker than that in 1998.This may explain the relatively stronger EASM and more abundant precipitation in North China in 2016than those in 1998.展开更多
基金financially supported by the Ministry of Research, Technology and Higher Education of the Republic of Indonesia under International Joint Collaboration and Scientific Publication Grant No. 02/UN.16.1.17/PP.KLN/LPPM/2017
文摘To date, the intraseasonal variation of raindrop size distribution(DSD) in response to the Madden–Julian Oscillation(MJO) has been examined only over the Indonesian Maritime Continent, particularly in Sumatra. This paper presents the intraseasonal variation of DSD over the Indian Ocean during the Cooperative Indian Ocean experiment on Intraseasonal Variability in the Year 2011(CINDY 2011) field campaign. The DSDs determined using a Joss–Waldvogel disdrometer,which was installed on the roof of the anti-rolling system of the R/V Mirai during stationary observation(25 September to 30 November 2011) at(8°S, 80.5°E), were analyzed. The vertical structure of precipitation was revealed by Tropical Rainfall Measuring Mission Precipitation Radar(version 7) data. While the general features of vertical structures of precipitation observed during the CINDY and Sumatra observation are similar, the intraseasonal variation of the DSD in response to the MJO at each location is slightly different. The DSDs during the active phase of the MJO are slightly broader than those during the inactive phase, which is indicated by a larger mass-weighted mean diameter value. Furthermore, the radar reflectivity during the active MJO phase is greater than that during the inactive phase at the same rainfall rate. The microphysical processes that generate large-sized drops over the ocean appear to be more dominant during the active MJO phase, in contrast to the observations made on land(Sumatra). This finding is consistent with the characteristics of radar reflectivity below the freezing level, storm height, bright band height, cloud effective radius, and aerosol optical depth.
基金supported by the CATT,Japanthe Scientific Research Foundation for the R.eturned Overseas Chinese Scholars,State Ed-ucation MinistryLASG,Institute of Atmospheric Physics,Chinese Academy of Sciences.
文摘The modulation of twin tropical cyclogenesis in the Indian-western Pacific Oceans by the Madden-Julian Oscillation (MJO) during the onset period of 1997/98 ENSO is explored for the period of September 1996 to June 1997 based on daily OLR, NCEP/NCAR wind vector, and JTWC best track datasets. The MJO westerly wind burst associated with its eastward propagation can result in a series of tropical cyclogeneses in a multi-day interval. Only in the transition seasons are pairs of tropical cyclones observed in both the tropical sectors of the Indian-western Pacific Oceans. Two remarkable twin tropical cyclogeneses probably modulated by the MJO westerly wind burst are found: one is observed in the Indian Ocean in the middle of October 1996, and the other is observed in the Western Pacific Ocean in late May 1997. The twin tropical cyclogenesis in mid-October 1996 is observed when the super cloud cluster separates into two isolated clusters by the enhanced westerly wind, which is accompanied by two independent vortices in the equatorial tropical sectors. The other one, in late-May 1997, however, is characterized by one cyclonic flow that later results in another cyclonic cell in its opposite equatorial sector. Thus, there are two very important conditions for twin cyclogenesis: one is the MJO westerly wind straddling the equator, and the other is the integral super cloud cluster, which later splits into two cloud convective clusters with independent vortices.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2010CB950400 and 2013CB956200)
文摘Tropical intraseasonal oscillation （including the Madden-Julian oscillation） is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect weather and climate both inside and outside the tropical region. The study of these phenomena therefore represents one of the frontiers of atmospheric sciences. This review aims to synthesize and summarize studies of intraseasonal oscillation （ISO） by Chinese scientists within the last 5-10 years. We focus particularly on ISO＇s mechanisms, its numerical simulations （especially the impacts of diabatic heating profiles）, relation- ships and interactions with ENSO （especially over the western Pacific）, impacts on tropical cyclone genesis and tracks over the northwestern Pacific, and influences on the onset and activity of the South and East Asian monsoons （especially rainfall over China）. Among these, focuses of ongoing research and unresolved issues related to ISO are also discussed.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2013CB430203)China Meteorological Administration Special Public Welfare Research Fund(GYHY201306033 and GYHY201406001)National Natural Science Foundation of China(41130960)
文摘The characteristics of droughts and floods in China during the summers（May–August）of 2016 and 1998 were compared in great detail,together with the associated atmospheric circulations and external-forcing factors.Following results are obtained.（1）The precipitation was mostly above normal in China in summer 2016,with two main rainfall belts located in the Yangtze River valley（YRV）and North China.Compared with 1998,a similar rainfall belt was located over the YRV,with precipitation 100%and more above normal.However,the seasonal processes of Meiyu were different.A typical＂Secondary Meiyu＂occurred in 1998,whereas dry conditions dominated the YRV in2016.（2）During May–July 2016,the Ural high was weaker than normal,but it was stronger than normal in 1998.This difference resulted from fairly different distributions of sea surface temperature anomalies（SSTAs）over the North Atlantic Ocean during the preceding winter and spring of the two years.（3）Nonetheless,tropical and subtropical circulation systems were much more similar in May–July of 2016 and 1998.The circulation systems in both years were characterized by a stronger than normal and more westward-extending western Pacific subtropical high（WPSH）,a weaker than normal East Asian summer monsoon（EASM）,and anomalous convergence of moisture flux in the mid and lower reaches of the YRV.These similar circulation anomalies were attributed to the similar tropical SSTA pattern in the preceding seasons,i.e.,the super El Ni？o and strong warming in the tropical Indian Ocean.（4）Significant differences in the circulation pattern were observed in August between the two years.The WPSH broke up in August 2016,with its western part being combined with the continental high and persistently dominating eastern China.The EASM suddenly became stronger,and dry conditions prevailed in the YRV.On the contrary,the EASM was weaker in August 1998 and the＂Secondary Meiyu＂took place in the YRV.The Madden–Julian Oscillation（MJO）was extremely active in August 2016 and stayed in western Pacific for 25 days.It triggered frequent tropical cyclone activities and further influenced the significant turning of tropical and subtropical circulations in August2016.In contrast,the MJO was active over the tropical Indian Ocean in August 1998,conducive to the maintenance of a strong WPSH.Alongside the above oceanic factors and atmospheric circulation anomalies,the thermal effect of snow cover over the Qinghai–Tibetan Plateau from the preceding winter to spring in 2016 was much weaker than that in 1998.This may explain the relatively stronger EASM and more abundant precipitation in North China in 2016than those in 1998.
