As the primary interannual signal of variability in the tropical ocean-atmosphere interaction, the El Ni?o-Southern Oscillation has a considerable impact on tropical cyclone(TC) activity over the western North Pacific...As the primary interannual signal of variability in the tropical ocean-atmosphere interaction, the El Ni?o-Southern Oscillation has a considerable impact on tropical cyclone(TC) activity over the western North Pacific(WNP). Both 2018 and2021 were La Ni?a decay years, but TC activity over the WNP during the two summers(June–August) showed notable differences. In 2018, summer TC activity was unusually high with a total of 18 TCs, and the region of TC genesis was mainly in the central and eastern WNP. In contrast, only 9 TCs were generated in summer 2021, and the region of TC genesis was primarily in the western WNP. By comparing the characteristics of the large-scale environmental conditions over the regions of TC genesis, the thermal factors of the tropical oceans, and the activity of the Madden-Julian Oscillation(MJO), this study revealed the possible causes for the marked differences in TC genesis over the WNP during the two summers, which both had a similar background of La Ni?a decay. The Indian Ocean Basin Mode(IOBM) transitioned of a cold anomaly in the winter of 2017/2018and persisted until summer 2018. At the same time, the Pacific Meridional Mode(PMM) maintained a positive phase, leading to eastward and northward displacement of the Western Pacific Subtropical High in summer, and eastward extension of the tropical monsoon trough, which presented conditions conducive to TC genesis over the Northwest Pacific. Moreover, the days when the MJO stagnated in phases 5 and 6 in the summer of 2018 increased by approximately 150% relative to climatological state,providing dynamic conditions favorable for TC formation. In 2021, the IOBM quickly turned to a warm anomaly in March and persisted until summer, whereas the PMM became a negative phase in January and remained so until summer. At the same time,the MJO stagnated in phases 2 and 3 for up to 47 days, with the center of convection located over the western Maritime Continent, producing conditions unconducive to TC genesis over the Northwest Pacific. Thus, despite being under a similar background of La Ni?a decaying year, the distinct evolutions of the IOBM, PMM, and MJO in spring and summer of 2018 and2021 were the main causes of the notable differences in TC activity over the WNP during these two summers, and the anomalies in IOBM and MJO contributed more significantly than those of the PMM.展开更多
In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Mo...In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Most of these TCs travelled northwest to northward,bringing in heavy rainfall and strong winds in eastern China and Japan.The present study investigates the impacts of decaying La Nina and intraseasonal oscillation(ISO)on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses.It is found that the La Nina episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST)over central–western Pacific,lower sea level pressure and 500-hPa geopotential height over WNP,and abnormally strong convective activities over the western Pacific in summer 2018.These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer.Detailed examination reveals that the monsoon trough was located further north and east,inducing more TCs in northern and eastern WNP;and the more eastward WNP subtropical high as well as the significant wave train with a"-+-+"height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC tracks.Further analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO)occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO)was also active over WNP,propagating northward significantly,corresponding to the more northward TC tracks.The MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere,conducive to TC occurrences.In a word,the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Nina,and the MJO and BSISO;their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.展开更多
We evaluated the sea surface temperature(SST)products derived from the visible infrared radiometer on board the Fengyun-3 satellites(FY-3/VIRR)during 2016-2018 from the perspective of climate applications.The data had...We evaluated the sea surface temperature(SST)products derived from the visible infrared radiometer on board the Fengyun-3 satellites(FY-3/VIRR)during 2016-2018 from the perspective of climate applications.The data had previously been reprocessed by the National Satellite Meteorological Center of China Meteorological Administration based on an updated SST retrieval algorithm.The overall consistency between the FY-3/VIRR SST data and the optimum interpolation SST version 2.1(OIv2.1)was better for monthly means than for pentad means,and showed a clear dependence on the season and location.There was better consistency in winter than in summer,and in the tropical central-eastern Pacific than in the western Pacific warm pool,tropical North Indian Ocean,and tropical Atlantic Ocean.The monthly deviation of the global average SST anomaly was-0.03±0.07℃ and the average root-meansquare errors(RMSEs)presented clear seasonal fluctuations with a maximum of approximately 0.5℃ in summer.The poor consistency of the FY-3/VIRR SST in summer may be partially attributed to the bias of the OIv2.1 data in global oceans(especially the Indian Ocean)as a result of the spatially heterogeneous in situ measurements from ships,buoys,and Argo floats.Convective activities and clouds in the tropics may also influence the accuracy of the FY-3/VIRR SST retrievals.The Nino SST indices based on both FY-3/VIRR and OIv2.1 SST data displayed a generally similar evolution,including the start and end of El Nino and La Nina events and their amplitudes,although the deviations were slightly larger when the Pacific SST anomaly was in the neutral state of the El Nino-Southern Oscillation(ENSO).The deviations varied greatly with season in the tropical Indian and Atlantic oceans,suggesting the need to perform further analyses and validation of the FY-3/VIRR SST products in these two basins.展开更多
基金supported by the National Key R&D Program of China (Grant No.2022YFF0801604)the National Natural Science Foundation of China (Grant No.42175056)+4 种基金the Provincial Natural Science Foundation of Anhui (Grant No.2208085UQ10)the Civilian Space Programme of China (Grant No.Do40305)the Fengyun Application Pioneering Project (Grant No.FY-APP-ZX-2023.02)the China Meteorological Administration Innovation and Development Project (Grant No.CXFZ2024J048)the China Meteorological Administration Youth Innovation Team (Grant No.CMA2024QN06)。
文摘As the primary interannual signal of variability in the tropical ocean-atmosphere interaction, the El Ni?o-Southern Oscillation has a considerable impact on tropical cyclone(TC) activity over the western North Pacific(WNP). Both 2018 and2021 were La Ni?a decay years, but TC activity over the WNP during the two summers(June–August) showed notable differences. In 2018, summer TC activity was unusually high with a total of 18 TCs, and the region of TC genesis was mainly in the central and eastern WNP. In contrast, only 9 TCs were generated in summer 2021, and the region of TC genesis was primarily in the western WNP. By comparing the characteristics of the large-scale environmental conditions over the regions of TC genesis, the thermal factors of the tropical oceans, and the activity of the Madden-Julian Oscillation(MJO), this study revealed the possible causes for the marked differences in TC genesis over the WNP during the two summers, which both had a similar background of La Ni?a decay. The Indian Ocean Basin Mode(IOBM) transitioned of a cold anomaly in the winter of 2017/2018and persisted until summer 2018. At the same time, the Pacific Meridional Mode(PMM) maintained a positive phase, leading to eastward and northward displacement of the Western Pacific Subtropical High in summer, and eastward extension of the tropical monsoon trough, which presented conditions conducive to TC genesis over the Northwest Pacific. Moreover, the days when the MJO stagnated in phases 5 and 6 in the summer of 2018 increased by approximately 150% relative to climatological state,providing dynamic conditions favorable for TC formation. In 2021, the IOBM quickly turned to a warm anomaly in March and persisted until summer, whereas the PMM became a negative phase in January and remained so until summer. At the same time,the MJO stagnated in phases 2 and 3 for up to 47 days, with the center of convection located over the western Maritime Continent, producing conditions unconducive to TC genesis over the Northwest Pacific. Thus, despite being under a similar background of La Ni?a decaying year, the distinct evolutions of the IOBM, PMM, and MJO in spring and summer of 2018 and2021 were the main causes of the notable differences in TC activity over the WNP during these two summers, and the anomalies in IOBM and MJO contributed more significantly than those of the PMM.
基金the National Key Research and Development Program of China(2018YFC1506001)National Basic Research(973)Program of China(2015CB453203)National Natural Science Foundation of China(41275073 and 41805067)
文摘In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Most of these TCs travelled northwest to northward,bringing in heavy rainfall and strong winds in eastern China and Japan.The present study investigates the impacts of decaying La Nina and intraseasonal oscillation(ISO)on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses.It is found that the La Nina episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST)over central–western Pacific,lower sea level pressure and 500-hPa geopotential height over WNP,and abnormally strong convective activities over the western Pacific in summer 2018.These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer.Detailed examination reveals that the monsoon trough was located further north and east,inducing more TCs in northern and eastern WNP;and the more eastward WNP subtropical high as well as the significant wave train with a"-+-+"height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC tracks.Further analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO)occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO)was also active over WNP,propagating northward significantly,corresponding to the more northward TC tracks.The MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere,conducive to TC occurrences.In a word,the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Nina,and the MJO and BSISO;their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.
基金Supported by the Guangdong Major Project of Basic and Applied Basic Research(2020B0301030004)National Key Reseach and Development Program of China(2018YFB0504905 and 2018YFB0504900)。
文摘We evaluated the sea surface temperature(SST)products derived from the visible infrared radiometer on board the Fengyun-3 satellites(FY-3/VIRR)during 2016-2018 from the perspective of climate applications.The data had previously been reprocessed by the National Satellite Meteorological Center of China Meteorological Administration based on an updated SST retrieval algorithm.The overall consistency between the FY-3/VIRR SST data and the optimum interpolation SST version 2.1(OIv2.1)was better for monthly means than for pentad means,and showed a clear dependence on the season and location.There was better consistency in winter than in summer,and in the tropical central-eastern Pacific than in the western Pacific warm pool,tropical North Indian Ocean,and tropical Atlantic Ocean.The monthly deviation of the global average SST anomaly was-0.03±0.07℃ and the average root-meansquare errors(RMSEs)presented clear seasonal fluctuations with a maximum of approximately 0.5℃ in summer.The poor consistency of the FY-3/VIRR SST in summer may be partially attributed to the bias of the OIv2.1 data in global oceans(especially the Indian Ocean)as a result of the spatially heterogeneous in situ measurements from ships,buoys,and Argo floats.Convective activities and clouds in the tropics may also influence the accuracy of the FY-3/VIRR SST retrievals.The Nino SST indices based on both FY-3/VIRR and OIv2.1 SST data displayed a generally similar evolution,including the start and end of El Nino and La Nina events and their amplitudes,although the deviations were slightly larger when the Pacific SST anomaly was in the neutral state of the El Nino-Southern Oscillation(ENSO).The deviations varied greatly with season in the tropical Indian and Atlantic oceans,suggesting the need to perform further analyses and validation of the FY-3/VIRR SST products in these two basins.
