Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the El Nino and La Nifia events. The result indicates that the typhoon tends to be inactive in...Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the El Nino and La Nifia events. The result indicates that the typhoon tends to be inactive in the El Nifio years and active in the La Nina years and it is also dependent on the onset and ending time and intensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the El Nifio and La Nina years and the time-lag correlation between the frequency and sea surface temperature (SST). useful information is provided for the prediction of typhoon occurrence. In addition, the singular values disassemble (SVD) method is applied to study the correlation between the geopotential field and SST field. The result shows that the air-sea coupling in the El Nino years is unfavorable for the typhoon to develop, which take place with a smaller number. Opposite situations are found with the La Nina years.展开更多
The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distr...The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distribution of the 20℃ isotherm, which is usually the replacement of thermocline. From the distribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved surface we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we found that, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays there several months and then to (urn north, usually moving westward near 10°N to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strong enough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive (negative) anomaly signal in equatorial western Pacific coexists with negative (positive) anomaly signal near 10°N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite directions. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino/ La Nina event.展开更多
Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Ni na events on the high and low flow ...Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Ni na events on the high and low flow in the upper Yellow River are discussed. The results show El Nino and La Nina events possess consanguineous relationship wi th runoff in the upper Yellow River. As a whole, the probability of low fl ow occurrence in the upper Yellow River is relatively great along wit h the occurrence of El Nino event. Moreover, the flood in the upper Yellow River occurs frequently with the occurrence of La Nina event. Besides, the results also show dissimilarity of El Nino event occurri ng time exerts greater impact on high flow and low flow in the uppe r Yellow River, that is, the probability of drought will be greater in the sam e year if El Nino event occurs in spring, the high-flow may happen in this y ear if El Nino occurs in summer or autumn; the longer the continuous period of El Nino is, the lower the runoff in the upper Yellow River is.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
文摘Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the El Nino and La Nifia events. The result indicates that the typhoon tends to be inactive in the El Nifio years and active in the La Nina years and it is also dependent on the onset and ending time and intensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the El Nifio and La Nina years and the time-lag correlation between the frequency and sea surface temperature (SST). useful information is provided for the prediction of typhoon occurrence. In addition, the singular values disassemble (SVD) method is applied to study the correlation between the geopotential field and SST field. The result shows that the air-sea coupling in the El Nino years is unfavorable for the typhoon to develop, which take place with a smaller number. Opposite situations are found with the La Nina years.
基金This work was supported by the National Natural Science Foundation of China under Grant No.40126002.
文摘The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distribution of the 20℃ isotherm, which is usually the replacement of thermocline. From the distribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved surface we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we found that, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays there several months and then to (urn north, usually moving westward near 10°N to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strong enough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive (negative) anomaly signal in equatorial western Pacific coexists with negative (positive) anomaly signal near 10°N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite directions. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino/ La Nina event.
基金Knowledge Innovation Project of Cold and Arid Regions Environmental and Engineering Research Institute of CAS, No.210100, No.210016 Knowledge Innovation Project of CAS, No.KZCX1-10-03National Natural Science Foundation of China, No.4
文摘Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Ni na events on the high and low flow in the upper Yellow River are discussed. The results show El Nino and La Nina events possess consanguineous relationship wi th runoff in the upper Yellow River. As a whole, the probability of low fl ow occurrence in the upper Yellow River is relatively great along wit h the occurrence of El Nino event. Moreover, the flood in the upper Yellow River occurs frequently with the occurrence of La Nina event. Besides, the results also show dissimilarity of El Nino event occurri ng time exerts greater impact on high flow and low flow in the uppe r Yellow River, that is, the probability of drought will be greater in the sam e year if El Nino event occurs in spring, the high-flow may happen in this y ear if El Nino occurs in summer or autumn; the longer the continuous period of El Nino is, the lower the runoff in the upper Yellow River is.
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.
