Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscilla...Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta- tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that in the winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone are mainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982— 1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonal changes of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinal progression or regression of about 40 day period.There are marked differences between propagat- ing passages of low frequency modes responsible for changes of subtropical jet stream in the normal year(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude show obvious phases.In general,the one in late winter is stronger than that in early winter,strongest one occurs in February.展开更多
Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman- CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near the equator are investigated.It is found ...Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman- CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near the equator are investigated.It is found that the theoretical results are in good agreement with the observational features of LFO.Besides,the planetary-scale LFO with the period of 30—60 d could be triggered by the Ekman-CISK mechanism,and the growth rate of perturbation with wave number 1 is in order of O (10^(-6)s^(-1)).The zonal propagation of LFO and the corresponding longitudinal-height structure of physical quantities are also discussed in detail.展开更多
In this paper. the coupling equations describing nonlinear three-wave interaction amongRossby waves including the forcing of an external vorticity source are obtained. Under certainconditions, the coupling equations w...In this paper. the coupling equations describing nonlinear three-wave interaction amongRossby waves including the forcing of an external vorticity source are obtained. Under certainconditions, the coupling equations with a constant amplitude forcing, the stability analysis indicates that when the amplitude of the external forcing increases to a certain extent, a pitchforkbifurcation occurs. Also. it is shown fi-o m numerical results that the bifurcation can lead to chaoticbehavior of' strange' attractor. For the obtained three-variable equation, when the amplitude ofmodulated external forcing gradually increases, a Period-doubling bifurcation is found to lead tochaotic behavior. Thus, in a nonlinear three-wave coupling model in the large-scale forcedbarotropic atmospheric flow, chaotic behavior can be observed. This chaotic behavior can explainin part 30-60-day low-flequency oscillations observed in mid-high latitudes.展开更多
Based on ECMWF daily grid point data in summer (May—August),1981,the distribution features of the source and sink of kinetic energy of atmosphere 30—60 day oscillation,including its horizontal distribution character...Based on ECMWF daily grid point data in summer (May—August),1981,the distribution features of the source and sink of kinetic energy of atmosphere 30—60 day oscillation,including its horizontal distribution characteristics and its vertical structure characteristics,are investigated systematically with diagnostic analysis methods over a latitude belt between 80°N and 60°S.Also,the probable reasons for the existence of the source and sink of low frequency kinetic energy (LFKE) are discussed preliminarily.Results show that the horizontal distribution of the sources and sinks of kinetic energy of atmospheric 30—60 day oscillation is extremely different.The significant sources and sinks of LFKE mainly exist in the oceans and the coastal regions of continents or islands in the mid-high latitudes.It is also found that,in the vertical direction,the sources and sinks of kinetic energy of 30—60 day oscillation display barotropic structure in the mid-high latitudes of both hemispheres,but dispaly baroclinic structure in the equtorial region,and in the horizontal direction, the sources and sinks mainly display zonal wave-like distribution.The source and sink of LFKE are determinded by ageostrophic wind effect,frictional effect,interaction between sub-grid-scale systems,nonlinear interaction,and the flux-divergence of LFKE transported by transient wind. There are some regional reasons for the generation of sources and sinks which are not completely identical in different areas.展开更多
30-60 day oscillations (also called intraseasonal oscillations )have been indicated in the early 1970s. A series of studies in the 1980s not only investigated the 30-60 day oscillations in the tropical atmosphere and ...30-60 day oscillations (also called intraseasonal oscillations )have been indicated in the early 1970s. A series of studies in the 1980s not only investigated the 30-60 day oscillations in the tropical atmosphere and revealed their structure characteristics and fundamental moving regularity, but also exposed the existence of these oscillations in展开更多
The propagation characteristics of the atmospheric low frequency （LF, 30-60 days） oscillation （LFO） around the Tibetan Plateau from troposphere to stratosphere and its relationship with the floods over the mid-low...The propagation characteristics of the atmospheric low frequency （LF, 30-60 days） oscillation （LFO） around the Tibetan Plateau from troposphere to stratosphere and its relationship with the floods over the mid-lower reaches of the Yangtze River in the summer of 1998 are studied, based on the GAME dataset from Meteorological Research Institute （MRI）/Japan Meteorological Agency, the TRMM satellite rainfall and the 730-station precipitation over China. The results show that the zonal propagation direction of LFOs in horizontal winds varies with seasons in the troposphere during May to August in 1998. The eastward propagation of LFOs is remarkable before the start of the rainy season in the Tibetan Plateau and the eastern Asian continent, while the westward propagation is significant after the start date. The northward LFOs from the south side of the plateau and the southward LFOs from the north are both significant before and after the start date. The plateau is a LFO sink in the meridional and zonal directions, but the west part of it is an intensifying area for the continual westward LFOs only after the start of the rainy season. Besides, the strongest LFOs occur at the tropopause （100 hPa） and rapidly decay after entering the stratosphere. The rainfall over the mid-low reaches of Yangtze River in the summer of 1998 exhibits two LFO cycles. According to the phases of the two rainfall LFO cycles, the composite analyses of precipitation distribution, LF circulations at 500 and 100 hPa, and LF vertical motion along 30°N are performed. It is the joint effect of the mid-upper tropospheric strong 30-60-day filtered cyclone （anticyclone） over the eastern plateau and the LFO anticyclone （cyclone） over the west subtropical Pacific that induces the whole layer LF descending （ascending） motion over the mid-lower reaches of Yangtze River, which provides the favorable condition for the break （maintenance） of precipitation.展开更多
Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of ...Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.展开更多
基金This work was supported by the National Natural Science Foundation of China.
文摘Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta- tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that in the winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone are mainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982— 1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonal changes of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinal progression or regression of about 40 day period.There are marked differences between propagat- ing passages of low frequency modes responsible for changes of subtropical jet stream in the normal year(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude show obvious phases.In general,the one in late winter is stronger than that in early winter,strongest one occurs in February.
基金This study was supported jointly by Chinese Academy of Sciences Key Project under Contract KZCX2-203 and National Natural Science Foundation of China under Grants 40125014 and 49805004.
文摘Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman- CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near the equator are investigated.It is found that the theoretical results are in good agreement with the observational features of LFO.Besides,the planetary-scale LFO with the period of 30—60 d could be triggered by the Ekman-CISK mechanism,and the growth rate of perturbation with wave number 1 is in order of O (10^(-6)s^(-1)).The zonal propagation of LFO and the corresponding longitudinal-height structure of physical quantities are also discussed in detail.
文摘In this paper. the coupling equations describing nonlinear three-wave interaction amongRossby waves including the forcing of an external vorticity source are obtained. Under certainconditions, the coupling equations with a constant amplitude forcing, the stability analysis indicates that when the amplitude of the external forcing increases to a certain extent, a pitchforkbifurcation occurs. Also. it is shown fi-o m numerical results that the bifurcation can lead to chaoticbehavior of' strange' attractor. For the obtained three-variable equation, when the amplitude ofmodulated external forcing gradually increases, a Period-doubling bifurcation is found to lead tochaotic behavior. Thus, in a nonlinear three-wave coupling model in the large-scale forcedbarotropic atmospheric flow, chaotic behavior can be observed. This chaotic behavior can explainin part 30-60-day low-flequency oscillations observed in mid-high latitudes.
基金This work is supported by the National Natural Science Foundation of China.
文摘Based on ECMWF daily grid point data in summer (May—August),1981,the distribution features of the source and sink of kinetic energy of atmosphere 30—60 day oscillation,including its horizontal distribution characteristics and its vertical structure characteristics,are investigated systematically with diagnostic analysis methods over a latitude belt between 80°N and 60°S.Also,the probable reasons for the existence of the source and sink of low frequency kinetic energy (LFKE) are discussed preliminarily.Results show that the horizontal distribution of the sources and sinks of kinetic energy of atmospheric 30—60 day oscillation is extremely different.The significant sources and sinks of LFKE mainly exist in the oceans and the coastal regions of continents or islands in the mid-high latitudes.It is also found that,in the vertical direction,the sources and sinks of kinetic energy of 30—60 day oscillation display barotropic structure in the mid-high latitudes of both hemispheres,but dispaly baroclinic structure in the equtorial region,and in the horizontal direction, the sources and sinks mainly display zonal wave-like distribution.The source and sink of LFKE are determinded by ageostrophic wind effect,frictional effect,interaction between sub-grid-scale systems,nonlinear interaction,and the flux-divergence of LFKE transported by transient wind. There are some regional reasons for the generation of sources and sinks which are not completely identical in different areas.
文摘30-60 day oscillations (also called intraseasonal oscillations )have been indicated in the early 1970s. A series of studies in the 1980s not only investigated the 30-60 day oscillations in the tropical atmosphere and revealed their structure characteristics and fundamental moving regularity, but also exposed the existence of these oscillations in
基金Supported by the General Project of National Natural Science Foundation under Grant No.40475029the Key Project of National Natural Science Foundation under Grant No.40633018.
文摘The propagation characteristics of the atmospheric low frequency （LF, 30-60 days） oscillation （LFO） around the Tibetan Plateau from troposphere to stratosphere and its relationship with the floods over the mid-lower reaches of the Yangtze River in the summer of 1998 are studied, based on the GAME dataset from Meteorological Research Institute （MRI）/Japan Meteorological Agency, the TRMM satellite rainfall and the 730-station precipitation over China. The results show that the zonal propagation direction of LFOs in horizontal winds varies with seasons in the troposphere during May to August in 1998. The eastward propagation of LFOs is remarkable before the start of the rainy season in the Tibetan Plateau and the eastern Asian continent, while the westward propagation is significant after the start date. The northward LFOs from the south side of the plateau and the southward LFOs from the north are both significant before and after the start date. The plateau is a LFO sink in the meridional and zonal directions, but the west part of it is an intensifying area for the continual westward LFOs only after the start of the rainy season. Besides, the strongest LFOs occur at the tropopause （100 hPa） and rapidly decay after entering the stratosphere. The rainfall over the mid-low reaches of Yangtze River in the summer of 1998 exhibits two LFO cycles. According to the phases of the two rainfall LFO cycles, the composite analyses of precipitation distribution, LF circulations at 500 and 100 hPa, and LF vertical motion along 30°N are performed. It is the joint effect of the mid-upper tropospheric strong 30-60-day filtered cyclone （anticyclone） over the eastern plateau and the LFO anticyclone （cyclone） over the west subtropical Pacific that induces the whole layer LF descending （ascending） motion over the mid-lower reaches of Yangtze River, which provides the favorable condition for the break （maintenance） of precipitation.
文摘Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.
