In order to investigate the conversion of kinetic energy from a synoptic scale disturbance （SSD; period≤seven days） to a low-frequency fluctuation （LFF; period〉seven days）, the budget equation of the LFF kinetic...In order to investigate the conversion of kinetic energy from a synoptic scale disturbance （SSD; period≤seven days） to a low-frequency fluctuation （LFF; period〉seven days）, the budget equation of the LFF kinetic energy is derived. The energy conversion is then calculated and analyzed for the summers of 1997 and 1999. The results show that the energy conversion from the SSD to the LFF is obviously enhanced in the middle and lower troposphere during the heavy rainfall, suggesting this to be one of mechanisms inducing the heavy rainfall, although the local LFF kinetic energy may not be enhanced.展开更多
The Atlantic inflow in the Fram Strait（78°50′N） has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant ...The Atlantic inflow in the Fram Strait（78°50′N） has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3–16 d, occurs mainly in winter and spring（from January to April） and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement（weakening） of Atlantic inflow in the Fram Strait is accompanied by less（more）polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport,leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean.展开更多
This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by...This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by the nonlinear effects of barotropic and baroclinic instability and advection of ambient large-scale flow.Also, foregoing nonlinear effects on the speed of development and decay of the system are presented in the processes deviating from or approaching to equilibrium state.It has been found that there is a resonance phenomenon between the time-oscillation of heat source and the atmospheric disturbance.展开更多
Following Wu and Chen(1989), in terms of the elliptical differential equation with mean meridional stream function, an equation similar in form to that developed by Kuo (1956) and by use of time average statistics of ...Following Wu and Chen(1989), in terms of the elliptical differential equation with mean meridional stream function, an equation similar in form to that developed by Kuo (1956) and by use of time average statistics of atmospheric circulation in wavenumber domains at the same intervals of time, a study is made of the con- tribution of the internal forcing of the atmosphere in two space scales to mean meridional circulation. Re- sults show that planetary waves have considerable influence on the intensity of the upper center of the bi- Hadley cell, and, in contrast, synoptic-scale waves exert vital effect on the Ferrel cell, and that in the Northern Hamisphere(NH)such internal forcings by planetary- and synoptic-scale waves are comparable on mean merid- ional circulations whereas the latter contribute far more than the former in the Southern Hemisphere (SH). Further, in the northern winter (summer)the contribution of heat (angular momentum) transport of planetary waves allows the descending (ascending) branch to occur as far as around 40°N, some kind of effect that makes quite important contribution to the winter (summer) monsoon circulation in eastern Asia.展开更多
An observational study is presented to confirm that the life cycle of blocking associated with synoptic—scale eddies is a transfer process between dispersion and nondispersion. In addition, numerical experiments are ...An observational study is presented to confirm that the life cycle of blocking associated with synoptic—scale eddies is a transfer process between dispersion and nondispersion. In addition, numerical experiments are conducted. It is found that the synoptic—scale eddies seem to play a dominant role in the amplification of blocking, while the topography effect appears to play a phase-locking role. At the same time, the synoptic eddies tend to split into two branches during the onset of blocking. This supports the observational results obtained.展开更多
In this study,power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heav...In this study,power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China.Two heavy rainfall episodes are selected during the months of April-June 2008-15,which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively.Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea(SCS)at the quasi-biweekly scale with 15.1%variance contributions,and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastward-moving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastwardpropagating anticyclonic anomaly from higher latitudes with 35.2%variance contribution.In contrast,the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasi-monthly scale with 23.2%variance contributions to the total rainfall variance,which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China,respectively.At the synoptic scale,it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3%variance contributions.In both cases,the lower-tropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions;it is the above synoptic,quasi-biweekly or quasimonthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China.展开更多
Based on NECP/NCAR reanalysis data and daily temperature data of 743 stations in China, possible causes of winter extreme low temperature events are explored from the perspective of the synoptic-scale transient wave (...Based on NECP/NCAR reanalysis data and daily temperature data of 743 stations in China, possible causes of winter extreme low temperature events are explored from the perspective of the synoptic-scale transient wave (STW) activity. Results suggest that there is a close linkage between STW activity and extreme low temperature events. Firstly, case studies are carried out on the years with the most and least frequent extreme low temperature events. In the winter of 1967, two strong and stable STW trains were maintained over the Eurasian continent, and the strong westerly jet provided a good channel for the propagation of STW. Located in the downstream area of those two STW trains, China was significantly influenced by them and experienced frequent extreme low temperature events. Further analysis suggest that the intensity of the upstream transient wave and the areas where the transient waves reached are completely consistent with the intensity of extreme low temperature and the areas where frequent extreme low temperature event happened, respectively. In contrast, Westerly jet in 2006 was weaker and the path of transient wave propagation was shorter and weaker, resulting in the low frequency of extreme temperature. Secondly, in their long term variations, westerly jet is also consistent with the extreme low temperature frequency. The transient wave path changed before and after the 1980s. Further investigation suggests that transient wave intensities in key areas exhibit in-phase changes with the frequency of extreme low temperature events in the periods of 1959-1979 and 1986-2006. Meanwhile, the main features of transient wave activities in high-frequent years and low-frequent years of extreme low temperature events are similar to those of 1967 and 2006, respectively. Results indicate that winter extreme low temperature events in China have a very close relationship with the transient wave activity, implying the propagation and activity of STW are important factors affecting the winter extreme low temperature events in China. This study can also provide a new clue for better understanding the mechanisms of the extreme temperature events.展开更多
文摘In order to investigate the conversion of kinetic energy from a synoptic scale disturbance （SSD; period≤seven days） to a low-frequency fluctuation （LFF; period〉seven days）, the budget equation of the LFF kinetic energy is derived. The energy conversion is then calculated and analyzed for the summers of 1997 and 1999. The results show that the energy conversion from the SSD to the LFF is obviously enhanced in the middle and lower troposphere during the heavy rainfall, suggesting this to be one of mechanisms inducing the heavy rainfall, although the local LFF kinetic energy may not be enhanced.
基金The Global Change Research Program of China under contract No.2015CB953900the General Program of National Natural Science Foundation of China under contract No.41276197+2 种基金the Natural Science Foundation of Zhejiang Province under contract Nos LY18D060004 and LQ18D060001the Foundation of Zhejiang Education Department under contract No.1260KZ0417982the Talent Start Foundation of Zhejiang Gongshang University under contract Nos 1260XJ2317015 and1260XJ2117015
文摘The Atlantic inflow in the Fram Strait（78°50′N） has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3–16 d, occurs mainly in winter and spring（from January to April） and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement（weakening） of Atlantic inflow in the Fram Strait is accompanied by less（more）polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport,leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean.
文摘This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by the nonlinear effects of barotropic and baroclinic instability and advection of ambient large-scale flow.Also, foregoing nonlinear effects on the speed of development and decay of the system are presented in the processes deviating from or approaching to equilibrium state.It has been found that there is a resonance phenomenon between the time-oscillation of heat source and the atmospheric disturbance.
基金The study is supported partially by National Natural Science Foundation of Chinapartially by the State Meteorological Administration Monsoon Research Funds.
文摘Following Wu and Chen(1989), in terms of the elliptical differential equation with mean meridional stream function, an equation similar in form to that developed by Kuo (1956) and by use of time average statistics of atmospheric circulation in wavenumber domains at the same intervals of time, a study is made of the con- tribution of the internal forcing of the atmosphere in two space scales to mean meridional circulation. Re- sults show that planetary waves have considerable influence on the intensity of the upper center of the bi- Hadley cell, and, in contrast, synoptic-scale waves exert vital effect on the Ferrel cell, and that in the Northern Hamisphere(NH)such internal forcings by planetary- and synoptic-scale waves are comparable on mean merid- ional circulations whereas the latter contribute far more than the former in the Southern Hemisphere (SH). Further, in the northern winter (summer)the contribution of heat (angular momentum) transport of planetary waves allows the descending (ascending) branch to occur as far as around 40°N, some kind of effect that makes quite important contribution to the winter (summer) monsoon circulation in eastern Asia.
基金Acknowledgments. This research was supported by the TRAPOYT and by the National Natural Science Foun-dation of China under Grant No. 40023001.
文摘An observational study is presented to confirm that the life cycle of blocking associated with synoptic—scale eddies is a transfer process between dispersion and nondispersion. In addition, numerical experiments are conducted. It is found that the synoptic—scale eddies seem to play a dominant role in the amplification of blocking, while the topography effect appears to play a phase-locking role. At the same time, the synoptic eddies tend to split into two branches during the onset of blocking. This supports the observational results obtained.
基金supported by Special project for Key Technology Development of Meteorological Forecast Operation [Grant No. YBGJXM (2019) 04-03]the National Key R&D Program of China (Grant No. 2018YFC1507403)+1 种基金the National Natural Science Foundation of China (Grant No. 41475043)the National Basic Research (973) Program of China (Grant Nos. 2014CB441402 and 2015CB954102)
文摘In this study,power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China.Two heavy rainfall episodes are selected during the months of April-June 2008-15,which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively.Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea(SCS)at the quasi-biweekly scale with 15.1%variance contributions,and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastward-moving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastwardpropagating anticyclonic anomaly from higher latitudes with 35.2%variance contribution.In contrast,the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasi-monthly scale with 23.2%variance contributions to the total rainfall variance,which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China,respectively.At the synoptic scale,it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3%variance contributions.In both cases,the lower-tropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions;it is the above synoptic,quasi-biweekly or quasimonthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China.
基金supported by National Science and Technology Supporting Program (Grant No.2007BAC29B03)Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Based on NECP/NCAR reanalysis data and daily temperature data of 743 stations in China, possible causes of winter extreme low temperature events are explored from the perspective of the synoptic-scale transient wave (STW) activity. Results suggest that there is a close linkage between STW activity and extreme low temperature events. Firstly, case studies are carried out on the years with the most and least frequent extreme low temperature events. In the winter of 1967, two strong and stable STW trains were maintained over the Eurasian continent, and the strong westerly jet provided a good channel for the propagation of STW. Located in the downstream area of those two STW trains, China was significantly influenced by them and experienced frequent extreme low temperature events. Further analysis suggest that the intensity of the upstream transient wave and the areas where the transient waves reached are completely consistent with the intensity of extreme low temperature and the areas where frequent extreme low temperature event happened, respectively. In contrast, Westerly jet in 2006 was weaker and the path of transient wave propagation was shorter and weaker, resulting in the low frequency of extreme temperature. Secondly, in their long term variations, westerly jet is also consistent with the extreme low temperature frequency. The transient wave path changed before and after the 1980s. Further investigation suggests that transient wave intensities in key areas exhibit in-phase changes with the frequency of extreme low temperature events in the periods of 1959-1979 and 1986-2006. Meanwhile, the main features of transient wave activities in high-frequent years and low-frequent years of extreme low temperature events are similar to those of 1967 and 2006, respectively. Results indicate that winter extreme low temperature events in China have a very close relationship with the transient wave activity, implying the propagation and activity of STW are important factors affecting the winter extreme low temperature events in China. This study can also provide a new clue for better understanding the mechanisms of the extreme temperature events.
