A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energ...A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energy of mean flow in terms of ECWMF daily 500 hPa grid data in winter, indicating that the energy transportation is closely associated with the westerly jet position, with zonal (meridional) propagation in the strong (weak) wind region, that considerable conversion of barotropic energy occurs at the jet exit region where low-frequency oscillation gains energy from the mean flow, leading to maximum kinetic energy for the oscillation observed there, which is marked by evident barotropy in striking contrast to the baroclinicity at low latitudes and that the teleconnection core is related to the center of action in the atmosphere and bound up with the pattern of the west wind.展开更多
Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current(SCSWC) in the northern South China Sea(NSCS) during winter monsoon relaxation. The model reproduce...Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current(SCSWC) in the northern South China Sea(NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea(SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.展开更多
By using the low-spectral model simplified from quasi-geostrophic approximation two-level model,we obtained the result that the equivalent barotropic state is an equilibrium state of the atmosphere in that model,and d...By using the low-spectral model simplified from quasi-geostrophic approximation two-level model,we obtained the result that the equivalent barotropic state is an equilibrium state of the atmosphere in that model,and discussed the conditions needed for existing the Rossby wave possessing the equivalent barotropic structure.And then we derived the oscillation equation reflecting the phase change of Rossby wave between higher and lower levels from the basic state of equivalent barotropic stationary Rossby wave,indicating the relations between the change of difference of phase at higher and lower levels and the disturbance of vertical shear,the amplitude disturbance of the part of waves of stream function and thermal wind stream function on the average level (A′ and B′).It is concluded that the inter-transformation exists between Rossby waves possessing the equivalent barotropic and baroclinic structure.展开更多
A two-dimensional,semi-geostrophic numerical model incorporating the tropopause and stratosphere is used to investigate the effects of a positive potential vorticity anomaly and latent heat release on the frontogeneti...A two-dimensional,semi-geostrophic numerical model incorporating the tropopause and stratosphere is used to investigate the effects of a positive potential vorticity anomaly and latent heat release on the frontogenetic process and the structure of the resulting frontal zone.It is demonstrated that(1)the inclusion of tropopause and stratosphere significantly changes the frontal structure only in the upper levels;(2)a clearly defined quasi-equivalent barotropic structure and a region of upward motion of finite width appear when a positive potential vorticity anomaly exists on the warm side of the maximum baroclinity in the lower troposphere,especially when it is located on the south edge of the baroclinic zone;(3)the above mentioned structure deteriorates as the frontogenesis proceeds in a dry atmosphere but can be maintained in a moist frontogenetic process with condensational heating;(4)the combination of a positive potential vorticity anomaly and the latent heat release is able to accelerate the frontogenesis significantly with the time needed to form an intense frontal zone reduced to less than 15 h.The results have significant theoretical importance in understanding the complex nature of frontal structure and frontogenesis,especially in understanding the dynamic structure of the subtropical frontal zone observed during early summer over East Asia.展开更多
基金This work is supported by National Natural Science Foundation of China.
文摘A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energy of mean flow in terms of ECWMF daily 500 hPa grid data in winter, indicating that the energy transportation is closely associated with the westerly jet position, with zonal (meridional) propagation in the strong (weak) wind region, that considerable conversion of barotropic energy occurs at the jet exit region where low-frequency oscillation gains energy from the mean flow, leading to maximum kinetic energy for the oscillation observed there, which is marked by evident barotropy in striking contrast to the baroclinicity at low latitudes and that the teleconnection core is related to the center of action in the atmosphere and bound up with the pattern of the west wind.
基金Supported by the National Natural Science Foundation of China(Nos.41606005,41430963)the National Science Foundation for Post-Doctoral Scientists of China(No.2015M582133)the Fundamental Research Funds for the Central Universities(No.201713023)
文摘Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current(SCSWC) in the northern South China Sea(NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea(SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.
文摘By using the low-spectral model simplified from quasi-geostrophic approximation two-level model,we obtained the result that the equivalent barotropic state is an equilibrium state of the atmosphere in that model,and discussed the conditions needed for existing the Rossby wave possessing the equivalent barotropic structure.And then we derived the oscillation equation reflecting the phase change of Rossby wave between higher and lower levels from the basic state of equivalent barotropic stationary Rossby wave,indicating the relations between the change of difference of phase at higher and lower levels and the disturbance of vertical shear,the amplitude disturbance of the part of waves of stream function and thermal wind stream function on the average level (A′ and B′).It is concluded that the inter-transformation exists between Rossby waves possessing the equivalent barotropic and baroclinic structure.
基金This research is supported by the National Natural Science Foundation of China.
文摘A two-dimensional,semi-geostrophic numerical model incorporating the tropopause and stratosphere is used to investigate the effects of a positive potential vorticity anomaly and latent heat release on the frontogenetic process and the structure of the resulting frontal zone.It is demonstrated that(1)the inclusion of tropopause and stratosphere significantly changes the frontal structure only in the upper levels;(2)a clearly defined quasi-equivalent barotropic structure and a region of upward motion of finite width appear when a positive potential vorticity anomaly exists on the warm side of the maximum baroclinity in the lower troposphere,especially when it is located on the south edge of the baroclinic zone;(3)the above mentioned structure deteriorates as the frontogenesis proceeds in a dry atmosphere but can be maintained in a moist frontogenetic process with condensational heating;(4)the combination of a positive potential vorticity anomaly and the latent heat release is able to accelerate the frontogenesis significantly with the time needed to form an intense frontal zone reduced to less than 15 h.The results have significant theoretical importance in understanding the complex nature of frontal structure and frontogenesis,especially in understanding the dynamic structure of the subtropical frontal zone observed during early summer over East Asia.
