Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical...Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper:(1) great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;(2) westerly duct theory,which suggests a "corridor" through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;(3) energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;(4) equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and(5) meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.展开更多
As the instant centers in planar mechanisms, the instantaneous poles (or instant poles, in brief) can be used for kinematic analysis in spherical mechanisms. One of the mandatory steps in this analysis is the determ...As the instant centers in planar mechanisms, the instantaneous poles (or instant poles, in brief) can be used for kinematic analysis in spherical mechanisms. One of the mandatory steps in this analysis is the determination of the location of these poles. This paper presents a theorem showing analytically that the locus of an unknown secondary instant pole in two-degree-of-freedom (2-DOF) spherical mechanisms is a great circle (GC). The exact location of the pole on its GC is obtained based on the configuration of the mechanism and velocity ratio of the two inputs. Moreover, using the results of the theorem, a geometrical technique is presented to determine the GC of the pole.展开更多
In this paper,the effects of first and second meridional derivative(i.e.h_s~,d^2f/dy^2,″)of the Coriolis parameter,Westerly profile and topography structure on ray routes are qualitatively analysed by use of a sim- p...In this paper,the effects of first and second meridional derivative(i.e.h_s~,d^2f/dy^2,″)of the Coriolis parameter,Westerly profile and topography structure on ray routes are qualitatively analysed by use of a sim- plified mathematical model.The analysis indicates that the second derivatives of the above relevant factors play an important role in the formation of great circle route.A profile of west wind similar to the real atmosphere may result in a“sine wave pattern”of ray.The effects of west wind shear,β factor and the slope of topography on the scale of radius of great circle,critical latitude of rays ard the amplitude of wave train of teleconnection aro also discussed.Additionally,the characters of critical velocity profile for meridionally trapped wave are men- tioned.展开更多
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2014CB953900)National Natural Science Foundation of China(41375081)+1 种基金LASW State Key Laboratory Special Fund(2013LASW-A05)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406018)
文摘Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper:(1) great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;(2) westerly duct theory,which suggests a "corridor" through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;(3) energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;(4) equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and(5) meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.
文摘As the instant centers in planar mechanisms, the instantaneous poles (or instant poles, in brief) can be used for kinematic analysis in spherical mechanisms. One of the mandatory steps in this analysis is the determination of the location of these poles. This paper presents a theorem showing analytically that the locus of an unknown secondary instant pole in two-degree-of-freedom (2-DOF) spherical mechanisms is a great circle (GC). The exact location of the pole on its GC is obtained based on the configuration of the mechanism and velocity ratio of the two inputs. Moreover, using the results of the theorem, a geometrical technique is presented to determine the GC of the pole.
基金supported jointly by National Natural Science Foundation of Chinathe State Meteorological Administration Monsoon Research Funds
文摘In this paper,the effects of first and second meridional derivative(i.e.h_s~,d^2f/dy^2,″)of the Coriolis parameter,Westerly profile and topography structure on ray routes are qualitatively analysed by use of a sim- plified mathematical model.The analysis indicates that the second derivatives of the above relevant factors play an important role in the formation of great circle route.A profile of west wind similar to the real atmosphere may result in a“sine wave pattern”of ray.The effects of west wind shear,β factor and the slope of topography on the scale of radius of great circle,critical latitude of rays ard the amplitude of wave train of teleconnection aro also discussed.Additionally,the characters of critical velocity profile for meridionally trapped wave are men- tioned.