Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetr...Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetric The result shows that the diabatic heating has important effects on the asymmetric structure in addition to the roll of the β term and nonlinear advection term in its formation. It again confirms the conclusion that the diabatic heating is a possible mechanism responsible for such structures in the tropical cyclone.展开更多
Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center,composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tr...Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center,composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010.The results are shown as follows.(1) With intensifying tropical cyclones,the flow field tends to become gradually more axisymmetric;however,the asymmetry of the specific humidity in the outer regions is more obvious.(2) In general,tropical cyclones have a non-uniform,vertical, "double warm-core" structure.The "warm-cores" in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two.(3) The distribution area of a "warm-core" is enhanced with cyclone intensification and tends to become more axisymmetric.At 200 hPa,the "warm-core" of a weak cyclone has a weak anticyclone in the center,whereas that of a strong cyclone has a weak cyclone in the center.(4)The "wet-core" of a tropical cyclone is primarily located in the lower level(700-850 hPa).With the cyclone's intensification,the intensity of the "wet-core" increases and the scope of the 0.8 g kg^(-1) specific humidity anomaly tends to expand to higher levels.(5) With the cyclone's deepening,the pseudo-equivalent potential temperature at different levels in different regions increases.In addition,the largest warming rates at each intensity level in the different regions occur in the core area,followed in turn by the envelope and outer areas.展开更多
A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity. It is found that TC intensity is reduced in a non-quiescent environment comp...A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity. It is found that TC intensity is reduced in a non-quiescent environment compared with the case of no uniform current. On an f-plane, the rate of intensification of a tropical cyclone is larger than that of the uniform flow. A TC on a β-plane intensifies slower than one on an f-plane. The main physical characteristic that distinguishes the experiments is the asymmetric thermodynamic (including convective) and dynamic structures present when either a uniform flow or β-effect is introduced. But a fairly symmetric TC structure is simulated on an f-plane. The magnitude of the warm core and the associated subsidence are found to be responsible for such simulated intensity changes. On an f-plane, the convection tends to be symmetric, which results in strong upper-level convergence near the center and hence strong forced subsidence and a very warm core. On the other hand, horizontal advection of temperature cancels part of the adiabatic heating and results in less warming of the core, and hence the TC is not as intense. This advective process is due to the tilt of the vortex as a result of the β-effect. A similar situation occurs in the presence of a uniform flow. Thus, the asymmetric horizontal advection of temperature plays an important role in the temperature distribution. Dynamically, the asymmetric angular momentum (AM) flux is very small on an f-plane throughout the troposphere. However, the total AM exports at the upper levels for a TC either on a β-plane or with a uniform flow environment are larger because of an increase of the asymmetric as well as symmetric AM export on the plane at radii >450 km, and hence there is a lesser intensification.展开更多
The effect of the horizontal variation of diabatic heating on the tropicalcyclone intensity and structure is studied in this paper. According to the potential vorticity (PV)equation in axis-symmetric cylindrical coord...The effect of the horizontal variation of diabatic heating on the tropicalcyclone intensity and structure is studied in this paper. According to the potential vorticity (PV)equation in axis-symmetric cylindrical coordinates, PV disturbance caused by the radial differenceof diabatic heating is positive (negative) inside (outside) the maximum heating radius, implyingthat the radial nonuniformity of diabatic heating should contribute positively to the intensity of atropical cyclone while negatively to its size. A primitive equation model is then used to get somequantitative ideas on the problem. Results show that the modeled tropical cyclone weakens by about20% but is larger in size if the effect of horizontal variety of convective heating is excluded inthermodynamic and dynamic equations. The PV disturbance originated from the horizontal nonuniformityof diabatic heating is positive inside the maximum heating radius and negative outside, inconsistent with the PV equation analyses. The maximum disturbance (both negative and positive)appears around the maximum heating level and their magnitude is comparable to that generated byvertical variance of heating. It is concluded that the effect of the horizontal heat nonuniformityon the intensity and structure of TC cannot be neglected.展开更多
Based on the tropical cyclone(TC)asymmetric disturbance as the superposition of the symmetric environmental circulation,the analytical solution of travelling wave is given by using the barotropical nondivergent model ...Based on the tropical cyclone(TC)asymmetric disturbance as the superposition of the symmetric environmental circulation,the analytical solution of travelling wave is given by using the barotropical nondivergent model with diabatic heating forcing and non-friction in a plane polar coordinate.Then,the TC radial inhomogeneous structure is analyzed on radial/tangential velocity and geopotential height.It is found that the different kinds of structures are influenced by the Coriolis parameter(f),TC intensity(Ω),disturbance circular frequency(ω),and TC angular wavenumber(m).And,the diabatic heating(Q_1)has significant impacts on the radial/tangential velocity distribution shaped like the inner-tight and outer-relaxed.展开更多
A model is proposed relating a variety of factors of tropical cyclones (TCs)to their tracks, and attentions are paid to the influence of the asymmetric wind structures of TCs.Ideal numerical calculation shows that the...A model is proposed relating a variety of factors of tropical cyclones (TCs)to their tracks, and attentions are paid to the influence of the asymmetric wind structures of TCs.Ideal numerical calculation shows that the asymmetric wind structures of TCs have conspicuousinfluence on their motion tracks. When moving due westward initially, an axisymmetric TC willdeflect right, and the overall trend is eastward. When it is asymmetric but the asymmetry is notsharp, wherever the area of maximum wind is, the TC deflects northwest first, and then, to variousareas depending on the positions of the areas of maximum wind, i.e. for the area of maximum wind inQuadrant Ⅰ, to the southeast; for in Quadrant Ⅱ, to the northeast; for in Quadrant Ⅲ, to thenorthwest; for in Quadrant IV, to the southwest. And in the above four cases, the TC tracks are allaccompanied by clockwise looping motions. With the asymmetry of the TC intensifiying, the track ofthe TC motion will be stretched further. For the area of maximum wind in Quadrants Ⅰ and Ⅱ, the TCtracks are still accompanied by clockwise looping motions; for the area of maximum wind inQuadrants Ⅲand Ⅳ, the TC tracks become oscillatory, without clockwise looping motions.展开更多
The mean kinematic and thermodynamic structures of tropical cyclones （TCs） making landfall in main-land China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanie...The mean kinematic and thermodynamic structures of tropical cyclones （TCs） making landfall in main-land China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center;however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation diff er, especially over the left-front and right-rear quadrants （relative to the direction of TC motion）. In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer, while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.展开更多
文摘Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetric The result shows that the diabatic heating has important effects on the asymmetric structure in addition to the roll of the β term and nonlinear advection term in its formation. It again confirms the conclusion that the diabatic heating is a possible mechanism responsible for such structures in the tropical cyclone.
基金Major State Basic Research Program of China(2013CB430305)National Natural Science Foundation of China(41475060,41275067,41305049)Public Benefit Research Foundation of China(GYHY201406010)
文摘Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center,composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010.The results are shown as follows.(1) With intensifying tropical cyclones,the flow field tends to become gradually more axisymmetric;however,the asymmetry of the specific humidity in the outer regions is more obvious.(2) In general,tropical cyclones have a non-uniform,vertical, "double warm-core" structure.The "warm-cores" in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two.(3) The distribution area of a "warm-core" is enhanced with cyclone intensification and tends to become more axisymmetric.At 200 hPa,the "warm-core" of a weak cyclone has a weak anticyclone in the center,whereas that of a strong cyclone has a weak cyclone in the center.(4)The "wet-core" of a tropical cyclone is primarily located in the lower level(700-850 hPa).With the cyclone's intensification,the intensity of the "wet-core" increases and the scope of the 0.8 g kg^(-1) specific humidity anomaly tends to expand to higher levels.(5) With the cyclone's deepening,the pseudo-equivalent potential temperature at different levels in different regions increases.In addition,the largest warming rates at each intensity level in the different regions occur in the core area,followed in turn by the envelope and outer areas.
基金sponsored by the National Natural Science Foundation of China under Grant Nos.49975014,40275018,and 40333025
文摘A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity. It is found that TC intensity is reduced in a non-quiescent environment compared with the case of no uniform current. On an f-plane, the rate of intensification of a tropical cyclone is larger than that of the uniform flow. A TC on a β-plane intensifies slower than one on an f-plane. The main physical characteristic that distinguishes the experiments is the asymmetric thermodynamic (including convective) and dynamic structures present when either a uniform flow or β-effect is introduced. But a fairly symmetric TC structure is simulated on an f-plane. The magnitude of the warm core and the associated subsidence are found to be responsible for such simulated intensity changes. On an f-plane, the convection tends to be symmetric, which results in strong upper-level convergence near the center and hence strong forced subsidence and a very warm core. On the other hand, horizontal advection of temperature cancels part of the adiabatic heating and results in less warming of the core, and hence the TC is not as intense. This advective process is due to the tilt of the vortex as a result of the β-effect. A similar situation occurs in the presence of a uniform flow. Thus, the asymmetric horizontal advection of temperature plays an important role in the temperature distribution. Dynamically, the asymmetric angular momentum (AM) flux is very small on an f-plane throughout the troposphere. However, the total AM exports at the upper levels for a TC either on a β-plane or with a uniform flow environment are larger because of an increase of the asymmetric as well as symmetric AM export on the plane at radii >450 km, and hence there is a lesser intensification.
基金Sponsored by the National Natural Science Foundation of China under Grant Nos. 49975014, 40275018 and 40333025.
文摘The effect of the horizontal variation of diabatic heating on the tropicalcyclone intensity and structure is studied in this paper. According to the potential vorticity (PV)equation in axis-symmetric cylindrical coordinates, PV disturbance caused by the radial differenceof diabatic heating is positive (negative) inside (outside) the maximum heating radius, implyingthat the radial nonuniformity of diabatic heating should contribute positively to the intensity of atropical cyclone while negatively to its size. A primitive equation model is then used to get somequantitative ideas on the problem. Results show that the modeled tropical cyclone weakens by about20% but is larger in size if the effect of horizontal variety of convective heating is excluded inthermodynamic and dynamic equations. The PV disturbance originated from the horizontal nonuniformityof diabatic heating is positive inside the maximum heating radius and negative outside, inconsistent with the PV equation analyses. The maximum disturbance (both negative and positive)appears around the maximum heating level and their magnitude is comparable to that generated byvertical variance of heating. It is concluded that the effect of the horizontal heat nonuniformityon the intensity and structure of TC cannot be neglected.
基金This work is supported by the National Natural Science Foundation of China(40175019,49975014).
文摘Based on the tropical cyclone(TC)asymmetric disturbance as the superposition of the symmetric environmental circulation,the analytical solution of travelling wave is given by using the barotropical nondivergent model with diabatic heating forcing and non-friction in a plane polar coordinate.Then,the TC radial inhomogeneous structure is analyzed on radial/tangential velocity and geopotential height.It is found that the different kinds of structures are influenced by the Coriolis parameter(f),TC intensity(Ω),disturbance circular frequency(ω),and TC angular wavenumber(m).And,the diabatic heating(Q_1)has significant impacts on the radial/tangential velocity distribution shaped like the inner-tight and outer-relaxed.
基金This research is jointly supported by the National Natural Science Foundation of China under Grant Nos. 40075011 and40633030, and the State Key Basic Program: CHERES.
文摘A model is proposed relating a variety of factors of tropical cyclones (TCs)to their tracks, and attentions are paid to the influence of the asymmetric wind structures of TCs.Ideal numerical calculation shows that the asymmetric wind structures of TCs have conspicuousinfluence on their motion tracks. When moving due westward initially, an axisymmetric TC willdeflect right, and the overall trend is eastward. When it is asymmetric but the asymmetry is notsharp, wherever the area of maximum wind is, the TC deflects northwest first, and then, to variousareas depending on the positions of the areas of maximum wind, i.e. for the area of maximum wind inQuadrant Ⅰ, to the southeast; for in Quadrant Ⅱ, to the northeast; for in Quadrant Ⅲ, to thenorthwest; for in Quadrant IV, to the southwest. And in the above four cases, the TC tracks are allaccompanied by clockwise looping motions. With the asymmetry of the TC intensifiying, the track ofthe TC motion will be stretched further. For the area of maximum wind in Quadrants Ⅰ and Ⅱ, the TCtracks are still accompanied by clockwise looping motions; for the area of maximum wind inQuadrants Ⅲand Ⅳ, the TC tracks become oscillatory, without clockwise looping motions.
基金Supported by the National Basic Research and Development(973)Program of China(2009CB421500)National Natural Science Foundation of China(40730948,40921160381,41275057,41275067,and 41305049)China Meteorological Administration Special Public Welfare Research Fund(GYHY201006008 and GYHY200906002)
文摘The mean kinematic and thermodynamic structures of tropical cyclones （TCs） making landfall in main-land China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center;however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation diff er, especially over the left-front and right-rear quadrants （relative to the direction of TC motion）. In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer, while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.
