Numerical Simulation of a Torrential Rain Event in the Northeast of Huaihe Basin. Part II: Instability Conditions and the Mechanism of Intensification and Maintenance

다국어 초록 (Multilingual Abstract)

Based on the simulation displayed in Part I of this study,the intensification and maintenance, the relationship between deep moist mesoscale convective system (DMMCS) and instability, convective vorticity vector (CVV) are analyzed in the present paper. Results show that: (1) middle-low level convective instability is the precondition of the occurrence of DMMCS. The convergence and merger enhancement of convection cells, as well as the convective instability energy transporting from the left-front of typhoon play an essential role in the re-establishment and enhancement of convective instability.
(2) Baroclinic instability and conditional symmetric instability appear not only in the middle-low level, but also are distinct in the middleupper level of DMMCS. (3) In DMMCS, there is an alternative distribution of inertial instability column and inertial stability column.
In the west and south, there are negative CVV columns, which is favorable for the burst of deep moist convection. (4) The strong slantwise convection induced by inertial instability, baroclinic instability,and conditional symmetric instability enhance the upper-level southerly component. Due to the appearance of the compensated downdraft at the low level of south side of DMMCS, the low level southerly intensified, and the enhancement of upper- and low-level cores is in favor of the development of DMMCS, which will be beneficial to the reinforcement and maintenance of inertial instability,baroclinic instability, and conditional symmetric instability. It is a positive feedback process. (5) There is a downshear circulation to the east of rainfall cell. Shallow convections near this cell absorb the vapor and instability energy coming from the south. In the meanwhile, the mesoscale convergence line and meso-β-scale vortex organize and intensify convective cells. In DMMCS, there is an alternative distribution of convergence and divergence columns, and the couple between strong divergence and vorticity columns. They are both conducive to the development of DMMCS, and the instability will be intensified and maintained for its development in depth.

참고문헌 (Reference)

1 Wu, G. X., "Vertical wind shear and down-sliding slantwise vorticity development" 21 : 273-282, 1997

2 Hoskins, B. J., "The role of potential vorticity in symmetric stability and instability" 100 : 480-482, 1974

3 Gao, S. T., "The instability of the vortex sheet along the shear line" 17 : 525-537, 2000

4 Charney, J. G., "The dynamics of long waves in a baroclinic westerly current" 4 : 135-163, 1947

5 Soong, S. T., "Response of deep tropical cumulus clouds to mesoscale processes" 37 : 2016-2034, 1980

6 Stone, P. H., "On non-geostrophic baroclinic stability" 23 : 390-400, 1966

7 Li, Y., "Numerical study on impacts of upper-level westerly trough on the extratropical transition process of typhoon Winnie (1997)" 64 : 552-563, 1997

8 Jiang, J. Y., "Numerical study of the evolution mechanism of meso-β scale convective system along the Meiyu front" 63 : 77-92, 2005

9 Zhu, P. J., "Numerical simulation of typhoon Winnie (1997) after landfall. Part II: Structure evolution analysis" 60 : 560-567, 1997

10 Zhu, T., "Numerical simulation of hurricane Bonnie (1998). Part I: Eyewall evolution and intensity changes" 132 : 225-241, 1998

11 Guo, D. M., "Numerical experiment study on the relation of latent heat, inertial instability and the explosive development of cyclone" 28 : 794-800, 2005

12 Wang, Y. P., "Numerical Simulation of a Torrential Rain event in the Northeast of Huaihe Basin. Part I : Model verification and analysis of MCSs" 23 : 223-231, 2009

13 Liu, H. Z., "Moist potential vorticity and the three dimensional structure of a cold front with heavy rainfall" 7 : 275-284, 1996

14 Wu, G. X., "Moist potential vorticity and slantwise vorticity development" 53 : 387-405, 1995

15 Shou, S. W., "Mesoscale Weather Dynamics" China Meteorological Press 251-, 1993

16 Eady, E. T., "Long waves and cyclone waves" 1 : 33-52, 1949

17 Emanuel, K. A., "Inertial instability and mesoscale convective systems. Part I: Linear theory of inertial instability in rotating viscous fluids" 36 : 2425-2449, 1979

18 Scorer, R. S., "Dynamics of Meteorology and Climate" PRAXIS Publishing Ltd 74-79, 1997

19 Duan, L., "Diagnostic analysis and numerical study of torrential rain associated with the tropical storm Fitow (0114)" 29 : 343-353, 2005

20 Wang, H., "Diagnostic analysis and numerical simulation of a mesocale torrential rain system in the Huaihe valley during the rainy season in 2003" 64 : 734-742, 2006

21 Bennetts, D. A., "Conditional symmetric instability - a possible explanation for frontal rainbands" 105 : 945-962, 1979

22 Wu, G. X., "Complete form of vertical vorticity tendency equation and slantwise vorticity development" 57 : 1-15, 1999

23 Sun, J. H., "A study on mesoscale convective systems of the severe heavy rainfall in north China by “9608” typhoon" 64 : 57-71, 2006

24 Shen, S. Q., "A study on meso-β scale system during an excessive heavy rain" 27 : 33-37, 2001

25 Bei, N. F., "A numerical simulation of sudden heavy rainfall occurred in Wuhan and Huangshi during July of 1998" 27 : 399-418, 2003

26 Yau, M. K., "A multiscale numerical study of hurricane Andrew (1992). Part VI: Small-scale innercore structures and wind streaks" 132 : 1410-1433, 1992

27 Zhang, D. L., "A multiscale numerical study of hurricane Andrew (1992). Part III: Dynamically induced vertical motion" 128 : 3772-3788, 1992

28 Liu, Y. B., "A multiscale numerical study of hurricane Andrew (1992). Part I: Explicit simulation and verification" 125 : 3073-3093, 1992

29 Xue, M., "A high-resolution modeling study of the 24 May 2002 dryline case during IHOP. Part I: Numerical simulation and general evolution of the dryline and convection" 134 : 149-171, 2006

30 Jiang, J. Y., "A diagnostic study to the multi-scale characteristics of a Meiyu front heavy rainfall process in 1998" 61 : 673-683, 2003

31 Gao, S. T., "A convective vorticity vector associated with tropical convection: A two-dimensional cloud-resolving modeling study" 109 : D14106-, 2004