# Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part ll: Numerical Simulation

• Corresponding author: Guoxiong WU, gxwu@lasg.iap.ac.cn
• Funds:

Supported by the National Key Research and Development Program of China (2018YFC1505706), Key Research Program of Fron-tier Sciences of Chinese Academy of Sciences (QYZDY-SSW-DQC018), and State Key Program of National Natural Science Foundation of China (41730963 and 91637312)

• doi: 10.1007/s13351-019-8606-z
• The surface air convergence on the eastern flank of the Tibetan Plateau (TP) can increase the in situ surface potential vorticity density (PVD). Since the elevated TP intersects with the isentropic surfaces in the lower troposphere, the increased PVD on the eastern flank of TP thus forms a PVD forcing to the intersected isentropic surface in the boundary layer. The influence of surface PVD forcing over the TP on the extreme freezing rain/snow over South China in January 2008 is investigated by using numerical experiments based on the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL). Compared with observations, the simulation results show that, by using a nudging method for assimilating observation data in the initial flow, this model can reasonably reproduce the distribution of precipitation, atmospheric circulation, and PVD propagation over and downstream of the TP during the extreme winter precipitation period. In order to investigate the impact of the increased surface PVD over the TP on the extreme precipitation in South China, a sensitivity experiment with surface PVD reduced over the TP region was performed. Compared with the control experiment, it is found that the precipitation in the TP downstream area, especially in Southeast China, is reduced. The rainband from Guangxi Region to Shandong Province has almost disappeared. In the lower troposphere, the increase of surface PVD over the TP region has generated an anomalous cyclonic circulation over southern China, which plays an important role in increasing southerly wind and the water vapor transport in this area; it also increases the northward negative absolute vorticity advection. In the upper troposphere, the surface PVD generated in eastern TP propagates on isentropic surface along westerly wind and results in positive absolute vorticity advection in the downstream areas. Consequently, due to the development of both ascending motion and water vapor transport in the downstream place of the TP, extremely heavy precipitation occurs over southern China. Thereby, a new mechanism concerning the influence of the increased surface PVD over the eastern TP slopes on the extreme weather event occurring over southern China is revealed.
• Fig. 1.  Distributions of (a) potential vorticity density − $\nabla \cdot \left({{V}W} \right)$ change (10–7 K s–2); (b) divergence and (c) its horizontal component and (d) vertical component (10–5 s–1), averaged over 24–27 January 2008 in the surface layer of the TP. Red and blue lines indicate the 1500- and 3000-m contours of the TP topography, respectively.

Fig. 2.  Location of the areas with surface wind speed altered in the sensitivity experiment (SEN). A represents the area to the south of 40°N and east of 95°E, where the altitude is equal or larger than 1500 m; B denotes the area to the west of 95°E, where the altitude is higher than 3000 m; and C denotes the area to the east of A, to the west of 25°–40°N, 110°E, where the altitude is less than 1500 m. Blue and red lines indicate the 1500- and 3000-m contours of the TP topography, respectively.

Fig. 6.  The 24–27 January mean distributions of (a, d, g, j) near-surface wind (m s–1), (b, e, h, k) divergence (10–6 s–1), and (c, f, i, l) velocity potential (shading; 10–6 m2 s–1) and divergent wind (vector; m s–1), calculated from the (a–c) MERRA2 data, (d–f) control run, (g–i) sensitivity run. Panels (j–l) show the difference between control and sensitivity runs. Blue and red contours indicate the 1500- and 3000-m contours of the TP, respectively.

Fig. 3.  Precipitation (mm day–1) during 24–27 January 2008 from (a) station observation, (b) TRMM retrieval, and (c) FAMIL simulation. The thick blue line indicates the 3000-m contour of terrain height.

Fig. 4.  Distributions of temperature (shading; °C) and wind (vector; m s–1) averaged over 24–27 January 2008 at (a, b) 200, (c, d) 500, and (e, f) 700 hPa. Left columns are from MERRA2 reanalysis data, and right columns are from FAMIL control simulation. The thick blue line indicates the 3000-m contour of TP topography.

Fig. 5.  Evolutions of the distributions of PVD (W) (shading; 10–4 s–1), wind (vector; m s–1), and pressure (contour; interval of 50 hPa) from 24 to 27 January 2008. (a–d) are from MERRA2 data at 295-K isentropic surface; (e–h) are from the FAMIL simulation at 290-K isentropic surface.

Fig. 7.  Time–longitude cross-sections averaged over 30°–35°N for 20–27 January 2008 of the PVD (10–4 s–1) at 295-K isentropic surface from (a) control run, (b) sensitivity run, and (c) their difference (control run minus sensitivity run).

Fig. 8.  The 24–27 January mean distributions of (a, d, g) geopotential height at 500 hPa, (b, e, h) geopotential height at 850 hPa, and (c, f, i) relative humidity (contour; interval of 10%) and divergence of water vapor flux (shaded; 10–7 g s–1 cm–1 hPa–1) at 700 hPa. Vector represents wind (m s–1); geopotential height unit is dagpm. (a–c) Control experiment, (d–f) sensitivity experiment, (g–i) their difference (control minus sensitivity). Blue solid curve indicates the 3000-m contour of terrain height.

Fig. 9.  Spatiotemporal evolutions of absolute vorticity advection (shading; 10–9 s–2) and its components (contour; interval: 0.2×10–9 s–2) during 23–27 January 2008: (a, b) control experiment, (c, d) sensitivity experiment, and (e, f) their difference. (a, c, e) Time–longitude cross-sections of absolute vorticity advection and its zonal component averaged over 20°–40°N on the 310-K isentropic surface. (b, d, f) Time–latitude cross-section of absolute vorticity advection and its meridional component averaged within100°–120°E on the 285-K isentropic surface.

Fig. 10.  Daily evolutions of the distributions of precipitation (shaded; mm day–1) and vertical velocity at 500 hPa (contour; interval: 2 Pa s–1) during 24–27 January 2008 from (a–d) control experiment, (e–h) sensitivity experiment, and (i–l) their difference. Red contour indicates the 3000-m contour of terrain height.

•  [1] Atmospheric Data Service Center of Nanjing University of Information Science & Technology, 2010: Introduction of MERRA satellite analysis data. Trans. Atmos. Sci., 33, 253–256. (in Chinese). [2] Bao, Q., J. Yang, Y. M. Liu, et al., 2010: Roles of anomalous Tibetan Plateau warming on the severe 2008 winter storm in central–southern China. Mon. Wea. Rev., 138, 2375–2384.. [3] Dee, D. P., S. M. Uppala, A. J. Simmons, et al., 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quart. J. Roy. Meteor. Soc., 137, 553–597. doi:  10.1002/qj.828. [4] Ding, Y. H., Z. Y. Wang, Y. F. Song, et al., 2008: Causes of the unprecedented freezing disaster in January 2008 and its possible association with the global warming. Acta Meteor. Sinica, 66, 808–825. (in Chinese). [5] Ertel, H., 1942: Ein neuer hydrodynamischer Wirbelsatz. Meteo-rol. Z., 59, 271–281. [6] Gao, H., L. J. Chen, X. L. Jia, et al., 2008: Analysis of the severe cold surge, ice–snow and frozen disasters in South China during January 2008. Ⅱ. Possible climatic causes. Meteor. Mon., 34, 101–106. (in Chinese). [7] Gao, Y., T. W. Wu, and B. D. Chen, 2011: Anomalous thermodynamic conditions for freezing rain in southern China in January 2008 and their causes. Plateau Meteor., 30, 1526–1533. (in Chinese). [8] Gu, L., K. Wei, and R. H. Huang, 2008: Severe disaster of blizzard, freezing rain and low temperature in January 2008 in China and its association with the anomalies of East Asian monsoon system. Climatic Environ. Res., 13, 405–418. (in Chinese). [9] Gu, X. Z., 2011: Diagnostic analysis on severe cold surge, rain and ice–snow in South China in January 2008. Plateau Meteor., 30, 150–157. (in Chinese). [10] Haynes, P. H., and M. E. McIntyre, 1987: On the evolution of vorticity and potential vorticity in the presence of diabatic heating and frictional or other forces. J. Atmos. Sci., 44, 828–841.. [11] Haynes, P. H., and M. E. McIntyre, 1990: On the conservation and impermeability theorems for potential vorticity. J. Atmos. Sci., 47, 2021–2031.. [12] Held, I. M., and T. Schneider, 1999: The surface branch of the zonally averaged mass transport in the troposphere. J. Atmos. Sci., 56, 1688–1697.. [13] Holton, J., 1992: Chapter 3: Elementary applications of the basic equations. An Introduction to Dynamic Meteorology, 3rd Ed., Academic Press, New York, 75–77. [14] Hoskins, B. J., 1991: Towards a PV-θ view of the general circulation. Tellus A, 43, 27–35.. [15] Hoskins, B. J., 1997: A potential vorticity view of synoptic development. Meteor. Appl., 4, 325–334.. [16] Hoskins, B. J., 2015: Potential vorticity and the PV perspective. Adv. Atmos. Sci., 32, 2–9.. [17] Hoskins, B. J., I. Draghici, and H. C. Davies, 1978: A new look at the ω-equation. Quart. J. Roy. Meteor. Soc., 104, 31–38.. [18] Hoskins, B. J., M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc., 111, 877–946.. [19] Huffman, G. J., D. T. Bolvin, and E. J. Nelkin, et al., 2007: The TRMM multi-satellite precipitation analysis: Quasi-global, multi-year, combined-sensor precipitation estimates at fine scales. J. Hydrometeor., 8, 38–55. doi:  10.1175/JHM560.1. [20] Li, C. Y., and W. Gu, 2010: Analysis of the anomalous activity of blocking high over the Ural Mountains in January 2008. Chinese J. Atmos. Sci., 34, 865–874. (in Chinese). [21] Li, J. X., Q. Bao, Y. M. Liu, et al., 2017: Evaluation of the computational performance of the finite-volume atmospheric model of the IAP/LASG (FAMIL) on a high-performance computer. Atmos. Ocean. Sci. Lett., 10, 329–336.. [22] Li, L. F., Y. M. Liu, and C. Y. Bo, 2011: Impacts of diabatic heating anomalies on an extreme snow event over South China in January 2008. Climatic Environ. Res., 16, 126–136. (in Chinese). [23] Liu, X., G. X. Wu, and W. P. Li, 2006: The diurnal variation of the atmospheric circulation and diabatic heating over the Tibetan Plateau. Adv. Earth Sci., 21, 69–78. (in Chinese). [24] Liu, Y., Y. H. Zhao, and Z. Y. Guan, 2008: Influences of stratospheric circulation anomalies on tropospheric weather of the heavy snowfall in January 2008. Climatic Environ. Res., 13, 548–555. (in Chinese). [25] Lucchesi, R., 2012: File Specification for MERRA Products. GMAO Office Note No. 1 (Version 2.3), 87 pp, available at https://gmao.gsfc.nasa.gov/pubs/docs/Lucchesi528.pdf. Accessed on 18 April 2019. [26] Ma, T. T., G. X. Wu, Y. M. Liu, et al., 2019: Impact of surface potential vorticity density forcing over the Tibetan Plateau on the South China extreme precipitation in January 2008. Part I: Data analysis. J. Meteor. Res., 33, 400–415.. [27] Nan, S., and P. Zhao, 2012: Snowfall over central–eastern China and Asian atmospheric cold source in January. J. Climate, 32, 888–899. doi:  10.1002/joc.2318. [28] Rienecker, M. M., M. J. Suarez, R. Gelaro, et al., 2011: MERRA: NASA’s modern-Era retrospective analysis for research and applications. J. Climate, 24, 3624–3648.. [29] Schneider, T., 2005: Zonal momentum balance, potential vorticity dynamics, and mass fluxes on near-surface isentropes. J. Atmos. Sci., 62, 1884–1900.. [30] Schneider, T., I. M. Held, and S. T. Garner, 2003: Boundary effects in potential vorticity dynamics. J. Atmos. Sci., 60, 1024–1040.. [31] Shaw, S. N., 1930: Manual of Meteorology, Volume III. The Physical Processes of Weather. Cambridge University Press, 473 pp. [32] Tan, G. R., H. S. Chen, Z. B. Sun, et al., 2010: Linkage of the cold event in January 2008 over China to the North Atlantic Oscillation and stratospheric circulation anomalies. Chinese J. Atmos. Sci., 34, 175–183. (in Chinese). [33] Tao, S. Y., and J. Wei, 2008: The severe snow and freezing-rain in January 2008 in southern China. Climatic Environ. Res., 13, 337–350. (in Chinese). [34] Tao, Z. Y., Y. G. Zheng, and X. L. Zhan, 2008: The southern China quasi-stationary front during the ice–snow disaster of January 2008. Acta Meteor. Sinica, 66, 850–854. (in Chinese). [35] Wang, D. H., C. J. Liu, Y. Liu, et al., 2008: A preliminary analy-sis of features and causes of the snow storm event over the southern China in January 2008. Acta Meteor. Sinica, 66, 405–422. (in Chinese). [36] Wang, L., G. Gao, and Q. Zhang, 2008: Analysis of the severe cold surge, ice–snow and frozen disasters in South China during January 2008. I: Climatic features and its impact. Meteor. Mon., 34, 95–100. (in Chinese). [37] Wang, Y. F., Y. Li, and P. Y. Li, 2008: The large scale circulation of the snow disaster in South China in the beginning of 2008. Acta Meteor. Sinica, 66, 826–835. (in Chinese). [38] Wang, Z. Y., Q. Zhang, Y. Chen, et al., 2008: Characters of meteorological disasters caused by the extreme synoptic process in early 2008 over China. Adv. Climate Change Res., 4, 63–67. (in Chinese). [39] Wen, M., S. Yang, A. Kumar, et al., 2009: An analysis of the large-scale climate anomalies associated with the snowstorms affecting China in January 2008. Mon. Wea. Rev., 137, 1111–1131.. [40] Yang, G. M., Q. Kong, D. Y. Mao, et al., 2008: Analysis of the long-lasting cryogenic freezing rain and snow weather in the beginning of 2008. Acta Meteor. Sinica, 66, 836–849. (in Chinese). [41] Zeng, M. J., W. S. Lu, X. Z. Liang, et al., 2008: Analysis of temperature structure for persistent disastrous freezing rain and snow over southern China in early 2008. Acta Meteor. Sinica, 66, 1043–1052. (in Chinese). [42] Zhu, Q. G., J. R. Lin, and S. W. Shou, 2007: Chapter 3. Synoptic Principles and Methods. China Meteorological Press, Beijing, 120–122. (in Chinese).
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• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part ll: Numerical Simulation

###### Corresponding author: Guoxiong WU, gxwu@lasg.iap.ac.cn
• 1. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, Beijing 100029
• 2. Tianjin Meteorological Service Center, Tianjin 300074
• 3. College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049
Funds: Supported by the National Key Research and Development Program of China (2018YFC1505706), Key Research Program of Fron-tier Sciences of Chinese Academy of Sciences (QYZDY-SSW-DQC018), and State Key Program of National Natural Science Foundation of China (41730963 and 91637312)

Abstract: The surface air convergence on the eastern flank of the Tibetan Plateau (TP) can increase the in situ surface potential vorticity density (PVD). Since the elevated TP intersects with the isentropic surfaces in the lower troposphere, the increased PVD on the eastern flank of TP thus forms a PVD forcing to the intersected isentropic surface in the boundary layer. The influence of surface PVD forcing over the TP on the extreme freezing rain/snow over South China in January 2008 is investigated by using numerical experiments based on the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL). Compared with observations, the simulation results show that, by using a nudging method for assimilating observation data in the initial flow, this model can reasonably reproduce the distribution of precipitation, atmospheric circulation, and PVD propagation over and downstream of the TP during the extreme winter precipitation period. In order to investigate the impact of the increased surface PVD over the TP on the extreme precipitation in South China, a sensitivity experiment with surface PVD reduced over the TP region was performed. Compared with the control experiment, it is found that the precipitation in the TP downstream area, especially in Southeast China, is reduced. The rainband from Guangxi Region to Shandong Province has almost disappeared. In the lower troposphere, the increase of surface PVD over the TP region has generated an anomalous cyclonic circulation over southern China, which plays an important role in increasing southerly wind and the water vapor transport in this area; it also increases the northward negative absolute vorticity advection. In the upper troposphere, the surface PVD generated in eastern TP propagates on isentropic surface along westerly wind and results in positive absolute vorticity advection in the downstream areas. Consequently, due to the development of both ascending motion and water vapor transport in the downstream place of the TP, extremely heavy precipitation occurs over southern China. Thereby, a new mechanism concerning the influence of the increased surface PVD over the eastern TP slopes on the extreme weather event occurring over southern China is revealed.

Reference (42)

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