# Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part I: Data Analysis

• Corresponding author: Yimin LIU, lym@lasg.iap.ac.cn
• Funds:

Supported by the China Meteorological Administration Special Public Welfare Research Fund for the Third Tibetan Plateau Atmospheric Science Experiment (GYHY201406001), Key Research Program of Frontier Sciences of Chinese Academy of Sciences (QYZDY-SSW-DQC018), and National Natural Science Foundation of China (41730963, 91437219, and 91637312)

• doi: 10.1007/s13351-019-8604-1
• The external source/sink of potential vorticity (PV) is the original driving force for the atmospheric circulation. The relationship between surface PV generation and surface PV density forcing is discussed in detail in this paper. Moreover, a case study of the extreme winter freezing rain/snow storm over South China in January 2008 is performed, and the surface PV density forcing over the eastern flank of the Tibetan Plateau (TP) has been found to significantly affect the precipitation over South China in this case. The TP generated PV propagated eastward in the middle troposphere. The associated zonal advection of positive absolute vorticity resulted in the increasing of cyclo-nic relative vorticity in the downstream region of the TP. Ascending air and convergence in the lower troposphere developed, which gave rise to the development of the southerly wind. This favored the increasing of negative meridio-nal absolute vorticity advection in the lower troposphere, which provided a large-scale circulation background conducive to ascending motion such that the absolute vorticity advection increased with height. Consequently, the ascending air further strengthened the southerly wind and the vertical gradient of absolute vorticity advection between the lower and middle troposphere in turn. Under such a situation, the enhanced ascending, together with the moist air transported by the southerly wind, formed the extreme winter precipitation in January 2008 over South China.
• Fig. 1.  Time–longitude cross-sections of (a) potential vorticity density (PVD) (shaded; 10–5 s–1) and (b) zonal PVD advection (shaded; 10–10 s–2) on 305-K isentropic surface averaged over 28°–34°N from 1 January to 5 February 2008. The black lines in (b) indicate 6-h accumulative precipitation (mm). The white area indicates the area with surface potential temperature greater than 305 K, i.e., the underworld.

Fig. 2.  Vertical cross-sections of PVD (shading; 10–7 K m s kg–1), potential temperature (contour; K), and wind (vector; m s–1; the vertical component has been multiplied by –50) averaged over (a, c, e) 30°–36°N and (b, d, f) 110°–120°E for (a, b) January–February climate mean, (c, d) the storm period, and (e, f) the difference of PVD and wind between these two periods (c minus a, d minus b). The dotted region in (e, f) represents the PVD difference exceeding three standard deviations.

Fig. 3.  Vertical cross-sections of (a, c, e) PVD advection term (shading; 10–13 K m kg–1) and PVD (contour; 10–7 K m s kg–1); and (b, d, f) diabatic heating term (shading; 10–13 K m kg–1) and diabatic heating rate (contour; 10–5 K s–1) over 110°–120°E for (a, b) January–February climate mean, (c, d) the storm period, and (e, f) the difference between these two periods.

Fig. 4.  Vertical cross-sections of (left columns) zonal PVD advection (shading; 10–13 K m kg–1) and wind (vector; m s–1), (middle columns) meridional PVD advection (shading; 10–13 K m kg–1) and wind (vector; m s–1), and (right columns) horizontal PVD advection (shading; 10–13 K m kg–1) and PVD (10–7 K m s kg–1) over 110°–120°E for (a–c) January–February climate mean, (d–f) the storm period, and (g–i) the difference between these two periods.

Fig. 5.  Vertical cross-sections of vertical PVD advection (shading; 10–13 K m kg–1), PVD (contour; 10–7 K m s kg–1), and wind (vector; m s–1) averaged over 110°–120°E for (a) January–February climate mean, (b) the storm period, and (c) the differences of PVD (shading; 10–7 K m s kg–1) and wind (vector; m s–1) between these two periods. Contour in (c) indicates PVD in the storm period

Fig. 6.  Distributions of surface PVD tendency for (a) the climate mean, (b) the storm period, and (c) their difference (10–7 K s–2). The black line indicates the elevation of 3000 m.

Fig. 7.  Distributions of (a) the total surface PVD tendency, and the surface PVD tendency resulting from (b) PVD flux divergence, (c) diabatic heating, and (d) friction from 18 January to 2 February. The unit of PVD tendency is 10–7 K s–2

Fig. 8.  Distributions of (a) surface PVD flux divergence term ($- \nabla \cdot \left({W{V}} \right)$; 10-7 K s–2), (b) divergence term ($- W\nabla \cdot {V}$; 10–7 K s–2), (c) PVD advection term ($- {V} \cdot \nabla W$; 10–7 K s–2), and (d) air divergence ($\nabla \cdot {V}$; 10–6 s–1) from 18 January to 2 February.

Fig. 9.  Vertical cross-sections of (a) absolute vorticity advection (shading; 10–10 s–2) and its vertical gradient (contour; 10–12 s–2 hPa–1), (b) relative vorticity (shading; 10–5 s–1) and temperature (contour; K) over 110°–120°E from 18 January to 2 February 2008. The red and blue curves in (b) indicate the zero isotherm in the storm period and that of January–February climate mean from 1980 to 2017

•  [1] Bao, Q., Y. M. 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. doi: 10.1175/2009MWR2950.1. [2] Bracegirdle, T. J., and S. L. Gray, 2009: The dynamics of a polar low assessed using potential vorticity inversion. Quart. J. Roy. Meteor. Soc., 135, 880–893. doi: 10.1002/qj.411. [3] Chen, S. J., and L. Dell’osso, 1984: Numerical prediction of the heavy rainfall vortex over eastern Asia monsoon region. J. Meteor. Soc. Japan, 62, 730–747. doi: 10.2151/jmsj1965.62.5_730. [4] Chen, Y. R., Y. Q. Li, and T. L. Zhao, 2015: Cause analysis on eastward movement of Southwest China vortex and its induced heavy rainfall in South China. Adv. Meteor. . doi: 10.1155/2015/481735. [5] Cheng, X. L., Y. Q. Li, and L. Xu, 2016: An analysis of an extreme rainstorm caused by the interaction of the Tibetan Plateau vortex and the Southwest China vortex from an intensive observation. Meteor. Atmos. Phys., 128, 373–399. doi: 10.1007/s00703-015-0420-2. [6] Ding, Y. H., Z. Y. Wang, and Y. F. Song, 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). [7] Egger, J., K. P. Hoinka, and T. Spengler, 2015: Aspects of potential vorticity fluxes: Climatology and impermeability. J. Atmos. Sci., 72, 3257–3267. doi: 10.1175/JAS-D-14-0196.1. [8] Ertel, H., 1942: Ein neuer hydrodynamische wirbelsatz. Meteor. Z. Braunschweig, 59, 33–49. [9] Fu, S. M., J. H. Sun, S. X. Zhao, et al., 2011: A study of the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the rainfall of the Yangtze–Huai River basin. Acta Meteor. Sinica, 69, 581–600. (in Chinese). [10] Gelaro, R., W. McCarty, M. J. Suarez, et al., 2017: The Mordern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). J. Climate, 30, 5419–5454. doi: 10.1175/JCLI-D-16-0758.1. [11] Griffiths, M., A. J. Thorpe, and K. A. Browning, 2000: Convective destabilization by a tropopause fold diagnosed using potential vorticity inversion. Quart. J. Roy. Meteor. Soc., 126, 125–144. doi: 10.1256/smsqj.56206. [12] 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). [13] Guo, Z., H. Lin, J. Jiang, et al., 2003: The features of MCS and their eastward moving and propagation over the Tibetan Plateau. J. Remote Sens., 7, 350–357. (in Chinese). [14] 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. doi: 10.1175/1520-0469(1987)044<0828:OTEOVA>2.0.CO;2. [15] 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. doi: 10.1175/1520-0469(1999)056<1688:TSBOTZ>2.0.CO;2. [16] Holton, J. R., 2004: An Introduction to Dynamic Meteology. Elsevier Academic Press, 535 pp. [17] Hoskins, B. J., 1991: Towards a PV-θ view of the general circulation. Tellus, 43AB, 27–35. [18] Hoskins, B. J., 1997: A potential vorticity view of synoptic development. Meteor. Appl., 4, 325–334. doi: 10.1017/S1350482797000716. [19] 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. doi: 10.1002/qj.49711147002. [20] Huo, Z., D. L. Zhang, and J. R. Gyakum, 1999: Interaction of potential vorticity anomalies in extratropical cyclogenesis. Part I: Static piecewise inversion. Mon. Wea. Rev., 127, 2546–2661. doi: 10.1175/1520-0493(1999)127<2546:IOPVAI>2.0.CO;2. [21] Jiang, J. X., X. K. Xiang, and M. Z. Fan, 1996: The spatial and temporal distributions of severe mesoscale convective system over Tibetan Plateau in summer. J. Appl. Meteor. Sci., 7, 473–478. (in Chinese). [22] Koh, T. Y., and R. Plumb, 2004: Isentropic zonal average formalism and the near-surface circulation. Quart. J. Roy. Meteor. Soc., 130, 1631–1653. doi: 10.1256/qj.02.219. [23] Li, G. P., and Q. Xu, 2005: Effect of dynamic pumping in the boundary layer on the Tibetan Plateau vortices. Chinese J. Atmos. Sci., 29, 965–972. (in Chinese). [24] Li, G. P., T. Y. Duan, S. Haginoya, et al., 2001: Estimates of the bulk transfer coefficients and surface fluxes over the Tibetan Plateau using AWS data. J. Meteor. Soc. Japan, 79, 625–635. doi: 10.2151/jmsj.79.625. [25] 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). [26] Li, Y. D., Y. Wang, S. Yang, et al., 2008: Characteristics of summer convective systems initiated over the Tibetan Plateau. Part I: Origin, track, development, and precipitation. J. Appl. Meteor. Climatol., 47, 2679–2695. doi: 10.1175/2008JAMC1695.1. [27] Liao, Z. J., and Y. C. Zhang, 2013: Concurrent variation between the East Asian subtropical jet and polar front jet during persistent snowstorm period in 2008 winter over southern China. J. Geophys. Res. Atmos., 118, 6360–6373. doi: 10.1002/jgrd.50558. [28] Ni, C. C., G. P. Li, and X. Z. Xiong, 2017: Analysis of a vortex precipitation event over Southwest China using AIRS and in situ measurements. Adv. Atmos. Sci., 34, 559–570. doi: 10.1007/s00376-016-5262-4. [29] Rossby, C. G., 1940: Planetary flow patterns in the atmosphere. Quart. J. Roy. Meteor. Soc., 66, 68–87. [30] Schneider, T., 2005: Zonal momentum balance, potential vorticity dynamics, and mass fluxes on near-surface isentropes. J. Atmos. Sci., 62, 1884–1900. doi: 10.1175/JAS3341.1. [31] Schneider, T., I. M. Held, and S. T. Garner, 2003: Boundary effects in potential vorticity dynamics. J. Atmos. Sci., 60, 1024–1040. doi: 10.1175/1520-0469(2003)60<1024:BEIPVD>2.0.CO;2. [32] Shaw, S. N., 1930: Manual of Meteorology. Vol III: The Physical Processes of Weather. Cambridge University Press, 86. [33] Shi, C. X., J. X. Jiang, and Z. Y. Fang, 2000: A study on the features of severe convective cloud clusters causing serious flooding over Changjiang River basin in 1998. Climatic Environ. Res., 5, 279–286. (in Chinese). [34] Shi, N., C. L. Bueh, L. R. Ji, et al., 2008: On the medium-range process of the rainy, snowy and cold weather of South China in early 2008. Part II: Characteristics of the western Pacific subtropical high. Climatic Environ. Res., 13, 434–445. (in Chinese). [35] Sun, J. H., and S. X. Zhao, 2008: Quasi-stationary front and stratification structure of the freezing rain and snow storm over southern China in January 2008. Climatic Environ. Res., 13, 368–384. (in Chinese). [36] Sun, J. H., and S. X. Zhao, 2010: The impacts of multiscale wea-ther systems on freezing and snowstorms over southern China. Wea. Forecasting, 25, 388–407. doi: 10.1175/2008WEF2222253.1. [37] Tao, S. Y., and Y. H. Ding, 1981: Observational evidence of the influence of the Qinghai–Xizang (Tibet) Plateau on the occurrence of heavy rain and severe convective storms in China. Bull. Amer. Meteor. Soc., 62, 23–30. doi: 10.1175/1520-0477(1981)062<0023:OEOTIO>2.0.CO;2. [38] Tao, S. Y., and J. Wei, 2008: Severe snow and freezing-rain in January 2008 in southern China. Climatic Environ. Res., 13, 337–350. (in Chinese). [39] Tao, Z. Y., Y. G. Zheng, and X. L. Zhang, 2008: Southern China quasi-stationary front during ice–snow disaster of January 2008. Acta Meteor. Sinica, 66, 850–854. (in Chinese). [40] Wang, B., and I. Orlanski, 1987: Study of a heavy rain vortex formed over the eastern flank of the Tibetan Plateau. Mon. Wea. Rev., 115, 1370–1393. doi: 10.1175/1520-0493(1987)115<1370:SOAHRV>2.0.CO;2. [41] Wang, W., Y. H. Kuo, and T. T. Warner, 1993: A diabatically driven mesoscale vortex in the lee of the Tibetan Plateau. Mon. Wea. Rev., 121, 2542–2561. doi: 10.1175/1520-0493(1993)121<2542:ADDMVI>2.0.CO;2. [42] Wang, X. M., and Y. Liu, 2017: Causes of extreme rainfall in May 2013 over Henan Province: The role of the southwest vortex and low-level jet. Theor. Appl. Climatol., 129, 701–709. doi: 10.1007/s00704-017-2054-4. [43] 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. doi: 10.1175/2008MWR2638.1. [44] Wu, G. X., Y. J. Zheng, and Y. M. Liu, 2013: Dynamical and thermal problems in vortex development and movement. Part II: Generalized slantwise vorticity development. Acta Meteor. Sinica, 27, 15–25. doi: 10.1007/s13351-013-0102-2. [45] Xiang, S. Y., Y. Q. Li, D. Li, et al., 2013: An analysis of heavy precipitation caused by a retracing plateau vortex based on TRMM data. Meteor. Atmos. Phys., 122, 33–45. doi: 10.1007/s00703-013-0269-1. [46] Yasunari, T., and T. Miwa, 2006: Convective cloud systems over the Tibetan Plateau and their impact on meso-scale disturbances in the Meiyu/Baiu frontal zonal. A case study in 1998. J. Meteor. Soc. Japan, 84, 783–803. doi: 10.2151/jmsj.84.783. [47] Yu, J. H., Y. M. Liu, T. T. Ma, et al., 2019: Impact of surface potential vorticity density forcing over the Tibetan Plateau on the South China extreme precipitation in January 2008. Part II: Numerical simulation. J. Meteor. Res., 33, 416–432. doi: 10.1007/s13351-019-8606-z. [48] Zhang, C. Y., and Y. C. Zhang, 2013: The characteristics of East Asian jet stream in severe snow storm and freezing rain processes over southern China in early 2008. J. Trop. Meteor., 29, 306–314. (in Chinese). [49] Zheng, Y. J., G. X. Wu, and Y. M. Liu, 2013: Dynamic and thermal problems in vortex development and movement. Part 1: A PV–Q view. Acta Meteor. Sinica, 27, 1–14. doi: 10.1007/s13351-013-0101-3. [50] Zhou, W., J. C. L. Chan, W. Chen, et al., 2009: Synoptic-scale controls of persistent low temperature and icy weather over southern China in January 2008. Mon. Wea. Rev., 137, 3978–3991. doi: 10.1175/2009MWR2952.1. [51] Zhuo, G., X. D. Xu, and L. S. Chen, 2002: Instability of eastward movement and development of convective cloud clusters over Tibetan Plateau. J. Appl. Meteor. Sci., 13, 448–456. (in Chinese). [52] Zuo, Q. J., S. T. Gao, and X. G. Sun, 2017: An effect study of the East Asian jet stream on the freezing rain and snowstorms event over southern China in early 2008 and possible reasons for the jet stream variation. Climatic Environ. Res., 22, 381–391. (in Chinese) doi: 10.3878/j.issn.1006-9585.2016.16072.
•  [1] Jiahui YU, Yimin LIU, Tingting MA, Guoxiong WU. Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part ll: Numerical Simulation. Journal of Meteorological Research, 2019, 33(3): 416-432.  doi: 10.1007/s13351-019-8606-z. [2] REN Rongcai, WU Guoxiong, CAI Ming, SUN Shuyue, LIU Xin, LI Weiping. Progress in Research of Stratosphere-Troposphere Interactions： Application of Isentropic Potential Vorticity Dynamics and the Effects of the Tibetan Plateau. Journal of Meteorological Research, 2014, 28(5): 714-731.  doi: 10.1007/s13351-014-4026-2. [3] WU Qiuxia, NI Yunqi. DIAGNOSTIC ANALYSIS OF THE INFLUENCE OF ANOMALOUS SURFACE SENSIBLE HEAT FLUX IN THE TIBETAN PLATEAU AND ITS VICINITY ON THE EAST ASIAN WINTER MONSOON*. Journal of Meteorological Research, 2004, 18(2): 147-166. [4] Sun Guowu, Yu Yaxun, Wang Baoling, Feng Jianying. NUMERICAL EXPERIMENTS ON THE INFLUENCES OF GENERAL CIRCULATION ANOMALY OVER THE TIBETAN PLATEAU AND SURFACE ALBEDO CHANGE IN NORTHWEST CHINA ON SUMMER PRECIPITATION. Journal of Meteorological Research, 1998, 12(3): 311-320. [5] Sijia ZHANG, Donghai WANG, Zhengkun QIN, Yaoyao ZHENG, Jianping GUO. Assessment of the GPM and TRMM Precipitation Products Using the Rain Gauge Network over the Tibetan Plateau. Journal of Meteorological Research, 2018, 32(2): 324-336.  doi: 10.1007/s13351-018-7067-0. [6] Xin LAI, Yuanfa GONG. Relationship between Atmospheric Heat Source over the Tibetan Plateau and Precipitation in the Sichuan–Chongqing Region during Summer. Journal of Meteorological Research, 2017, 31(3): 555-566.  doi: 10.1007/s13351-017-6045-2. [7] Jie TANG, Xueliang GUO, Yi CHANG. A Numerical Investigation on Microphysical Properties of Clouds and Precipitation over the Tibetan Plateau in Summer 2014. Journal of Meteorological Research, 2019, 33(3): 463-477.  doi: 10.1007/s13351-019-8614-z. [8] YUAN Yuan, LI Chongyin, YANG Song. Decadal Anomalies of Winter Precipitation over Southern China in Association with El Niño and La Niña. Journal of Meteorological Research, 2014, 28(1): 91-110.  doi: 10.1007/s13351-014-0106-6. [9] Ping ZHAO, Yueqing LI, Xueliang GUO, Xiangde XU, Yimin LIU, Shihao TANG, Wenming XIAO, Chunxiang SHI, Yaoming MA, Xing YU, Huizhi LIU, La JIA, Yun CHEN, Yanju LIU, Jian LI, Dabiao LUO, Yunchang CAO, Xiangdong ZHENG, Junming CHEN, An XIAO, Fang YUAN, Donghui CHEN, Yang PANG, Zhiqun HU, Shengjun ZHANG, Lixin DONG, Juyang HU, Shuai HAN, Xiuji ZHOU. The Tibetan Plateau Surface–Atmosphere Coupling System and Its Weather and Climate Effects: The Third Tibetan Plateau Atmospheric Science Experiment. Journal of Meteorological Research, 2019, 33(3): 375-399.  doi: 10.1007/s13351-019-8602-3. [10] ZOU Han, ZHU Jinhuan, ZHOU Libo, LI Peng, MA Shupo. Validation and Application of Reanalysis Temperature Data over the Tibetan Plateau. Journal of Meteorological Research, 2014, 28(1): 139-149.  doi: 10.1007/s13351-014-3027-5. [11] Wei HUA, Guangzhou FAN, Yiwei ZHANG, Lihua ZHU, Xiaohang WEN, Yongli ZHANG, Xin LAI, Binyun WANG, Mingjun ZHANG, Yao HU, Qiuyue WU. Trends and Uncertainties in Surface Air Temperature over the Tibetan Plateau, 1951–2013. Journal of Meteorological Research, 2017, 31(2): 420-430.  doi: 10.1007/s13351-017-6013-x. [12] LI Guoping, DUAN Tingyang, GONG Yuanfa, LU Huiguo. A MODEL FOR QUANTITATIVELY ESTIMATING SHORT-RANGE PRECIPITATION BASED ON GMS DIGITALIZED CLOUD MAPS—PART Ⅰ: ANALYSIS OF QUANTITATIVE CLOUD-PRECIPITATION RELATIONS AND MODEL DESIGN. Journal of Meteorological Research, 2003, 17(2): 218-229. [13] LI Chiqin, ZUO Qunjie, XU Xiangde, GAO Shouting. Water Vapor Transport around the Tibetan Plateau and Its Effect on Summer Rainfall over the Yangtze River Valley. Journal of Meteorological Research, 2016, 30(4): 472-482.  doi: 10.1007/s13351-016-5123-1. [14] ZHANG Xia, YAO Xiuping, MA Jiali, MIMA-Zhuoga. Climatology of Transverse Shear Lines Related to Heavy Rainfall over the Tibetan Plateau during Boreal Summer. Journal of Meteorological Research, 2016, 30(6): 915-926.  doi: 10.1007/s13351-016-6952-7. [15] BAO Yan, GAO Yanhong, Lü Shihua, WANG Qingxia, ZHANG Shaobo, XU Jianwei, LI Ruiqing, LI Suosuo, MA Di, MENG Xianhong, CHEN Hao, CHANG Yan. Evaluation of CMIP5 Earth System Models in Reproducing Leaf Area Index and Vegetation Cover over the Tibetan Plateau. Journal of Meteorological Research, 2014, 28(6): 1041-1060.  doi: 10.1007/s13351-014-4032-4. [16] Siqiong LUO, Xuewei FANG, Shihua LYU, Yu ZHANG, Boli CHEN. Improving CLM4.5 Simulations of Land–Atmosphere Exchange during Freeze–Thaw Processes on the Tibetan Plateau. Journal of Meteorological Research, 2017, 31(5): 916-930.  doi: 10.1007/s13351-017-6063-0. [17] Duan Tingyang. CHARACTERISTICS OF ATMOSPHERIC HEATING AND ATMOSPHERIC CIRCULATION DURING ACTIVE PERIOD OF 500 hPa HIGH OVER THE TIBETAN PLATEAU IN SUMMER*. Journal of Meteorological Research, 1994, 8(1): 72-78. [18] CONG Chunhua, LI Weiliang. THE EXCHANGE OF MASS BETWEEN STRATOSPHERE AND TROPOSPHERE OVER THE TIBETAN PLATEAU AND ITS SURROUNDINGS IN 1998. Journal of Meteorological Research, 2002, 16(4): 481-488. [19] SONG Ci, PEI Tao, ZHOU Chenghu, HE Yawen. Patterns of Multiscale Temperature Variability over the Eastern and Central Tibetan Plateau During 1960-2008. Journal of Meteorological Research, 2013, 27(4): 521-540.  doi: 10.1007/s13351-013-0407-1. [20] Peng JI, Xing YUAN. Underestimation of the Warming Trend over the Tibetan Plateau during 1998–2013 by Global Land Data Assimilation Systems and Atmospheric Reanalyses. Journal of Meteorological Research, 2020, 34(1): 88-100.  doi: 10.1007/s13351-020-9100-3.
###### 通讯作者: 陈斌, bchen63@163.com
• 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 I: Data Analysis

###### Corresponding author: Yimin LIU, lym@lasg.iap.ac.cn;
• 1. Key Laboratory of Meteorological Disaster of Ministry of Education/Joint International Research Laboratory of Climate and Environmental Change, Nanjing University of Information Science & Technology, Nanjing 210044
• 2. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
• 3. College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049
• 4. Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101
Funds: Supported by the China Meteorological Administration Special Public Welfare Research Fund for the Third Tibetan Plateau Atmospheric Science Experiment (GYHY201406001), Key Research Program of Frontier Sciences of Chinese Academy of Sciences (QYZDY-SSW-DQC018), and National Natural Science Foundation of China (41730963, 91437219, and 91637312)

Abstract: The external source/sink of potential vorticity (PV) is the original driving force for the atmospheric circulation. The relationship between surface PV generation and surface PV density forcing is discussed in detail in this paper. Moreover, a case study of the extreme winter freezing rain/snow storm over South China in January 2008 is performed, and the surface PV density forcing over the eastern flank of the Tibetan Plateau (TP) has been found to significantly affect the precipitation over South China in this case. The TP generated PV propagated eastward in the middle troposphere. The associated zonal advection of positive absolute vorticity resulted in the increasing of cyclo-nic relative vorticity in the downstream region of the TP. Ascending air and convergence in the lower troposphere developed, which gave rise to the development of the southerly wind. This favored the increasing of negative meridio-nal absolute vorticity advection in the lower troposphere, which provided a large-scale circulation background conducive to ascending motion such that the absolute vorticity advection increased with height. Consequently, the ascending air further strengthened the southerly wind and the vertical gradient of absolute vorticity advection between the lower and middle troposphere in turn. Under such a situation, the enhanced ascending, together with the moist air transported by the southerly wind, formed the extreme winter precipitation in January 2008 over South China.

Reference (52)

/