Numerical Simulation of Impacts of the Tibetan Plateau Heating on a Persistent Heavy Rainfall in Western Sichuan Basin
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摘要: 通过对四川盆地西部一次持续性暴雨过程的半理想数值模拟,研究了青藏高原热力作用对四川盆地持续性暴雨过程的影响。研究表明,高原的热力作用对于下游地区有着显著的影响,主要表现为:(1)关闭高原地面感热和潜热后,高原地区和四川盆地西部的降水明显减弱,而盆地中东部降水却有所加强,且四川盆地降水的日变化特征稍有减弱;(2)500 hPa青藏高原上的短波槽减弱,位于四川盆地中西部的背风槽强度、范围有所减弱,但低层盆地东部的气旋性涡旋加强;(3)涡度收支的定量分析发现,关闭高原热力作用后,盆地东部对流层低层垂直风切变的增强使得夜间倾斜项的正贡献增强,从而使该区域涡旋发展加强,盆地东部降水增强。Abstract: The influence of sensible and latent heat anomalies over the Tibetan Plateau (TP) on a persistent rainfall in western Sichuan Basin is investigated via a semi-idealized mesoscale numerical model WRF (Weather Research and Forecasting) simulation. Analyses of the simulation show that when the heating on the TP is turned off, rainfall decreases in the TP and western Sichuan Basin but increases in central and eastern Sichuan Basin, while the diurnal variation of precipitation weakens; the trough over the TP on 500 hPa disappears, the strength and scope of the westerly trough reduces slightly, but the meso-cyclone at low levels in eastern Sichuan Basin enhances; quantitative analysis of vorticity budget during the heavy rain period indicates that the intensification of vertical wind shear in the lower troposphere makes positive contribution to strengthening the TILT (tilting term) in eastern Sichuan Basin, and thus facilitates vortex development in the key area of Sichuan Basin, which also leads to increases in precipitation in eastern Sichuan Basin.
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Key words:
- Sichuan Basin /
- Persistent heavy rainfall /
- Numerical simulation /
- Tibetan Plateau
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图 2 2013年7月1~10日平均环流形势:(a)实况;(b)对照试验。黑色等值线为500 hPa位势高度场(单位:gpm),绿色实线为位势高度5880 gpm线,蓝色风标为200 hPa高空急流(≥30 m s–1,风羽:10 m s–1),红色风标为850 hPa低空急流(≥12 m s–1,风羽:10 m s–1),填色区为整层可降水量大于55 mm的区域(单位:mm)
Figure 2. Composite mean synoptic weather patterns from 1 to 10 July 2013: (a) Observation; (b) control experiment. Black solid lines indicate geopotential height in gpm at 500 hPa with the 5880 gpm shown by green solid line (units: gpm), blue barbs indicate wind speeds exceeding 30 m s–1 at 200 hPa (units: m s–1, full barb:10 m s–1), red barbs represent wind speeds exceeding 12 m s–1 at 850 hPa (units: m s–1, full barb:10 m s–1), the colored areas are for precipitable water ≥55 mm
图 6 2013年7月2~10日平均的对照试验500 hPa位势高度场(蓝色等值线,单位:gpm)、500 hPa正涡度(红色等值线,单位:10—5 s—1)、小时降水量(填色,单位:mm)的日变化,灰色阴影为地形高度大于3000 m区域
Figure 6. Simulated diurnal variation of geopotential height at 500 hPa (blue lines, units: gpm), positive relative vorticity at 500 hPa (red lines, units: 10—5 s—1), and hourly rainfall (colored areas, units: mm h—1) averaged during 2—10 July 2013. Areas shaded in gray indicate where terrain ≥3000 m in the control experiment
图 8 2013年7月2~10日敏感试验与对照试验沿雨带(29°N~32°N)平均的(a)每小时降水差值(单位:mm)和(b)2013年7月2~10日平均的每小时降水量日变化差值(单位:mm h—1)
Figure 8. Time—longitudinal diagram of (a) hourly rainfall difference (mm) and (b) hourly rain rate difference (units: mm h—1) between sensitivity experiment and control experiment averaged over 29°N—32°N during 2—10 July 2013
图 10 2013年7月2~10日平均的敏感试验与对照试验700 hPa风场差值(单位:m s–1)和每小时雨量差值(填色,单位:mm),红线区域地形高度大于3000 m
Figure 10. 700 hPa wind differences (m s–1) and hourly rainfall differences between sensitivity experiment and control experiment (colored, units: mm) averaged during 2—10 July 2013. The area surrounded by red line indicates elevation ≥3000 m
图 11 2013年7月7日12:00至9日12:00关键区平均850 hPa涡度收支项(单位:10—9 s—2),HADV为绝对涡度的水平平流项,VADV为相对涡度的垂直平流项,DIV为散度项,TILT为扭转项,SUM为以上四项的总和,LHS为方程左边项:(a)对照试验;(b)敏感试验
Figure 11. Terms in the vorticity equation at 850 hPa from 1200 UTC 7 July to 1200 UTC 9 July 2013 (units: 10—9 s—2): (a) Control experiment; (b) sensitivity experiment. HADV is horizontal vorticity advection; VADV is vertical vorticity advection; DIV is the term of divergence; TILT is the tilting term; SUM is the sum of the former four terms; LHS represents the term on the left-hand side of the vorticity equation
图 12 2013年7月7日12:00至9日12:00平均850 hPa与700 hPa垂直风切变(单位:m s–1):(a)对照试验;(b)敏感试验。红色圈代表分析差异区域
Figure 12. Averaged wind shears (units: m s–1) between 850 hPa and 700 hPa from 1200 UTC 7 July to 1200 UTC 7 July 2013: (a) Control experiment; (b) sensitivity experiment. The red circles are used for comparisom
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