Simulation Study on the Radiation Impacts on the Formation and Development of a Tibetan Plateau Vortex
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摘要: 已有研究表明辐射对热带气旋发生发展具有明显调制作用,高原涡与热带气旋有类似的暖心低压结构,辐射在高原涡发生发展过程中的作用也值得探讨。本文利用ERA-Interim再分析资料,通过中尺度数值模式WRF-ARW研究了辐射日变化对高原涡个例发展的影响机制。模拟结果表明,太阳短波辐射对高原涡的发生发展具有明显的调制作用。控制试验(CTL;即保留太阳辐射日变化)较好的再现了高原涡的发展过程。在去掉短波辐射过程的夜间试验(All_night)中,前期高原涡发展速度较快。而在白天(All_day)试验中,短波辐射过程抑制了高原涡的发展。诊断分析表明,夜间长波辐射冷却加强对流层温度递减率,减弱大气静力稳定度;同时,大气温度的降低使得夜间相对湿度增大,有利于对流层低层出现位势不稳定,进而促使高原涡的形成和发展。反之,太阳短波辐射有利于对流层高层增温,加强大气静力稳定度,从而抑制对流活动发展。夜间低层辐合更为强盛,有利于上升运动的加强并诱发高原涡形成;非平衡项结果显示,在高原涡环流中心区域存在正值区,而低涡四周为明显的负值区。从动力学和热力学特征来看,高原涡的发展与热带气旋具有一定的相似性。Abstract: Existing studies have shown that radiation has a significant effect on the occurrence and development of a tropical cyclone (TC). A Tibetan Plateau vortex (TPV) and a TC have a similar structure, the same as that of a warm-hearted and low-pressure structure, so the roles of radiation in the occurrence and development of the TPV is also worth discussing. In this study, the influence of the diurnal cycle of radiation on TPV development was examined using the Advanced Research Weather Research and Forecasting model. The results showed that solar shortwave radiation has a significant effect on the occurrence and development of the TPV. The control run (CTL; with the diurnal cycle of solar shortwave radiation) well reproduced the development process of the TPV. In the experiment with turning off the shortwave radiation (All_night), the TPV developed much faster at the early stage, whereas in the daytime experiment (All_day), the shortwave radiation suppressed the TPV development. The diagnostic analysis indicated that the longwave radiation cooling steepened the tropospheric lapse rate, thus weakening the atmospheric static stability. Additionally, the temperature reduction increased the relative humidity at night, which was conducive to potential instability in the lower troposphere and thus promoted TPV formation and development. Conversely, solar shortwave radiation warmed the upper troposphere and strengthened the static stability, which inhibited the convection development. The convergence at the lower layer is stronger at night than at day, which is beneficial to the ascending motion enhancement and the TPV formation. The unbalanced term indicated that the center of the TPV corresponded to the positive area of the unbalanced term and the outer edge of the TPV with the negative area of the unbalanced term. Numerical results showed that the TPV development bears many similarities to tropical cyclogenesis in terms of dynamics and thermodynamics.
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图 1 2013年6月4日12:00至10日00:00高原涡观测路径。红色数字表示时间,括号内数值为500 hPa最低位势高度(单位: dagpm)
Figure 1. Observation track of the TPV (Tibetan Plateau vortex) from 1200 UTC 4 to 0000 UTC 10 June 2013. Red numbers indicate the time (UTC), the lowest geopotential height (units: dagpm) at 500 hPa is indicated in the brackets
图 2 2013年6月4日(a、c)06:00、(b、d)12:00(a、b)基于再分析资料以及(c、d)CTL试验模拟的500 hPa等压面上的流场(矢量,单位:m s−1)分布,等值线为地形高度在3000 m以上的区域,三角形为高原涡所处的位置
Figure 2. Distributions of wind field (vectors, units: m s−1) from (a, b) reanalysis data, (c, d) CTL (control run) experiment at 500 hPa at 0600 UTC (left column), 1200 UTC (right column) June 4, 2013. Contours outline the Tibetan Plateau with an altitude higher than 3000 m; the triangle shows the location of the TPV
图 3 2013年6月4日09:00(左列)、15:00(中间列)和21:00(右列)模拟的500 hPa等压面上的环境场大尺度相对涡度(阴影,单位:10−5 s−1)、小尺度系统相对涡度(等值线,单位:10−5 s−1)和风场(矢量,单位:m s−1)分布:(a–c)CTL试验;(d–f)All_night试验;(g–i)All_day试验。绿色方框为涡旋中心区域(300 km×300 km)
Figure 3. Distributions of large-scale relative vorticity (shaded, units: 10−5 s−1), small-scale system vorticity (contours, units: 10−5 s−1) and wind field (vectors, units: m s−1) from (a–c) CTL, (d–f) All_night experiment, and (g–i) All_day experiment at 500 hPa at 0900 UTC (left column), 1500 UTC (middle column), and 2100 UTC (right column) 4 June 2013. The green box indicates the central area of the TPV(300 km×300 km)
图 4 2013年6月4日高原涡中心附近(300 km×300 km)12:00~18:00时间平均的CFAD(Contoured Frequency by Altitude Diagram,阴影)分布:(a)CTL试验;(b)All_night试验;(c)All_day试验
Figure 4. Averaged CFAD ( Contoured Frequency by Altitude Diagram; shaded) during 1200 UTC–1800 UTC 4 June 2013, calculated over a box area with a radius of 300 km around the vortex center: (a) CTL; (b) All_night experiment; (c) All_day experiment
图 5 2013年6月4日00:00~23:00低涡中心附近区域平均(300 km×300 km)相对涡度(阴影,单位: 10−5 s−1)的垂直分布:(a)CTL试验;(b)All_night试验;(c)All_day试验
Figure 5. Time evolution of the vertical profile of vorticity (shaded, units: 10−5 s−1) during 0000 UTC–2300 UTC 4 June 2013, averaged over a box area with a radius of 300 km around the vortex center: (a) CTL experiment; (b) All_night experiment; (c) All_day experiment
图 8 2013年6月4日09:00(左列)、15:00(中间列)和21:00(右列)500 hPa等压面上的环境场大尺度相对涡度(阴影,单位:10−5 s−1)、OW指数(等值线,单位:10−9 s−2)分布:(a)CTL试验;(b)All_night试验;(c)All_day试验
Figure 8. Distributions of environmental vorticity (shaded, units: 10−5 s−1), OW index (contour, units: 10−9 s−2) at 500 hPa at 0900 UTC (left column), 1500 UTC (middle column) and 2100 UTC (right column) 4 June 2013: (a) CTL experiment; (b) All_night experiment; (c) All_day experiment
图 9 2013年6月4日09:00(左列)、15:00(中间列)和21:00(右列)500 hPa等压面上非平衡项(阴影,单位:10−9 s−2)、风场(矢量,单位:m s−1)分布:(a)CTL试验;(b)All_night试验;(c)All_day试验
Figure 9. Distributions of non-balance terms (shaded, units: 10−9 s−2 ), wind field (vectors, units: m s−1) at 500 hPa at 0900 UTC (left column), 1500 UTC (middle column) and 2100 UTC (right column) 4 June 2013: (a) CTL experiment; (b) All_night experiment; (c) All_day experiment
图 10 2013年6月4日21:00(a)CTL、(b)All_night和(c)All_day试验中垂直运动(阴影,单位:10−2 m s−1)和切向风速(等值线,单位:m s−1)的轴对称分量的半径—高度的垂直剖面
Figure 10. Radius–height cross sections of the axisymmetric component of vertical velocity (shaded, units: 10−2 m s−1) and tangential wind speed (contour, units:
$ m{s}^{-1} $ ) in (a) CTL, (b) All_night, and (c) All_day experiments at 2100 UTC 4 June 2013图 12 2013年6月4日(a–c)CTL、(d–f)All_night和(g–i)All_day试验的500 hPa等压面上公式(2)中扰动动能倾向
$\displaystyle\frac{\partial K'}{\partial t}$ (左列)、纬向风辐合$-\overline{u{'}^{2}}\displaystyle\frac{\partial }{\partial x}\overline{u}$ (中间列)和径向风辐合$-\overline{v{'}^{2}}\displaystyle\frac{\partial }{\partial y}\overline{v}$ (右列)00:00~12:00时间平均结果分布(阴影,单位:10−5 m2 s−3),三角形为高原涡所处的位置Figure 12. Horizontal pattern of kinetic energy tendency
$\displaystyle\frac{\partial K'}{\partial t}$ (left column), latitudinal wind convergence$-\overline{u{'}^{2}}\displaystyle\frac{\partial }{\partial x}\overline{u}$ (middle column ) and radial wind convergence$-\overline{v{'}^{2}}\displaystyle\frac{\partial }{\partial y}\overline{v}$ (right column ) in Eq. 2 on the 500 hPa (shaded, units: 10−5 m2 s−3), the triangle reflects the location of the TPV in (a-c) CTL, (d-f) All_night, and (g-i) All_day. Time averaged from 0000 UTC–1200 UTC 4 June 2013图 13 2013年6月4日00:00~23:00(a)CTL、(b)All_night和(c)All_day试验中低涡中心附近区域平均(300 km×300 km)相对湿度(阴影)垂直分布随时间的变化
Figure 13. Time evolution of the vertical profile of relative humidity (shaded), averaged over a box area centered at the TPV during 0000 UTC–2300 UTC 4 June 2013: (a) CTL experiment; (b) All_night experiment; (c) All_day experiment
图 14 2013年6月4日00:00~23:00(a)CTL、(b)All_night和(c)All_day试验中低涡中心附近区域平均(300 km×300 km)的降水效率随时间的变化
Figure 14. Time evolution of PE (Precipitation Efficiency) in CTL, All_night, and All_day experiments during 0000 UTC–2300 UTC 4 June 2013. Averaged over a box area with a radius of 300 km around the vortex center
图 15 2013年6月4日00:00~23:00(a)三组试验中低涡中心附近区域(300 km×300 km),辐射导致的平均加热廓线(单位:K h−1),低涡中心附近区域(300 km×300 km)平均温度垂直分布随时间变化的差异,(b)All_night 减CTL试验(c)All_day减 CTL试验(等值线,单位:K, 实线为正值,虚线为负值)
Figure 15. (a) Vertical profiles of radiative heating (units: K h−1) in the three experiments, which are averaged over a box area centered at TPV during 0000–2300 UTC 4 June 2013. Time evolution of the vertical profile of temperature contrast (units: K, solid lines indicate positive value, dash lines indicate negative value) which are averaged over the box area centered at the TPV for (b) All_night minus CTL and (c) All_day minus CTL
图 16 2013年6月4日09:00、15:00和21:00(a)CTL、(b)All_night和(c)All_day试验中低涡中心附近(300 km×300 km)区域平均的
$ {\partial \theta }/{\partial p} $ 垂直廓线(单位:K hPa−1)分布Figure 16. Vertical profiles of
$ {\partial \theta }/{\partial p} $ (units: K hPa−1) at 0900 UTC, 1500 UTC, and 2100 UTC 4 June 2013, which are averaged over the box area centered at the TPV: (a) CTL experiment; (b) All_night experiment; (c) All_day experiment表 1 试验的描述
Table 1. Description of the experiments
试验名称 描述 CTL 太阳短波辐射具有完整的日循环 All_night 太阳短波辐射的强度固定在午夜(00:00) All_day 太阳短波辐射的强度固定在正午(12:00) -
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