辐射对高原涡形成和发展影响的模拟研究

Simulation Study on the Radiation Impacts on the Formation and Development of a Tibetan Plateau Vortex

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。

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 warmhearted 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.