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

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.