Diurnal variation in the intensity of nascent Tibetan Plateau vortices

Abstract

Tibetan Plateau vortices (TPVs) are major rain‐producing systems forming over the Tibetan Plateau, and the ones moving off the plateau can trigger heavy rainfall over eastern China. The survival probability of a nascent TPV is closely related to its intensity, which is important in the prediction of the precipitation over and to the east of the Tibetan Plateau. In this study, diurnal variation of the intensity of nascent TPVs (ITPV) occurring in four local time periods (hours 00–06 LT, 06–12 LT, 12–18 LT, 18–00 LT; LT = UTC + 6 h) during May–August of 2000–2016 was investigated. The average ITPV shows a robust diurnal variation, with the maximum from evening to midnight (18–00 LT) and minimum from morning to noon (06–12 LT). In 18–00 LT, the ratios of the strong and weak TPVs are 46 and 22.2%, respectively, while those in 06–12 LT are 26.3 and 42.4%. The strong TPVs occurring in 18–00 LT are mainly located over the western and central Tibetan Plateau, while in 06–12 LT over the central and eastern Tibetan Plateau. The dynamic and thermodynamic processes associated with the diurnal variation of ITPV are studied, revealing the important roles of large‐scale circulations and condensational latent heat related to precipitation. In 18–00 LT, the strongest convergence at 500 hPa, divergence at 200 hPa, and the accordingly strongest ascending motion, as well as the largest amount of net water vapour budget are observed, benefiting the precipitation and the related latent heat release. On the contrary, the situations in 06–12 LT result in little latent heat release. The diagnosis of potential vorticity budget further verifies the important effect of condensational latent heating on ITPV.