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The Tibetan Plateau (TP) is one of the regions with the most remarkable diurnal variations in the global atmosphere. The zonal shear line (ZSL) is the primary synoptic system inducing precipitation over the TP in boreal summer. It is of great significance in studying its diurnal variation. This study objectively identified and composited 11 ZSL cases inducing anomalous heavy precipitation based on the ERA5 hourly reanalysis datasets from June to August during 1980–2019. The diurnal variation characteristics and mechanisms of ZSL's intensity were explored based on the composited ZSL. Results suggest that the intensity of ZSL has significant diurnal variation, reaching the peak at midnight (about 23 Local Solar Time). The dynamical and thermal structures near the ZSL both show significant diurnal variations. There is a significant heating effect near the ZSL after sunrise, followed by strong divergence (convergence) in the upper (lower) layer and significant increases in water vapor flux convergence and ascending motions. The vorticity is strongest at midnight. Diagnosis by the complete‐form vertical vorticity tendency equation reveals that the thermal effect, dominated by vertically non‐uniform distribution of atmospheric diabatic heating, is the most crucial factor affecting the diurnal variation of ZSL's intensity. The configuration of solar radiation and sensible heat in the near‐ground layer and latent heat in the middle and upper layers jointly dominate the vertically non‐uniform heating. The horizontally non‐uniform heating only contributes little to the local change of vorticity at 500 hPa. Ascending motion and vorticity advection have only weak effects. Key Points: The intensity of ZSL peaks at midnight (about 23 LST), and its dynamical and thermal structures also have significant diurnal variationsThe non‐uniform vertical distribution of atmospheric diabatic heating is the primary mechanism of the diurnal variation of ZSL's intensityThe vertically non‐uniform heating is related to configurations of Q–QLH in the near‐ground layer and QLH ${Q}_{LH}$ in the middle and upper layers [ABSTRACT FROM AUTHOR]

The zonal shear line (ZSL) over the Tibetan Plateau (TP) is one of the most crucial synoptic systems inducing precipitation over the TP in boreal summer. However, few studies have comprehensively explored the thermal mechanism of the intensity evolution of the ZSL. In this study, the mechanism of the atmospheric diabatic heating (hereafter referred to as diabatic heating) effect on the intensity of the ZSL was explored by the methods of composite and diagnostic analysis. Based on the fifth generation European Centre for Medium‐Range Weather Forecasts atmospheric reanalysis of the global climate hourly data sets from June to August during 1980–2019, 11 cases of the ZSL were selected by using the objective identification method. Results suggest that a close relationship exists between the ZSL's intensity and the 10‐h‐earlier vertically integrated diabatic heating , with a high correlation coefficient of 0.81. The intensity of peaks at around 13 LST (Local Solar Time) within a day. The diabatic heating rate Q reaches the maximum values at 350 hPa. The vertical transport of temperature is the main contributor to the intensity of Q during the intensity evolution of the ZSL. The vertically non‐uniform diabatic heating effect is the primary mechanism for the intensity evolution of the ZSL. When the vertically non‐uniform diabatic heating near the ZSL enhances (weakens), it will be favorable (unfavorable) to enhance the ZSL's intensity. Key Points: A close relationship exists between the zonal shear line's (ZSL) intensity and the 10‐h‐earlier diabatic heating, with a correlation coefficient of 0.81The vertical transport of temperature is the main contributor to the diabatic heating during the intensity evolution of the ZSLThe vertically non‐uniform diabatic heating effect is the primary mechanism of the ZSL's intensity [ABSTRACT FROM AUTHOR]