Spatial and temporal patterns of planetary boundary layer height during 1979-2018 over the Tibetan Plateau using ERA5

Planetary boundary layer height (PBLH) is a key meteorological parameter that is affected by and influences exchanges of energy, momentum, and mass between the surface and the atmosphere, but there are few comprehensive studies on the PBLH climatology over the Tibetan Plateau (TP). This study presents a multi-decadal climatology of PBLH over the TP by using high-resolution reanalysis data (ERA5) for the period 1979-2018. The ERA5 PBLH was first evaluated against radiosonde-derived PBLH from four sites. For most of the observation periods and sites, ERA5 captured the diurnal cycles reasonably well, although the highest peaks in the radiosonde-derived PBLH were often not captured. Next, long-term means and trends, seasonality and diurnal cycles of the PBLHs were examined. The results show that average PBLHs in the central and southwestern TP are higher than those in the west and east. On an interannual time scale, the PBLH is positively correlated with the North Atlantic Oscillation in western and southeastern TP in winter, eastern TP in summer, and central TP in autumn, while a negative correlation is seen for northeastern TP in winter. The summertime PBLH in the central and southwestern TP is negatively correlated to the Indian summer monsoon. As for the seasonal cycle, the PBLH in the western TP reaches its peak in August, while the PBLH in the eastern TP exhibits an earlier summer peak in June. In the central TP, the PBLH is the highest in April and displays a minimum during summer, corresponding to a precipitation peak and a dip in surface sensible heat flux. The climatological diurnal cycles of PBLH are generally affected by the insolation and reach their peaks in the afternoon when a large range in PBLH variation is also found.