Search

The atmospheric boundary layer (ABL) is one of the most fundamental yet complex components of the Earth's atmosphere. Hence, studying the ABL has important theoretical value and practical significance. In this paper, the structural characteristics and heating (cooling) rate of the ABL in summer over the Northern Tibetan Plateau (NTP) were analysed using radiosonde observation data from the Amdo and Nagqu regions. The results indicate that the summertime ABL height over the NTP exhibited obvious diurnal variations, with the ABL height during the dry season being greater than that during the rainy season. The maximum convective boundary layer (CBL) height during the daytime reached 3200 m and 2500 m in the dry and rainy seasons, respectively, and the mean maximum CBL height was approximately 2500 m; the maximum stable boundary layer (SBL) height at night reached 900 m, and the mean maximum SBL height was approximately 500 m. The wind speed dominated by westerly wind in the dry season was greater than that dominated by easterly wind in the rainy season, and the zonal (meridional) wind speed (shear) on sunny days was greater than that on cloudy days. The inverse humidity phenomenon occurred in both Amdo and Nagqu, and the strong humidity inversion occurred mainly at midnight on sunny days and at noon on cloudy days. The heating (cooling) rate of the ABL displayed obvious diurnal variations, with the rates being greater on sunny days and lower on cloudy and rainy days. Furthermore, the mean values of the daytime heating rate and nighttime cooling rate of the ABL were relatively equal, indicating that the atmospheric energy budget was, for the most part, balanced. • The ABL height in summer over the Northern Tibetan Plateau was determined. • The heating and cooling rates of the ABL in summer were calculated. • The wind speed (shear) in the dry season was greater than that in the rainy season. • The inverse humidity phenomenon occurred at both Amdo and Nagqu. [ABSTRACT FROM AUTHOR]

• Dryline formation is favoured by the advection of mid-level dry air from the Pacific. • Local circulations impact the dryline movement and strength in quiescent conditions. • Nocturnal LLJ and local circulations reinforce the moisture gradient at night. • In synoptically active periods, dry advection and diurnal mixing are more important. Drylines are a frequent feature of the atmospheric circulation in Argentina. Recent work described their climatological characteristics and synoptic-scale processes associated with their formation. However, little is known about the mesoscale processes that are relevant for their life cycle. In this paper, we investigate the influence of these mechanisms on the formation and movement using a case-study approach. Also, the relationship between these mechanisms and convective initiation near the dryline is investigated. A typical northern Patagonia dryline is simulated using the Weather Research and Forecasting (WRF) with an horizontal resolution of 3 km. The FLEXible PARTicle dispersion-WRF is also used to study some of the processes from a Lagrangian perspective. During the quiescent period corresponding to dryline formation and intensification, the dryline strengthens along the axis of a thermally-induced surface trough that promotes differential moisture advection. Also, convergence along the dryline is enhanced during night-time by the inertial oscillation ahead of the dryline and by the development of a thermally-driven circulation between the elevated terrain in northern Patagonia and the adjacent plains. These two mechanisms contribute to enhancing the intensity of the moisture gradient and to trigger deep moist convection. Under a period of stronger synoptic forcing, the dryline intensifies in response to the confluence induced by the deepening surface trough and moves away from the terrain elevations. Its movement during this period is driven by horizontal dry advection and the vertical mixing enhanced by the entrainment into the boundary layer of extremely dry air, whose origin can be traced back to the mid-levels over the Pacific Ocean. When the magnitude of the low-level westerly winds increase, moister air from lower levels cross the barrier, contributing to weakening the moisture gradient at the dryline. [ABSTRACT FROM AUTHOR]