Atmospheric Meridional Circulation Between South Asia and Tibetan Plateau Caused by the Change of Planetary Boundary Layer Depth

Planetary boundary layer (PBL) influences the vertical exchanges of momentum, heat, water vapor, atmospheric pollutants, and the efficacy of climate forcing between land surface and atmosphere. Over the western Tibetan Plateau (TP), PBL can stretch into the middle-upper troposphere. In this study, we investigate an effect of the PBL depth change on atmospheric circulations between South Asia and the TP through the formula derivation, the observation, and the model data set. The derivation first gives the PBL depth-generalized pressure equation. It reveals an effect of PBL depth on the pressure change with time. The data analysis further shows that an increase of PBL depth in the western TP can cause the subsequent development of the PBL low (high) pressure anomalies in the northwestern TP (northern South Asia) and the upper-tropospheric high (low) pressure anomalies over the TP (South Asia), with an anticlockwise meridional-vertical circulation (MVC) anomaly from South Asia to the TP. In this process, the peak of PBL depth may be ahead of that of the low-pressure occurrence, which may cause the MVC development to lag behind surface heating. The anticlockwise MVC anomaly strengthens the transport of water vapor from the lower troposphere over South Asia to the TP PBL, producing convective precipitation in the TP.

Automated summary

This study investigates the impact of the changes in planetary boundary layer (PBL) depth on atmospheric circulations between South Asia and the Tibetan Plateau (TP). The results show that an increase in PBL depth can lead to the development of low-pressure anomalies in the TP and high-pressure anomalies in South Asia, creating an anticlockwise meridional-vertical circulation anomaly. This circulation anomaly enhances the transport of water vapor from South Asia to the TP, resulting in convective precipitation in the TP.