The relationship between the tropopause folds and deep convective activities over the Tibetan Plateau

Abstract

Tropopause folds (TFs) are crucial in the development of certain meteorological events. Using ERA5 reanalysis data from 1979 to 2015 and the “3D-labelling” algorithm for identifying TFs, along with OLR and TRMM precipitation data, this study conducted a composite analysis to explore the relationship between TFs and deep convective activities (DCAs) over Tibetan Plateau (TP) and to investigate the underlying physical mechanisms. The results indicate that TFs have a strong inhibitory effect on DCAs at the locations of folds. Conversely, medium and deep folds significantly enhance DCAs to the northeast of folds, with the degree of enhancement intensifying with the depth of fold. During medium and deep fold occurrences, an increase in specific humidity from the surface to near the tropopause is observed northeast of the folds, coupled with significant lifting of the tropopause east of the deep folds, favoring the initiation and development of DCAs. Positive potential vorticity (PV) anomalies resulting from the downward intrusion of stratospheric air with high PV generate cyclonic circulation in the upper troposphere at the locations of folds. This is complemented by anticyclonic circulations triggered on both sides of medium and deep folds. These circulation anomalies induce upper-level divergence and lower-level convergence, leading to anomalous upward motion northeast of the folds and thereby promoting DCAs. Furthermore, the increased low-level static stability northeast of medium and deep folds aid in accumulating potential instability. The anomalous ascent in this region facilitates the release of this instability, and in conjunction with reduced static stability near the tropopause, enables DCAs to reach higher altitudes.