Impact of the summer atmospheric heat source over the Tibetan Plateau on interannual variability of meridional circulation on the north side of Tibetan Plateau

The summer atmospheric heat source (AHS) over the Tibetan Plateau (TP) induces meridional circulations in TP and its surrounding areas. Previous studies mainly focused on the monsoon circulation on the south side of TP, while the formation and maintaining mechanism of meridional circulation on its north side remain unclear. This study compared three calculation methods of the AHS, analyzed spatial-temporal variability of the summer AHS over the TP, and discussed its influence on interannual variability of meridional circulation on the north side of TP based on the two-dimensional decomposition method of atmospheric circulation and sensitivity experiments. The results indicate that in the positive AHS anomalies years, the diabatic heating of condensation latent release in southeastern TP could motivate anomalous ascending motion. Simultaneously, the increased meridional temperature gradient between the middle and high latitudes of East Asia leads to an enhanced southward westerly jet. In this context, the region on the north side of TP, located on the north side of westerly jet entrance, is affected by negative anomalous relative vorticity advection, prevailing anomalous descending motion, which makes the descending branch of meridional circulation significantly presented. Unlike previous studies considered the descending branch of meridional circulation as the compensation for upward flow, the results of LBM model verify the descending branch is mainly influenced by the vorticity advection related to regional scale variability of westerly jet. This study reveals the physical mechanism of meridional circulation on the north side of TP, which offers valuable implications for seasonal forecasting in TP and Northwest China.