Linking quasi-biweekly variability of the South Asian high to atmospheric heating over Tibetan Plateau in summer

Abstract

This study investigates the summertime day-to-day variability of the South Asian high (SAH) driven by atmospheric heating over Tibetan Plateau (TP) using the NCEP/NCAR reanalysis dataset. We first isolate the day-to-day variability of SAH in summertime based on the intensity of the summertime Tibetan Plateau upper-atmospheric heat source (TPUHS). It shows that anomalously stronger TPUHS days are accompanied with SAH center over Iranian Plateau (IP or the IP phase of the SAH) and the SAH center moves to TP (or the TP phase) during weaker TPUHS days, which contrasts with the corresponding relationship between SAH IP/TP phase and weaker/stronger TP heating in monthly and longer timescale. We further demonstrate that the SAH IP/TP phase coincides with stronger/weaker low surface pressure anomalies over TP. The stronger ascending and upper-tropospheric divergence anomalies above TP during stronger TPUHS days connect to compensatory stronger descending and upper-tropospheric convergence anomalies over IP. Such day-to-day SAH variability associated with TPUHS exhibits a quasi-biweekly time scale with a pronounced westward propagating signal.