13 June 2017

East Asian Summer Rainfall Variation Tied to Latitudinal Migration of Westerlies across the Tibetan Plateau

Science

The authors show that the leading ‘tripole’ mode of summer rainfall variation over East Asia comes about because the Meiyu terminates early in some years, due to the westerlies migrating northwards earlier away from the Tibetan Plateau.The authors show that the leading ‘tripole’ mode of summer rainfall variation over East Asia comes about because the Meiyu terminates early in some years, due to the westerlies migrating northwards earlier away from the Tibetan Plateau.

Impact

East Asia undergoes significant year-to-year variation in summer rainfall, but dynamical causes are yet to be established. Our study shows direct observational evidence for latitudinal position of westerlies to control the timing and duration of the intraseasonal stages of the East Asian summer monsoon, in particular the timing of Meiyu termination.  This link suggests a way forward to dynamically understand controls of East Asian summer rainfall variations.

Summary

Observed gridded land rainfall over East Asia is analyzed to show that one phase of the ‘tripole’ mode of July-Aug rainfall variation is associated with an earlier (by 2-3 weeks) Meiyu termination and longer Midsummer rainfall stage. NCEP reanalysis westerly fields over the same period shows the core of the westerlies shifts off the northern edge of the Plateau earlier in this phase, in sync with the earlier Meiyu termination.  Our study thus show direct observational evidence for latitudinal position of westerlies to control the timing and duration of the intraseasonal stages of the East Asian summer monsoon. 

Contact
John Chiang
University of California - Berkeley