Associations between China monsoon rainfall and tropospheric jets

Strong associations, in both the annual cycle and interannual variations, b etween east China monsoon rainfall and tropospheric jets are established wi th the use of observations and general-circulation model simulations. Two d istinct systems dominate regional rainfall: the east Asian jet stream (EAJ) in the north and the Hadley cell in the south. The EAJ is associated with Mei-Yu and polar fronts as well as vigorous jet-transverse circulations, wh ereas the Hadley cell is allied to tropical upper-level easterlies and inte rtropical convergence zone convection. An equatorward EAJ displacement caus es precipitation to increase over south-central (south) China during June A ugust (January-March). Conversely, a poleward shift of the summer (winter) EAJ brings heavier precipitation over north (central-north) China. On the o ther hand, over the South China Sea the Hadley cell influence prevails and, consequently, increased rainfalls concur with enhanced lower-level westerl ies. Furthermore, the EAJ fluctuations are strongly coupled with southern o scillation variations. Their interactions tend to precede (follow) El Nino phenomena during October through May (summer). The EAJ related flow anomali es also have potential skill to predict China rainfall interannual variabil ity. To conclude, a realistic China monsoon simulation requires accurate re presentation of the EAJ and Hadley cell. Both features link regional rainfa ll to tropical and extratropical planetary-scale circulations and, in turn, to global surface characteristics.