Change in the tilting of the ridgeline surface of the subtropical anticyclone and the predictability of the onset of the Asian summer monsoon
MAO Jiangyu, DUAN Anmin, LIU Yimin WU Guoxiong State Key Laboratory of Numerical Modeling for Almospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
The NCEP/NCAR reanalysis data are used to study the relationships among the change in the tilting of the ridgeline surface of the subtropical anticyclone, the estab- lishment of the so-called "seasonal transition axis (STA)" and the onset of the Asian summer monsoon. It is shown that the monsoon onset is characterized by the overturning of the meridional temperature gradient (MTG) in the vicinity of the ridgeline surface. A MTG index is then constructed to inves- tigate the predictability of the Asian summer monsoon onset conceptually. Data diagnoses show that if the initial MTG is known and the meridional gradient across the ridgeline sur- face of the local temperature tendency can be estimated, a late or early onset of the summer monsoon can be qualita- tively predicted in advance.