Interannual variability of the Asian Summer Monsoon Anticyclone

Definition of the boundaries of the Asian summer monsoon anticyclone (ASMA) is a known challenge that highly impacts the information about the anticyclone's behavior and affects the study of its interannual variability. We present a novel method based on the absolute vortex moments that defines the ASMA boundaries by solving an optimization problem. The results show climatology (1980–2023), interannual variability, start and end dates range and the duration of the anticyclone peak phase calculated with help of the defined method. In addition, three individual years – 2017, 2022 and 2023 are highlighted during which StratoClim, ACCLIP and PHILEAS campaigns took place respectively. The interannual analysis is based on the anticyclone's centroid latitude and longitude, excess kurtosis, angle, aspect ratio and using 4 isentropic surfaces: 350, 370, 390 and 410K. The work determined correlation of the centroid position of the anticyclone with a set of month lag ENSO considering the whole year equatorial pacific sea surface temperature anomalies (DJF–NDJ) using ONI index. The ASMA centroid latitude is negatively correlated with 5-month lag ENSO ( ∼ -0.6) when the anticyclone is still in its formation phase and then the correlation starts to decline when the anticyclone enters its peak phase.