[AOS17-P07] Intraseasonal Variability over the Arabian Sea and Its Impact on the Indian Summer Monsoon Onset
Keywords:Indian Summer Monsoon, intraseasonal variability, air-sea interaction
Based on the NCEP/NCAR and ERA-Interim reanalysis data, the processes associated with intraseasonal convection over the Arabian Sea (AS) are investigated during the Indian Summer Monsoon (ISM) onset. Onsets of the years 1980-2016 are sorted into early and late onset categories. Composites reveal that warm SST over the northern AS plays an active role in triggering anomalous convection and the reversal of prevailing winds through regional air-sea interaction before early onset of ISM. Increased latent heat release favors static instability and enhances convergence in lower troposphere which develops into Monsoon onset vortex (MOV). This convergent flow is well coupled with strong divergence pumping in upper troposphere, leading to appreciable growth of intraseasonal convection in early onset years.
On the other hand, the regional air-sea interaction contributes to intraseasonal convection after the late onset of ISM. The static instability plays a small role in the convection development which decays after onset due to anomalous diabatic heating in upper troposphere. Along with the decay of static instability, the de-coupled 3-dimentional circulation also results in the weak convection in late onset years.
On the other hand, the regional air-sea interaction contributes to intraseasonal convection after the late onset of ISM. The static instability plays a small role in the convection development which decays after onset due to anomalous diabatic heating in upper troposphere. Along with the decay of static instability, the de-coupled 3-dimentional circulation also results in the weak convection in late onset years.