Extraction and prediction of monsoon intraseasonal 1 oscillations : An approach based on nonlinear 2 Laplacian spectral analysis

An improved index for real-time monitoring and forecast verification 7 of monsoon intraseasonal oscillations (MISOs) is introduced using the recently de-8 veloped nonlinear Laplacian spectral analysis (NLSA) technique. Using NLSA, a 9 hierarchy of Laplace-Beltrami (LB) eigenfunctions are extracted from unfiltered 10 daily rainfall data from the Global Precipitation Climatology Project over the 11 south Asian monsoon region. Two modes representing the full life cycle of the 12 northeastward-propagating boreal summer MISO are identified from the hierar-13 chy of LB eigenfunctions. These modes have a number of advantages over MISO 14 modes extracted via Extended Empirical Orthogonal Function (EEOF) analysis, 15 including higher memory and predictability, stronger amplitude and higher frac