Effect of low frequency oscillation of Monsoon on the heavy rainfall from the landing typhoon based on the Wavelet analysis

By using Wavelet analysis and Lanczos filter, a study is performed of the influences of low frequency oscillation of Monsoon on the torrential rain from the landing typhoon Bilis based on the dataset of CMA-STI Tropical Cyclone Optimal Tracks, NCEP/NCAR reanalysis and intensive surface observations. Results show that before the Bilis´s landfall, 2006 East Asian low frequency southwesterly experienced remarkable northward propagation. After its landing, the strongest low frequency southwesterly and powerful low frequency vapor convergence were just on the south side of the Bilis, resulting in sharply increased rainfall. In addition, a broad belt of high-valued vapor fluxes extended from the eastern Arabian Sea via the Bay of Bengal, Indo-China Peninsula and the South-China Sea into South China. The belt was linked with the low frequency southwesterly forming a moist tongue stretching from the Bay of Bengal to South China, which supplied continuously abundant vapor for the Bilis along with the surge propagating poleward, allowing its long stay over land instead of erosion and disappearance.