Basin dependence of the MJO modulating tropical cyclone genesis

Abstract

The modulation of tropical cyclone (TC) genesis over the western North Pacific (WNP) and the tropical North Atlantic (ATL) by the Madden–Julian Oscillation (MJO) is investigated based on observational analysis and numerical simulations. A genesis potential index (GPI) is used to investigate relative contributions of environmental parameters associated with the MJO to TC genesis. It is found that relative humidity plays the most important role in modulating TC genesis in the WNP, the Gulf of Mexico and the western Caribbean Sea (GOM), while vertical wind shear associated with the MJO has the most significant impact on TC activities in the eastern Atlantic (EAT). To further understand the relative importance of the MJO dynamic and thermodynamic impact on TC activities, idealized numerical model experiments are conducted using the Advanced Research version of the Weather Research and Forecasting model (WRF-ARW). The results are consistent with that of observational analysis, indicating that TC activities in the WNP, the GOM and the EAT are modulated by the MJO. Specific humidity anomalies related to the MJO exert the strongest impact on TC development in the WNP and the GOM, while the vertical wind shear is the most critical factor in the EAT.