Evolution and Intensification of Cyclone Pam (2015) from Active Convective Populations within a Madden-Julian Oscillation Event in March 2015

Abstract:

Cyclone Pam (2015) that developed in the southern tropical Pacific in March 2015 caused severe damages over the islands states in the southern Pacific. According to JTWC warning, Cyclone Pam was a category-5 storm and its maximum wind speed reached about 75 m/s. Because the islands of Vanuatu were severely damaged by the cyclone, the quantitative assessment of hazards induced by the cyclone is important in order to mitigate and prevent resulting disasters. In addition, this cyclone is of meteorological interest, because the cyclone developed and evolved from active convection of an MJO signal. This study numerically investigates the evolution and intensification of Cyclone Pam from the transformation of convective populations into a vortical structure with the use of a regional meteorological model, the WRF model. By examining the impacts of the size of the computational domain, the grid spacing, and the cumulus parameterization scheme employed to the simulated cyclone, we have found that the most intense cyclone with the most rapid intensification is reproduced with doubly nested domains at 6- and 2-km horizontal resolutions and without a cumulus parameterization; the simulated cyclone achieved the minimum central pressure of about 890 hPa. Transition processes from convective populations of MJO into a tropical cyclone are investigated. It was found that at the pre-storm stage when no cyclonic storm developed there was a very weak low within active convective areas of the MJO when they pass over the equatorial Pacific. The low generates weak cyclonic convergence off the equator. From the sensitivity experiments, there is a clear difference in the environmental moisture field among the experiments. This result suggests that the MJO provided a sufficient amount of moisture, which positively contribute to the intensification of the tropical cyclone.