Effects of the Madden-Julian Oscillation on the cyclogeneses of Hurricane Fausto (2002) and Hurricane Emily (2005)

Equatorial waves and the Madden-Julian Oscillation (MJO) play significant roles in the modulation of tropical convection and development of cyclones in all of the major storm basins. Using the Weather Research and Forecasting (WRF) model, case studies are examined for Hurricane Fausto (2002), which formed in the east Pacific during a convectively active phase of the MJO, and Hurricane Emily (2005), which formed in the north Atlantic during a neutral to somewhat convectively inactive phase of the MJO. First, control simulations are run with initial conditions interpolated from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis; the model then is reinitialized and run with the statistically correlated components of the MJO removed. Owing to the newness of the procedure, the case studies are run as an ensemble to ensure that the results are statistically significant. Five ensemble members, created by varying the model parameter physics, are performed for each simulation.

In response to modified intial conditions, both Hurricane Fausto and Hurricane Emily evolve in very different ways. Mechanisms responsible for these differences and how they are related to the MJO are discussed, including the large scale environment, location of formation, storm track, intensity, and structure. Varying physical parameterizations within the ensemble also has significant effects on the storms and is considered in the results.

In the case of Hurricane Fausto, the orientation and structure of the monsoon trough are modified by the MJO, affecting the location of formation. In addition, the MJO altered the large-scale vertical wind shear profiles in both case studies. These results suggest that accurate forecasts of tropical cylones are subject to a correct representation of the MJO in numerical weather prediction models.