Madden-Julian Oscillations simulated with the Reduce Acceleration in the VErtical (RAVE) approach

The Madden-Julian Oscillation (MJO) is a dominant mode of tropical intra-seasonal variability and has far-reaching influences within and beyond the tropics. Despite numerous studies, its mechanism is still not well understood and General Circulation Models in general do not simulate MJO well. In this talk, we present results from near-global simulations using the Reduced Acceleration in the VErtical (RAVE) approach (Kuang et al. 2005). The Weather Research and Forecasting (WRF) model is modified for this purpose and is forced with realistic surface boundary conditions and run with a horizontal resolution of ~40km. While the model is found to overestimate the precipitation, the simulated precipitation patterns agree quite well with the observed ones, providing a reasonable climatology to study intraseasonal variability. The simulated spectra compare favorably with the observations, so do the spatial distribution of the MJO-filtered variance and the MJO composite structures. A simulation at the same resolution but without using the RAVE approach did not produce realistic MJOs. We will also present idealized MJO simulations and discuss implications to the mechanisms of MJO.

Reference:

Kuang, Z, P. N. Blossey, C. S. Bretherton, A new approach for 3D cloud resolving simulations of large scale atmospheric circulation, Geophys. Res. Letts., Vol. 32, No. 2, L02809, 10.1029/2004GL021024, (2005).