Abstract
The Madden-Julian Oscillation (MJO) is the leading mode of
intra-seasonal climate variability, having profound impacts on a range
of weather and climate phenomena. Here, we use a wavelet-based spectral
Principal Component Analysis (wsPCA) to evaluate the skill of 20
state-of-the-art CMIP6 models in capturing the magnitude and dynamics of
the MJO. The advantages of wsPCA are its ability to focus on desired
frequencies and capture each propagative physical mode with one
principal component (PC). We show that the MJO contribution to the total
intra-seasonal climate variability is substantially underestimated in
most CMIP6 models. The joint distribution of the modulus and angular
frequency of the complex wavelet PC series associated with MJO is used
to rank models relatively to the observations through the Wasserstein
distance. Using Hovmöller phase-longitude diagrams, we show that
precipitation variability associated with MJO is underestimated in most
CMIP6 models for the Amazonia, Southwest Africa, and Maritime Continent.