Simulations of MJO cases using NICAM with the K-computer

Masaki Satoh

University of Tokyo and JAMSTEC

Abstract:

A case sweep simulation of winter MJOs through 2003 - 2012, including the two MJO cases observed in CINDY/DYNAMO, is conducted using a global non-hydrostatic model NICAM (Satoh et al. 2008), powered by the new peta-flops computer "K" (RIKEN AICS, Kobe, Japan). A total of 54 initial dates are objectively chosen for 19 winter (October – March) MJO cases based on Real-time Multivariate MJO index 1 (RMM1) and RMM2 diagrams (Wheeler and Hendon 2004). The average skill limit of the MJO reproduction was measured by bivariate correlations (Lin et al. 2008, Gottschalck et al. 2010). The duration of reproduction skill (the duration that the bivariate correlation between observation/reanalysis and NICAM stays above 0.6) was as long as 27 days. Figure 1 shows OLR Hövmoller diagrams of an MJO case observed intensively in CINDY/DYNAMO field campaign. The NICAM simulation is successful in reproducing the eastward migration of the highly convective envelope throughout the 40 day integration. On the other hand, there were also cases in which NICAM produced relatively poor or no eastward propagation of the MJO. The MJO ensemble dataset allows our studies to proceed beyond case studies and distinguish the essence of the MJO from case-to-case varieties.

Fig. 1. Equatorial Hovmöller diagrams of OLR averaged over 5S - 5N, date starting from 15 Nov 2011. Left) NOAA satellite and right) NICAM.