The Roles of DYNAMO Observations and Advances in GEOS-5 AGCM in Improving NASA GMAO Reanalysis Representation of MJO Initiation over the Tropical Indian Ocean

The fidelity of reanalyses data in representing the observed MJO initiation over the tropical Indian Ocean is subject to the observations that are assimilated and any biases in the assimilating models. The recent in-situ observations collected in the Indian Ocean during 1 October 2011-31 March 2012 from the DYNAMO field campaign provide an excellent opportunity to evaluate and improve reanalyses over the tropical Indian Ocean.

In this study, we investigate the impact of DYNAMO observations and recent advancements in the GEOS-5 AGCM on the representation of the MJO over the tropical Indian Ocean in NASA GMAO reanalyses. The role of the DYNAMO observations is investigated by contrasting two global GMAO reanalyses that assimilate global observations with and without the DYNAMO observations for the DYNAMO period. The impact of system improvements is investigated by comparing MERRA with a newer GMAO data assimilation product (MERRA2), both of which assimilate DYNAMO GTS soundings. The results show that GMAO reanalysis benefits substantially from the assimilation of DYNAMO observations and recent improvements in the GEOS-5 AGCM. The DYNAMO observations play a crucial role in shaping the vertical profiles of air temperature and humidity in the GMAO reanalysis, making them more realistic and consistent with the DYNAMO observations. Further, MERRA2 shows distinct improvement over MERRA in the vertical profiles of atmospheric fields, and provides a more realistic depiction of convective sensitivity to environmental moisture, a key process-oriented diagnostic for the MJO evolution. The distinct spurious wetness at about 650mb in MERRA is no longer present in MERRA2. In the upper troposphere, MERRA2 places the wet regime between 200-300mb, which is also more realistic than MERRA whose wet regime is at about 200mb with a rather narrow vertical extent.