Title: Impact of DYNAMO observations on NASA GEOS‐5 reanalyses and the representation of MJO initiation
Abstract: Abstract This study examines the impact of the Dynamics of the Madden‐Julian Oscillation (DYNAMO) campaign in situ observations on NASA Goddard Earth Observing System version 5 (GEOS‐5) reanalyses and the improvements gained thereby in the representation of the Madden‐Julian Oscillation (MJO) initiation processes. To this end, we produced a global, high‐resolution (1/4° spatially) reanalysis that assimilates the level‐4, quality‐controlled DYNAMO upper air soundings from about 87 stations in the equatorial Indian Ocean region along with a companion data‐denied control reanalysis. The DYNAMO reanalysis produces a more realistic vertical structure of the temperature and moisture in the central tropical Indian Ocean by correcting the model biases, namely, the cold and dry biases in the lower troposphere and warm bias in the upper troposphere. The reanalysis horizontal winds are substantially improved, in that, the westerly acceleration and vertical shear of the zonal wind are enhanced. The DYNAMO reanalysis shows enhanced low‐level diabatic heating, moisture anomalies and vertical velocity during the MJO initiation. Due to the warmer lower troposphere, the deep convection is invigorated, which is evident in convective cloud fraction. The GEOS‐5 atmospheric general circulation model (AGCM) employed in the reanalysis is overall successful in assimilating the additional DYNAMO observations, except for an erroneous model response for medium rain rates, between 700 and 600 hPa, reminiscent of a bias in earlier versions of the AGCM. The moist heating profile shows a sharp decrease there due to the excessive convective rain re‐evaporation, which is partly offset by the temperature increment produced by the analysis.