Impact of Latent Heat Flux Modifications on the Reproduction of a Madden–Julian Oscillation Event during the 2015 Pre-YMC Campaign Using a Global Cloud-System-Resolving Model

摘要

We show that a modification to the latent heat flux (LHF) formulation in Non-hydrostatic Icosahedral Atmospheric Model (NICAM) impacts the representation of a Madden–Julian oscillation (MJO) event during the Pre-Years of the Maritime Continent (Pre-YMC) field campaign in 2015. First, we compare the LHFs computed by the standard NICAM setting with those estimated from the ship observation during Pre-YMC. In this comparison, the NICAM LHF is smaller than observation in the low wind speed region and larger in the high wind speed region. Consequently, the MJO signal weakens when it passes over the Maritime Continent (MC). Next, sensitivity experiments are conducted with a modification to the threshold minimum wind speed in the bulk formula, to enhance the LHFs in the low wind speed region. With this modification, propagation of the MJO is better simulated over the MC, although a bias still remains without corrections in the high wind speed regions. This result indicates that increasing the LHF in the low wind speed region likely contributes to a more effective accumulation of moisture over the eastern MC region and consequently allows the MJO to pass over the MC in the model.