Upper Ocean Processes Associated with the Madden-Julian Oscillation in the Indian Ocean

“Dynamics of Madden-Julian Oscillation (DYNAMO)” is a US research program with the goal of expediting our understanding of the physical and dynamical processes key to MJO initiation in the Indian Ocean. The proposed research aims at contributing to testing one of the hypotheses in the DYNAMO program. The primary goal of this proposed study is to improve our understanding of upper ocean processes that control sea surface temperature variability in the central Indian Ocean on the diurnal to intraseasonal time scales, which may play an important role in the initiation of the MJO. We propose to conduct ocean general circulation model (OGCM) and one-dimensional ocean model experiments forced with satellite-derived surface forcing fields. An important difference from previous ocean modeling work is an emphasis on upper ocean processes during MJO initiation. The primary OGCM to be used is the Hybrid Coordinate Ocean Model (HYCOM), which has been successfully used for examining the oceanic response to the MJO. In advance of the field phase of DYNAMO, we will first analyze the existing model outputs of global and Indo-pacific basin HYCOM experiments. The analysis will include the computation of upper ocean heat, momentum and salinity budgets, which is expected to provide useful information for the further improvement of the current plan of field observations.

We will then conduct OGCM experiments which cover the period of filed programs of DYNAMO during 2011-2012 using surface fluxes derived from a variety of recent satellite measurements. The performance of the OGCM will be evaluated based on the comparison with in-situ data of the upper ocean and satellite observations including those obtained during the intensive field measurements. A particular emphasis of the analysis is given to the role of surface freshwater flux and barrier layer, mixed layer entrainment, Wyrtki Jets, diurnal cycle, and oceanic equatorial waves in diurnal to intraseasonal SST variations.

We will also use high vertical resolution one-dimensional ocean models to examine the impact of upper ocean mixing processes on SST variability, in conjunction with the OGCM experiments, to help understand the relative importance of vertical versus horizontal oceanic processes.