The effect of the air–sea interaction on the Madden–Julian Oscillation
(MJO) was investigated using the one-column ocean model
Snow–Ice–Thermocline (SIT 1.06) embedded in the Community Atmosphere Model
5.3 (CAM5.3; hereafter CAM5–SIT v1.0). The SIT model with 41 vertical
layers was developed to simulate sea surface temperature (SST) and
upper-ocean temperature variations with a high vertical resolution that
resolves the cool skin and diurnal warm layer and the upper oceanic
temperature gradient. A series of 30-year sensitivity experiments were
conducted in which various model configurations (e.g., coupled versus
uncoupled, vertical resolution and depth of the SIT model, coupling domains,
and absence of the diurnal cycle) were considered to evaluate the effect of
air–sea coupling on MJO simulation. Most of the CAM5–SIT experiments
exhibit higher fidelity than the CAM5-alone experiment in characterizing the
basic features of the MJO such as spatiotemporal variability and the
eastward propagation in boreal winter. The overall MJO simulation
performance of CAM5–SIT benefits from (1) better resolving the fine
vertical structure of upper-ocean temperature and therefore the air–sea
interaction that results in more realistic intraseasonal variability in both
SST and atmospheric circulation and (2) the adequate thickness of a
vertically gridded ocean layer. The sensitivity experiments demonstrate the
necessity of coupling the tropical eastern Pacific in addition to the
tropical Indian Ocean and the tropical western Pacific. Coupling is more
essential in the south than north of the Equator in the tropical western
Pacific. Enhanced MJO could be obtained without considering the diurnal
cycle in coupling.</p