Seo, H., A. C. Subramanian, A. J. Miller, and N. R. Cavanaugh, 2014:
Coupled impacts of the diurnal cycle of sea surface temperature on the Madden-Julian Oscillation.
Journal of Climate, 27, 8422-8443.
This study quantifies, from a systematic set of regional ocean-atmosphere coupled model
simulations employing various coupling intervals, the effect of sub-daily sea surface temperature
(SST) variability on the onset and intensity of Madden-Julian Oscillation (MJO) convection in
the Indian Ocean. The primary effect of diurnal SST variation (dSST) is to raise time-mean SST
and latent heat flux (LH) prior to deep convection. Diurnal SST also strengthens the diurnal
moistening of the troposphere by collocating the diurnal peak in LH with those of SST. Both
effects enhance the convection such that the total precipitation amount scales quasi-linearly with
pre-convection dSST and time-mean SST. A column integrated moist static energy (MSE)
budget analysis confirms the critical role of diurnal SST variability in the buildup of column
MSE and the strength of MJO convection via time-mean stronger mean LH and diurnal
moistening. Two complementary atmosphere-only simulations further elucidate the role of SST
conditions in predictive skill of MJO. The atmospheric model forced with the persistent initial
SST, lacking enhanced pre-convection warming and moistening, produces a weaker and delayed
convection than the diurnally coupled run. The atmospheric model with prescribed daily-mean
SST from the coupled run, while eliminating the delayed peak, continues to exhibit a weaker
convection due to the lack of strong moistening on a diurnal basis. The fact that time-evolving
SST with diurnal cycle strongly influences the onset and intensity of MJO convection is
consistent with previous studies that identified an improved representation of diurnal SST as a
potential source of MJO predictability.