Vertical structure and spatial-temporal evolution of the Madden-Julian Oscillation based on the Atmospheric Infrared Sounder data

The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU) on the NASA Aqua mission and the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis in combination with the precipitation from the Tropical Rainfall Measurement Mission (TRMM) are employed to study the vertical moist thermodynamic structure and spatial-temporal evolution of the Madden and Julian Oscillation (MJO). The AIRS data indicates that, in the equatorial Indian and West Pacific Oceans, MJO convection is generally preceded by moistening and warming in the boundary layer, while cooling and drying prevails aloft in the free troposphere associated with suppressed MJO convection. This is followed by a rapid rise of moisture and warming into the free troposphere at the onset of deep convection. At the peak of the MJO convection, moistening and warming is found throughout the free troposphere with a maximum at the mid-troposphere. Meanwhile, drying and cooling is developing at the boundary layer under and behind the MJO convection, which will lead to the suppression of the MJO convection.

The AIRS data suggest some new boundary-layer structure not embodied by the NCEP-NCAR reanalysis especially in the Indian Ocean and Western Pacific where there is very little conventional data to constrain the analyses. such as near-surface warming and moistening under suppressed MJO convection, near-surface cooling and drying under enhanced MJO convection, a much well defined and shallower boundary-layer structure, and a sharp transition from boundary-layer shallow convection to deep convection. The MJO vertical moist thermodynamic structure based on the AIRS data is consistent with the MJO frictional convergence feedback theory proposed by Wang (1988, 2005), which suggests that the interaction of deep convection, large-scale equatorial waves, and boundary-layer dynamics are fundamental physical components of the MJO. This result indicates that the accurate representation of the moist thermodynamic processes in the boundary layer and the interaction between shallow and deep convection may be the key for climate models to accurately simulate and predict the MJO.