Seasonal Variations of Tropical Intraseasonal Oscillations

Abstract

This study has investigated whether the monsoon intraseasonal oscillation (MISO) and Madden Julian Oscillation (MJO) are same or different over the Indo-Pacific tropical region. The results are based on observational analysis with high-resolution diabatic heating as central to all the mechanisms discussed and atmospheric general circulation model experiments using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 4 (CAM4.0). The MISO and MJO are extracted as nonlinear oscillations during boreal summer and winter, respectively, by applying multi-channel singular spectrum analysis on daily anomalies of diabatic heating over the Indo-Pacific region. The boreal summer leading oscillatory mode in diabatic heating gives the three-dimensional structure of MISO over the tropics, while the boreal winter leading oscillatory mode shows the three-dimensional structure of MJO. The existence of MISO was also found in the control simulation of CAM4.0, but the MJO was found to be less realistic. To understand the mechanisms involved in MISO and MJO, certain experiments with CAM4.0 were conducted by imposing idealized and observed profiles of three-dimensional diabatic heating. Lead and lag relations among the circulation, moisture and other fields in response to the imposed diabatic heating were analyzed to compare the mechanisms of MISO and MJO.