Influence of the Maritime Continent on the Boreal Summer Intraseasonal Oscillation

Abstract The e¤ect of the Maritime Continent (MC) on the propagation characteristics of the boreal summer intraseasonal oscillation (ISO) over the Indo-western Pacific region were investigated by performing high-resolution (T159) atmospheric general circulation model (AGCM) simulations that remove and retain the MC. The most significant di¤erence, as revealed by a finite domain wavenumber-frequency spectral analysis is the weakening of the northward propagation of ISO over the Asian monsoon region (65 -160 E) when the MC is removed; a less significant di¤erence is the enhancement of the eastward propagation along the equator. The diagnosis of the vertical structure of the simulated ISO and the model mean flow indicates that the weakening of the northward propagation is primarily attributed to the reduction of the background easterly shear, low-level southerly and meridional humidity gradient, all of which contribute to the weakening of meridional asymmetries of vorticity and humidity fields with respect to the ISO convection center. The enhanced eastward propagation is possibly attributed to the strengthening of the mean convection over the MC in association with the increase of the local surface moisture and moist static energy

Incorporating Additional Sounding Observations in Weather Analysis and Rainfall Prediction During the Intensive Observing Period of 2006 TWP-ICE

Using additional sounding observations during the Intensive Observing Period (IOP) of the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) in 2006, the characteristics of weather systems and associated environmental conditions are further analyzed during four temporal regimes (active wet monsoon, suppressed dry monsoon, clear day, and monsoon break). Monsoon low-pressure systems are predominant during the active wet monsoon and monsoon break periods. During the active monsoon period, heavy rainfall (> 100 mm day-1) is produced over the nearby tropical ocean of north Australia and the maritime continent centered on the Tiwi Islands, where the apparent southerly-to-southwesterly winds dominate at low levels over the ocean under the influence of the monsoon low in contrast to the westerly winds during a typical active north Australia summer monsoon regime. In the monsoon break, limited scattered rainfall is distributed over coastal regions of northern Australia and inland

Respective roles of shallow convection and stratiform rainfall on the simulation of Madden-Julian Oscillation.

Respective Roles of Shallow Convection and Stratiform Rainfall on the Simulation of Madden Julian Oscillation Joshua Xiouhua Fu IPRC, SOEST, University of Hawaii The IPRC/UH Hybrid-coupled GCM (HcGCM), which combined ECHAM-4 AGCM with UH intermediate ocean model, produces robust Tropical Intra-Seasonal Oscillations including the boreal-winter MJO and boreal-summer Monsoon Intra-Seasonal Oscillation. In this study, two sets of sensitivity experiments (i.e., short-term retrospective forecast of one MJO event observed during TOGA COARE and long-term free integrations) have been carried out to understand the respective roles of shallow-convection and stratiform rainfall on the simulations and predictions of the MJO. Major findings are summarized as following: Shallow-convection ahead of MJO deep convection moistens the lower-troposphere and preconditions the movement of the MJO. Present study shows that this process is very important to the eastward propagating speed of the MJO. A significant fraction of stratiform rainfall (~30%; stratiform part vs. total rainfall) is needed for ECHAM-4 to have a robust MJO. The above findings suggest that in addition to deep convection, shallow convection and stratiform rainfall needs to be well represented in conventional GCMs to ensure a robust model MJO