Convective Momentum Transport Associated with the Madden-Julian Oscillation Based on Reanalysis Dataset

Friday, 19 December 2014: 2:40 PM
Ji-Hyun Oh1, Xianan Jiang1, Duane Edward Waliser2, Mitchell W Moncrieff3 and Richard H Johnson4, (1)JIFRESSE/UCLA, Pasadena, CA, United States, (2)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)Colorado State Univ, Fort Collins, CO, United States
As one of the most prominent tropical atmospheric variability modes, the Madden-Julian Oscillation (MJO) exerts profound influences on global weather and climate, and serves as a critical predictability source for extend-range forecast. In spite of the recent effort toward improving the ability of general circulation models (GCMs) to simulate the MJO, significant challenges still remain for current GCMs to produce more realistic MJO simulations. Previous studies have highlighted the important role of multi-scale interactions within the MJO including the momentum exchanges in order to improve MJO prediction skill. In this study, convective momentum transport (CMT) associated with the MJO is analyzed based on the recent NOAA Climate Forecast System Reanalysis (CFSR), in particular, by capitalizing on its archive of the parameterized subgrid CMT. Consistent with previous cloud-resolving model study, a three-layer vertical structure associated with the MJO is clear in the subgrid CMT from the CFSR. In association with enhanced MJO convection over both the Indian Ocean (IO) and western Pacific (WP), within and to the west (east) of the MJO convection, positive (negative), negative (positive), positive (negative) subgrid CMT momentum tendency anomalies are evident in the upper, middle, and lower troposphere, respectively. This subgrid CMT vertical structure tends to damp the large-scale MJO circulation in the middle and upper troposphere, but enhances MJO winds in a shallow near-surface layer. Further analyses illustrate that this three-layer vertical structure in subgrid momentum tendency of the MJO is largely balanced by grid-scale u-momentum transport. The momentum tendency structure associated with the MJO based on the CFSR is also confirmed with the European Centre for Medium-Range Forecasts (ECMWF) analysis for the two-year period of the Year of the Tropical Convection (YOTC), which further lends confidence to our results.