A23D-0344
Momentum Budget Analysis of Westerly Wind Events Associated with the Madden-Julian Oscillation during DYNAMO

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Ji-Hyun Oh1,2, Xianan Jiang1, Duane Edward Waliser3, Mitchell W Moncrieff4, Richard H Johnson5 and Paul E Ciesielski6, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)APEC Climate Center, Busan, South Korea, (3)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (4)National Center for Atmospheric Research, Boulder, CO, United States, (5)Colorado State Univ, Fort Collins, CO, United States, (6)Deptment of Atmoshpheric Science, Department of Atmospheric Science, Fort Collins, CO, United States
Abstract:

The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign was conducted over the

Indian Ocean (IO) from October 2011 to February 2012 to investigate the initiation of the Madden-Julian

Oscillation (MJO). Three MJOs accompanying one or more westerly wind events (WWEs) occurred in

late October, late November, and late December 2011, respectively. Momentum budget analysis is

conducted in this study to understand the contributions of the dynamical processes involved in the wind

evolution associated with the MJO active phases over the IO during DYNAMO using European Centre

for Medium-Range Weather Forecasts (ECMWF) analysis. This analysis shows that westerly acceleration

at lower levels associated with the MJO active phase generally appears to be maintained by the pressure

gradient force (PGF), which is partly canceled by meridional advection of the zonal wind. Westerly

acceleration in the mid-troposphere is mostly attributable to vertical advection.

In addition, the MJO in late November (MJO2), accompanied by two different WWEs (WWE1, WWE2)

spaced a few days apart, is further diagnosed. Unlike other WWEs during DYNAMO, horizontal

advection is more responsible for the westerly acceleration in the lower troposphere for the WWE2 than

the PGF. Interactions between the MJO2 convective envelope and convectively coupled waves (CCWs)

have been further analyzed to illuminate the dynamical contribution of these synoptic scale equatorial

waves to the WWEs during MJO2. We suggest that differences in the developing processes among

WWEs can be attributed to the different types of CCWs.The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign was conducted over the

Indian Ocean (IO) from October 2011 to February 2012 to investigate the initiation of the Madden-Julian

Oscillation (MJO). Three MJOs accompanying one or more westerly wind events (WWEs) occurred in

late October, late November, and late December 2011, respectively. Momentum budget analysis is

conducted in this study to understand the contributions of the dynamical processes involved in the wind

evolution associated with the MJO active phases over the IO during DYNAMO using European Centre

for Medium-Range Weather Forecasts (ECMWF) analysis. This analysis shows that westerly acceleration

at lower levels associated with the MJO active phase generally appears to be maintained by the pressure

gradient force (PGF), which is partly canceled by meridional advection of the zonal wind. Westerly

acceleration in the mid-troposphere is mostly attributable to vertical advection.

In addition, the MJO in late November (MJO2), accompanied by two different WWEs (WWE1, WWE2)

spaced a few days apart, is further diagnosed. Unlike other WWEs during DYNAMO, horizontal

advection is more responsible for the westerly acceleration in the lower troposphere for the WWE2 than

the PGF. Interactions between the MJO2 convective envelope and convectively coupled waves (CCWs)

have been further analyzed to illuminate the dynamical contribution of these synoptic scale equatorial

waves to the WWEs during MJO2. We suggest that differences in the developing processes among

WWEs can be attributed to the different types of CCWs.

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