Evolution of 2007-08 Madden-Julian Oscillation (MJO07-08) Passing Over the New Guinea Highlands (Part II): Effects of Mechanical and Thermal Forcing on the Modification of Heavy Orographic Rain| Chapter 5 | Current Research Progress in Physical Science Vol. 2

 

In Part II of a series of studies on the evolution of airflow and precipitation associated with the 2007-08 Madden-Julian Oscillation (MJO07-08) over the New Guinea Highlands (NGH), we focus on how the mechanical and thermal forcings affecting the enhancement and the essential ingredients of heavy orographic rain. In this study, the mechanical and thermal forcing effects of the NGH on MJO07-08’s propagation and rainfall over the island of New Guinea are investigated by adopting the Advanced Research Weather Research and Forecasting (WRF) model. It is found that both forcings affect the propagation of MJO07-08, which lead to heavy orographic rainfall production with the mechanical forcing of NGH playing a stronger role in the orographic blocking than the thermal forcing. In addition, it is found that there are two flow regimes associated with MJO07-08 over the NGH: (1) the flow-around regime and (2) the flow-over regime. In the flow-around regime, the convective system associated with the MJO split into two while passing over the NGH due to the strong orographic blocking and this flow regime occurs when the mountain height is approximately above 50% of the original mountain height. In this flow regime, the orographic rainfall increases as the mountain height increases. Based on a series of systematic sensitivity tests, the flow-over regime occurs when the mountain is approximately below 50% of the original mountain height. Finally, it is found that the essential orographic rain ingredients associated with the MJO07-08 event are like those associated with TCs over a mountain. With a series of sensitivity tests with varying mountain height, it is found that once the mountain height reaches 75% of the original height of the NGH, the maximum rainfall amount starts to decrease as the mountain height reaches approximately 75% of the original height.

 

Author(s) Details

Justin G. Riley

North Carolina A&T State University, Greensboro, North Carolina, USA and NOAA Cooperative Institute for Great Lakes Research (CIGLR), Ann Arbor, Michigan, USA.

Yuh-Lang Lin

North Carolina A&T State University, Greensboro, North Carolina, USA.

 

Please see the link:- https://doi.org/10.9734/bpi/crpps/v2/296