Abstract
To reveal key parameter-related physical mechanisms in simulating Madden-Julian Oscillation (MJO), seven physical parameters in the convection and cloud parameterization schemes of Beijing Climate Center Climate System Model (BCC_CSM1.2) are perturbed with Latin hypercube sampling method. A new strategy is proposed to select runs with good and poor MJO simulations among 85 generated ones. Outputs and parameter values from good and poor simulations are composited separately for comparison. Among the seven chosen parameters, a decreased value of precipitation efficiency for shallow convection, higher values of relative humidity threshold for low stable clouds and evaporation efficiency for deep convective precipitation are crucial to simulate a better MJO. Changes of the three parameters act together to suppress heavy precipitation and increase the frequency of light rainfall over the Indo-Pacific region, supplying more moisture in low and middle troposphere. As a result of a wetter lower troposphere ahead of the MJO main convection, the low-level moisture preconditioning along with the leading shallow convection tends to be enhanced, favorable for MJO’s further development and eastward propagation. The MJO’s further propagation across the Maritime Continent (MC) in good simulations is accompanied with more land precipitation dominated by shallow convection. Therefore, the above-mentioned three parameters are found to be crucial parameters out of the seven ones for MJO simulation, providing an inspiration for better MJO simulation and prediction with this model. This work is valuable as it highlights the key role of moisture-shallow convection feedback in the MJO dynamics.
Highlights
The Madden-Julian Oscillation (MJO), named after its discoverers [1,2], is characterized by a large-scale convection ensemble initiated over India Ocean
It emphasizes the importance of the interaction between convective heating, the low-frequency equatorial waves, and the boundary layer (BL) frictional moisture convergence
Only dynamical wave feedback is resolved in this theory [12]
Summary
The Madden-Julian Oscillation (MJO), named after its discoverers [1,2], is characterized by a large-scale convection ensemble initiated over India Ocean. Atmosphere 2019, 10, 241 slowly (~5 m/s) and dies after crossing the dateline, while the coupled planetary-scale baroclinic circulation still propagates throughout the whole tropical belt at a relatively faster speed [3,4,5]. Among the four basic theories, the first one, i.e., the convectively coupled Kelvin-Rossby wave theory was firstly proposed by Wang and Rui [11]. It emphasizes the importance of the interaction between convective heating, the low-frequency equatorial waves, and the boundary layer (BL) frictional moisture convergence. Only dynamical wave feedback is resolved in this theory [12]
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