The Effects of Explicit versus Parameterized Convection on the MJO in a Large-Domain High-Resolution Tropical Case Study. Part I: Characterization of Large-Scale Organization and Propagation
The Effects of Explicit versus Parameterized Convection on the MJO in a Large-Domain High-Resolution Tropical Case Study. Part I: Characterization of Large-Scale Organization and Propagation
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DOI：
10.1175/jas-d-12-0227.1
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发表时间：
2013-05-01
影响因子：
3.1
通讯作者：
Lister, Grenville M. S.
中科院分区：
文献类型：
--
作者：
Holloway, Christopher E.;Woolnough, Steven J.;Lister, Grenville M. S.
使用显式和参数化对流对大型热带区域（类似于 20 度南纬 20 度北纬、42 度东经 180 度）进行的高分辨率模拟进行了分析，并与活跃马登-朱利安振荡 (MJO) 事件为期 10 天的案例研究期间的观测结果进行了分析。 40 公里和 12 公里网格间距的参数化对流模型模拟的 MJO 信号非常弱，向东传播很少。在垂直和水平维度上使用 Smagorinsky 子网格混合的 4 公里显式对流模拟表现出最佳的 MJO 强度和传播速度。 12 公里处的显式对流模拟也比 12 公里参数化对流运行表现得更好，这表明对流方案（而不是水平分辨率）是这些 MJO 模拟的关键。有趣的是，使用传统边界层方案进行垂直亚网格混合（但仍使用 Smagorinsky 水平混合）的 4 公里显式对流模拟完全失去了大规模 MJO 组织，这表明显式对流的相对高分辨率并不能保证良好的 MJO 模拟。具有良好 MJO 表示的模型在低自由对流层水分和降水之间具有更真实的关系，支持水分对流反馈是 MJO 传播的关键过程的观点。在具有更真实的 MJO 的模型中，可用势能的生成以及该能量转化为动能的数量也有所增加，这与对流加热和垂直速度的较大纬向变化、200 hPa 左右较大的纬向温度变化以及 500 至 400 hPa 之间温度与上升（以及温度与非绝热加热之间）之间较大的相关性有关。
High-resolution simulations over a large tropical domain (similar to 20 degrees S-20 degrees N, 42 degrees E-180 degrees) using both explicit and parameterized convection are analyzed and compared to observations during a 10-day case study of an active Madden-Julian oscillation (MJO) event. The parameterized convection model simulations at both 40- and 12-km grid spacing have a very weak MJO signal and little eastward propagation. A 4-km explicit convection simulation using Smagorinsky subgrid mixing in the vertical and horizontal dimensions exhibits the best MJO strength and propagation speed. Explicit convection simulations at 12 km also perform much better than the 12-km parameterized convection run, suggesting that the convection scheme, rather than horizontal resolution, is key for these MJO simulations. Interestingly, a 4-km explicit convection simulation using the conventional boundary layer scheme for vertical subgrid mixing (but still using Smagorinsky horizontal mixing) completely loses the large-scale MJO organization, showing that relatively high resolution with explicit convection does not guarantee a good MJO simulation. Models with a good MJO representation have a more realistic relationship between lower-free-tropospheric moisture and precipitation, supporting the idea that the moisture-convection feedback is a key process for MJO propagation. There is also increased generation of available potential energy and conversion of that energy into kinetic energy in models with a more realistic MJO, which is related to larger zonal variance in convective heating and vertical velocity, larger zonal temperature variance around 200 hPa, and larger correlations between temperature and ascent (and between temperature and diabatic heating) between 500 and 400 hPa.