The representation of the West African monsoon vertical cloud structure in the Met Office Unified Model: an evaluation with CloudSat
The representation of the West African monsoon vertical cloud structure in the Met Office Unified Model: an evaluation with CloudSat
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DOI：
10.1002/qj.2614
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发表时间：
2015-10
影响因子：
8.9
通讯作者：
T. Stein;D. Parker;R. Hogan;C. Birch;C. Holloway;G. Lister;J. Marsham;S. Woolnough
中科院分区：
文献类型：
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作者：
T. Stein;D. Parker;R. Hogan;C. Birch;C. Holloway;G. Lister;J. Marsham;S. Woolnough
西非季风（WAM）的天气和气候模式模拟的降雨分布和季风环流的代表性普遍较差，因为关键的过程，如云和对流，是不好的特点。WAM期间云和降水的垂直分布在气象局统一模型模拟CloudSat观测进行了评估。模拟运行在40和12公里的水平网格长度使用对流参数化方案，并在12，4，和1.5公里的网格长度与对流方案有效地关闭，研究模式分辨率和对流参数化方案对热带对流组织的影响。使用CloudSat模拟器从模型云场对雷达反射率进行正演模拟，以与CloudSat雷达观测进行类似比较。当对流参数化被关闭时，云和降水在12公里水平网格长度上的代表性显着提高，主要是因为白天（潮湿）对流减少。当将模式网格长度减少到4或1.5 km时，特别是在薄砧和中层云的表示方面，得到了进一步的改进，但在所有模式配置中仍然存在三个问题。首先，所有的模拟都低估了云顶高度超过12公里的铁砧的比例，这可以归因于与卫星反演相比，模型中的冰水含量太低。其次，与CloudSat观测的较高海拔相比，该模型始终将中层云排除在太接近冻结水平的位置。最后，在所有模拟中有太多的低空云量，当调整微物理方案中的降雨参数时，这种偏差没有得到改善。为了改进WAM的模式模拟，需要对这些非降水云类型进行更详细的动力学和微物理学原位观测。
Weather and climate model simulations of the West African Monsoon (WAM) have generally poor representation of the rainfall distribution and monsoon circulation because key processes, such as clouds and convection, are poorly characterized. The vertical distribution of cloud and precipitation during the WAM are evaluated in Met Office Unified Model simulations against CloudSat observations. Simulations were run at 40 and 12 km horizontal grid length using a convection parametrization scheme and at 12, 4, and 1.5 km grid length with the convection scheme effectively switched off, to study the impact of model resolution and convection parametrization scheme on the organisation of tropical convection. Radar reflectivity is forward‐modelled from the model cloud fields using the CloudSat simulator to present a like‐with‐like comparison with the CloudSat radar observations. The representation of cloud and precipitation at 12 km horizontal grid length improves dramatically when the convection parametrization is switched off, primarily because of a reduction in daytime (moist) convection. Further improvement is obtained when reducing model grid length to 4 or 1.5 km, especially in the representation of thin anvil and mid‐level cloud, but three issues remain in all model configurations. Firstly, all simulations underestimate the fraction of anvils with cloud‐top height above 12 km, which can be attributed to too low ice water contents in the model compared to satellite retrievals. Secondly, the model consistently detrains mid‐level cloud too close to the freezing level, compared to higher altitudes in CloudSat observations. Finally, there is too much low‐level cloud cover in all simulations and this bias was not improved when adjusting the rainfall parameters in the microphysics scheme. To improve model simulations of the WAM, more detailed and insitu observations of the dynamics and microphysics targeting these non‐precipitating cloud types are required.