Application and Evaluation of an Explicit Prognostic Cloud-Cover Scheme in GRAPES Global Forecast System
Application and Evaluation of an Explicit Prognostic Cloud-Cover Scheme in GRAPES Global Forecast System
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显式预测云量方案在 GRAPES 全球预报系统中的应用和评估
DOI：
10.1002/2017ms001234
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发表时间：
2018
影响因子：
6.8
通讯作者：
Yuk Yung
中科院分区：
文献类型：
--
作者：
Zhanshan Ma;Qijun Liu;Chuanfeng Zhao;Xueshun Shen;Yuan Wang;Jonathan H. Jiang;Zhe Li;Yuk Yung
为了提高全球中期数值天气预报系统(GRAPES_GFS)对云量和辐射的模拟能力，在全球/区域同化预报系统(GRAPES)中引入了一个显式预报云量方案(PROGCS)。与以前的诊断云层方案(DIAGCS)不同，PROGCS通过将云层与积云对流和大尺度层状凝结过程物理联系起来来考虑云层的形成和消散。我们的模拟结果表明，中高纬度的云主要是由大尺度层状凝结过程产生的，而积云对流和大尺度凝结过程共同决定了低纬地区的云量。与DIAGCS相比，PROGCS利用大气辐射测量(ARM)计划在南大平原(SGP)站点的观测资料捕捉到了更一致的云量垂直分布，并使用ERA中期再分析资料模拟了更真实的海洋平流层积云的日循环。与卫星反演相比，PROGCS确定的低、高和总云量似乎比DIAGCS模拟的更逼真，尽管前者有轻微的负偏差。此外，PROGCS运行对大气顶部出射长波辐射(TOA)的模拟也有了很大的改进，使得GRAPES_GFS在850 hpa以下和400 hpa以上高度的辐射加热率偏差较小。结果表明，云量计算预报方法比传统的诊断预报方法有明显的优势，应在天气气候模拟预报中采用。
An explicit prognostic cloud‐cover scheme (PROGCS) is implemented into the Global/Regional Assimilation and Prediction System (GRAPES) for global middle‐range numerical weather predication system (GRAPES_GFS) to improve the model performance in simulating cloud cover and radiation. Unlike the previous diagnostic cloud‐cover scheme (DIAGCS), PROGCS considers the formation and dissipation of cloud cover by physically connecting it to the cumulus convection and large‐scale stratiform condensation processes. Our simulation results show that clouds in mid‐high latitudes arise mainly from large‐scale stratiform condensation processes, while cumulus convection and large‐scale condensation processes jointly determine cloud cover in low latitudes. Compared with DIAGCS, PROGCS captures more consistent vertical distributions of cloud cover with the observations from Atmospheric Radiation Measurements (ARM) program at the Southern Great Plains (SGP) site and simulates more realistic diurnal cycle of marine stratocumulus with the ERA‐Interim reanalysis data. The low, high, and total cloud covers that are determined via PROGCS appear to be more realistic than those simulated via DIAGCS when both are compared with satellite retrievals though the former maintains slight negative biases. In addition, the simulations of outgoing longwave radiation (OLR) at the top of the atmosphere (TOA) from PROGCS runs have been considerably improved as well, resulting in less biases in radiative heating rates at heights below 850 hPa and above 400 hPa of GRAPES_GFS. Our results indicate that a prognostic method of cloud‐cover calculation has significant advantage over the conventional diagnostic one, and it should be adopted in both weather and climate simulation and forecast.