Sensitivity of tropical climate to low-level clouds in the NCEP climate forecast system
Sensitivity of tropical climate to low-level clouds in the NCEP climate forecast system
复制标题
NCEP气候预报系统中热带气候对低层云的敏感性
DOI：
10.1007/s00382-010-0797-z
复制
发表时间：
2011
期刊：
影响因子：
4.6
通讯作者：
E. Schneider
中科院分区：
文献类型：
--
作者：
Zeng‐Zhen Hu;Bohua Huang;Yu;Wanqiu Wang;Fanglin Yang;C. Stan;E. Schneider
在这项工作中，我们研究了热带平均气候和季节循环的敏感性低云和云液态水路径（CLWP）规定他们在NCEP气候预报系统（CFS）。结果表明，低云覆盖的变化对到达地面的净短波辐射量和东南大西洋的暖偏差影响较小。在实验中，CLWP规定使用观测，热带地区的平均气候显着改善，这意味着短波辐射吸收CLWP是主要负责减少过多的表面净短波辐射在南部海洋的CFS。对应于东南部海洋的大CLWP值，该模型产生了大量的低云量。这导致海洋表面的净短波辐射减少，东南部海洋的海洋表面温度出现暖偏差。与此同时，东部海洋的冷舌和相关的表面风应力变得更强和更真实。由于热带平均气候的总体改善，热带大西洋的季节循环也得到改善。基于这些敏感性实验的结果，我们提出了一个模式偏差校正方法，其中CLWP只规定在东南大西洋通过使用观测的年平均气候CLWP。结果表明，东南大西洋的暖偏差在很大程度上被消除，热带大西洋的季节循环明显改善。在CFS中规定CLWP是一种有效的过渡技术，以减少模式偏差，提高热带季节循环的模拟。
In this work, we examine the sensitivity of tropical mean climate and seasonal cycle to low clouds and cloud liquid water path (CLWP) by prescribing them in the NCEP climate forecast system (CFS). It is found that the change of low cloud cover alone has a minor influence on the amount of net shortwave radiation reaching the surface and on the warm biases in the southeastern Atlantic. In experiments where CLWP is prescribed using observations, the mean climate in the tropics is improved significantly, implying that shortwave radiation absorption by CLWP is mainly responsible for reducing the excessive surface net shortwave radiation over the southern oceans in the CFS. Corresponding to large CLWP values in the southeastern oceans, the model generates large low cloud amounts. That results in a reduction of net shortwave radiation at the ocean surface and the warm biases in the sea surface temperature in the southeastern oceans. Meanwhile, the cold tongue and associated surface wind stress in the eastern oceans become stronger and more realistic. As a consequence of the overall improvement of the tropical mean climate, the seasonal cycle in the tropical Atlantic is also improved. Based on the results from these sensitivity experiments, we propose a model bias correction approach, in which CLWP is prescribed only in the southeastern Atlantic by using observed annual mean climatology of CLWP. It is shown that the warm biases in the southeastern Atlantic are largely eliminated, and the seasonal cycle in the tropical Atlantic Ocean is significantly improved. Prescribing CLWP in the CFS is then an effective interim technique to reduce model biases and to improve the simulation of seasonal cycle in the tropics.