A new vertical diffusion package with an explicit treatment of entrainment processes
A new vertical diffusion package with an explicit treatment of entrainment processes
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DOI：
10.1175/mwr3199.1
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发表时间：
2006-09-01
影响因子：
3.2
通讯作者：
Dudhia, Jimy
中科院分区：
文献类型：
--
作者：
Hong, Song-You;Noh, Yign;Dudhia, Jimy
本文提出了一个修正的带有非局部湍流混合系数的行星边界层垂直扩散程序包。在Noh等人研究的基础上，对Hong和Pan算法的性能进行了总结，提出了一种适用于天气预报和气候预报模式的修正垂直扩散算法。修订的主要内容是在PBL顶部明确处理夹带过程。新的传播包被称为延世大学PBL（YSU PBL）。在一个一维的离线测试框架中，修改后的方案被发现，以改善几个功能相比，洪和潘的实现。YSU边界层在热诱导的自由对流区增加边界层混合，在机械诱导的强迫对流区减少边界层混合，这使中期预报（MRF）边界层中的已知问题更加复杂。解决了强风时混合层中的过度混合问题。在红和潘的情况下，PBL的过快增长也得到了纠正。该方案已成功地实施在天气研究和预报模式产生一个更现实的PBL结构及其发展。在一次锋面龙卷风爆发的个例研究中，发现一些大尺度特征的系统偏差，如850 hPa午后冷偏差在MRF边界层中得到解决。因此，新方案在再现对流抑制方面做得更好。由于对流抑制的准确预测，广泛的轻降水前面的一个锋，在MRF PBL的情况下，减少。在锋区，YSU边界层方案改善了一些特征，如强对流双线。这是因为来自YSU PBL方案的边界层仍然较少被夹带稀释，当锋面触发时，留下更多的燃料用于严重对流。
This paper proposes a revised vertical diffusion package with a nonlocal turbulent mixing coefficient in the planetary boundary layer (PBL). Based on the study of Noh et al. and accumulated results of the behavior of the Hong and Pan algorithm, a revised vertical diffusion algorithm that is suitable for weather forecasting and climate prediction models is developed. The major ingredient of the revision is the inclusion of an explicit treatment of entrainment processes at the top of the PBL. The new diffusion package is called the Yonsei University PBL (YSU PBL). In a one-dimensional offline test framework, the revised scheme is found to improve several features compared with the Hong and Pan implementation. The YSU PBL increases boundary layer mixing in the thermally induced free convection regime and decreases it in the mechanically induced forced convection regime, which alleviates the well-known problems in the Medium-Range Forecast (MRF) PBL. Excessive mixing in the mixed layer in the presence of strong winds is resolved. Overly rapid growth of the PBL in the case of the Hong and Pan is also rectified. The scheme has been successfully implemented in the Weather Research and Forecast model producing a more realistic structure of the PBL and its development. In a case study of a frontal tornado outbreak, it is found that some systematic biases of the large-scale features such as an afternoon cold bias at 850 hPa in the MRF PBL are resolved. Consequently, the new scheme does a better job in reproducing the convective inhibition. Because the convective inhibition is accurately predicted, widespread light precipitation ahead of a front, in the case of the MRF PBL, is reduced. In the frontal region, the YSU PBL scheme improves some characteristics, such as a double line of intense convection. This is because the boundary layer from the YSU PBL scheme remains less diluted by entrainment leaving more fuel for severe convection when the front triggers it.