Evaluation of the Quasi-Biennial Oscillation in global climate models for the SPARC QBO-initiative
Evaluation of the Quasi-Biennial Oscillation in global climate models for the SPARC QBO-initiative
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DOI：
10.1002/qj.3765
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发表时间：
2020-03-14
影响因子：
8.9
通讯作者：
Yukimoto, S.
中科院分区：
文献类型：
--
作者：
Bushell, A. C.;Anstey, J. A.;Yukimoto, S.
本文分析了13个大气环流模式在实测海温和年重复海温强迫下的准两年振荡。在大多数模型中，QBO周期接近但短于28个月的观测周期。振幅在10 hPa观测到的QBO振幅的+/-20%以内，但通常约为在较低高度（50和70 hPa）观测到的振幅的一半。对于几乎所有的模式，振荡的振幅剖面显示出整体向上移动的再分析相比，其纬向范围太窄。在东向和向西向阶段的持续时间的不对称性是相当好的捕捉，虽然不是所有的模型复制观察到的下降向西切变的减缓。向西的相位通常太弱，大多数模式在QBO的整个深度都有一个向东的时间平均风偏差。与重复的年周期SST的实验相比，周期间的变率是现实的，在某些模式中，在观测到的SST的实验中得到了增强。平均周期也是敏感的SST之间的这种差异，但只有当参数化的非地形重力波（NOGW）源耦合到对流层参数，而不是规定一个固定的值。然而，总体而言，无论规定的SST是否年际变化，模拟的QBO都非常相似。通过QBO度量的归一化分级提供整体集成性能的画像。为了模拟QBO，除了一个模型外，所有模型都使用参数化NOGW，在大多数模型中，NOGW提供了70 hPa以上高度的大部分总波强迫。因此，NOGW的表示，无论是明确的或通过参数化仍然是一个主要的不确定性QBO模拟在这些目前的实验。
Quasi-biennial oscillations (QBOs) in thirteen atmospheric general circulation models forced with both observed and annually repeating sea surface temperatures (SSTs) are evaluated. In most models the QBO period is close to, but shorter than, the observed period of 28 months. Amplitudes are within +/- 20%of the observed QBO amplitude at 10 hPa, but typically about half of that observed at lower altitudes (50 and 70 hPa). For almost all models, the oscillation's amplitude profile shows an overall upward shift compared to reanalysis and its meridional extent is too narrow. Asymmetry in the duration of eastward and westward phases is reasonably well captured, though not all models replicate the observed slowing of the descending westward shear. Westward phases are generally too weak, and most models have an eastward time mean wind bias throughout the depth of the QBO. The intercycle period variability is realistic and in some models is enhanced in the experiment with observed SSTs compared to the experiment with repeated annual cycle SSTs. Mean periods are also sensitive to this difference between SSTs, but only when parametrized non-orographic gravity wave (NOGW) sources are coupled to tropospheric parameters and not prescribed with a fixed value. Overall, however, modelled QBOs are very similar whether or not the prescribed SSTs vary interannually. A portrait of the overall ensemble performance is provided by a normalized grading of QBO metrics. To simulate a QBO, all but one model used parametrized NOGWs, which provided the majority of the total wave forcing at altitudes above 70 hPa in most models. Hence the representation of NOGWs either explicitly or through parametrization is still a major uncertainty underlying QBO simulation in these present-day experiments.