Abstract. The Mesosphere and Lower Thermosphere (MLT) is a critical region that must be accurately reproduced in General Circulation Models (GCMs) that aim to include the coupling between the lower & middle atmosphere and the thermosphere. An accurate representation of the MLT is important for improved climate modelling and the development of a whole atmosphere model. This is because the atmospheric waves at these heights are particularly large, and so the energy and momentum they carry is an important driver of climatological phenomena through the whole atmosphere, affecting terrestrial and space weather. The Extended Unified Model (ExUM) is the recently developed version of the Met Office's Unified Model which has been extended to model the MLT. The capability of the ExUM to model atmospheric winds and tides in the MLT is currently unknown. Here, we present the first study of winds & tides from the ExUM. We make a comparison against meteor radar observations of winds and tides from 2006 between 80 and 100 km over two radar stations – Rothera (68° S, 68° W) and Ascension Island (8° S, 14° W). These locations are chosen to study tides in two very different tidal regimes – the equatorial regime, where the diurnal (24 hour) tide dominates, and the polar regime, where the semi-diurnal (12 hour) tide dominates. The results of this study illustrate that the ExUM is capable of reproducing atmospheric winds and tides that capture many of the key characteristics seen in meteor radar observations, such as zonal & meridional wind maxima and minima, the increase in tidal amplitude with increasing height, and the decrease in tidal phase with increasing height. In particular, in the equatorial regime some essential characteristics of the background winds, tidal amplitudes and tidal phases are well captured, but with significant differences in detail. In the polar regime, the difference is more pronounced. The ExUM zonal background winds in austral winter are primarily eastward rather than westward, and in austral summer are larger than observed above 90 km. The ExUM tidal amplitudes here are in general consistent with observed values, but are also larger than observed values above 90 km in austral summer. The tidal phases are generally well replicated in this regime. We propose that the bias in background winds in the polar regime is a consequence of the lack of in-situ gravity wave generation to generate eastward fluxes in the MLT. The results of this study indicate that the ExUM has a good natural capability for modelling atmospheric winds and tides in the MLT, but that there is room for improvement in the model physics in this region. This highlights the need for modifications to the physical parameterization schemes used in the model in this region – such as the non-orographic spectral gravity wave scheme – to improve aspects such as polar circulation. To this end, we make specific recommendations of changes that can be implemented to improve the accuracy of the ExUM in the MLT.

中文翻译：

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流星雷达观测验证了中层和下热层扩展统一模型的风潮

摘要。中层大气层和下层热层（MLT）是必须在通用循环模型（GCM）中精确复制的关键区域，该模型旨在包括下层和中层大气层与热层之间的耦合。MLT的准确表示对于改善气候模型和开发整个大气模型很重要。这是因为在这些高度的大气波特别大，因此它们所携带的能量和动量是整个大气中气候现象的重要驱动因素，从而影响了陆地和太空天气。扩展统一模型（ExUM）是Met Office统一模型的最新开发版本，已对其进行扩展以对MLT进行建模。目前尚不知道ExUM对MLT中的大气风和潮汐进行建模的能力。这里，我们展示了来自ExUM的风与潮的首次研究。我们将2006年流星雷达观测到的80到100公里之间的风和潮与两个雷达站-罗瑟拉（68°S，68°W）和升天岛（8°S，14°W）进行比较。选择这些位置来研究两种截然不同的潮汐模式中的潮汐–赤道模式（昼夜（24小时）潮占主导地位）和极地模式（半日潮（12小时）占主导地位）。这项研究的结果说明，ExUM能够再现捕捉到在流星雷达观测中看到的许多关键特征的大气风和潮汐，例如纬向和经向风的最大值和最小值，潮汐振幅随高度的增加而增加以及随着高度的增加潮汐相的减少。特别是，在赤道地区，背景风，潮汐振幅和潮汐相位的一些基本特征已被很好地捕捉到，但细节上却有显着差异。在极地政权中，差异更为明显。在南方冬季，ExUM纬向本底风主要是东风，而不是西风，而在南方夏季，ExUM纬向风大于90 km以上的观测值。这里的ExUM潮汐振幅通常与观测值一致，但也比南方夏季90 km以上的观测值大。在这种情况下，潮汐阶段通常可以很好地复制。我们认为，极地地区背景风的偏见是由于缺乏原地引力波产生以在MLT中产生向东通量的结果。这项研究的结果表明，ExUM具有对MLT中的大气风和潮汐进行建模的良好自然能力，但该地区的模型物理仍有改进的空间。这突出表明需要修改该地区模型中使用的物理参数化方案（例如非地形光谱重力波方案），以改善极性循环等方面。为此，我们对可以实施的更改提出了具体建议，以提高MLT中ExUM的准确性。这突出表明需要修改该地区模型中使用的物理参数化方案（例如非地形光谱重力波方案），以改善极性循环等方面。为此，我们对可以实施的更改提出了具体建议，以提高MLT中ExUM的准确性。这突出表明需要修改该地区模型中使用的物理参数化方案（例如非地形光谱重力波方案），以改善极性循环等方面。为此，我们对可以实施的更改提出了具体建议，以提高MLT中ExUM的准确性。