Abstract. Atmospheric tides play a key role in coupling the lower, middle and upper atmosphere/ionosphere. The tides reach large amplitudes in the Mesosphere and Lower Thermosphere (MLT) where they can have significant fluxes of energy and momentum and so strongly influence the coupling and dynamics. The tides must therefore be accurately represented in Global Circulation Models (GCMs) that seek to model the coupling of atmospheric layers and impacts on the ionosphere. The tides consist of both migrating (sun-following) and non-migrating (not sun-following) components, both of which have important influences on the atmosphere. The Extended Unified Model (ExUM) is a recently developed version of the Met Office's Unified Model GCM which has been extended to include the MLT. Here, we present the first in-depth analysis of migrating and non-migrating modes in the ExUM. We show that the ExUM produces both non-migrating and migrating tides in the MLT of significant amplitude across a rich spectrum of spatial and temporal modes. The dominant non-migrating modes in the MLT are found to be the DE3, DW2 and DW3 in the diurnal tide and the S0, SW1 and SW3 in the semidiurnal tide. These modes can have monthly mean amplitudes at a height of 95 km as large as 35 ms⁻¹ / 10 K. All the non-migrating modes exhibit a strong seasonal variability in amplitude and significant short-term variability is evident. Both the migrating and non-migrating modes exhibit notable variation with latitude. For example, the temperature and wind diurnal tides maximise at low latitudes and the semidiurnal tides include maxima at high latitudes. Our results demonstrate the capability of the ExUM for modelling atmospheric migrating and non-migrating tides and lays the foundation for its future development into a whole atmosphere model. To this end, we make specific recommendations on further developments which would improve the capability of the model.

中文翻译：

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中层和下层热层扩展统一模型的迁徙潮汐和非迁徙潮汐分析

摘要。大气潮在耦合低层，中层和高层大气/电离层中起着关键作用。潮汐在中层和下热层（MLT）处达到很大的振幅，在那里潮汐会产生大量的能量和动量通量，因此会强烈影响耦合和动力学。因此，必须在全球环流模型（GCM）中准确表示潮汐，该模型试图模拟大气层的耦合及其对电离层的影响。潮汐包括迁移（跟随太阳）和非迁移（不跟随太阳）两个部分，它们都对大气产生重要影响。扩展统一模型（ExUM）是Met Office统一模型GCM的最新开发版本，现已扩展为包括MLT。这里，我们将对ExUM中的迁移和非迁移模式进行首次深入分析。我们表明，ExUM会在丰富的空间和时间模式频谱中在幅度显着的MLT中产生非迁移潮汐和迁移潮汐。发现MLT中主要的非迁移模式是日潮中的DE3，DW2和DW3，半日潮中的S0，SW1和SW3。这些模式在95 km的高度上可以具有35 ms的月平均振幅^-1  / 10K。所有非迁移模式在振幅上都表现出强烈的季节性变化，并且明显的短期变化是明显的。迁移模式和非迁移模式都显示出明显的纬度变化。例如，温度和风的日潮在低纬度时最大，半日潮包括高纬度时的最大值。我们的结果证明了ExUM对大气迁移和非迁移潮汐进行建模的能力，并为将其将来发展为整个大气模型奠定了基础。为此，我们对进一步的发展提出了具体的建议，以改善模型的功能。