Abstract

After the release of the ERA-Interim reanalysis, many changes have been made to the Integrated Forecasting System model and data-assimilation system, resulting in an improved reanalysis, ERA5. One of the changes in the model allows the model version in ERA5 to represent the moisture sensitivity of deep convection more realistically than the model version in ERA-Interim. A previous modeling study showed that this change alone improved the representation of the tropical atmosphere, e.g. tropical variability and precipitation distribution. Here we compare the vertical structures of average temperature and moisture over tropical oceans in ERA5, ERA-Interim and radiosonde observations to see whether ERA5 is also closer to observations for those regions and variables. Our results reveal that at many levels, temperature and relative humidity in ERA5 and ERA-Interim differ from observations, however ERA-Interim is generally closer to observations than ERA5 in the low-to-midtroposphere. Most notably, in many stations, ERA5 is on average colder than observations at ∼550-800 hPa. Large vertical gradients occur in the profile of the mean temperature difference between ERA5 and observations at ∼700-900 hPa, but are absent in ERA-Interim. Relative humidity differences are not as robust as temperature differences, however in many stations ERA5 is on average moister than observations at ∼650-800 hPa while ERA-Interim is closer to observations there. Below the ∼950 hPa-level ERA5 and ERA-Interim are generally colder and moister than observations.

Our results indicate that ERA5 deviates more than ERA-Interim from tropical radiosonde observations in the low-to-midtroposphere. It seems plausible that this deviation is, at least partly, due to the newer formulation of organised deep entrainment in ERA5 and the associated mechanism for the moisture sensitivity. However, more extensive model evaluation is needed to understand the reasons for the differences between the reanalyses and radiosonde observations.

摘要

ERA-Interim重新分析发布后，对集成预测系统模型和数据同化系统进行了许多更改，从而改进了重新分析ERA5。模型中的一项更改使ERA5中的模型版本比ERA-Interim中的模型版本更真实地表示深对流的湿度敏感性。先前的建模研究表明，这种变化本身就改善了热带大气的代表性，例如热带变率和降水分布。在这里，我们比较了ERA5，ERA-Interim和探空仪观测值中热带海洋平均温度和湿度的垂直结构，以查看ERA5是否也更接近于这些区域和变量的观测值。我们的结果表明，在许多层面上，ERA5和ERA-Interim中的温度和相对湿度与观测值不同，但是在中低层对流层中，ERA-Interim通常比ERA5更接近观测值。最值得注意的是，在许多站点中，ERA5的平均温度要比550-800 hPa时的观测值低。大约在700-900 hPa处，ERA5和观测值之间的平均温差曲线中出现了较大的垂直梯度，但是在ERA-Interim中却没有。相对湿度差异不如温度差异强，但是在许多站点，ERA5的平均湿度要比650-800 hPa时的观测结果要潮湿，而ERA-Interim则更接近于那里的观测结果。低于950 hPa的水平，ERA5和ERA-Interim的温度通常比观测的温度低和潮湿。然而，在中低层对流层中，ERA-Interim通常比ERA5更接近观测值。最值得注意的是，在许多站点中，ERA5的平均温度要比550-800 hPa时的观测值低。大约在700-900 hPa处，ERA5和观测值之间的平均温差曲线中出现了较大的垂直梯度，但是在ERA-Interim中没有。相对湿度差异不如温度差异强，但是在许多站点，ERA5的平均湿度要比650-800 hPa时的观测结果要潮湿，而ERA-Interim则更接近于那里的观测结果。低于950 hPa的水平，ERA5和ERA-Interim的温度通常比观测的温度低和潮湿。然而，在中低层对流层中，ERA-Interim通常比ERA5更接近观测值。最值得注意的是，在许多站点中，ERA5的平均温度要比550-800 hPa时的观测值低。大约在700-900 hPa处，ERA5和观测值之间的平均温差曲线中出现了较大的垂直梯度，但是在ERA-Interim中却没有。相对湿度差异不如温度差异强，但是在许多站点，ERA5的平均湿度要比650-800 hPa时的观测结果要潮湿，而ERA-Interim则更接近于那里的观测结果。低于950 hPa的水平，ERA5和ERA-Interim的温度通常比观测的温度低和潮湿。大约在700-900 hPa处，ERA5和观测值之间的平均温差曲线中出现了较大的垂直梯度，但是在ERA-Interim中没有。相对湿度差异不如温度差异强，但是在许多站中，ERA5的平均湿度要比650-800 hPa时的观测结果要潮湿，而ERA-Interim则更接近那里的观测结果。低于950 hPa的水平，ERA5和ERA-Interim的温度通常比观测的温度低和潮湿。大约在700-900 hPa处，ERA5和观测值之间的平均温差曲线中出现了较大的垂直梯度，但是在ERA-Interim中却没有。相对湿度差异不如温度差异强，但是在许多站中，ERA5的平均湿度要比650-800 hPa时的观测结果要潮湿，而ERA-Interim则更接近那里的观测结果。低于950 hPa的水平，ERA5和ERA-Interim的温度通常比观测的温度低和潮湿。

我们的结果表明，从中低层对流层的热带探空仪观测结果来看，ERA5的偏差比ERA-Interim偏差大。看来这种偏差至少部分是由于ERA5中较新的有组织的深度夹带形式和有关湿度敏感性的机制所致。但是，需要进行更广泛的模型评估，以了解再分析和探空仪观测结果之间差异的原因。